Myocardial Adrenergic Receptors and Adenylate Cyclase in the Developing Spontaneously Hypertensive Rat

Cardiac membrane preparations from developing spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats (0 to 125 days of age) were analyzed for the apparent numbers of alpha-and beta-adrenergic receptors and adenylate cyclase activities in an attempt to correlate biochemical changes with the reported functional changes occurring with the development of hypertension in the SHR. Although the apparent number of alpha- and beta-adrenergic receptors were similar in both strains of rats, isoproterenol-stimulated adenylate cyclase activities were significantly higher (P<0.05) in the prehypertensive SHRs when compared to WKY rats and declined to lower values as hypertension appeared. The percent stimulation produced by isoproterenol remained similar in cardiac membranes from normotensive WKY rats at all ages of development whereas this percent stimulation was 40% higher at birth in the SHRs and declined to approximately one half the original value by 100 days of age (P<0.05). The elevated adenylate cyclase activity observed during the prehypertensive state may contribute to the genesis of hypertension.