Studies on the mechanism of the decreased guanine nucleotide stimulatory effects on adenylate cyclase after adrenalectomy in rat adipocytes.

In adipocyte membranes from adrenalectomized rats: (i) the defect in the stimulatory effects of guanine nucleotides on adenylate cyclase is greater with GTP than with GppNHp and appears to concern the GS-C complex and not the HR-GS-C ternary complex; (ii) the GTP-ase activity is enhanced; (iii) maximal alpha S-C interaction (tested by the responses to forskolin, cholera toxin or NaF) is unaltered and (iv) the alpha S affinity for guanine nucleotides and the GDP/GppNHp exchange reaction are both unimpaired. These data suggest that the enhanced GTP-ase activity together with a decrease in the catalytic activity of the alpha S-GTP-C complex are the likely mechanisms whereby adrenalectomy causes a defect in the fat cell adenylate cyclase response to guanine nucleotides.