Showing papers in "Circulation Research in 1981"

Similarities of genetic (spontaneous) hypertension. Man and rat.

Abstract: IN 1963, Okamoto and Aoki introduced a new model of experimental hypertension that required no physiological, pharmacological, or surgical intervention. This spontaneously hypertensive rat (SHR) was developed by meticulous genetic (brother-to-sister) inbreeding that uniformly resulted in 100% of the progeny having naturally occurring hypertensive disease (Okamoto and Aoki, 1963; Okamoto et al., 1966a). Since then, several expert panels have reported that the SHR is an excellent model of experimental hypertension that could serve as a counterpart for clinical essential hypertension (Undenfriend and Spector, 1972; ILAR, 1976). In this discourse we take the affirmative position that the SHR is, indeed, an excellent model for the study of essential hypertension. We do so, however, with four important caveats. First, we recognize that it is unlikely that both forms of naturally occurring hypertension (man and rat) are identical expressions of genetically determined hypertensive disease. Second, we take the position that both forms of hypertension are polygenic in origin and that both are influenced by environmental factors. Thirdly, since the control of normal arterial pressure in both man and rat is multifactorial, it follows that certain pressor mechanisms might well operate in one form of genetic hypertension that do not necessarily occur in the other (although in both, some similar factors could be involved). This same reasoning also may be applied to hypertensive in-

Myosin isoenzyme changes in several models of rat cardiac hypertrophy.

Abstract: We studied the effect of chronic mechanical overloading on the isoenzyme composition of rat cardiac myosin in several experimental models: aortic stenosis (AS), aortic incompetence (AI), aortocaval fistula (ACF), overload of the non-infarcted area after left coronary ligation (INF), and overload of the spontaneously hypertensive rats (SHR). Samples of the left and right ventricles were isolated from these hearts, and myosins were analyzed by electrophoresis in non-dissociating conditions. The myosin isoenzymes were called V1, V2, and V3 in order of decreasing mobility, according to the nomenclature of Hoh et al. Controls of the Wistar and Wistar Kyoto (WKY) strains were almost exclusively V1, A slow age-dependent shift toward V3 was observed in the left ventricles of adult Wistar rats, which at 30 weeks of age (body weight 600 g) contained approximately 15% of this form. In all models of cardiac hypertrophy, an isoenzymic redistribution was observed with a significant increase in V3. The level of V3 was statistically correlated with the degree of hypertrophy in the AS, (n = 11, r - 0.6, P less than 0.05), the AI (n = 14, 4 = 0.88, P less than 0.001), and the AS + AI(n = 14, 4 = 0.69, P less than 0.01) but not in the ACF (n = 16, r = 0.46). The isoenzymic changes could account for the decreases in both myosin ATPase activity and cardiac contractility described previously in our laboratory and by others. They also demonstrate that changes in myosin isoenzymes represent a general response of the rat heart, to chronic mechanical overloading.

Volume loading slows left ventricular isovolumic relaxation rate. Evidence of load-dependent relaxation in the intact dog heart.

Abstract: We studied the effects of volume loading on left ventricular isovolumic relaxation rate in 16 intact anesthetized dogs. End-diastolic pressure, mean aortic systolic pressure, dp/dtmnx, and heart rate were measured at end expiration and end inspiration. Volume loading to approximately 5, 10, 15, and 20 mm Hg above initial end-diastolic pressure was performed. In nine dogs, simultaneous ventricular dimensions were measured with previously implanted tantalum screws using biplane cineangiography. Similar volume loading was done in open-chest and open-pericardium states. Relaxation rate was measured in 3413 beats using T, the time constant of exponential isovolumic pressure fall. T was calculated as reported previously by others and also from a linear regression of dp/dt against p, to eliminate the effects of extracavity pressure changes. T always increased significantly with volume loading, indicating slower relaxation. (For example, with the chest intact, mean T increased from 26 ± 2 (SEM) msec before volume loading to 41.5 ± 4 msec after volume loading.) Using multiple linear regression analysis, we found, in agreement with previous reports, that T decreased significantly as dp/dtMAX, and heart rate increased. In contrast to previous reports, we also found that T increased significantly as end-diastolic and mean aortic systolic pressure increased. These four variables taken together accurately predicted T [SEE (standard error of estimate) = 3.2 msec, R = 0.94, P < 0.001]. Geometric variables, including ventricular dimensions and ejection fraction, did not have a statistically significant effect on T independent of the hemodynamic variables. Opening the chest or pericardium did not have a consistent effect on T. Volume loading slows isovolumic relaxation rate in the intact canine heart. This effect appears to be a reflection of the dependence of relaxation on both end-diastolic and mean aortic systolic pressures.

Left ventricular diastolic pressure-volume relations in rats with healed myocardial infarction. Effects on systolic function.

Abstract: To determine the effects of healed myocardial infarction on the diastolic compliance of the left ventricle, we studied 36 rats 26 days after left coronary artery ligation. Peak cardiac output and stroke volume were measured under ether anesthesia during volume loading, and peak left ventricular developed pressure was determined during occlusion of the ascending aorta. During a slow infusion of saline into the potassium-arrested left ventricle, diastolic pressure and volume were measured continuously over the pressure range -5 to 30 mm Hg. Infarct size was determined by planimetry of serial sections taken from each heart at 1-mm intervals from apex to base. In rats with healed infarcts, left ventricular volume was increased in proportion to infarct size and the diastolic pressure-volume relationship was shifted so that at pressures below 2.5 mm Hg volume was increased, resulting in an increased ventricular compliance in this low pressure range. Above this pressure, the slopes of the pressure-volume curves were similar in rats with and without infarctions. Peak cardiac output and pressure-generating capacity were impaired in proportion to infarct size. This impairment of cardiac performance correlated with the infarct size-related increase in diastolic volume, which served to offset the reduction in flow generating capacity caused by systolic dysfunction, while contributing directly to the impairment of pressure generating capacity.

Ventricular wall stress.

Abstract: SUMMARY Quantification of ventricular wall stress is necessary for an understanding of both normal and pathological ventricular mechanics. At present there are no reliable means to measure, directly, wall stresses in the intact ventricle. Thus, we must rely on mathematical models to predict these stresses, knowing that the predictions cannot be validated directly. Since each model employs certain simplifying assumptions, one must be aware of the limitations of stress predictions derived from that model. All of the models currently used to calculate wall stresses were reviewed and the following major conclusions were reached: (1) For most applications, detailed knowledge of the stress distribution across the wall is not essential and cannot be verified by current means. The midwall or stress averaged across the wall is adequate. Hence, the Falsetti et al. (1970) thin-walled or the MJrksy (1969, 1979) thick-walled ellipsoidal formulas derived from a generalized Laplace's law are probably the best compromise in terms of ease of computation, and incorporation of realistic albeit greatly oversimplified geometry. Use of thin-or thick-walled spherical formulas underestimate circumferential stresses by about 20-40% and overestimate longitudinal stresses by about 10-20%, respectively. (2) The wide qualitative and quantitative differences predicted by the various analytical thick-walled formulas make it difficult to judge which gives the most realistic representation of the actual stress distribution across the wall and are, thus, of little practical utility. (3) The finite-element method offers an extremely powerful method for analyzing regional variations in stress. This method can account for variations in material properties , complex geometry, anisotropy, and variations in fiber angle from region to region. However, until faster and better methods of accurate three-dimensional reconstruction of the heart are available and until more data on the multiaxial constitutive properties of myocardium are obtained, this method cannot be utilised to its full capabilities. In addition, the effort and expense involved in using the finite-element method are considerable and will limit its widespread application. (4) Until accurate and reliable methods to measure wall stresses are developed and the predictions of the models are validated, our quantitative knowledge of ventricular wall stress will be incomplete. CARDIOLOGISTS, physiologists, and engineers have long been intensely interested in quantifica-tion of the forces or stresses acting in the wall of the heart. The extent of this interest is evident in the voluminous literature containing references to ventricular wall stress since Woods' publication late in the last century (Woods, 1892). …

Diastolic-systolic coronary flow differences are caused by intramyocardial pump action in the anesthetized dog.

Abstract: The effect of cardiac contraction on coronary arterial flow has been described in terms of an intramyocardiaJ pump, which displaces blood backward and forward during systole and diastole, respectively. Normally, the mean forward flow exceeds, and consequently conceals, this backflow. The main left coronary artery of six anesthetized open-chest dogs was perfused with a Gregg cannula from a constant pressure source via a pcrfusion line containing an adjustable stenosis. At mean left main arterial pressures, P^, of 65, 90, 125, and 155 mm Hg, the hearts were perfused via different grades of stenosis, while a constant mean perfusion pressure (Pu,) distal to the stenosis was maintained. Mean coronary flow was then independent of stenosis grade. However, with increasing stenosis grade, the systolic-diastolic coronary flow difference decreased, whereas the dlastolic-systolic coronary pressure difference increased. By varying the stenosis grade at constant P^ linear relationships between diastolic-systolic pressure difference and flow difference were obtained and were interpreted as being a result of an electrical analog potential-source equivalent. From the potential-source equivalent, the diastolic-systolic pressure changes of the intramyocadial pump, pi_, can be determined as well as the coronary resistance, R., impeding the flow variations originated by p^. We found p^ = 53.1 ± 7.02 (SD) nun Hg, and independent of P^. R. was correlated with the resistance to coronary flow, Re, via R. = 0.63 x R,. — 12.9 mm Hg»s/ml (r — 0.939, n — 25). R* was defined as (Pic 14 nun Hg)/mean coronary flow. The waterfall model extended to allow for autoregulation to achieve an equal division of mean flow over the myocardium could not explain these results. From a decay curve of coronary arterial pressure following clamping of the perfusion line, intramyocardial coronary capacitance was estimated to be approximately 0.07 ml/mm rig/100 g LV. This value is in agreement with published volume pressure relationships of the intramyocardial blood compartment. The phasic coronary blood flow component requires intramyocardial arterial volume. We conclude that systolic-diastolic variations in coronary blood flow are not due to varying resistances but are caused by an active intramyocardial pump. Circ Res 49.-SS4-593, 1981

Electrophysiological changes and ventricular arrhythmias in the early phase of regional myocardial ischemia.

Abstract: IN RECENT years, a number of review articles devoted entirely or partly to electrical changes and arrhythmias during ischemia and infarction have appeared (Wit and Bigger, 1975; Coraboeuf et al., 1976; Arnsdorf, 1977; Elharrar and Zipes, 1977; Bigger et al., 1977; Wit and Cranefield, 1978; Lazzara et al., 1978; Carmeliet, 1978; Cranefield and Wit, 1979). Most of what is known about cellular electrophysiological changes is derived from experiments on isolated tissue, either excised at different times after coronary artery occlusion, or taken from normal hearts and superfused with solutions altered in such a way as to imitate conditions occurring in ischemic hearts. (Friedman et al., 1973; Lazzara et al., 1974; Cranefield, 1975). The acquisition of electrophysiological data from intact hearts with the same degree of accuracy as in isolated tissue is limited by the techniques available at present. Therefore the description of the mechanisms for arrhythmias and conduction disturbances observed in intact hearts is based mainly on indirect evidence. Most experimental work on ischemia has been conducted in late stages (hours or days) after occlusion. The changes occurring in the very first minutes after coronary occlusion follow a very rapid time course, and a stable electrical situation is not present. Thus anlaysis of the electrophysiological changes in the very early phase of ischemia is hampered by both the technical difficulties of obtaining reliable recordings from intact hearts and by the rapidly changing electrical conditions.

Measurements of coronary velocity and reactive hyperemia in the coronary circulation of humans

Abstract: An acceptable method for measuring phasic coronary velocity and reactive hyperemia in humans has not been available. We have developed a doppler probe which can be coupled to surface coronary vessel* at the time of cardiac surgery with a small suction cup. Phasic coronary velocity can be measured with a signal to noise ratio that exceeds 20:1. Animal studies have shown that the probe does not alter myocardial perfusion or cause tissue damage. In addition, changes in mean coronary velocity are closely related (r = 0.97) to changes in coronary flow over a wide range (15–400 ml/min). The characteristics of reactive hyperemia in the coronary circulation of dogs determined with the doppler system are similar to those obtained simultaneously with an electromagnetic flow meter. Transient occlusions of branch coronary vessels in patients with normal coronary arteries are not associated with significant changes in heart rate, left atrial, or mean arterial pressure. The characteristics of reactive hyperemia in normal vessels of 13 patients were as follows: although reactive hyperemia responses were demonstrable following 1 to 2-aecond coronary occlusions, maximal responses usually occurred with 20-second coronary occlusions; following 20 seconds of coronary occlusion, the ratio of peak to resting velocity was 5.8 ± 0.6 (mean ± SE); the ratio of repayment to debt area was 3.1 ± 0.2, and the duration of the reactive hyperemia response was 20.8 ± 0.3 seconds. These studies provide the first quantitative measurements of coronary reactive hyperemia in humans.

Total ischemia in dog hearts, in vitro. 1. Comparison of high energy phosphate production, utilization, and depletion, and of adenine nucleotide catabolism in total ischemia in vitro vs. severe ischemia in vivo.

Abstract: This study was done to compare rates of high energy phosphate (HEP) utilization and depletion, as well as the production and distribution of catabolic products of adenine nucleo tides in dog heart during total ischemia in vitro and severe ischemia in vivo. Both HEP production from anaerobic glycolysis and HEP utilization occurred much more quickly during the first 15 mmtuet of severe ischemia in vivo than in total ischemia in vitro. HEP utilization exceeded production in both types of ischemia and tissue HEP decreased progressively. Much of the creatine phosphate (CP) was lost within the first 1–3 minutes; adenosine triphosphate (ATP) depletion occurred more slowly than CP and more slowly in vitro than in vivo. ATP was reduced from control contents of 5–6 μmol/g to 1.0 μmol/g by 75 minutes of total ischemia in vitro, but reached a similar level within only 30 minutes of severe ischemia in vivo. HEP utilization and production during ischemia were estimated from the rate of accumulation of myocardial lactate and essentially ceased when the ATP reached 0.4 μmol/g wet weight. At this time, more than 80% of the HEP that had been utilized in ischemia in vivo or in total ischemia in vitro had been derived from anaerobic glycolysis. ATP depletion was paralleled by dephosphorylation of adenine nucleottdeg. The lost nucleotides were recovered stoichiometrically as adenosine, inosine, hypoxantbine, and xanthine in both models of ischemia, a finding which demonstrates that the low collateral flow of severe ischemia allows little washout of nucleosides, bases, or lactate to the systemic circulation. These results Indicate that total ischemia in vitro can be used as a model of severe ischemia in vivo in that the pathways of energy production and depletion and of adenine nucleotide degradation generally are similar.

Tissue osmolality, cell swelling, and reperfusion in acute regional myocardial ischemia in the isolated porcine heart.

Abstract: We divised a method to determine tissue osmolality in intact beating hearts. After occlusion of the left anterior descending coronary artery (LAD) of isolated porcine hearts, tissue osmolality in the ischemic myocardium increased within 50 minutes by about 40 mOsm/kg. This rise in osmolality could be accounted for by metabolic processes, notably the conversion of glycogen into lactate, and the hydrolysis of high energy phosphates. Concomitant with the rise in osmolality, the ischemic myocardium during the 1-hour period of LAD occlusion took up fluid and increased tistue water volume by an average of 16.5%. We demonstrated that the osmolality of fixatives used for morphological studies markedly influences ischemic cell morphology. Thus, normotonic fixation of the ischemic myocardium accentuates cell swelling, whereas nearly normal cell volumes result from hypertonic fixation, adjusted according to the rise hi ischemic tissue osmolality. Normotonic reperfusion of the ischemic area after 1 hour of LAD occlusion resulted in the “no-refiow” phenomenon in the mldmural and subendocardial regions. Epicardial and intramural DC-electrograms showed persistent ischemic changes, i.e., T-Q depression, S-T elevation, and monophasic potentials. Tissue resistivity, which during ischemia had risen twofold, remained high. Lacate levels remained high, creatinephosphate (CP) and adenosinetriphosphate (ATP) levels remained low. Selective hypertonic reperfusion of the LAD, followed by a gradual return to normotonic perfnsion, resulted in a normalization of DC extracellular elcctrograms, restoration of electrical resistivity to near normal, low levels of lactate, and higher levels of CP and ATP although control values were not reached. Cell morphology was correspondingly normalized following this procedure. We conclude that ischemic cells become hyperosmotic and consequently take up additional fluid when exposed to normotonic blood. This increased cell swelling compresses capillaries, prevents reperfusion, and may be a major factor in causing reperfusion damage. This damage can be prevented to a large extent by selective hypertonic reperfusion.

Canine ventricular arrhythmias in the late myocardial infarction period. 8. Epicardial mapping of reentrant circuits.

Abstract: We made simultaneous recordings from 48 bipolar electrodes to obtain epicardial isochronal maps during induced ventricular arrhythmias in dogs 3-5 days after ligation of the left anterior descending artery. There was strong evidence of a reentrant circuit (RC) that was discernible largely on the epicardial surface in 21% of ectopic beats that were analyzed. Epicardial recordings were of limited value in analyzing the arrhythmia in other beats. The reentrant circuit consisted of an arc of conduction block around which the activation front advanced in a circular fashion at slow but uneven speeds while the rest of the ventricle was activated by radial spread. The arc of conduction block around which the RC was formed was usually functional in nature, since the same area of myocardium was excitable at relatively long cardiac cycle lengths. Both the length of the arc of conduction block which defines the length of the reentrant circuit and the degree of conduction delay were crucial factors for the occurrence of reentry. A premature beat that initiated reentry resulted in a longer arc of conduction block and slower conduction compared to one that failed to induce reentry.

Time course of changes in porcine myocardial phospholipid levels during ischemia. A reassessment of the lysolipid hypothesis.

Abstract: This study was performed to determine the early and delayed metabolic effects of myocardial ischemia on the major membrane phospholipids and to reassess the potential role of lysophospholipids in the genesis of malignant dysrhythmias induced by ischemia. Samples taken from in situ hearts before ant at various intervals up to 40 minutes after abrupt ligation of LAD were extracted by the classical Folch technique with modifications to avoid artifactual lysophospholipid production and losses. Following thin layer chromatography of lipid extracts, phospholipid fractions were quantified by phosphorus estimation and lysophospholipids by a more sensitive method employing gas liquid chromatography. The total phospholipid content with the exception of lysophospholipids remained essentially constant throughout the early phases of acute ischemia, but fell by 6 and 14% after 8 and 24 ours, respectively. At 8 minutes, lysophospholipid levels n ischemic myocardium were significantly increased by 60% compared to pre-occlusion controls in the ischemic zone and by 25% in post-occlusion controls. They changed little thereafter. The molecular species of lysophospholipids remained unchanged throughout the period of ischemia studied. The mole fraction of other phospholipids as well as their fatty acyl and aldehyde profiles also were unchanged. Despite significant elevations in lysophospholipids levels, their absolute quantities were very small (0.6% of total phospholipid P) and 15-fold smaller than that reported in vitro to simulate electrophysiological manifestation of ischemia. However, such small amounts in vivo, if produced in the microenvironment of certain membrane-bound enzymes along with acidosis, hypoxia, and fatty acids, could be potentially deleterious to cell functions.

Leukocytes are required for increased lung microvascular permeability after microembolization in sheep.

Abstract: We studied the effects of uneven pulmonary artery obstruction by microemboli on steady state transvascular fluid and protein exchange in normal and leukopenic sheep. We measured pulmonary artery and left atrial pressures, cardiac output, lung lymph flow, and lymph plasma protein concentrations. Sheep were made profoundly leukopenic by administration of intra-arterial mechlorethamine hydrochloride (0.4 mg/kg, two doses) and colchicine (0.1-0.2 mg/kg, anesthetized sheep only). In anesthetized sheep, we injected glass beads 200 micrometers in diameter via the right atrium to raise pulmonary vascular resistance to 2-3 times baseline values. With normal levels of circulating leukocytes, sheep developed an increased protein-rich lymph flow from the lung characteristic of increased permeability edema. Leukopenic sheep had a significantly attenuated response after embolization for equivalent degrees of vascular obstruction. In unanesthetized sheep, we continuously infused air bubbles 1 mm in diameter via the right atrium to raise pulmonary vascular resistance to about 2 times baseline values. Each sheep served as its own control. With normal circulating leukocyte levels, there was an increase in protein-rich lymph flow from the lung during embolization. When the air infusion ended, the sheep recovered to the baseline condition in 24 hours. We induced emboli with the same amount of air when the sheep were profoundly leukopenic; lymph and protein flow from the lung were significantly less for equivalent degrees of obstruction. We conclude that circulating leukocytes are essential for the microvascular injury that results in increased permeability in the lungs of sheep after microembolization.

Capillary fluid filtration. Starling forces and lymph flow.

Abstract: STARLING (1894, 1896) described the basic forces responsible for producing fluid shifts between the circulating blood and the surrounding tissue spaces. On page 324 of his classical article entitled \"On the absorption of fluids from the connective tissue spaces,\" Starling described how capillary pressure determines transudation into the tissues and the osmotic pressure of the proteins determines absorption from the tissues. The paper also investigated how tissue pressure affects absorption, and Starling came to the correct conclusion that tissue pressure would not cause fluid to be absorbed from the tissue unless this pressure was not transmitted to the veins. Starling also recognized that a small amount of fluid was lost continually from the circulation (\"frictional resistance of the capillary wall\") and formed lymph, but believed that this was small and that the forces tending to move fluid out of and into the circulation were almost balanced. Finally, Starling postulated that tissue colloidal osmotic pressure decreased following elevation of capillary pressure and provided the opposing forces to limit transudation of fluid into interstitial spaces. Thus, Starling defined the basic forces responsible for maintaining fluid balance between the microcirculation and interstitium, and physiologists have termed tissue pressure (Pt), capillary pressure (Pc), plasma colloidal osmotic (TTP), and tissue colloidal osmotic (wt) pressure as Starling forces. However, a mathematical relationship between those forces was not formulated by Starling in his original papers. Staub (1978) presents a delightful discourse concerning the historical development of the mathematical description of the Starling hypothesis:

The effect of streptozotocin-induced diabetes in rats on cardiac contractile proteins.

Abstract: In order to determine whether diabetic cardiomyopathy in rats is associated with altered contractile proteins, male and female rats were made diabetic with intravenous streptozotocin (STZ). Calcium ATPase activity of cardiac actomyosin was significantly decreased after 1 week of diabetes and was depressed by 60% by 2 weeks. Rats pretreated with 3-O-methyl glucose to prevent the hyperglycemia caused by STZ had normal Ca2+-actomyosin ATPase activities, and non-diabetic rats whose food was restricted to keep their body and heart weights similar to those found in diabetic animals had only a slight fall in actomyosin ATPase activity. Ca2+-ATPase and actin-activated ATPase activities of pure myosin were similarly depressed in preparations from hearts of diabetic animals. Sodium dodecylsulfate gel electrophoresis and isoelectric focusing failed to reveal differences in the patterns of contractile proteins or light subunits between diabetics and controls, but pyrophosphate gels showed a shift in the myosin pattern. Because of depressed circulating thyroid hormone levels in diabetic animals, cardiac contractile proteins were also studied in preparations from thyroidectomized rats. Calcium activities of actomyosin and myosin ATPase were lower than values found in hearts of diabetic rats. When diabetic animals were kept euthyroid with thyroid replacement, actomyosin ATPase activity was still depressed. Thus STZ diabetes causes a significant decrease in cardiac contractile protein ATPase activity. This may be related to altered proportions of myosin isoenzymes.

Relationship between blood flow direction and endothelial cell orientation at arterial branch sites in rabbits and mice.

Abstract: The orientation of endothelial cells near arterial branch sites has been compared with flow streamlines near the arterial wall. We detected cell orientation by examining cell impressions in vascular casts of rabbit and mouse arterial branch sites. Flow streamlines were assessed in glass models with flow parameters approximating mean in vivo values. At high Reynolds numbers (large arteries), secondary flow develop near branch sites, and this was reflected in the pattern of streamlines near the vessel wall. At symmetrical Y bifurcations, streamlines originating near the inner wall of the branches are directed toward the lateral wall; thus they appear to wind around the daughter vessels and merge on the lateral wall. A similar phenomenon was observed on a 90 degree side branch. When flow conditions in the Y bifurcation and side branch models approximated those at the iliac bifurcation and renal artery origin, respectively, the streamlines near the walls were almost identical to the patterns of endothelial cell orientation. At very low Reynolds numbers, no secondary flow phenomena occurred and streamlines followed branch geometry. This mimicked endothelial cell orientation in very small vessels. Hence the influence of mean blood flow on endothelial cell was well predicted by the model studies.

Inhibition by free radical scavengers and by cyclooxygenase inhibitors of pial arteriolar abnormalities from concussive brain injury in cats.

Abstract: We studied the role of prostaglandins and free radicals in the induction of the functional and morphological pial arteriolar abnormalities produced by concussive brain injury. Anesthetized cats equipped with a cranial window for the observation of the pial microcirculation were subjected to concussive brain injury using a fluid-percussion device following administration of cyclooxygenase inhibitors (indomethacin or AHR-5850) or the vehicle for the solution of these agents (NaCl or Na2CO3 solution). Pial arterioles from vehicle-treated animals displayed sustained dilation, reduced responsiveness to the vasoconstrictor effect of arterial hypocapnia, and a high density of endothelial lesions. Animals pretreated with cyclooxygenase inhibitors showed less pronounced vasodilation, normal responsiveness to hypocapnia, and a significantly reduced number of lesions. The vasodilation and reduced responsiveness to the vasoconstrictor effects of hypocapnia after brain injury also were inhibited by topical application of free radical scavengers (nitroblue tetrazolium, superoxide dismutase, or mannitol). The vessels from cats pretreated with free radical scavengers also had a lower density of endothelial lesions than controls. The results support the view that the immediate cause of cerebral arteriolar damage in concussive brain injury is the generation of free oxygen radicals associated with increased prostaglandin synthesis.

Uneven distribution of postjunctional alpha 1-and alpha 2-like adrenoceptors in canine arterial and venous smooth muscle.

Abstract: We studied isolated canine arteries and veins to compare the pharmacological properties of their postjunctional alpha-adrenoceptors. Rings of femoral and splenic arteries and of femoral and saphenous veins were mounted for isometric tension recording in organ chambers filled with Krebs-Ringer bicarbonate solution. The four blood vessels contracted when exposed to methoxamine, norepinephrine, phenylephrine, and tramazoline; clonidine failed to induce contraction only in the splenic artery. The relative sensitivity to methoxamine was comparable in the arteries and veins, but that for phenylephrine was larger in the former. The veins, but not the arteries, were more sensitive to clonidine and tramazoline than to phenylephrine or methoxamine. Phentolamine was a competitive antagonist against norepinephrine in the arteries and the veins. Prazosin was a competitive antagonist arteries. The competitive antagonistic properties of yohimbine were more pronounced in the veins than in the arteries. Verapamil depressed to the same extent the contractile responses of saphenous veins to clonidine and norepinephrine, but reduced the contractions caused by methoxamine more than those due to norepinephrine. These results indicate the presence of both alpha 1- and alpha 2-like adrenoceptors on venous smooth muscle cells, whereas arterial smooth muscle cells contain mainly postjunctional alpha 1-adrenoceptors.

Phospholipid alterations in canine ischemic myocardium. Temporal and topographical correlations with Tc-99m-PPi accumulation and an in vitro sarcolemmal Ca2+ permeability defect.

Abstract: Experimental myocardial ischemia produced in dogs by proximal left anterior descending coronary artery (LAD) ligation results in a small but measurable decrease in total phospholipid content in the subendocardium of the ischemic region. After 3 hours of fixed occlusion, there is a 10% decrease in total phospholipid content. Silica gel chromatography reveals this decrease to be reflected predominantly by decreases in phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE). If technetium 99m stannous pyrophosphate (Tc-99m-PPi) is injected intravenously after various intervals of LAD occlusion and 10 minutes prior to Vh hours of reflow, there is a close temporal and topographical correlation between the extent of PE depletion and Tc-99m-PPi uptake. To measure the effects of phospholipid degradation on cardiac sarcolemmal membranes, an enriched sarcolemmal preparation was treated with an exogenous phospholipase (0.01 mg/ml). Phospholipid degradation, even without depleting total phospholipid content, resulted in more than a 50% increase in net Ca2+ efflux from vesicles preloaded by Na+:Ca2+ exchange. In addition, sarcolemmal vesicles isolated from ischemic myocardium after 3 hours of LAD occlusion have an increased Ca2+ permeability and phosphatidyl choline depletion compared to vesicles obtained from the corresponding nonischemic myocardium. These studies suggest that an alteration in phospholipid metabolism is related closely to the development of irreversible damage in ischemic canine myocardium. The biochemical mechanism responsible for this relationship may be the degradation of sarcolemmal membrane phospholipids and the associated increase in sarcolemmal Ca2+ permeability.

The selective inhibition of serotonin-induced contractions of rabbit cerebral vascular smooth muscle by calcium-antagonistic dihydropyridines. An investigation of the mechanism of action of nimodipine.

Abstract: I studied the role of calcium in the activation of isolated rings of saphenous and basilar arteries of the rabbit by comparing the effect of calcium withdrawal with the effect of the calcium antagonist nimodipine [isopropyl(2-methoxyethyl)-1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate]. Serotonin-induced contractions of both vessels were inhibited quickly by incubation in calcium-free solution, showing the contractions of both vessels to be dependent on extracellular calcium. Potassium-induced contractions of both vessels were inhibited markedly by nimodipine (basilar: ID50 = 1.7 X 10(-10) mol/liter; saphenous: ID50 = 2.6 X 10(-10) mol/liter), showing depolarization-induced calcium influx (probably through "potential sensitive channels", PSCs) to be sensitive to nimodipine. In the basilar artery the sustained, tonic phase of serotonin-induced contractions (probably through "receptor operated channels," ROCs) was potently inhibited (ID50 = 7.3 X 10(-10) mol/liter) by nimodipine. However, the initial short-lived phase of this contraction of the basilar artery was relatively unaffected (ID50 = 2 X 10(-6) mol/liter), indicating that the inhibitory action of nimodipine on tonic contractions of the basilar artery was not due to antagonism at the serotonin receptor level. In contrast, in the saphenous artery the serotonin-induced contractions were unaffected by nimodipine in doses up to 2.4 X 10(-5) mol/liter. It is postulated that the selective inhibition of the sustained tonic contraction of the basilar artery is due to a selective inhibition by nimodipine of calcium movement through ROCs in this vessel. Agonist-induced activation of ROCs in peripheral blood vessels does not seem to be affected by calcium antagonists.

Total ischemia in dog hearts, in vitro 2. High energy phosphate depletion and associated defects in energy metabolism, cell volume regulation, and sarcolemmal integrity.

Abstract: This study was done to assess the capacity of tissue, injured by varying periods of total ischemia, to perform integrated cellular functions. The principal aim was to learn the nature of the associations between the decreasing ATP of the ischemic tissue and the appearance of defective high energy phosphate regeneration, cell volume and ion regulation, and membrane permeability. Total ischemia in vitro was produced by incubating papillary muscles from dog hearts at 37°C. Slices were cut from control tissue and from injured tissue after 60–150 minutes of total ischemia. We incubated these slices in oxygenated phosphate Krebs-Ringer phosphate buffer containing MC-inulin in order to assess their capacity to resynthesize ATP and CP. to maintain ion gradients and water content, and to retain membrane impermeability to inulin and creatine. The results demonstrate that there was a close association between ATP depletion and the failure of the damaged tissue to regenerate high energy phosphates, and to preserve cell volume and ionic regulation. As long as the ATP of the tissue was not depleted below 6 μmol/g dry weight prior to incubation, no cellular abnormalities were detected by subsequent aerobic incubation of slices of the injured tissue. However, lower ATP levels were associated with depressed high energy phosphate resynthesis and failure of cell volume regulation. These defects preceded the development of overt membrane damage, which occurred only after the tissue ATP content decreased to less than 2.0 μmol/g. When overt membrane damage was present, it was associated with marked Impairment of other integrated cellular functions. Although the pathogenesis of the membrane damage in ischemia is unknown, its presence is an objective sign of lethal injury in this system.

Regional myocardial blood flow during exercise in dogs with chronic left ventricular hypertrophy.

Abstract: We compared the response of myocardial blood flow to exercise in normal dogs and in dogs with left ventricular hypertrophy (LVH) produced by banding the ascending aorta at 6-9 weeks of age. Blood flow was measured with 15-fim microspheres after the animals with LVH had reached adulthood when left ventricular:body weight ratios were approximately 80% greater than normal. During resting conditions, left ventricular systolic pressure was 202 ± 18 mm Hg in the dogs with LVH and 119 ± 6 mm Hg in the normal dogs (P < 0.01). Three levels of treadmill exercise which increased heart rates to 190, 230 and 260 beats/min resulted in progressive increases in left ventricular systolic pressure to a maximum of 343 ± 18 mm Hg in the dogs with LVH as compared to 165 ± 10 mm Hg in the control dogs (P < 0.01). Unlike normal dogs which showed a significant transmural perfusion gradient favoring the- subendocardium at rest [mean subendocardial: subepicardial ratio (endo:epi) = 1.25 ± 0.07], subendocardial flow did not significantly exceed subepicardial flow in the animals with LVH (mean endo: epi = 1.10 ± 0.08; P > 0.05 between normal and LVH). Myocardial blood flow increased as a direct linear function of heart rate during exericse in both groups of dogs. Exercise decreased the mean endo: epi ratio in both normal dogs (mean endo: epi = 1.10 ± 0.08 during heavy exercise; P < 0.01) and in the animals with LVH (mean endo:epi = 0.94 ± 0.03; P < 0.05), while the endo:epi ratios remained consistently less in the LVH dogs than in the normal animals (P< 0.05). The relative reduction of subendocardial flow in dogs with LVH was most apparent in the posterior papillary muscle region where the endo:epi ratio fell significantly below unity during heavy exercise (endo:epi = 0.79 ± 0.02; P < 0.01). These data demonstrate that relative blood flow to the subendocardium of the left ventricle is significantly less than normal, both at rest and during exercise, in dogs with LVH produced by supravalvular aortic stenosis. Circ Res 48: 76-87, 1981

Reversibility of diabetic cardiomyopathy with insulin in rats.

Abstract: Diabetes appears to cause a cardiomyopathy independent of atherosclerotic coronary artery disease and hypertension. Left ventricular papillary muscle function studies in rats made severely diabetic with streptozotocin have shown a slowing of relaxation and a depression of shortening velocity. However, the effects of insulin therapy on the myocardial mechanics of diabetic rats have not been studied. Therefore, rats diabetic for 6-10 weeks were treated with PZI insulin for 2, 6, 10, or 28 days and the mechanical performance of their left ventricular papillary muscles was compared to that of untreated diabetics and age-matched controls; cardiac contractile protein enzymatic activity was also measured. Neither 2 nor 6 days of therapy had any effects on the depressed cardiac muscle performance of diabetic animals, although plasma glucose concentration was restored to normal. By 10 days of therapy, recovery of mechanical performance was nearly complete, and by 28 days of therapy, complete reversal of the altered myocardial mechanics was observed. Crystalline insulin added to the bath (9 mU/ml) had no effect on myocardial mechanics in either diabetics or controls. A gradual recovery of actomyosin and myosin ATPase activity in the hearts of insulin-treated diabetic animals was also found, complementing the mechanical studies. In addition to demonstrating a gradual but complete reversibility of the abnormalities in papillary muscle function in diabetic rats (although control of hyperglycemia was less than ideal), this study confirms that this model of a cardiomyopathy is not a result of streptozotocin-induced cardiac toxicity. Additional data are provided indicating that depressed thyroid hormone levels in diabetic rats are not responsible for the mechanical changes observed.

Redundancy reduction for improved display and analysis of body surface potential maps. I. Spatial compression.

Abstract: The Karhunen-Loeve technique of random process representation was investigated as a method of quantitatively characterizing body surface potential maps. One hundred ninety-two lead body surface potential maps from 124 normal subjects and 97 patients with independently documented heart disease were used in the study. Each map frame in QRS and ST-T of 34 maps in a test set was represented as a linear sum of orthonormal distributions derived from the covariance matrix estimated from all QRS frames in the 221 training maps. A 16:1 reduction in spatial data of the test set was achieved with rms errors of 45 and 21 microV in QRS and ST-T, respectively. Results suggest that 12 independent waveforms, derived from the 192 measured ECGs, may be used in place of those 192 ECGs. In addition to providing a convenient and familiar method of display for map data, the technique puts the data in an appropriate form for quantitative statistical analysis.

Nuclear uptake of sex steroid hormones in the cardiovascular system of the baboon.

Abstract: Cardiac and arterial tissues of six male and six female adult baboons were examined for nuclear uptake of tritiated 5-alpha-dihydrotestosterone (3H-DHT) or tritiated estradiol-17 beta (3H-E2) by autoradiography. 3H-DHT uptake occurred in nuclei of most atrial and ventricular myocardial fibers, no cardiac interstitial tissues, some arterial endothelial cells, most smooth muscle cells of the intima and inner arterial media, and a few smooth muscle cells of the outer arterial media. 3H-E2 uptake occurred in nuclei of a few atrial and ventricular myocardial fibers, many cardiac interstitial cells, occasional arterial endothelial cells, a few smooth muscle cells of the intima and inner arterial media, smooth muscle cells of the outer arterial media, and nearly all adventitial cells. These observations are consistent with other autoradiographic and biochemical findings which indicate that the heart and major arteries of several mammalian species contain androgen and estrogen receptors in distinctive patterns of distribution among muscle and connective tissue cells.

The relationship between myocardial blood flow and contraction by myocardial layer in the canine left ventricle during ischemia.

Abstract: We investigated the relationship between regional myocardial blood flow (MBF) and segmental shortening in 17 open-chest dogs. The left anterior descending coronary artery was cannulated and perfused from the left carotid while measuring perfusion pressure. Graded occlusion was produced by a screw clamp. Extent of occlusion was monitored by perfusion pressure. Percent systolic shortening (% delta L) was measured using ultrasonic crystals implanted in normal and ischemic endocardium and ischemic epicardium. MBF was measured in ischemic and normal endocardium and epicardium with tracer microspheres. Dogs underwent 1 to 4 grades of coronary stenosis. Myocardial blood flow both to endocardium and epicardium was found to be linearly related to diastolic perfusion pressure below 50 mmHg (r = 0.803 and 0.748, respectively). Normalized % delta L (N% delta L) was best related to fraction normal zone MBF in the endocardium by the sigmoidal equation, N% delta L = e9.01 MBF-4.03/1 + e9.01 MBF-4.03. % delta L was only weakly related to myocardial blood flow in the epicardium (r = 0.584), and, in four dogs, % delta L was zero in the epicardium despite normal regional blood flow. However, % delta L in the epicardium was linearly related to % delta L in the endocardium (r = 0.78). Thus, endocardial wall motion is related to MBF by a sigmoidal relationship while epicardial wall motion is tethered to endocardial wall motion.