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Interaction between bretylium, calcium and promoters of calcium on the cardiac and the smooth muscle
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INTERACTION BETWEEN BRETYLIUM, CALCIUM AND PROMOTERS OF CALCIUM ON THE CARDIAC AND THE SMOOTH MUSCLE. G.S. Singh, M.P. Srivastava, P.K. Mediratta and A.G. Singh. Department of Pharmacology, Lady Hardinge Medical College, New Delhi, India. Acetylcholine (0.1 yg) when injected into the cannula of the frog heart perfused with high calcium medium produces positive inotropic action, presumably mediated by making more coupling calcium available for excitation-contraction coupling. This action is blocked by bretylium (10m5 G/ml) Bretylium also blocks the action of caeffine on the perfused frog heart. Paradoxically it enhances the cardiotonic action of calcium on the frog heart during the summer months. Propranolol (loo6 G/ml) failed to But modify the enhancement of cardiotonic action of calcium by bretylium. the action of calcium on the perfused frog heart is blocked by bretylium during the winter months. The type of antagonism between calcium and bretylium has been studied on the depolarized rat uterus because calcium chloride produces the dose dependent contraction of this organ, thus, permitting the construction of the dose response curve. Bretylium causes parallel shift to the right of the dose response curve of calcium on the depolarized rat uterus.
ULTRASTRUCTURAL CHANGES IN THE MYOCARDIUM OF PRESSURE-OVERLOADED SWINE. Sarjant Singh, Francis C. White, Muhammad Ashraf, and Colin M. Bloor. Department of Pathology, UCSD School of Medicine, La Jolla, CA 92093. We studied ultrastructural changes in nine swine, whose aortas were constricted for 30 days and who were acutely exercised. A similar number of animals were used as control. The tissues from twenty different sites in the heart including right and left ventricles and septum, from both endocardial and epicardial regions, were obtained and processed for electron microscopy. Electron micrographs showed ischemic damage especially in the endocardium. The regional myocardial blood flow, as measured by the tracer microsphere technique, at exercise, showed that the flow in the subendocardial region of these animals was only 60% of the control flow. This ischemia was further corroborated by histologic findings and was in addition to the gross hypertrophy induced. Morphometric study of the ultrastructural changes shows quantitative changes in the volumes occupied by myofibrils, mitochondria, T-systems, and sarcoplasmic reticulum in the hypertrophied heart. This study suggests that exercise stress in the hypertrophied heart may induce ischemic injury. Supported
by NIH Grants
HL 07104,
HL 18122,
and RCDA K04-HL
00190.
INTERACTION BETWEEN BRETYLIUM, CALCIUM AND PROMOTERS OF CALCIUM ON THE CARDIAC AND THE SMOOTH MUSCLE. G.S. Singh, M.P. Srivastava, P.K. Mediratta and A.G. Singh. Department of Pharmacology, Lady Hardinge Medical College, New Delhi, India. Acetylcholine (0.1 yg) when injected into the cannula of the frog heart perfused with high calcium medium produces positive inotropic action, presumably mediated by making more coupling calcium available for excitation-contraction coupling. This action is blocked by bretylium (10m5 G/ml) Bretylium also blocks the action of caeffine on the perfused frog heart. Paradoxically it enhances the cardiotonic action of calcium on the frog heart during the summer months. Propranolol (loo6 G/ml) failed to But modify the enhancement of cardiotonic action of calcium by bretylium. the action of calcium on the perfused frog heart is blocked by bretylium during the winter months. The type of antagonism between calcium and bretylium has been studied on the depolarized rat uterus because calcium chloride produces the dose dependent contraction of this organ, thus, permitting the construction of the dose response curve. Bretylium causes parallel shift to the right of the dose response curve of calcium on the depolarized rat uterus.
ULTRASTRUCTURAL CHANGES IN THE MYOCARDIUM OF PRESSURE-OVERLOADED SWINE. Sarjant Singh, Francis C. White, Muhammad Ashraf, and Colin M. Bloor. Department of Pathology, UCSD School of Medicine, La Jolla, CA 92093. We studied ultrastructural changes in nine swine, whose aortas were constricted for 30 days and who were acutely exercised. A similar number of animals were used as control. The tissues from twenty different sites in the heart including right and left ventricles and septum, from both endocardial and epicardial regions, were obtained and processed for electron microscopy. Electron micrographs showed ischemic damage especially in the endocardium. The regional myocardial blood flow, as measured by the tracer microsphere technique, at exercise, showed that the flow in the subendocardial region of these animals was only 60% of the control flow. This ischemia was further corroborated by histologic findings and was in addition to the gross hypertrophy induced. Morphometric study of the ultrastructural changes shows quantitative changes in the volumes occupied by myofibrils, mitochondria, T-systems, and sarcoplasmic reticulum in the hypertrophied heart. This study suggests that exercise stress in the hypertrophied heart may induce ischemic injury. Supported
by NIH Grants
HL 07104,
HL 18122,
and RCDA K04-HL
00190.