Beta-adrenergic receptors and salivary gland secretion during aging

Beta-adrenergic signal transduction is primarily responsible for the control of the protein secretions by salivary cells. To examine the relationship between beta-adrenergic signal transduction and beta-adrenergic agonist-stimulated salivary secretion, we simultaneously assessed beta-adrenergic receptor number and pilocarpine-isoproterenol-stimulated salivary flow and secreted proteins in parotid and submandibular glands from 3-, 12- and 24-month-old female NNIA F-344 rats. There were no age-related changes in the density of beta-adrenergic receptors in the parotid gland or in the submandibular gland. In the parotid gland there was a significant increase in saliva flow rate in the oldest age group and no changes in the amount of total proteins secreted over 30 min. However, when normalized to gland weight, flow rate was unchanged and the amount of total secreted proteins decreased with age. In the submandibular gland there were age-related increases in both absolute volume and total secreted protein, but when normalized to gland weight there were no longer changes with age. Changes in flow rate were paralleled by reciprocal changes in protein secretory function such that changes in the salivary protein concentrations for the most part were unchanged with age for both the parotid and the submandibular gland. These parameters were compared to our previous data on adenylate cyclase activity, and collectively, these data suggest that in the submandibular gland salivary secretory function does not correlate with changes in beta-adrenergic receptor density or isoproterenol-stimulated adenylate cyclase activity.