title: Changes in cardiac myofibrillar ATPase activity during development of hyperthyroidism in the rabbit.
abstract: This study examined changes in cardiac myofibrillar ATPase activity during the development of hyperthyroidism and the relationships between changes in myofibrillar ATPase activity and hemodynamic parameters in rabbits. Calcium-stimulated, magnesium-dependent ATPase (Ca-ATPase) activity of cardiac myofibrils exhibited about a 30% increase after the first week of treatment with excess desiccated thyroid tissue powder (thyroid-treatment) and did not show further increase during thyroid-treatment. Development of cardiac hypertrophy and increases in systolic and diastolic blood pressure were dependent upon prolonged periods of thyroid-treatment lasting from 3 days to 4 weeks, whereas the maximal increase (about 55%) in heart rate was seen after the first week of thyroid-treatment. The elevated level lasted throughout subsequent thyroid-treatment. Lineweaver-Burk plots showed an increase in Km and Vmax values for Ca-ATPase activity of myofibrillar preparation from the thyrotoxic hearts of treated animals. Increased Ca-ATPase activity was correlated with thyroid-induced changes in heart rate. Propranolol partially reduced the thyroid-induced increase in Ca-ATPase activity and heart rate, suggesting participation of beta-adrenoceptors in the thyroid-induced increases of Ca-ATPase activity and heart rate.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001794:Blood Pressure; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002302:Cardiac Output; D006332:Cardiomegaly / Q000201:enzymology; D005260:Female; D006339:Heart Rate; D006439:Hemodynamics; D006980:Hyperthyroidism / Q000201:enzymology* / Q000503:physiopathology; D008274:Magnesium / Q000502:physiology; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000201:enzymology*; D009210:Myofibrils / Q000201:enzymology*; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D051381:Rats
chemical_list: D011433:Propranolol; D000251:Adenosine Triphosphatases; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D010646:Phentolamine