Adrenergic binding sites and enzyme activities in the heart of hyperthyroid rats

In present study interactions of some adrenergic drugs with the binding of 3H-norepinephrine (NE) and response of some enzymatic systems in the heart of rats with pharmacological hyperthyroidism have been investigated. Binding of NE to cardiac particles was inhibited by isoproterenol, propranolol and in lower concentrations by another beta-blocking drug trimepranol both in control and hyperthyroid hearts in the same degree. However, after addition of nonradioactive norepinephrine (10(-3) M) the degree of displacement was lower in hyperthyroid than in euthyroid group. Activity of adenylate cyclase was lower in hyperthyroid cardiac particles. This difference remained preserved after stimulation by norepinephrine or NaF. The activities of hormone-sensitive lipase and lipoprotein lipase were increased in preparation of hyperthyroid hearts. The phosphorylase "a" activity was also increased in hyperthyroid cardiac particles. There was no change in cardiac adrenergic binding sites properties in hyperthyroidism with the exception of less displacement of NE by nonlabelled hormone. The results indicate that the increased lipolytic and phosphorylase "a" activities in hyperthyroid hearts are not necessarily linked to elevated activity of adenylate cyclase.