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Biomedical subjects

K Wildenthal

Publications and source records attributed to K Wildenthal.

At least 55 records · Page 3Linked to original sources
PubMed1978

Regulation of cardiac protein balance by hydrocortisone: interaction with insulin.

In fetal mouse hearts in organ culture the rate of protein synthesis was substantially reduced and the rate of protein degradation slightly increased by hydrocortisone in the absence of insulin, but in the presence of insulin the steroid caused a small increase in protein synthesis and a significant reduction in protein degradation. Hydrocortisone promoted the net uptake (or reduced the net release) of branched-chain amino acids independent of insulin and independent of simultaneous changes in protein balance. The specific activities of the lysosomal enzymes cathepsin D and glucosaminidase were reduced by hydrocortisone in all media, whereas the specific activity of creatine kinase increased when the medium contained insulin but decreased in the absence of insulin. It is concluded that hydrocortisone regulates cardiac protein balance via alterations both in synthesis and in degradation. Some of the hormone's myocardial effects are influenced by insulin so that hydrocortisone is anabolic in its presence but catabolic in its absence.

Amino Acids↗
PubMed1978

Species differences in responses to hyperosmolality and D600 in cat and rat heart.

The direct inotropic effect of hypertonic mannitol was compared in isolated rat and cat papillary muscles. The inotropic effects of paired electrical stimulation and D600 were also evaluated in the same species. At extracellular calcium concentrations of 2.5 mM, hypertonic mannitol (25--100 mosmol/kg H2O above normal) depressed contractility in isolated rat myocardium; hyperosmolality exerted a positive effect only when extracellular Ca2+ was low (e.g., 0.3 mM). Paired pacing exerted a small but significant inotropic effect in rat heart when extracellular Ca2+ was 2.5 mM, and a larger effect at lower Ca2+. As previously noted, hypertonic mannitol and paired pacing both produced significant positive effects in isolated cat heart at an extracellular Ca2+ concentration of 2.5 mM. D600 exerted less of a depressant effect on contractility in rat than in cat heart at concentrations of 10(-6)--10(-7) M. The data suggest that 1) in contrast to results in cat heart, the positive inotropic effect of hyperosmolality in isolated rat cardiac muscle is apparent only when extracellular calcium concentration is reduced; 2) the inotropic effect of paired pacing in rat heart is greatest at low Ca2+ levels, but persists to a lesser degree at extracellular calcium concentrations of 2.5 mM; and 3) D600-inhibitable calcium channels appear to be relatively less important in the maintenance of cardiac contractility in rat than in cat cardiac muscle.

Animals↗
PubMed1978

Inhibition of protein degradation in mouse hearts by agents that cause lysosomal dysfunction.

Although the heart contains lysosomes, it has been uncertain whether these organelles and their proteolytic enzymes can play an important role in cardiac protein degradation. Recent studies have demonstrated that fetal mouse hearts in organ culture sustain selective derangements in lysosomal structure and function during exposure to chloroquine or nonmetabolizable sugars. Accordingly, we tested the effects of these agents on cardiac proteolysis under controlled conditions in vitro using two techniques (measurement of loss of radioactivity from trichoroacetic acid-precipitable protein after prelabeling with tritiated phenylalanine and measurement of loss of cold phenylalanine after blockade of protein synthesis with cycloheximide). Chloroquine (0.1 mM) reduced the average rate of protein breakdown in hearts of matched littermates from 45%/24 hours to 32%/24 hours (P less than 0.01) and decreased the release of cold phenylalanine by 31 +/- 5% (0.108 vs 0.075 nmol/mg per hour, P less than 0.01). Exposure to 100 mM sucrose for 24-48 hours reduced the rate of breakdown from 44%/24 hours to 33%/24 hours (P less than 0.01) and decreased the release of cold phenylalanine by 35 +/- 9% (0.092 vs. 0.060 nmol/mg per hour, P less than 0.01). The results suggest that interference with lysosomal function in cultured fetal mouse hearts causes a significant reduction in the cardiac capacity to degrade proteins.

Amino Acids↗
PubMed1978

Synthesis and degradation of myocardial protein during the development and regression of thyroxine-induced cardiac hypertrophy in rats.

Cardiac hypertrophy was induced in rats by daily injections of L-thyroxine (1.0 mg/kg). Regression from hypertrophy was studied 4 days after discontinuing thyroxine. Isolated, Langendorff-perfused hearts were perfused with Krebs-Henseleit buffer, glucose, insulin, and amino acids. To measure protein synthesis, left ventricular tissue was assayed for incorporation of tritiated phenylalanine into protein. Indices of rates of protein degradation were obtained by measuring the release of cold phenylalanine after blocking protein synthesis with cycloheximide. After 3 days of thyroxine (when cardiac growth was maximally increased), the rate of protein synthesis increased by 22% (P less than 0.001). After 1 week, synthesis was 8% greater than control (P less than 0.05), and by 2 weeks (when hypertrophy was stable and the rate of cardiac growth was similar to controls), synthesis had returned to control levels. In hearts regressing from hypertrophy, synthesis was reduced to 68% of control (P less than 0.001). The rate of protein degradation was decreased by 12% (P less than 0.05) after 3 days of thyroxine, but was not different from control at 1 or 2 weeks. During regression, degradation was 12% below control (P less than 0.05). Changes in the release of several amino acids that are synthesized or metabolized in heart (e.g., alanine, glycine, serine) were different from changes in phenylalanine release. In conclusion thyroxine-induced cardiac hypertrophy and regression are accompanied by changes in protein synthesis and degradation, and amino acid metabolism. The predominant change in hypertrophy is increased protein synthesis with a minor contribution from reduced degradation. Regression of hypertrophy is accompanied by decreased synthesis, not increased degradation.

Amino Acids↗
PubMed1978

Influence of methylprednisolone of the sequential redistribution of cathepsin D and other lysosomal enzymes during myocardial ischemia in rabbits.

Occlusion of the circumflex coronary artery induced a profound redistribution in ischemic rabbit myocardium of several lysosomal acid hydrolases, including cathepsin D, B-acetylglycosaminidase, and acid phosphatase. 30-45 min after ligation non-sedimentable cathepsin D activity rose from 36% of the total activity to 42-48%, and in immunohistochemical preparations cathepsin D appeared to have diffused from lysosomes into the cytosol of injured cells. A pharmacologic dose of methylprednisolone (50mg/kg) significantly delayed the subcellular redistribution of cathepsin D and the other hydrolases in ischemic heart. Thus, in treated hearts the nonsedimentable activity of cathepsin D rose to only 38% after 30 min of ischemia and 42% after 45 min (P is less than 0.05 compared to untreated ischemia at each time). Similarly, unlike untreated hearts, noevidence of enzyme diffusion from lysosomes could be demonstrated immunohistochemically in corticosteroid-treated ischemic hearts for over 45 min. After 1-2 h of ischemia, however, steroid-protected myocytes deteriorated and the biochemical activity and anatomical distribution of cathepsin D were indistinguishable from untreated ischemic hearts. This study demonstrates that corticosteroid pretreatment does not prevent alterations in cardiac lysosomes during severe ischemia indefinitely, but does delay their development significantly.

Acetylglucosaminidase↗
PubMed1978

Influence of methylprednisolone on ultrastructural and cytochemical changes during myocardial ischemia. Selective effects on various cell inclusions and organelles including lysosomes.

Occlusion of the circumflex branch of the coronary artery of rabbit hearts for 45 minutes elicits structural and cytochemical changes in myocytes similar to those observed in ischemic dog myocardium, which are indicative of irreversible cell injury. When methylprednisolone is administered prior to occluding the artery, myocytes are transiently protected and many of the electron microscopic signs of irreversible damage are delayed for 15 minutes or more. During this period, the steroid preferentially protects mitochondria, lysosomes, and sarcolemma from the ischemic changes that normally develop. However, some other events, including depletion of glycogen and margination of nuclear chromatin, are only minimally influenced by the therapy, if at all. In all hearts, treated and untreated, the development of severe cell damage, whenever it occurs, is closely associated with cell swelling, mitochondrial dilation with concomitant appearance of amorphous osmiophilic densities, and abnormalities in and, ultimately disappearance of lysosomes, suggesting that damage to cell membranes is a central event in the progression of reversible injury to irreversible infarction and that protection of membrane integrity should be a reasonable aim in efforts to ameliorate or delay ischemic injury.

Animals↗
PubMed1977

Cardiac lysosomal derangements in mouse heart after long-term exposure to nonmetabolizable sugars.

Hearts of late fetal mice were maintained in organ culture in the presence of 30-100 mM sucrose or mannitol. Activities of several lysosomal enzymes (cathepsin D, beta-acetylglucosaminidase, acid phosphatase) were increased by up to 30% after 18-24 hours and by up to 50% after 48-72 hours, as compared to enzyme activities in litter-matched hearts maintained in control medium or medium supplemented with equimolar urea. Simultaneously, the ratio of nonsedimentable to sedimentable enzyme activity was significantly increased, suggesting increased lysosomal fragility. Light and electron microsopic examination of the hearts revealed marked vacuolization in myocytic, interstitial, and endothelial cells. The vacuoles were limited by single membranes, often contained particulate or amorphous cellular debris resulting from autophagocytosis, and in cytochemical preparations frequently exhibited an electron-dense reaction product indicative of acid phosphatase activity. Hydrocortisone failed to prevent the marked lysosomal activation induced by the sugars. In conclusion, prolonged exposure to nonmetabolizable sugars induces severe lysosomal derangements with prominent autophagy, in fetal mouse heart maintained in organ culture.

Acetylglucosaminidase↗
PubMed1977

Altered distribution of lysosomal cathepsin D in ischemic myocardium.

To determine the influence of cardiac ischemia on the activity and subcellular localization of lysosomal cathepsin D, anesthetized rabbits were subjected to ligation of the circumflex coronary artery. Total enzyme activity remained unchanged throughout the 2-h ischemic period, but the subcellular distribution of cathepsin D, as analyzed by biochemical and immunohistochemical techniques, was altered dramatically. A marked increase in nonsedimentable (i.e., 40,000-g supernate) activity developed by 30-45 min and increased further by 2 h. Simultaneously, the immunofluorescent localization of cathepsin D was also changed significantly. Within 30-60 min after occlusion, the fine, particulate staining observed in control myocytes was replaced by bright fluorescent patches composed of large granules. Many of these structures displayed prominent halos of diffuse fluorescent staining in the neighboring myocytic cytoplasm, apparently outside lysosomes per se. After 2 h, when nonsedimentable activity was maximally elevated, most of the fluorescent particles had disappeared completely. During this same interim there was no detectable change in the distribution of lysosomal cathepsin D within interstitial cells. These results are consistent with the hypothesis that an early feature of cardiac ischemia is the release of cathepsin D from myocytic lysosomes into the cytosol of damaged cells.

Animals↗
PubMed1976

Reduction by cycloheximide of lysosomal proteolytic enzyme activity and rate of protein degradation in organ-cultured hearts.

Cycloheximide, an agent whose primary action is inhibition of protein synthesis, also causes a decrease in the rate of protein degradation in cultured fetal mouse hearts. This is associated with marked decreases in the activities of cathespin D and other lysosomal hydrolases. It is suggested that reduced lysosomal proteolytic capacity may contribute to cycloheximide-induced inhibition of protein degradation.

Acetylglucosaminidase↗
PubMed1976

Role of creatine in the regulation of cardiac protein synthesis.

The observation that increased muscular activity leads to muscle hypertrophy is well known, but identification of the biochemical and physiological mechanisms by which this occurs remains an important problem. Experiments have been described (5, 6) which suggest that creatine, an end product of contraction, is involved in the control of contractile protein synthesis in differentiating skeletal muscle cells and may be the chemical signal coupling increased muscular activity and the increased muscular mass. During contraction, the creatine concentration in muscle transiently increases as creatine phosphate is hydrolyzed to regenerate ATP. In isometric contraction in skeletal muscle for example, Edwards and colleagues (3) have found that nearly all of the creatine phosphate is hydrolyzed. In this case, the creatine concentration is increased about twofold, and it is this transient change in creatine concentration which is postulated to lead to increased contractile protein synthesis. If creatine is found in several intracellular compartments, as suggested by Lee and Vissher (7), local changes in concentration may be greater then twofold. A specific effect on contractile protein synthesis seems reasonable in light of the work of Rabinowitz (13) and of Page et al. (11), among others, showing disproportionate accumulation of myofibrillar and mitochondrial proteins in response to work-induced hypertrophy and thyroxin-stimulated growth. Previous experiments (5, 6) have shown that skeletal muscles cells which have differentiated in vitro or in vivo synthesize myosin heavy-chain and actin, the major myofibrillar polypeptides, faster when supplied creatine in vitro. The stimulation is specific for contractile protein synthesis since neither the rate of myosin turnover nor the rates of synthesis of noncontractile protein and DNA are affected by creatine. The experiments reported in this communication were undertaken to test whether creatine selectively stimulates contractile protein synthesis in heart as it does in skeletal muscle.

Acid Phosphatase↗
PubMed1976

Inhibition of inotropic effect of hyperosmotic mannitol by lactate in vitro.

Isolated, isometrically contracting cat papillary muscles were used to evaluate the inotropic interactions of lactic acidosis, hypercarbic acidosis, and lactate ion with hypertonic mannitol. These studies have documented that both lactic acidosis (pH less than 7.0) and lactate ion at a normal pH inhibit the inotropic effect of hyperosmotic mannitol in vitro. In contrast, hypercarbic acidosis does not prevent the inotropic effect of mannitol. Inhibition by lactic acid of mannitol's effects on contractility persists in the presence of beta-receptor blockade. The results suggest that inhibition by severe lactic acidosis of the direct inotropic effect of hyperosmolality in isolated cardiac muscle is mediated by lactate ion rather than acidosis per se.

Acidosis↗