Beta-adrenergic receptors and cAMP levels of rat parotid and submandibular glands during chronic isoproterenol treatment.

The number of cell surface beta-adrenergic receptors and the level of cyclic AMP of the parotid and the submandibular gland were examined in rats treated for up to 10 days with twice daily injections of the beta-adrenergic agonist, isoproterenol. Receptor densities of 125 +/- 8.7 fmol/mg membrane protein for the parotid and 60.1 +/- 5.6 fmol/mg for the submandibular glands were found with [3H]dihydroalprenolol (beta-adrenergic receptor antagonist) binding of glands from control rats. No change from levels of controls was found in the number of beta-receptors of the submandibular gland with chronic isoproterenol stimulation; the parotid glands, on the other hand, showed a 22% decrease in dihydroalprenolol binding from the 4th until the 8th day of treatment. By day 10 of isoproterenol treatment the parotid gland demonstrated a shift from a population consisting of primarily beta-adrenergic receptors to one consisting of equal numbers of beta 1- and beta 2-adrenoceptors. The basal level of cAMP present in cell lysates remained unchanged in the isoproterenol-treated submandibular gland while the parotid gland showed a 30-40% decrease. Control and isoproterenol-treated animals demonstrated the same time course of cAMP accumulation after a single challenge with isoproterenol.