Alterations in Myocardial Adenylate Cyclase in Spontaneously Hypertensive Rats

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Abstract
Particulate fractions of myocardium taken from spontaneously hypertensive rats (SHR) contained an adenylate cyclase system that was less responsive than normotensive Wistar Kyoto rats to norepinephrine, isoproterenol (mixed β-agonist), salbutamol (β2-agonist), do-butamine β1-agonist), dopamine, histamine, and glucagon. Addition of 5’-guanylylimidodiphosphate to the SHR myocardial preparation again yielded a lessened sensitivity to all agents except norepinephrine, dopamine, and histamine. Chronic treatment of SHR with clonidine and a high dose of propranolol produced a cardiac enzyme that was insensitive to activation by norepinephrine. Similar treatment with a low dose of propranolol did not alter myocardial responses to norepinephrine.