Alterations in cardiac function and subcellular membrane activities after hypervitaminosis D3.

The present study was designed to induce massive accumulation of calcium in the myocardium and to evaluate the effect of calcium overload on myocardial contractile function and biochemical activity of cardiac subcellular membranes. Rats were treated with an oral administration of 500,000 units/kg of vitamin D3 for 3 consecutive days, and their hearts were sampled on the 5th day for biochemical analysis. On the 4th and 5th days, heart rate, mean aortic pressure, left ventricular systolic pressure and left ventricular dP/dt were significantly lowered in vitamin D3-treated rats, demonstrating the existence of appreciable myocardial contractile dysfunction. Marked increases in the myocardial calcium (67-fold increase) and mitochondrial calcium contents (24-fold increase) were observed by hypervitaminosis D3. Mitochondrial oxidative phosphorylation and ATPase activity were significantly reduced by this treatment. A decline in sarcolemmal Na+, K(+)-ATPase activity was also observed, while relatively minor or insignificant changes in calcium uptake and ATPase activities of sarcoplasmic reticulum were detectable. Electron microscopic examination revealed calcium deposits in the mitochondria after vitamin D3 treatment. The results suggest that hypervitaminosis D3 produces massive accumulation of calcium in the myocardium, particularly in the cardiac mitochondrial membrane, which may induce an impairment in the mitochondrial function and eventually may lead to a failure in the cardiac contractile function.

Naftidrofuryl oxalate improves impaired brain glucose metabolism after microsphere-induced cerebral embolism in rats.

The present study was designed to elucidate possible therapeutic effects of naftidrofuryl on the brain glucose metabolism after cerebral ischemia. Cerebral ischemia was induced by injecting 680 microspheres with a diameter of 48 microns into the right internal carotid artery of the rat. After ensuring the onset of symptoms of stroke on the first day after the operation, the rats were treated with intraperitoneal injections of 15 mg/kg naftidrofuryl oxalate twice a day. The behavioral and metabolic changes of operated rats were monitored up to the 5th day after surgery. The symptoms gradually faded away, from the 3rd day on, after microsphere-induced cerebral embolism. Tissue glucose and glycogen greatly increased after cerebral embolism, suggesting embolism-induced inhibition of glycolysis. To elucidate which steps in the glycolytic catabolism are inhibited after cerebral ischemia, biochemical activities of the glycolytic enzymes in the Embden-Meyerhof pathway and tricarboxylic acid cycle were determined on the 3rd day after surgery. Enzyme activities of hexokinase, phosphofructokinase and pyruvate kinase were not inhibited, but rather increased slightly after cerebral embolism. Malate dehydrogenase activity in the brain mitochondria was markedly increased after microsphere-embolism, whereas other enzyme activities in the tricarboxylic acid cycle were never inhibited by the cerebral embolism. Treatment of naftidrofuryl resulted in an appreciable reverse of the brain glucose and glycogen levels and a substantial recovery of altered enzyme activities to normal levels in the Embden-Meyerhof pathway and tricarboxylic acid cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Time course of changes in brain energy metabolism of the rat after microsphere-induced cerebral embolism.

The present study was designed to elucidate pathophysiological changes in the brain energy metabolism after cerebral ischemia. Cerebral ischemia was induced in rats by administering microspheres into the right carotid canal, and the time course of changes in cerebral energy metabolism was examined up to the 7th day after the operation. Approximately 50% of the operated rats revealed typical symptoms of stroke. In the right hemisphere, cerebral ATP and creatine phosphate of the rat on the 1st to 7th day were greatly reduced by the microsphere-induced cerebral embolism (maximally 52 and 61%, respectively), whereas the tissue lactate level was increased on the 1st, 3rd and 5th day after the embolism (maximally 125%), suggesting an induction of microsphere-induced cerebral ischemia. These changes in the tissue metabolites were accompanied by a decrease in the mitochondrial oxidative phosphorylation measured in the presence of succinate. A similar trend in the changes of biochemical markers was observed in the left hemisphere, but to a lesser degree or to an insignificant degree. The pathophysiological alterations in behavior and cerebral metabolism of microsphere-injected rats tended to return toward the normal levels on the 7th day after the operation. The results provided information on a useful model for therapeutic studies of anti-ischemic agents in the brain.