Effect of isoproterenol on physiological and biochemical changes in euthyroid and hyperthyroid rat hearts

Penelope Anne Longhurst
The effect of triiodothyronine pretreatment on the physiological and biochemical properties of the rat heart was Investigated In a number of cardiac preparations. Pretreatment with triiodothyronine for three days produced an increased chronotropic effect in the isolated right atrium, and a decreased Inotropic effect In the isolated left atrium and Langendorff heart. Following administration of isoproterenol there was a dose-dependent increase in rate of the right atrium. The absolute increase
more » ... absolute increase in rate was similar in euthyroid, and hyperthyrold. tissues; the hyperthyroid atria maintained a higher rate than the euthyroid atria, with no sign of supersensitivity. In the electrically stimulated left atrium and right ventricle, isoproterenol produced a dose-dependent increase in tension. The absolute increase in tension was slightly greater in the euthyroid tissues than in the hyperthyrold tissues. In all three preparations, the contractile changes produced by isoproterenol were accompanied by an increase in phosphorylase activity which was similar in euthyroid and hyperthyrold animals. Five nanograms of isoproterenol produced a similar increase in tension in euthyroid and hyperthyrold Langendorff rat hearts. The increase in tension was accompanied by an increase in phosphorylase a activity. This effect of isoproterenol on phosphorylase activation was potentiated in the hyperthyroid hearts. The possibility that the potentiation of phosphorylase activation in the perfused. heart was a result of the increase in coronary blood flow, noted in hearts from hyperthyroid animals, was investigated. Coronary blood flow was reduced in a group of hearts from hyperthyroid animals to the same level as that of hearts from euthyroid animals, and the phosphorylase-activating effect of isoproterenol was again tested. Under these conditions the phosphorylase-actlvating effect of isoproterenol was still enhanced. A pA₂ study carried out on the rat right atrium showed that beta-adrenoceptors in the euthyroid and hyperthyroi [...]
doi:10.14288/1.0094288 fatcat:bjoh4qf5w5hbvjp7ovzsiax6vu