Showing papers by "University of Texas Southwestern Medical Center published in 1984"

Homologies between signal transducing G proteins and ras gene products

Abstract: The guanosine triphosphate-binding proteins (G proteins) found in a variety of tissues transduce signals generated by ligand binding to cell surface receptors into changes in intracellular metabolism. Amino acid sequences of peptides prepared by partial proteolysis of the alpha subunit of a bovine brain G protein and the alpha subunit of rod outer-segment transducin were determined. The two proteins show regions of sequence identity as well as regions of diversity. A portion of the amino-terminal peptide sequence of each protein is highly homologous with the corresponding region in the ras protein (a protooncogene product). These similarities suggest that G proteins and ras proteins may have analogous functions.

Leydig Cell Numbers, Daily Sperm Production, and Serum Gonadotropin Levels in Aging Men

Abstract: Age-related changes in Leydig cell number, daily sperm production, and circulating hormone levels were studied in 15 men between 20 and 48 yr of age and 15 men between 50 and 76 yr of age. Testes and blood samples were obtained at autopsy less than 15 h after death due to trauma or heart attack. Leydig cell number was determined by quantitative histometric estimation of the proportion of glutaraldehyde-perfused, decapsulated testicular parenchyma occupied by Leydig cell nuclei of measured average volume in both testes of each subject. Daily sperm production was determined by phase contrast cytometry of round spermatid nuclei in homogenates of both fixed testes from each individual. LH, FSH, PRL, and testosterone in serum from the heart or large veins were quantified by RIA. No relationship was detected between any of the testicular or hormonal values and postmortem time. The average total number of Leydig cells was reduced by 44% in the older men and was negatively correlated with age (p = -0.62) in all men. Mean serum LH was elevated more than 2-fold in the older men and was positively correlated with age (p = +0.53) in all men. Neither serum testosterone nor serum PRL changed significantly with age. Daily sperm production was more than 50% lower in older men and was negatively correlated with age (p = -0.76) in all men. Serum FSH was more than 3-fold higher in the older men and was positively correlated with age (p = +0.72) in all men. The highest FSH levels were found in men with the lowest rates of sperm production, and FSH and daily sperm production were inversely correlated even after the effects of age were removed. These findings show that the response of the human testis to aging is variable and that the predictive value of age for most testicular characteristics is weak at the level of individual men. Nevertheless, age accounts for more than a third of the variation in Leydig cell number, and it explains more than half the variation in daily sperm production. Hence, age is the largest single contributing factor yet identified in the search for explanations underlying the variation in testicular structure and function found in groups of normal men.

Increased expression of Ia antigens on resting B cells: an additional role for B-cell growth factor.

Abstract: The present studies demonstrate that both T-cell-derived supernatants containing B-cell growth factor (BCGF or BSF) and a partially purified preparation of the B-cell growth factor (BSF-p1) induce an increase in the expression of IA and IE-encoded antigens on small resting B cells. This increase is detectable by 6-8 hr after initiation of culture and is relatively selective, since levels of surface immunoglobulin and H-2 antigens do not increase to the same extent. Although interferon-gamma induces increased expression of Ia antigens on macrophages and dividing neoplastic B cells, it does not induce an increase in the expression of Ia antigens on resting B cells. These results demonstrate that BSF-p1 may play two roles: (i) it acts on resting B cells to increase the levels of Ia antigen expression; and (ii) it sustains the growth of B cells that have been previously activated with mitogens, antigens, or anti-Ig.

Liver transplantation to provide low-density-lipoprotein receptors and lower plasma cholesterol in a child with homozygous familial hypercholesterolemia.

Abstract: A six-year-old girl with severe hypercholesterolemia and atherosclerosis had two defective genes at the low-density-lipoprotein (LDL) receptor locus, as determined by biochemical studies of cultured fibroblasts. One gene, inherited from the mother, produced no LDL receptors; the other gene, inherited from the father, produced a receptor precursor that was not transported to the cell surface and was unable to bind LDL. The patient degraded intravenously administered 125I-LDL at an extremely low rate, indicating that her high plasma LDL-cholesterol level was caused by defective receptor-mediated removal of LDL from plasma. After transplantation of a liver and a heart from a normal donor, the patient's plasma LDL-cholesterol level declined by 81 per cent, from 988 to 184 mg per deciliter. The fractional catabolic rate for intravenously administered 125I-LDL, a measure of functional LDL receptors in vivo, increased by 2.5-fold. Thus, the transplanted liver, with its normal complement of LDL receptors...

Angiotensin II directly stimulates sodium transport in rabbit proximal convoluted tubules.

Abstract: Numerous previous studies have proposed a role for angiotensin II (AII) in the renal regulation of salt balance. At least one nephron site, the proximal convoluted segment, has been implicated in this role. We used in vitro microperfusion of rabbit proximal convoluted tubules to further examine this question. To insure use of appropriate in vivo concentrations as well as potency of the hormone in vitro, we measured plasma AII levels by radioimmunoassay in normal, sodium-depleted, and adrenalectomized rabbits, and measured AII activity by bioassay after incubation in various microperfusion baths. Plasma levels ranged from approximately 2 X 10(-11) to 5 X 10(-11) M. AII activity was stable in Ringer's solution plus albumin, but not in rabbit serum or Ringer's solution plus fetal calf serum. In Ringer's solution plus albumin, physiologic concentrations of AII stimulated volume reabsorption (Jv). 10(-11) M AII increased Jv by 16% (P less than 0.01). 10(-10) M AII produced a lesser increase, 7.5% (P less than 0.05). At a frequently studied, but probably pharmacologic dose, 10(-7) M AII inhibited Jv by 24% (P less than 0.001). AII at 10(-11) M did not stimulate Jv in the presence of 10(-7) M saralasin. Though previous studies have suggested agonistic effects of saralasin alone in epithelia, we found no significant effect of 10(-7) M saralasin on Jv. None of the AII doses measurably changed transepithelial voltage. We conclude that AII in physiologic doses directly stimulates Jv in proximal convoluted tubules and this effect is probably receptor mediated and, within the limits of detection, electroneutral.

Myosin light chain phosphorylation in fast and slow skeletal muscles in situ

Abstract: The physiological properties of contraction-induced phosphate incorporation into the phosphorylatable light chain (P-light chain) of myosin were examined in fast-twitch white, fast-twitch red, and slow-twitch skeletal muscles in situ. Neural stimulation of rat gastrocnemius muscles between 0.5 and 100 Hz produced an increase in the phosphate content of the P-light chain from the white portion of the muscle, and the rate of P-light chain phosphorylation was frequency dependent. The extent of phosphorylation of P-light chain from the fast-twitch red portion of the gastrocnemius muscle was less. In contrast to fast-twitch skeletal muscle, only high-frequency stimulation (30-100 Hz) produced a small increase in the phosphate content of P-light chain from the slow-twitch soleus muscle. Fast white muscle contained 2.2 and 3.5 times more myosin light chain kinase activity than did the fast red and slow muscle, respectively. The rate of P-light chain dephosphorylation was four times faster in slow muscle than in fast white muscle. Thus the greater extent of phosphorylation of P-light chain in fast-twitch white skeletal muscle fibers may be due in part to the presence of more kinase and less phosphatase activities. Isometric twitch tension potentiation was correlated to the extent of phosphorylation of P-light chain from fast white muscle. The physiological consequences of P-light chain phosphorylation are likely to be of greatest importance in fast-twitch white muscle.

Effect of ischemia on responses of group III and IV afferents to contraction

Abstract: Static contraction of the hindlimb muscles of cats reflexly increases cardiovascular function, an effect that is potentiated by occlusion of the arterial supply to the working muscles. Although group III and IV afferents are known to be stimulated by and to cause the reflex cardiovascular responses to static muscular contraction, little is known about the responses of these afferents to static contraction when the arterial supply to a working muscle is occluded. We therefore recorded the impulse activity of 24 group III afferents and 30 group IV afferents with endings in the triceps surae while we statically contracted this muscle group, both when the abdominal aorta was occluded and when it was patent. A chi 2 analysis revealed that ischemia increased the responses to static contractions of a significantly higher percentage of group IV afferents than group III afferents (46.7% vs. 12.5%, respectively; P less than 0.02). In addition, two patterns of responses to ischemic contraction were observed. The first pattern was displayed by afferents (n = 10) that were stimulated by nonischemic contraction but were stimulated more by ischemic contraction. The second pattern was displayed by afferents (n = 7) that were not stimulated by nonischemic contraction but were stimulated by ischemic contraction. We conclude that afferents displaying both patterns are likely to contribute to the reflex cardiovascular responses to ischemic contraction.

Accumulation of Unesterified Arachidonic Acid in Ischemic Canine Myocardium Relationship to a Phosphatidylcholine Deacylation-Reacylation Cycle and the Depletion of Membrane Phospholipids

Abstract: Studies in ischemic canine left ventricle have shown that the depletion of membrane phospholipids is a critical event in the development of a sarcolemmal calcium permeability defect and associated irreversible myocyte injury. The mechanism of phospholipid loss is unclear, but may be due to the activation of endogenous phospholipases. Since arachidonic acid is a fatty acid found almost entirely in phospholipid, increases in arachidonate provide evidence for increased phospholipase activity. The present study was designed to examine the temporal relationship of the accumulation of free arachidonate with the onset of phospholipid depletion during fixed ligation of the left anterior descending coronary artery in canine myocardium. The following results were demonstrated in ischemic canine myocardium: (1) the accumulation of unesterified arachidonate is minimal during 10-30 minutes of ischemia, but is significantly increased after prolonging the duration of ischemia to 1-3 hours; (2) significant increases in arachidonate precede the development of a significant decrease in total phospholipid content; (3) the decrease in the arachidonate content of phosphatidylcholine is accompanied by similar decreases in all of the fatty acyl moieties; (4) the arachidonate content of lysophosphatidylcholine and diacylglycerol are unchanged during myocardial ischemia; (5) there is evidence of a deacylation-reacylation cycle in phosphatidylcholine prior to the accumulation of free arachidonate; (6) the fatty acyl specificity of the lysophosphatidylcholine acyltransferase corresponds to the pattern of fatty acyl remodeling of phosphatidylcholine during early myocardial ischemia. These data suggest that the accumulation of arachidonate may be a more sensitive measure of phospholipid degradation than the decrease in total phospholipid content in ischemic canine myocardium. It is postulated that the defective reacylation of arachidonate into phosphatidylcholine may contribute to the net loss of membrane phospholipid during myocardial ischemia.

Reorganization of hydrated collagen lattices by human skin fibroblasts

Abstract: Fibroblasts were cultured on top of or at the bottom of hydrated collagen lattices. Shortly after initially interacting with the collagen lattices, fibroblasts appeared to attach to individual collagen fibrils and in many cases cell processes were found wrapped around clusters of collagen fibrils. Tension generated by cells during spreading resulted in proximal collagen fibrils becoming aligned distal in the plane of spreading and more densely packed. During subsequent culture, the collagen fibrils to the cells underwent a similar reorganization and the lattice thinned to one-tenth of its original thickness. The rate of thinning was similar regardless of whether the cells were originally above or at the bottom of the lattices. The presence of cells distributed throughout the lattice was unnecessary for lattice reorganization to occur. When the lattices were allowed to come off the underlying substratum, compaction of the collagen gels was observed, and the resulting matrix had the typical appearance of dermis as observed by both light and electron microscopy. Collagen fibrils associated with the cell surface often appeared to be under tension and, in regions of close fibril binding, there was a prominent reorganization of submembranous microfilaments. It is suggested that reorganization of the collagen lattice by fibroblasts may depend upon secreted cell factors as well as physical forces generated by the cells.

Limitations of qualitative angiographic grading in aortic or mitral regurgitation

Abstract: This study was performed to assess the accuracy of qualitative angiographic grading in persons with aortic regurgitation (AR) or mitral regurgitation (MR) and to determine the factors that may influence the reliability of such grading. In 230 patients (152 men, 78 women, aged 52 +/- 14 years) with AR or MR, forward cardiac index was measured by the Fick and indicator dilution techniques and left ventricular (LV) angiographic index by the area-length method, from which the regurgitant volume index was calculated. In 124 other patients (89 men, 35 women, aged 52 +/- 11 years) without regurgitation, there was good agreement between forward and angiographic cardiac indexes (r = 0.87, p less than 0.001). In the 83 patients with AR, the regurgitant volume indexes in those with 1+ (0.87 +/- 0.57 liters/min/m2) and 2+ (1.72 +/- 1.19 liters/min/m2) angiographic regurgitation were not significantly different from one another, but were significantly different from those with 3+ (3.0 +/- 1.42 liters/min/m2) and 4+ (4.80 +/- 2.25 liters/min/m2) regurgitation; at the same time, the regurgitant volume indexes of patients with 3+ and 4+ AR were not significantly different from one another. In the 147 patients with MR, the regurgitant volume indexes in patients with 1+ regurgitation (0.61 +/- 0.64 liters/min/m2) were significantly lower than other grades, but the regurgitant volume indexes of 2+ (1.14 +/- 0.85 liters/min/m2) vs 3+ (2.14 +/- 1.37 liters/min/m2) and of 3+ vs 4+ (4.60 +/- 2.31 liters/min/m2) were not significantly different. With AR and MR, regurgitant flow within each angiographic grade varied widely, especially in grades 3+ and 4+, and there was considerable overlap of regurgitant volume indexes between grades.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercalcemia associated with increased serum calcitriol levels in three patients with lymphoma

Abstract: A radioreceptor assay for serum 1,25-dihydroxyvitamin D (calcitriol) was used to screen patients with hypercalcemia of malignancy. Three patients with non-Hodgkin's lymphoma and hypercalcemia (serum Ca, 12.0, 13.4, and 13.0 mg/dL, respectively) had increased serum calcitriol levels (56, 72, and 77 pg/mL, respectively; normal, less than 50 pg/mL). Elevated levels of calcitriol, an active vitamin D metabolite, occurred in the presence of significant renal impairment (creatinine clearance, 8 to 19 mL/min) and relative parathyroid suppression (serum immunoreactive parathyroid hormone, 17 to 39 microL-eq/mL; mean value in end-stage renal disease, 182 +/- 39 microL-eq/mL). Hypercalcemia and excessive serum calcitriol levels responded to glucocorticosteroid therapy. In two patients, the hypercalcemia and increased serum calcitriol level were related to a tumor, but not to the serum immunoreactive parathyroid hormone level. Fractional intestinal 47Ca absorption, measured in one patient, was increased (0.94; normal, less than 0.61) and varied directly with the serum calcitriol level. No patient had evidence of sarcoidosis. Hypercalcemia associated with certain lymphomas may be caused by the increased synthesis of calcitriol by lymphoma cells.

Nucleotide sequence of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, a glycoprotein of endoplasmic reticulum

Abstract: The nucleotide sequence of a 4.8-kilobase mRNA for hamster 3-hydroxy-3-methylglutaryl coenzyme A reductase, the endoplasmic reticulum enzyme that controls cholesterol biosynthesis, shows that it is a protein of 887 amino acids (molecular weight 97,092) which contains three potential sites for asparagine-linked glycosylation. The reductase is a transmembrane glycoprotein, but in contrast to many other transmembrane glycoproteins, it lacks a cleavable or Hydrophobie NH2-terminal signal sequence.

Visualization of acidic organelles in intact cells by electron microscopy

Abstract: We report the synthesis of a probe that permits the visualization by electron microscopy of acidic organelles in intact cells. This probe, 3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine (DAMP), is a basic congener of dinitrophenol that readily diffuses into intact cells. Its primary and tertiary amino groups (apparent pKa, 10.6) allow it to be concentrated in acidic organelles and to be retained there after fixation with aldehydes. The dinitroarene moiety of DAMP can then be localized with mouse monoclonal antibodies directed against dinitrophenol. The antibodies, in turn, can be visualized by light or electron microscopy by reaction with rabbit anti-mouse antibodies coupled to rhodamine or horseradish peroxidase, respectively. We have used these methods to show that DAMP concentrates in a variety of membrane-bound structures in cultured fibroblasts, including classic multivesicular bodies (resembling lysosomes), intermediate-sized vesicles with multiple shapes (resembling endosomes), and an abundant population of very small spherical vesicles. A small fraction of coated vesicles is labeled with DAMP. Labeling with DAMP does not occur when the pH gradient of fibroblasts is disrupted by the ionophore monensin or the weak base chloroquine. DAMP should be a useful probe for exploring the assembly, distribution, and function of acidic organelles by electron microscopy.

CSF Shunt Infections in Pediatrics: A Seven-Year Experience

Abstract: • The medical records of children who had had CSF shunt procedures were reviewed for the seven-year period from 1975 through 1981. There were 516 procedures performed in 297 patients. Only three were ventriculoatrial shunts; the remainder were ventriculoperitoneal shunts. Fifty-nine infectious episodes (11%) occurred in 50 patients (17%); there were three relapses and six reinfections. The infecting pathogen was staphylococci in 75% of the infections and gram-negative bacilli in 19%, and there were two or more pathogens in 15% of the infections. The onset of the infection was within 15 days of surgery in 53% of the cases. The main symptoms were fever, irritability, and shunt malfunction. Gram's stain of the CSF was positive in 46% of the episodes and blood cultures were positive in 29%. Nineteen percent of patients had wound infection and 7% had peritonitis; in most of these cases there were no neurologic signs or symptoms. Thirteen episodes were managed with antibiotic therapy alone; among these, there were three relapses and two reinfections. Thirty-seven episodes were treated with antibiotics and immediate removal of the shunt; there were no relapses and three reinfections. Nine episodes were managed with antibiotics and delayed removal of the shunt; there was one reinfection. The median duration of antibiotic treatment was 15 days, and the time to defervescence was 24 hours in those with immediate removal of the shunt and six days in those in whom the shunt was not removed. ( AJDC 1984;138:1103-1108)

Increased ionized calcium and left ventricular contractility during hemodialysis.

Abstract: Routine hemodialysis is associated with an increase in left ventricular contractility that is independent of a change in preload, but the mechanisms responsible are unknown. We investigated the importance of three distinct effects that regularly occur in hemodialysis and could potentially improve left ventricular contractility: the removal of uremic toxins, the increase in the plasma ionized calcium concentration, and the increase in the plasma bicarbonate concentration. Three different dialysates were used for each of eight stable patients on long-term hemodialysis, and left ventricular contractility was assessed by two-dimensional echocardiography before and after each dialysis. In the first procedure neither the ionized calcium nor the bicarbonate concentration was allowed to increase, and left ventricular contractility did not improve. In the second procedure, ionized calcium increased (from 4.4 to 5.4 mg per deciliter, P<0.001), bicarbonate concentration was held constant, and contractility ...

Effects of static and rhythmic twitch contractions on the discharge of group III and IV muscle afferents

Abstract: Although both static and rhythmic twitch contractions of the hindlimb muscles of anaesthetised cats have been shown to reflexly evoke pressor responses, the increase in arterial pressure evoked by the former type of contraction has been shown to be substantially larger than that evoked by the latter. We have therefore recorded the impulse activity of single group III and IV muscle afferents, whose activation reflexly increases arterial pressure, while we both statically and rhythmically twitch-contracted the triceps surae muscles of anaesthetised cats. We found that group III afferents (n=17) discharged significantly more impulses in response to static contraction than in response to rhythmic contraction. By contrast, group IV afferents (n=18) fired approximately the same number of impulses in response to the two types of contraction. In addition, we found that many of the group III but only a few of the group IV afferents displayed discharge properties suggestive that these afferents were mechanoreceptors. We conclude that the discharge of group III afferents are likely to be responsible for the difference in the magnitudes of the reflex pressor responses evoked by static and rhythmic contraction.

A coralline hydroxyapatite bone graft substitute. Preliminary report.

Abstract: Experimental histologic and biomechanical studies were performed in 52 dogs by use of a bone substitute composed of hydroxyapatite converted from sea coral calcite. The results demonstrate some potentially useful practical applications. The material was totally incorporated in bone. Although initially too weak to tolerate physiologic stresses, once incorporated it becomes almost as strong as the native bone. Clinical experience with internal fixation of fractures with hydroxyapatite in 18 patients is encouraging.

Conversion from chronic to acute coronary artery disease: speculation regarding mechanisms.

Abstract: The factors that are primarily responsible for the conversion from chronic to acute coronary artery disease (CAD), including the development of unstable angina pectoris and acute myocardial infarction, remain uncertain. Some patients with angiographic evidence of extensive and severe coronary arterial stenoses anatomically do well with appropriate medical therapy, whereas others with similar or even anatomically less impressive coronary arterial stenoses have clinical manifestations of acute CAD. Improved insight into mechanisms responsible for the conversion of chronic CAD to acute CAD is essential for efforts directed at preventing acute myocardial infarction and sudden cardiac death. The purpose of this editorial is to emphasize recent developments in knowledge relating to alterations in prostaglandin production that may play a role in the development or perpetuation of acute CAD.