Fred A. Kruger

Role of anaerobic metabolism in the preservation of functional capacity and structure of anoxic myocardium

Employing an isolated perfused rat heart preparation, we investigated the contribution of anaerobic metabolic energy to the performance, recoverability, and ultrastructure of the heart perfused at 32 degrees C in 5% albumin in Krebs-Ringer Bicarbonate solution. During exposure to anoxia for 30 min, inclusion in the perfusate of the anaerobic substrate, glucose, resulted in marked improvement in electrical and mechanical performance of the heart and in enhanced recovery during the subsequent period of reoxygenation. Lactate production was fivefold greater in the glucose-supported anoxic heart than in the anoxic heart without glucose. Electron microscope sections of the hearts exposed to anoxia in the absence of glucose revealed alterations in mitochondrial morphology and dilatation of the longitudinal tubules. These morphologic changes during anoxia were averted by inclusion of glucose in the perfusion fluid. The data are consistent with the hypothesis that anaerobic energy generation plays a significant role in preserving myocardial function and structure and in promoting recoverability of the anoxic mammalian heart.

Calcium tolerance of isolated rat heart cells.

Abstract Freshly isolated adult rat heart cells, which initially show the elongated, rod-shaped morphology typical of heart cells in situ , are almost quantitatively converted to rounded contracture forms by exposure to 1 m m Ca 2+ . These Ca 2+ -sensitive cells became Ca 2+ -tolerant following a short period of metabolic activity in a low-Ca 2+ medium, in that they retain their rod-shaped configuration when challenged with Ca 2+ after this preincubation step. Tolerance to Ca 2+ develops in parallel with the establishment of low Na + /K + ratios in these cells and both processes are sensitive to ouabain. The initial net uptake of Ca 2+ is greater in Ca 2+ -sensitive than in Ca 2+ -tolerant cells. These results suggest that contracture in the Ca 2+ -sensitive cells is a consequence of the rapid entry of excessive amounts of Ca 2+ in exchange for internal Na + .

Effect of Insulin on the Performance and Metabolism of the Anoxic Isolated Perfused Rat Heart

When the oxygen supply to the myocardium is compromised, glycolysis may provide the critical energy necessary for the hearts survival. We investigated whether insulin, through its effects on myocardial glycolysis, influences the performance and the metabolism of the perfused rat heart during anoxia. Hearts in a modified Langendorff apparatus were perfused for 30 minutes with anoxic media containing glucose (50–500 mg/100 ml) with and without insulin (100 munits/ml) or with anoxic media containing 200 mg glucose/100 ml and varying insulin concentrations (0.1–100 munits/ml). Hearts were paced, and left ventricular pressure, maximum rate of rise of left ventricular pressure, and lactate production were monitored. Increasing glucose concentration alone progressively enhanced performance and lactate generation in the beating anoxic heart. Addition of insulin resulted in significant increases in left ventricular performance and lactate production at all levels of glucose concentration. The myocardial content of high energy intermediates (creatine phosphate, adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate) after 30 minutes of anoxia was not altered by varying concentrations of glucose or insulin. To assess the effects of insulin and glucose in the absence of contraction, hearts were arrested with media containing a high potassium concentration (26 mEq/liter). Although lactate production was lower in arrested hearts than it was in beating hearts, it was enhanced by insulin. Insulin also produced significant increases in high-energy intermediates in arrested hearts. It was concluded that insulin increases the utilization of glucose and thus causes the enhancement of ventricular performance in the anoxic heart.

Studies on the Site and Mechanism of Action of Phenformin: II. Phenformin Inhibition of Glucose Transport by Rat Intestine

The effect of oral phenformin on the active transport of glucose by everted sacs of rat intestine was investigated. Pretreatment of the animals with a single dose of the drug resulted in an inhibition of active transport. A log-dose relationship was found in the range studied (5 to 150 mg./kg.). These findings could explain the observation that phenformin increases the tolerance to orally administered glucose but has no effect on intravenous glucose tolerance in humans.

The Mechanism of Action of Hypoglycemic Guanidine Derivatives

Renewed interest in guanidine derivatives as possible oral therapeutic agents in the treatment of diabetes has followed the discovery by Ungar et al. that certain biguanides are hypoglycemic agents of low toxicity. This report is concerned with the mechanism of action of this new group of compounds as exemplified by one of them, phenethylbiguanide (DBl), as compared with that of other guanidine derivatives. As long ago as 1918, Watanabe showed that guanidine elicited a pronounced hypoglycemic response in rabbits. However, the toxic manifestations of this substance precluded its trial as a possible therapeutic agent in diabetes mellitus. An intensive search by Frank et al. led to the synthesis of decamethylenediguanidine (Synthalin) which was found to exhibit enhanced hypoglycemic activity associated with markedly diminished toxicity. However, after intensive clinical trial the therapeutic use of Synthalin as an oral hypoglycemic agent was abandoned. Disagreeable side effects including nausea and weakness were frequent. Furthermore, except for lowering blood sugar and diminishing glycosuria, Synthalin therapy did not really correct the aberrant metabolism of the diabetic individual. Elevations in blood and urinary lactate, citrate and other organic acids were observed. In a balance study of diabetics undergoing Synthalin therapy, Kaufmann-Cosla and Vasilco found that urinary glucose was supplanted by large excretions of other organic compounds.

Alterations in adrenal cortical function in fasting obese subjects

Abstract The effect of short periods of starvation on adrenal function was evaluated in a group of obese females. Normal plasma cortisol levels were maintained during the fast period, while urinary excretion of 17-hydroxycorticoids, 17-ketosteroids, and unconjugated 11-hydroxycorticoids fell. Evidence indicates that a reduction of cortisol secretion occurs during brief periods of fasting. In addition, the measurement of urinary 11-hydroxycorticoids may be a rapid and efficient method for differentiating exogenous obesity from Cushings syndrome.

The diabetogenic action of human growth hormone: Glucose - fatty acid interrelationships

Abstract Intravenous glucose tolerance was determined in seven normal subjects. Growth hormone administered 4 1 2 hours prior to the tests resulted in an elevation of plasma free fatty acids and an impairment in glucose tolerance. When 5 - methylpyrazole - 3 - carboxylic acid, an inhibitor of lipolysis, was administered 4 1 2 hours prior to the tests, there was a significant decrease in plasma free fatty acid levels and a slight improvement in glucose tolerance which was not statistically significant. When both compounds were administered 4 1 2 hours prior to the tests, the circulating free fatty acid levels were low and glucose tolerance was significantly improved when compared to the results seen after growth hormone alone but significantly impaired when compared to the results seen after administration of the pyrazole derivative alone. It is concluded that the impairment of glucose tolerance produced by growth hormone is partially but not entirely mediated by the elevated plasma free fatty acid levels produced by the hormone. The mechanism responsible for the residual impairment is unknown.

Anaerobic performance and metabolism of the hyperthyroid heart

Anaerobically periused hearts from rats with experimentally induced hyperthyroidism exhibited accelerated deterioration of pacemaker activity and ventricular performance. The diminished anaerobic performance of hyperthyroid hearts was associated with decreased adenosine triphosphate (ATP) levels and a reduced rate of anaerobic glycolysis as reflected in decreased lactic acid production during 30 min of anoxic perfusion.Studies on whole heart homogenates demonstrated inhibition at the phosphofructokinase (PFK) step of the glycolytic pathway. Such inhibition was not demonstrated in the hyperthyroid heart cytosol. It is postulated that an inhibitor of PFK which resides dominantly in the particulate fraction is probably responsible for the diminished anaerobic glycolysis and performance of the hyperthyroid heart.

Chromatographic studies on the composition of commercial samples of triolein-I131 and oleic acid-I131, and the distribution of the label in human serum lipids following oral administration of these lipids☆

Abstract “Triolein”-I 131 and oleic acid-I 131 (“Raolein” and “Raoleic acid,” Abbott) were chromatographed on a standardized silicic acid column to determine their elution patterns. Triolein-I 131 was found to contain methyl esters and tri-, di-, and monoglycerides of labeled oleic acid. Gas chromatographic, infrared spectrographic, and chemical analyses confirmed the presence of these components. The radioactivity distribution showed a lower proportion of triglycerides than did chemical analysis. Following oral administration of triolein-I 131 or oleic acid-I 131 to normal individuals, the chromatographic fractionation of the serum lipids showed that about 90% of the radioactivity was in the triglyceride fraction and the remainder was mostly in the diglyceride and non-esterified fatty acid fractions.

False Elevation of Plasma 17-Hydroxycorticoids in Diabetic Ketosis

Plasma corticoids were measured by an acid-fluorescent method and a modification of the Porter-Silber reaction in diabetic patients under good control and in states of poor control including ketoacidosis. In patients with significant ketonemia the plasma ketone bodies may produce a falsely high estimation of adrenal corticoid secretion when measured as Porter-Silber chromogens. Evaporation of the plasma extract, or preferably use of the acid-fluorescent procedure, will obviate such interference.