Cardiac Beta Adrenoceptors and Adenylate Cyclase in Normotensive and Renal Hypertensive Rabbits During Changes in Autonomic Activity

Abstract

The effects of hypertrophy and alterations in cardiac autonomic activity on left ventricular (LV) beta adrenoceptors and adenylate cyclase were measured in rabbits. Normotensive and renal hypertensive animals were exposed to three levels of chronic sympathetic activity: (i) ‘normal’ activity; (ii) reduced activity after 2 weeks treatment with guanethidine; (iii) 2 weeks increased sympathetic activity following sino-aortic denervation. In hypertensive animals with ‘normal’ activity LV beta receptor sarcolemma concentration was reduced by 36% compared with the normotensive subgroup whilst total LV receptor numbers were unaltered. Isoprenaline activated adenylate cyclase was similarly affected whilst other sarcolemma marker enzymes were unaffected. Chronic guanethidine administration to normotensive rabbits increased beta receptor concentration (16%, P < 0.05), basal and isoprenaline activated adenylate cyclase whilst in hypertensive animals these parameters were unaffected. Sino-aortic denervation did not significantly affect beta receptor concentration in either group. The small changes in beta receptor concentration during alterations in sympathetic activity suggest that only a small proportion of LV beta receptors appear to be innervated. The reduction in sarcolemma beta receptor concentration in hypertensive animals appears to be a specific effect due to hypertrophy of the cardiocyte.