Supersensitivity of beta-adrenoceptor coupled adenylate cyclase in pulmonary tissue of the spontaneously hypertensive rat

Abstract

Basal adenylate cyclase activity was similar in plasma membranes prepared from the lungs of 12 week old spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). However, sensitivity to Gpp [NH]p, isoproterenol plus GTP or Gpp [NH]p was significantly greater in the SHR. Beta-receptor density measured by [ 3H]DHA binding was unaltered. The dissociation constant, K d, revealed a significantly greater binding affinity of the radioligand in the SHR (6.23 ± 0.45 nM) compared with the WKY (8.53 ± 0.82 nM). Activity of G s was assessed by complementing S49 cyc − acceptor membranes with lung cholate extract. Basal activity of the reconstituted system was decreased 43% in the SHR. However, sensitivity to NaF, Gpp [NH]p, and isoproterenol plus Gpp [NH]p was significantly elevated. These data suggest that desensitization of the adenylate cyclase complex is not a generalized r response to chronic hypertension. A tissue specific increase in sympathetic drive appears to be responsible for the lowered concentration of cardiac beta-adrenoceptors in the SHR. In contrast, both indirect and direct evidence indicate an enhanced functional sensitivity of pulmonary G S in the hypertensive rats.