Effect of physical exercise on plasma, erythrocyte and tissue cholesterol and phospholipids in rats

same extent as M-( -)-propranolol (by 80%). Treatment of membranes with isoprenaline + GMP converts N from the closed GDP-bound state to an open Gpp(NH)presponsive form (Braun et af . , 1982). This form of N was found to be relatively insensitive to propranolol and also attenuated the filipin inhibition of Gpp(NH)p stimulation, but to a lesser extent. The reason for this is unclear, but may be due to a small portion of the filipin effect occurring at the N-C level. An inhibitory effect of propranolol on GDP release from N has been proposed (Morris & Bilezikian, 1982). We have studied the release of [3H]GDP induced by Gpp(NH)p with and without isoprenaline and propranolol, while simultaneously measuring adenylate cyclase activity in the presence of these agents. Gpp(NH)p alone induced release of [3H]GDP which was not significantly affected by propranolol or isoprenaline under conditions where propranolol inhibited and isoprenaline amplified the effects of Gpp(NH)p stimulation. We infer from these results that the inhibition of Gpp(NH)p-stimulated adenylate cyclase is a receptormediated event, not explained by an inhibition of Gpp(NH)p-induced release of GDP from N, and probably due to an uncoupling of receptor from N.