Sympathetic denervation fails to produce beta adrenergic supersensitivity in adult rat parotid gland

Parotid acinar cells, prepared from pharmacologically sympathectomized adult rats (reserpine, 0.1 mg/kg/day for 1 week), display decreased responsiveness to beta adrenergic stimulation in vitro compared to cells from control and surgically sympathectomized rats. Both methods of denervation increase amylase content (amylase activity per microgram of DNA). Percent release of amylase activity and percent release of CCl3COOH-precipitable [14C]leucine were used as indicators of protein secretion. Exposure of cells from pharmacologically sympathectomized rats to the beta adrenergic agonist, isoproterenol, resulted in a marked reduction in receptor-coupled secretion (67% and 75% relative to controls, respectively). 8-Bromo-cyclic AMP, like isoproterenol, was unable to surmount this reserpine-induced inhibition of stimulated secretion, suggesting that an alteration in receptor-adenylate cyclase coupling is not responsible for the observed secretion defect. Cells prepared from surgically sympathectomized rats displayed modest decreases in stimulated secretion when the same secretory markers were monitored (30% and 25% relative to controls, respectively). The number of beta adrenoreceptors [( 3H]dihydroalprenolol binding sites) increased (35%), with no change in binding affinity, in membrane preparations from reserpine-treated rats. Thus, the observed inhibition of beta adrenergic agonist-induced secretion is not likely the result of alterations in beta adrenergic receptor characteristics. Short-term (1 week) surgical denervation had no effect on the number of beta adrenergic receptor sites; however, an increase in ligand binding affinity was noted. The decrease in the apparent Kd (30%) was not the result of a shift in receptor subtype as determined by competition studies with specific beta-1 (atenolol) and beta-2 (ICI 118,551) receptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)