Protein secretion by rat submandibular glands in response to isoproterenol, alpha-methylnoradrenaline and clonidine during aging

Changes in salivary volumes and the three types of proteins secreted by the submandibular salivary gland (SMG) of male rats at 3.5, 5.5, 8, 12, 13, 14, 15, 19, 21 and 24 months of age in response to the beta 1-, alpha 1- and alpha 2-adrenoceptor agonists, isoproterenol (IPR), alpha-methylnoradrenaline (alpha-mNA) and clonidine (Clonid), were studied and compared by measuring the weight and by isoelectric focusing electrophoresis with the Phast System on both the gradient pH 3.5-5 and 3.5-9 gels with silver staining. A protein (protein A, tentatively termed in this study) purified by FPLC from saliva elicited by IPR was also analyzed by SDS-polyacrylamide gel electrophoresis, the immuno-thermoblotting method, carbohydrate determination and neuraminidase treatment. Unexpected findings were observed that salivary volumes, but not the protein concentration, were substantially increased by Clonid-, but not IPR-, stimulation with ages up to 24 months of age and that the three types of proteins elicited by each agonist were different during aging. The gamma-type of proteins elicited by Clonid was not greatly changed during aging, whereas several proteins at about neutral pI in the alpha-type, elicited by alpha-mNA, at 5.5 to 21 months of age and a protein A in the beta-type, elicited by IPR, at 13 to 24 months of age were greatly increased. This protein A without any carbohydrate and sialic acid, located only in the acinar cells, but not in any duct system, had a molecular weight of 16,000 and a pI of 4.05. We conclude that the secretory function of the SMG in the aged animals is in general little changed.