Regulation of cardiac adenylate cyclase activity in rodent models of obesity.

We have investigated beta-adrenergic regulation of adenylate cyclase activity in heart tissue membranes from the genetically obese Zucker rat, the genetically obese CBA mouse and the genetically obese diabetic (db/db) mouse. Responsiveness to beta-adrenergic stimulation was impaired in membranes from the obese Zucker rat, but not in the other models. The membranes from obese Zucker rats showed both decreased beta-adrenergic-receptor number and altered coupling between beta-adrenergic receptors and the stimulatory guanine-nucleotide-binding protein, Gs. In contrast, no alterations in either the levels of Gs or the functional interaction between this protein and the catalytic moiety of adenylate cyclase were observed. In these three genetic models of obesity we observe dissimilar alterations in the control of adenylate cyclase.