Induction of a specific (LM) protein in the submandibular gland of the rat by repeated amputation of the lower incisor teeth

Chronic administration of the β‐adrenergic agonist isoproterenol (IPR) leads to marked hyperplastic/hypertrophic enlargements of the parotid and submandibular glands in rats and mice with concomitant changes in the composition of both the glands and the saliva. Conspicuous among the alterations of the submandibular saliva is the appearance of a 13,000 M_r protein, termed LM (large mobile) protein. Repeated amputation of the lower incisor teeth also causes enlargements of the major salivary glands in rats. In this study, we have compared the enlargements of submandibular glands of rats produced by IPR administration or teeth amputation with respect to the relative levels of the LM protein in gland extracts and saliva. Adminstration of IPR‐HCI (40 mg/kg) twice daily for 5 days or amputation of the lower incisor teeth 3 times a week for 3 weeks resulted in a 2.2‐fold increase in the weight of the submandibular gland. Amputation for one week led to a 1.4‐fold increase in gland weight. Double immunodiffusion in agar antibodies against the purified LM protein gave a single preciptin line with gland extracts and saliva of IPR‐treated and teeth‐amputated rats, indicating immunological identity of the reacting antigens. No precipitin lines were seen with gland extracts or saliva of untreated rats. Immunoblots of pooled saliva obtained from IPR‐treated or teeth‐amputated rats revealed a single protein band of the same electrophoretic mobility in SDS‐polyacrylamide gels when stained using anti‐LM antibodies. The relative concentrations of LM protein in gland extracts and saliva were measured by a solid‐phase enzyme‐linked immunoabsorption assay using antibodies aginast the purified LM protein. In gland extracts of untreated rats, LM protein was not measurable. Both amputation and adminstration of IPR resulted in marked increase in the relative concentrations of the LM protein. However, the relative concentration of LM protein in extracts of glands of teeth‐amputated rats was only about one‐fifth of that found in extracts of glands of IPR ‐treated animals irrespective of the duration of the amputation. LM protein was localized immunocytochemically in the cytoplasm of acinar cells and in the striated duct cells. These data indicate that both amputation of incisor teeth and β‐agonist administration lead to the induction of the same protein in the submandibular glands of rats, although the mechanism by which these two types of interventions cause enlargement of the gland may not be identical.