Beta-adrenergic receptors and adenylate cyclase activity in diabetic rat fat cells

Our study describes the effect of norepinephrine on adenylate cyclase activity in adipocytes from control and diabetic rats. The results show that diabetes induced an increase in both basal and norepinephrine-stimulated adenylate cyclase activity. This higher activity was not suppressed when the animals were treated for 2 days with the beta-blocking agent propranolol. On the other hand, adipocytes from control animals treated with propranolol showed a higher adenylate cyclase activity (basal and in response to norepinephrine). beta-Adrenergic receptors were examined in adipocytes from control and diabetic rats with and without treatment with propranolol. The results show a higher beta-receptor density in adipocytes from diabetic animals. When the animals were treated with propranolol, the beta-blocker induced a higher receptor density in adipocytes from control animals without affecting the already increased receptor density in diabetic preparations. The data suggest that adenylate cyclase activity in response to norepinephrine in adipose tissue is increased during at least a certain period of the diabetic state. This increase in adenylate cyclase activity is accompanied with an increase in beta-receptor density, but in contrast to control animals, this receptor density is not further increased with propranolol treatment.