Showing papers in "Basic Research in Cardiology in 1985"

The coronary endothelium: a highly active metabolic barrier for adenosine.

Abstract: Cultured coronary endothelial cells and the coronary endothelium of isolated perfused guinea-pig hearts are characterized by a very active adenosine and adenine nucleotide metabolism. Adenosine applied to the endothelium at low concentrations is avidly metabolized and preferentially incorporated into different nucleotide pools—only a minor amount is degraded to uric acid. Physiologically, the coronary endothelium therefore functions as an impermeable metabolic barrier for interstitially or intravascularly accumulating adenosine. Only at concentrations≧10−6M adenosine can pass the endothelial barrier. As a consequence, the vasodilatory action of adenosine formed in or administered into the coronary system cannot be induced by a direct association of the nucleoside with the putative adenosine receptor of the arteriolar smooth muscle cells, but must be mediated by the endothelium. High molecular weight derivatives of adenosine, clearly confined to the coronary system, can also induce a coronary dilation. The endothelium-mediated smooth muscle relaxation is therefore obviously due to triggering of an extracellular adenosine receptor at the luminal surface of the endothelium. Since this process is accompanied by a rapid and pronounced activation of the adenylate cyclase system, the endothelial receptor conforms to an A2-type.

The role of endothelium in the control of vascular tone

Abstract: In the last few years, experimental evidence has accumulated which suggests a substantial role for the endothelium in the control of vascular tone. Endothelium-dependent dilatations have been demonstrated in various arteries of numerous mammalian species including man. Among the stimuli which elicit endothelium-dependent dilatation are such varying stimuli as increases in blood flow and hypoxia, as well as endogenous (acetylcholine, ATP, ADP, bradykinin, substance P) and pharmacological agents (calcium ionophore A 23187, ergometrine, hydralazine, melittin). The functional importance of endothelium-dependent dilatation is emphasized by the fact that the direct vasoconstrictor effects of some of these substances (acetylcholine, histamine, norepinephrine, serotonin) on vascular smooth muscle is attenuated or even reversed by their simultaneous stimulatory effect on endothelial cells, resulting in the release of a vasodilator signal. Bioassay experiments have shown that a humoral vasodilator agent with a biological half-life in the range of seconds is released from the endothelium (native or cultured) during stimulation with acetylcholine, ATP and calcium ionophore. Experimental data are presented, which suggest that EDRF may act by direct stimulation of guanylate cyclase, resulting in smooth muscle relaxation due to increased smooth muscle cyclic GMP levels. The chemical nature of this nonprostaglandin endothelium-derived relaxant factor (EDRF) is still not known. The possible physiological and pathophysiological significance of endothelium-dependent dilatation in situ is discussed. Special attention is paid in this context to the potential role of EDRF activity in coronary vasomotor control.

Effect of adenosine and AICAR on ATP content and regional contractile function in reperfused canine myocardium.

Abstract: We investigated whether the postischemic acceleration of adenosine triphosphate (ATP) synthesis by means of precursor infusion is beneficial for the contractile function of reperfused myocardium. A coronary artery was occluded for 45 min in 21 dogs to produce a marked but reversible ischemia. During the following 3 hours of reperfusion either adenosine (n = 6) or AICAR (5-amino-imidazole-4-carboxamide-riboside) (n = 6) was infused intracoronarily by a small transfemoral catheter positioned in the LAD. ATP repletion by adenosine was nearly 50% of the deficit caused by the previous ischemia, the effect of AICAR on steady-state tissue ATP concentration was insignificant. Regional systolic function of these both groups was compared to that of a control group (n = 9) receiving only a saline infusion. We measured the regional function by subendocardially implanted ultrasound transducers using the transit time method. All three groups showed a reduction to about 25% of the initial segment shortening at the end of ischemia, followed by a quick recovery to half of the preocclusion segment shortening after reopening of the vessel. No further changes were observed in the control series during the 3 hours of reperfusion (50 +/- 10% SE segment shortening at the end). With adenosine infusion - in spite of the resulting considerable ATP elevation - no significant change of segmental contractile function occurred (44 +/- 5% SE segment shortening). Only the AICAR treated group differed from control. It produced a continuous deterioration during reflow resulting in a holosystolic bulging of -20% +/- 10% SE at the end of 3 hours of reperfusion. Our results show that there is no correlation between different ATP tissue levels achieved by adenosine infusion and systolic function in reperfused myocardium after regional reversible ischemia. We hypothesize that reperfusion dyskinesia is caused by a failure of energy utilisation rather than of energy supply.

The vascular endothelium: a survey of some newly evolving biochemical and physiological features.

Abstract: The morphological, biochemical and functional characterization of the vascular endothelium has become possible through the broad use of electron microscopic methods, the successful elaboration and application of techniques for the isolation and cultivation of endothelial cells in vitro and through sophisticated studies on vessel and organ preparations, both in vitro and in vivo. In this survey emphasis is placed on certain methodological aspects of endothelial cell culture as well as on biochemical, physiological and pathophysiological features of the vascular endothelium. Endothelial cells can be propagated in culture dishes, the most commonly applied method, on suspended microbeads (dextrane, polyacrylamide), a technique giving large yields, or on thin porous membranes, a procedure suited for the study of transport processes across the endothelial layer. Different structural, biochemical and functional properties of the luminal (apical) and abluminal (basal) cell membrane determine important polarity features of the endothelium. Endothelial cells exhibit a variety of biochemical pathways and are characterized by high metabolic activities. Of particular interest is the large content of ATP in endothelial cells of different vascular origin. The rapid intracellular degradation of adenine nucleotides to nucleosides and bases, which are constantly released, is balanced by synthesis, mainly via salvage pathways. In endothelial cells of microvascular origin uric acid predominates by far as the final purine degradative because of the presence of xanthine dehydrogenase in these cells; in the macrovascular endothelium purine breakdown proceeds only to hypoxanthine, since xanthine dehydrogenase is lacking. In this connection interrelations between nucleotide catabolism in myocardial tissue and in coronary endothelial cells are discussed, also with respect to the participation of endothelial xanthine oxidase in the formation of oxygen radicals during post-ischemic reperfusion of the heart. Vascular endothelial cells of different origin are also capable of a rapid extracellular degradation of ATP, ADP and AMP to adenosine by means of specific ecto-nucleotidases. The subsequent fate of extracellularly formed adenosine appears to be different for endothelial cells of microvascular (preferential adenosine uptake) and macrovascular origin (preferential extracellular adenosine accumulation), thus implying functional consequences for platelet aggregation. Experimentally well supported aspects of endothelial functions under physiological and pathophysiological conditions include:

Ischemia aggravating effects of platelet-activating factor in acute myocardial ischemia

Abstract: The effect of platelet-activating factor (PAF) was studied during the acute phase of myocardial ischemia in cats. PAF infusion (0.75 μg/kg/h for 4.5 h) in anesthetized, open-chest cat decreased arterial blood pressure, but did not influence heart rate or biochemical indices of cell integrity. The same dose of PAF, however, started 30 min after coronary ligation, resulted in a significantly higher elevation of plasma creatine phosphokinase (CK) activity and a reduced CK content in the region of the ischemic myocardium. Treatment with the thromboxane A2 synthetase inhibitor, CGS-13080, significantly attenuated the PAF-aggravated ischemic cellular damage. These experiments suggest that hypoxiagenerated PAF may contribute to the aggravation of myocardial ischemia, part of which appears to be due to PAF-induced release of thromboxane A2.

Prostaglandins, Other Eicosanoids and Endothelial Cells

Abstract: Endothelial cells are an important source of eicosanoid formation in the cardiovascular systems. All major pathways of eicosanoid production have been demonstrated in endothelial cells, yielding significant amounts of prostacyclin (PGI2), PGE2, PGF2α, thromboxane A2, leukotrienes and a number of hydroxy fatty acids. The regulation of eicosanoid formation by endothelial cells is poorly understood. There is evidence that precursors, such as arachidonic acid or prostaglandin endoperoxides, may also be provided by other cell types. Endothelial cell-derived eicosanoids are involved in the regulation of local vessel tone, intravascular platelet activation, cell locomotion and, eventually, cell proliferation. Most of the available information considers PGI2. This compound is the quantitatively dominating eicosanoid in endothelial cells. Major actions of PGI2 include inhibition of platelet activation and aggregation, relaxation of arterial vessels and inhibition of growth-factor release. There is probably a tight interaction with other biologically active mediators which needs further evaluation. This also applies to the clinical significance of eicosanoid-related pathways for the mechanism of action of cardiovascular drugs, such as organic nitrates or acetylsalicylic acid. The unique property of the cicosanoid system to become activated only in response to stimulation, the local nature of this reaction, the multiplicity of products formed and the short half-time of most of them are currently the most significant obstacles to define the role of endothelial cell-derived eicosanoids in clinical practice.

On the mechanism of enhanced ATP formation in hypoxic myocardium caused by glutamic acid

Abstract: The effect of glutamic acid on the cardiac contractile function and sources of anaerobic ATP formation in hypoxic myocardium was studied in isovolumic rat hearts. The presence of glutamic acid (5 mM) in the perfusate significantly diminished an increment in diastolic pressure caused by 60 min hypoxia, and facilitated its complete recovery during 30 min reoxygenation. This effect was combined with the maintenance of a higher ATP level during hypoxia and reoxygenation. The total content of lactate in the heart-perfusate system rose exactly as during hypoxia without glutamic acid, while pyruvate content decreased due to increased alanine formation. Restoration of tissue content of glutamate and aspartate in the presence of exogenous glutamic acid was accompanied by a more than 2-fold increase in succinate formation, the end-product of the Krebs' cycle under anaerobic conditions. The products of glutamic acid transamination with oxaloacetic acid, aspartic and α-ketoglutaric acids 95 mM each), induced the same functional and metabolic alterations as glutamic acid. Amino-oxyacetic acid, a tramsaminase inhibitor, eliminated the effects caused by glutamic acid. Moreover, the inhibition of transamination was accompanied by a decreased succinate and alanine synthesis as well as insignificantly increased lactate formation compared to hypoxia without additives. The results suggest that the beneficial effect of glutamic acid is due to the activation of anaerobic ATP formation in the mitochondria rather than stimulation of glycolysis.

Lipid peroxidation and scavenger mechanism in experimentally induced heart infarcts

Abstract: Dog experiments were performed to describe the time course of lipid peroxidation after various ischemic influences of the heart measured by formation of malondialdehyde (MDA), and the scavenger action determined by reduced glutathione (GSH) content and superoxide dismutase (SOD) activity. Experimental groups consisted of control dogs having intact hearts and dogs with acute ramus descendens anterior ligature (LAD) having ischemic areas through 15, 30, 45 minutes and 1, 2, 3, 24 hours. Heart tissue for biochemical assays was excised from both the ischemic areas and from nonischemic left ventricle. The acute ischemia caused characteristic alterations in the biochemical parameters: MDA level gradually increased with its peak value being found at the end of 3 hours ligature. GSH levels decreased moderately, whereas SOD levels reduced sharply. As incrcased MDA formation indicates breakdown of the polyunsaturated fatty acids (PUFA) in the membranes and decreaased GSH and SOD levels indicate impairment of the natural scavengering, the observed changes clearly outline the extent of disintegration of membrane structure and function.

The influence of endurance training on mechanical catecholamine responsiveness, β-adrenoceptor density and myosin isoenzyme pattern of rat ventricular myocardium

Abstract: An investigation was carried out on the effects of 4 weeks' swimming training (2×90 min/day) on myocardial isometric tension development and rate of tension rise, and also on the changes induced therein by in vitro application of isoproterenol. This was done in 9 isolated papillary muscles of 9-weekold male Wistar rats and the results were compared with the data of age-matched sedentary controls. Ventricular β-adrenoceptors ([3H]-dihydroalprenolol binding) and the isoenzyme pattern of myosin (pyrophosphate gel electrophoresis) were examined in the same individuals. Isometric tension (T) and its first derivative (dT/dt) measured at the optimum of the length-tension diagram were moderately increased by long-term swimming training. Isoproterenol (10−5 mol/l) induced a greater absolute and relative increase of both mechanical parameters in specimens of trained animals than in age-matched controls (†T: 3.6±1.6 vs. 1.9±0.6×10−2 N/mm2, p<0.05. †dT/dt: 43.4±14.0 vs. 30.4±9.5×10−2 N/mm2·s, p<0.05). K d decreased significantly (4.23±1.0 vs. 2.44±0.3 nM, p<0.02), indicating an increase in receptor affinity, whereas receptor density revealed a tendency to decrease (98.8±22.6 vs. 67.1±18.0 fmol/mg protein, p<0.1). In addition, there was a shift in the isoenzyme pattern of myosin towards VM-1 after swimming training. Thus, under the conditions of the present experiments, the mechanical response to isoproterenol does not correlate to β-adrenoceptor density. It is probable that, apart from the altered sensitivity of the receptors, other membrane or post-membrane processes, are responsible for the increased mechanical responsiveness to catecholamines. Although a relationship between myosin isoenzyme pattern and mechanical responsiveness to catecholamines is apparent taking into account our results and the findings on hypertensive rats as reported in the literature, it cannot be accounted for simply by altered β-adrenoceptor density.

The microsphere method facilitates statistical assessment of regional blood flow.

Abstract: When microspheres are injected into the circulation, they are trapped in the arteriolar or capillary system within various organs It has been confirmed in animal experiments that the number of microspheres in a myocardial sample approximately follows a Poisson distribution, under adequate experimental conditions On the basis of this result, we arrived at the following hypothesis: When regional blood flow is measured under a steady state by the reference sample method, the 95% relative error can be approximated by +/- 196 square root 1/v + 1/w, where v and w represent the number of microspheres in blood sample and myocardial sample, respectively The equation is valid if v and w are greater than 400 and 49, respectively We obtained an expression of the relation among the percent of increase or decrease in regional blood flow being verified, the probability of increase or decrease, as a statistically significant variation and the number of microspheres in a myocardial sample An investigator can work out an approximate experimental design using this expression For instance, when the increase in regional blood flow required for verification is expected to be 20% and he wants this increase to be verified by 90%-probability and as a statistically significant increase, he can predict from this expression that the number of microspheres in a myocardial sample should be 472 and 567 before and after the experimental intervention on the coronary circulation, respectively The expression is useful as index for experiments involving use of the microsphere method

Biochemical and morphological study of cardiac hypertrophy. Effects of thyroxine on enzyme activities in the rat myocardium

Abstract: Experimental hyperthyroidism induced in rats by daily injections of 3,3′,5,5′-tetraiode-l-thyroxine (0.5 mg/kg i.p.) for 14 days resulted in a significant increase in heart weight and heart weight/body weight ratio. Hemodynamic and morphological studies were performed in one group. Thyroxine-treated rats showed a characteristic cardiovascular hyperdynamic state, such as tachycardia and augmented rate of contraction, but no evidence of heart failure such as elevated end-diastolic pressures. The cardiac cells in hyperthyroid rats had a significantly larger diameter and more mitochondria than did those of the control rats. In another group the activities of cardiac enzymes involved in energy utilization and liberation were measured biochemically and compared with those of normal controls. Hyperthyroidism resulted in increased specific activity of cytochrome C oxidase and actomyosin ATPase in the myocardium. The specific activity of long-chain acyl-CoA synthetase, carnitine palmityltransferase, carnitine acetyltransferase, malate dehydrogenase and citrate synthase showed a moderate to marked increment, whereas the specific activity of lactate dehydrogenase and pyruvate kinase remained at the control values. These results suggest that in hyperthyroid rat hearts the functions of both energy liberation and utilization systems are enhanced to meet the added workload. Moreover, the increased activity of the enzymes participating in fatty acid metabolism suggest that in thyroxine-induced hypertrophic and hyperdynamic rat hearts, fatty acids contribute more to the energy supply than do carbohydrates.

Spontaneous versus triggered contractions of "calcium-tolerant" cardiac cells from the adult rat ventricle.

Abstract: Cardiac cells were isolated from the adult rat ventricle by an enzymatic treatment. The cells considered intact were quiescent in the presence of 2.5 mM free Ca2+ but responded to an electrical stimulation by an homogeneous and brief contraction. When the procedure failed, spontaneous cyclic contractions occurred. Often they propagated as a wave from an intercalated disk, and the tension recording showed several components in each contraction. Electrical stimulation at a frequency higher than that of the spontaneous contractions induced synchronous activation with a single component of the tension. Experiments in skinned cardiac cells suggested that the spontaneous cyclic contractions observed in enzymatically separated cardiac cells are caused by a spontaneous cyclic release of Ca2+ from the sarcoplasmic reticulum (SR). This spontaneous release requires a Ca2+ overload of the SR. Its mechanism is different from that of the Ca2+-induced release of Ca2+, which is elicited by a rapid increase of [free Ca2+] at the outer surface of the SR of a previously quiescent skinned cell.

Energetic changes of myocardium as an adaptation to chronic hemodynamic overload and thyroid gland activity.

Abstract: Pressure-overload cardiac hypertrophy and hypothyroidism were shown to be associated with a decreased maximum shortening velocity of the myocardium. To investigate the nature of these intrinsic myocardial changes, we studied the energetic consequences in left ventricular papillary muscles of the rat by using standard HILL planar vacuum-deposited antimony-bismuth thermopiles. To evaluate the economy of isometric force generation and maintenance, we analyzed the ratio of liberated heat and developed tension or developed tension-time integral in twitches and experimentally induced tetanic contractions. Hypothyroidism was induced by treatment with propylthiouracil (PTU), and hypertension by operative narrowing of the left renal artery of rats according to Goldblatt (GOP). In the myocardium of hypothyroid as well as hypertensive rats, initial heat per peak twitch tension and total activity-related heat per tension-time integral were significantly reduced compared to controls. In tetanic contractions, total activity-related heat per tension-time integral was also decreased in PTU and GOP myocardium when compared to controls. Thus, the economy of force generation and maintenance is improved in the myocardium of the experimental animals. The data is interpreted in terms of altered cross-bridge cycling rates which are shown to be associated with changes in the myosin isoenzyme pattern. The intrinsic changes of the myocardium due to pressure-overload hypertrophy and hypothyroidism are considered to be adaptive rather than pathologic reactions of the myocardium.

Platelet depletion in experimental myocardial infarction.

Abstract: Accumulation of platelets in the microvasculature after acute myocardial ischemia may exacerbate tissue injury through the formation of microthrombi and by the release of vasoactive substances. To assess the role of platelets in myocardial ischemic injury and infarction, circulating platelets were reduced by 94±2% (mean±S.E.M.) with sheep antiserum to canine platelets. Regional myocardial ischemia was produced by occlusion of the left circumflex coronary artery (LCCA) for 90 min followed by reperfusion for 5 hours. Infarct size did not differ significantly between antiplatelet serum and nonimmune serum groups: 36±8vs. 43±4% of the area at risk, determined by a post-mortem dual staining technique (p>0.05). A second occlusion-reperfusion control group, sacrificed at 24 hours, did not differ from 5 hr reperfused groups with regard to infarct size. Coronary sinus thromboxane B2 (TXB2) concentrations were not altered significantly by platelet depletion. Histopathologic examination confirmed the presence of necrosis in the infarcted myocardium and revealed substantial leukocytic infiltration in both groups. The results suggest that circulating platelets are not required for the full expression of myocardial ischemic injury resulting from temporary coronary artery occlusion followed by reperfusion.

Mechanisms of ischemic injury in the heart.

Abstract: Cardiac ischemia is characterized by rapid deterioration of cardiac function, which has been linked to the fall in intracellular pH, increased levels of inorganic phosphate and reduction in free energy change of ATP-hydrolysis. Biochemical events responsible for irreversible myocardial injury involve various mechanisms which change the properties of the cardiac cell membrane (disorders in lipid metabolism, free radical formation). Recent evidence suggests that in the heart, xanthine oxidase is a major source of free radical formation. During ischemia, adenine-nucleotide breakdown in the cardiomyocyte proceeds only to the stage of inosine. Due to the localisation of nucleoside phosphorylase and xanthine-oxidase in vascular endothelium, further degradation of inosine to hypoxanthine, xanthine and uric acid occurs predominantly in the vascular space. It is therefore conceivable that the primary site of reperfusion injury in the ischemic heart may be the coronary endothelium damaged by free radicals.

The protective mechanism of estrogen on high blood pressure.

Abstract: In 2 series of experiments on 144 SHRSP, the influence of treatment with different doses of 17-beta-estradiolbenzoate (EB) (0.031, 0.125, 0.5 mg/kg EB or placebo) on the development of hypertension from the 9th to 22nd week of life (increase of blood pressure (BP) of untreated male rats from 178 to 252 mm Hg and of untreated female rats from 151 to 192 mm Hg) and in well established hypertension from the 23th to 36th weeks of life (male untreated rats 238 mm Hg (prior to the observation] was investigated. In both series, observation periods consisted of a therapy phase of 14 weeks and a follow-up phase of the same duration. The untreated female rats had a longer life-span (88.5 weeks) than the untreated male rats (68.0 weeks). The estrogen treatment of female animals had an effect on BP only with the highest dose of EB and had no effect on the life-span of the animals. However, in male rats, the development of hypertension was inhibited by EB. Male rats treated at an earlier stage had a life-span equal to that of the female animals. When hypertension was already well-established treatment with EB had an antihypertensive effect in male rats (BP fall: 27-36 mm Hg), but no prolongation of the life-span was obtained.

The calcium and the oxygen paradox: non-existent on the cellular level.

Abstract: Ca2+-tolerant isolated adult heart cells can be exposed to 1 mM EGTA and then again to 1 mM CaCl2 without developing irreversible hypercontracture. Thus, they are not subject to the calcium paradox, even though they apparently become more permeable to Na+ during Ca2+-free incubation. When these cells are incubated anoxically without substrate they slowly lose their energetic reserves. The process resembles that of the arrested anoxic myocardium. The appearance of irreversibly hypercontracted cells is neither accompanied by a parallel increase in enzyme release nor by an aggravation of the anoxia-induced damage by reoxygenation. Thus these cells are not subject to the oxygen paradox. It is suggested that the differences between the myocytes' behaviour in tissue and in the isolated state are due to the fact that the isolated cells are free from mechanical interactions with adjacent cells.

Formation and release of nucleosides in the ischemic myocardium. Is the guinea-pig the exception?

Abstract: In this study evidence is provided to suggest that nucleoside formation with hypoxia in myocardial tissue from the guinea-pig follows a different course from that in the rat, rabbit or dog. 1) After ischemia, tissue levels of adenosine remain barcly detectable in the guinea-pig but rise considerably in the rat and the dog. 2) IMP, remaining almost absent in the dog, does not change in the rat but strongly increases (×6) in the guinea-pig heart with ischemia. 3) Mioflazine, a nucleoside transport inhibitor, completely reverses the ratio adenosine/inosine in dog myocardium after 8 min of ischemia, making adenosine by far the major nuclcoside. No effect could be detected in the guinea-pig. 4) In contrast with the rat and rabbit, ischemia in the guinea-pig does not lead to any considerable release of adenosine upon reperfusion. 5) In the rabbit, the presence of a nucleoside transport inhibitor completely reverses the adenosine/inosine ratio in reperfusates after ischemia. Although the release is strongly inhibited under these conditions in the guinea-pig, adenosine release remains negligible when compared with inosine. 6) Even in the presence of high concentrations of an adenosine deaminase inhibitor, inosine remains the major metabolite released upon reperfusion after ischemia, in the guinea-pig heart.

Adrenergic innervation of coronary arteries and ventricular myocardium in the pig: fluorescence microscopic appearance in the normal state and after ischemia.

Abstract: A fluorescence histochemical study was performed to describe the adrenergic innervation of the coronary arteries and the left ventricular myocardium in the pig. Large bundles of adrenergic nerve fibres were almost exclusively found running along the large coronary arteries. The arteries usually show a dense innervation of the vessel wall, evenly distributed throughout the adventitia in the larger arteries and more concentrated to the adventitia-medial border in the smaller arteries and arterioles. Most parts of the left ventricular myocardium showed a dense adrenergic innervation, however, a moderate dense and in some areas even sparse innervation was observed towards the apex of the left ventricle. Following 10 or 20 min of ischemia a small reduction in fluorescence intensity was observed in 2 out of 6 hearts. In 4 of the hearts other changes of the appearance of the adrenergic terminals were found, e.g., an unsharp, spread-out or interrupted appearance.

A new device for slow progressive narrowing of vessels.

Abstract: The purpose of this work was to develop a device which allows slow progressive banding of a great artery in infants within 4 to 5 weeks. Employed was the hygroscopic casein ameroid. When brought in contact with fluids, an ameroid cylinder expands characteristically. An early phase of fast expansion proceeds gradually to a phase of slow growth. Size, shape, and encasement of ameroid as well as temperature and type of surrounding fluid modify but do not alter the typical pattern of expansion. The developed constrictor (weight: 5.8 kg, length: 18 mm, diameter: 12 mm) includes a stainless steel socket containing an ameroid cylinder (length: 8.5 mm, diameter: 8 mm). The expanding ameroid pushes a piston with a concave extension (makrolon) a maximum of 2 mm against the artery, which is fixed to the metal housing by a teflon band (width: 4 mm, thickness: 0.5 mm). The band runs in 2 fitting grooves on the metal housing to which it is fixed by a metal ring with a precisely manufactured internal thread allowing exact tightening and loosening of the band around the artery. Utilization of inert materials like teflon, makrolon, and stainless steel warrants experimental and possibly clinical application of the developed small constrictor.

Molecular mechanisms regulating myocardial glucose oxidation.

Abstract: In heart muscle regulation of pyruvate dehydrogenase (PDH) complex activity by reversible phosphorylation is the major determinant of glucose oxidation under physiological conditions and in diabetes. Altered mitochondrial concentrations of effectors of PDH kinase and phosphatase (metabolites, Ca2+, H+) appear to explain effects of oxidation of lipid fuels, myocardial contraction and ischaemia on PDH complex activity. The effects of diabetes and starvation are mediated in addition by protein(s) which increase the activity of PDH kinase. End product inhibition by NADH may be important in ischaemia.

Relation of early mononuclear and polymorphonuclear cell infiltration to late scar thickness after experimentally induced myocardial infarction in the rat.

Abstract: This report describes the relationship between the intensity of early inflammation after acute myocardial infarction and the later thickness of the left ventricular (LV) scar Histologic sections of hearts from methylprednisolone-treated (MP), cobra venom factor-treated (CVF), and untreated control rats that had been subjected to either 2 or 21 days of coronary artery occlusion were studied In the rats examined at 2 days (n=20 for MP, n=16 for CVF, and n=20 for controls), a semiquantitative inflammation score (1–4) was attributed to each infarct Mononuclear (MN) cells were counted in 4 oil-immersion fields per section and polymorphonuclear (PMN) cells in 9 oil-immersion fields per section In the rats examined at 21 days (n=22 for MP, n=22 for CVF, and n=26 for controls), the thickness of the LV scar was measured every 16 mm along its circumference Inflammation scores at 2 days were 35±6 for controls, 15±5 for MP, and 29±8 for CVF (p<05 among groups) The MN cells counted were 73±7 for controls, 47±5 for MP, and 61±9 for CVF (p<05 among groups) There was no difference in PMN infiltrate among groups Scar thickness at 21 days were 9±1 mm for controls, 7±1 mm for MP, and 9±1 mm for CVF (MP compared to CVF and controls, p<01)

Blood pressure and arginine vasotocin in normonatremic and hypernatremic ducks

Abstract: As a model to study effects of chronic, excessive salt loading on circulation, Pekin ducks were adapted to 2% saline solution as their sole water supply, while fresh-water-adapted animals were used as controls. Due to the development of salt-climinating glands, salt-adapted ducks are able to cope indefinitely with this salt stress which means a daily ingestion of 5–6 g NaCl per kg body weight per day, associated with a chronic elevation of plasma osmolality and plasma sodium by 5–8% above normal and an up to 3-fold increase of antidiuretic hormone concentration in comparison to animals maintained on fresh water. Salt loading for up to 14 months did neither increase arterial mean, nor diastolic, nor pulse pressure. On the contrary, arterial mean and diastolic pressure were slightly lower in the salt-adapted than in the fresh-water-adapted animals, while pulse pressure and heart rate did not differ. Circulatory adaptation to removal and reinfusion of 10% of the estimated blood volume was identical in salt-water and fresh-water-adapted ducks. It is concluded that even excessive chronic salt loading resulting in chronic hyperosmolality with high plasma levels of sodium and antidiuretic hormone does not alter hemodynamic adaptation, provided that efficient compensating mechanisms are at the animal's disposal.

Uncoupler- and hypoxia-induced damage in the working rat heart and its treatment. II. Hypoxic reduction of aortic flow and its reversal.

Abstract: In the isolated working rat heart, the damaging effect of 0.05–0.06 μM Carbonylcyanide-p-trifluoro-methoxyphenylhydrazone (FCCP) was reversible within 20 sec by perfusion with fresh buffer. Cysteine 3 mM restored the aortic flow to the initial value within an additional 15–20 sec. Thereafter, the FCCP effect became irreversible due to a progressive structural membrane change. The structural change by FCCP is probably brought about by ‘internalization’ of polar groups (R-SH; R−NH3+) of the mitochondrial (and other) membrane.

Adenosine-induced increase in myocardial adenine nucleotides without adenosine-induced systemic hypotension.

Abstract: In anaesthetized rabbits, the i.v. application of 1% adenosine (Ado) for 3 hours at a rate of 4 ml·h−1·kg−1 body weight increased the myocardial tissue levels of adenine nucleotides (AN) above the normal values by 39%. This increase in ATP and the sum of AN is a metabolic effect of the continuous and high supply of Ado and does not result from the Ado-induced systemic hypotension: Neither a comparable hypotension and reduction of circulatory work induced by phentolamine nor a massive volume loading caused changes in the AN. The compensation of the Ado-induced hypotension by a simultaneous i.v. application of caffeine or xylometazoline did not interfere with the accumulation of AN. The increase in AN was less pronounced, if norepinephrine was infused to maintain normotension. The increase in AN occurred in left and right ventricular myocardium to a similar extent, although the pressure-volume-work of the left ventricle decreased, and that of the right ventricle increased during Ado-application.

Response of the right ventricle to progressive pressure loading in pigs.

Abstract: The purpose of this study was to determine the speed and duration of progressive pressure loading of the right ventricle to systemic pressure levels, which allows right ventricular adaptation without myocardial impairment at rest. In 8 pigs with an average weight of 22 kg progressive right ventricular pressure loading of different speeds and durations was induced with a newly developed constrictor. Pressures in the right atrium, right ventricle, and pulmonary artery as well as angiocardiographic volume parameters of the right ventricle were determined weekly over a period of 4 to 7 weeks. A fast progressive right ventricular pressure increase of 3.4 mm Hg/day during 3 weeks was associated with a 20–30% reduction of ejection fraction and a 100% increase of the end-systolic volume. Increase of end-diastolic pressure was 3 to 5 fold. A slow progressive pressure increase of 1.5 to 2.2 mm Hg/day to 100 mm Hg within 4 to 5 weeks was associated with an increase of the end-diastolic pressure to a level observed in systemic ventricles, while change of ejection fraction and end-systolic volume was minimal. The faster the increase of right ventricular pressure the flatter was the peak systolic pressure/end-systolic volume relationship. It is concluded that in contrast to sudden and fast progressive increase of afterload slow progressive increase of afterload to systemic levels does not impair right ventricular myocardial function.

Presystolic calcium-loading of the sarcoplasmic reticulum influences time to peak force of contraction. X-ray microanalysis on rapidly frozen guinea-pig ventricular muscle preparations

Abstract: 1. Guinea-pig ventricular small papillary muscles and trabeculae were rapidly frozen presystolically after prolonged rest following positive inotropic interventions which strongly influenced peak of force and time to peak force. The possible sources of activator calcium for the different types of contraction were investigated. 2. After rest in the presence of noradrenaline (10−5mol/l) the first post-rest contraction showed a retarded activation and a “late” peak of force. Muscle strips frozen after a rest period of 5 min in a bath solution containing noradrenaline were cryosectioned and analyzed with X-ray microanalysis for elemental distribution: although at this time an applied stimulus would induce a potentiated contraction, intracellular membrane systems such as sarcoplasmic reticulum and mitochondria failed to reveal any accumulation of calcium. 3. After rest in a low sodium Tyrode the first post-rest contraction showed an “early” peak of force. Muscles frozen after rest in a low sodium solution revealed intracellular Ca accumulation on the sarcoplasmic reticulum, in the network at the level of the Z-lines. 4. The results support the hypothesis that 1. the sarcoplasmic reticulum (SR) accumulates calcium presystolically when “early” contractions follow stimulation; 2. the network of sarcoplasmic reticulum at the level of the Z-lines is a crucial source of activator calcium; 3. the activator calcium for late contractions is probably of extracellular origin.

Cyclical coronary flow reductions in conscious dogs equipped with ameroid constrictors to produce severe coronary narrowing.

Abstract: In conscious dogs equipped with ameroid constrictors to produce gradual coronary occlusion, coronary flow velocity was monitored prior to complete occlusion when coronary constriction was severe (resting flow velocity reduced by 10–50% from control recordings made 7–10 days after ameroid implantation). In six of the ten dogs, we observed spontaneous cyclical variations in coronary flow velocity, characterized by gradual reduction in flow followed by very abrupt restoration of flow. The cyclic coronary flow reductions were observed between 20 and 31 days after ameroid implantation. These changes in flow bear striking similarity to those observed by previous investigators using anesthetized, open-chest canine preparations, in which the role of platelets was clearly demonstrated. Consequently, we hypothesize that spontaneous platelet aggregation and de-aggregation within the severely narrowed coronary lumen (enclosed by the ameroid constrictors) could account for our observations.

Myocellular calcium regulation by the sarcolemmal membrane in the adult and immature rabbit heart.

Abstract: Previous studies have suggested ontogenic differences in Ca-mediated excitation-contraction coupling in mammalian heart. Sarcolemmal (SL) Ca regulation may predominate prior to the development of the specialized Ca-regulatory properties of the sarcoplasmic reticulum (SR). The effect of development on selected Ca-regulatory properties of cardiac SL was evaluated utilizing membrane vesicles obtained from immature (14 to 21-day-old) and adult rabbit heart.

Nifedipine limits infarct size for 24 hours in closed chest coronary embolized dogs.

Abstract: We studied the ability of nifedipine, a calcium antagonist, to limit infarct size in the closed chest, coronary embolized dog. Immediately after embolization141Ce labelled microspheres were administered into the left ventricle. Myocardium not receiving microspheres was considered to be the region at risk. The nifedipine group (10 dogs) received a bolus (16 μg/kg i.v. over 8 minutes as a loading dose) followed by continuous infusion (1,000 μg/24 hours) 10 min after embolization. The control group (9 dogs) received an equal volume of saline. Twenty-four hours after embolization the dogs were sacrificed, the heart sectioned into 4-mm slices and the slices were stained with tetrazolium to reveal the infarct. The region at risk was determined by autoradiography of the microspheres in the heart slices. Infarct and risk zone volume were determined by planimetric methods. The nifedipine group had a significantly smaller infarct volume to risk zone voluem ratio than the control group (38.7±4.7% vs. 79.5±4.3%, p<0.001). We conclude that nifedipine produces a sustained limitation of infarct size following permanent occlusion of a dog's coronary artery.