The role of zinc status in altered cardiac adenylate cyclase activity in diabetic rats

Zinc deficiency and altered myocardial adenylate cyclase activity commonly occur in diabetes. To determine whether the zinc intake of the animal can account for the altered beta-adrenergic receptor activity in the diabetic heart, we determined the beta-adrenergic receptor number and isoproterenol-, NaF- and forskolin-stimulated adenylate cyclase activity in diabetic and control rats maintained on low, normal and high zinc diets for 3 weeks. Scatchard analysis of [125I]iodocyanopindolol binding to control heart membrane preparations revealed a binding capacity of 17.3 +/- 1.3 fmol/mg protein with a Kd of 35 +/- 1.0 pmol/l. Neither the diabetic state nor the zinc status altered these binding parameters. The isoproterenol-stimulated adenylate cyclase activity was significantly lower in diabetic rats on low zinc diets compared with controls. The NaF- (65.1 +/- 5.4 vs 60.8 +/- 6.4 pmol cAMP.mg protein-1.min-1) and forskolin-stimulated adenylate cyclase activities (161 +/- 9.3 vs 154 +/- 21.2 pmol cAMP.mg protein-1. min-1) were not significantly altered in diabetic rats. Low dietary zinc intake compared with high zinc diet significantly increased NaF- and forskolin-stimulated adenylate cyclase activity both in diabetic rats and controls. The effect of dietary zinc content on isoproterenol-stimulated adenylate cyclase was significant in control rats only. Thus zinc intake appears to be an important determinant of cardiac adenylate cyclase activity level. Additional factors peculiar to the diabetic state are involved in the modulation of beta-adrenergic responsiveness of the diabetic heart.