Beta-adrenergic regulation of rat parotid gland exocrine protein secretion during aging.

beta-Adrenergic regulation of exocrine protein secretion from the parotid gland was studied over the adult rat life span. Enzymatically dispersed cell aggregates were prepared from 3-, 6-, 12-, and 24-month-old rats and exocrine protein secretion (amylase release) measured. No age differences were seen in the time course of amylase release following (-)-isoproterenol stimulation or in the (-)-isoproterenol dose-response curve. the beta-adrenergic antagonist (+/-)-propanolol inhibited (-)-isoproterenol-stimulated protein secretion from parotid cell aggregates of young and old animals equally. Similarly dibutyryl cyclic AMP induced comparable rates of protein secretion from cells of different aged rats. Direct examination of beta-adrenergic receptor characteristics in parotid gland membranes from 3- to 24-month-old rats revealed no differences in the equilibrium dissociation constant (Kd) or maximum specific ligand binding capacity (receptor number). These results suggest that the rat parotid beta-adrenergic system remains functionally intact throughout the animals' lifetime.