Characterization of the insulin-signaling pathway in lacrimal and salivaryglands of rats

Purpose. Insulin has been acknowledged as a mediator of several physiologic al events in lacrimal and salivary glands. We investigated the presence of insulin receptors and of insulin-induced autophosphorylation of the insulin receptor and activation of elements involved in the early steps of insulin signaling in lacrimal and salivary glands of rats. Methods. Lacrimal and salivary glands of Wistar rats were removed and proce ssed for immunohistochemistry using antiinsulin receptor and anti-IGF-1 rec eptor antibodies. The activation of insulin receptors following insulin tre atment, and the involvement of insulin receptor substrates-1 and -2, Shc, J AK-2 and STAT-1, were analyzed by immunoprecipitation, followed by SDS-PAGE and immunoblotting of rat lacrimal and salivary glands after exposure to i nsulin. Results. Insulin and IGF-1 receptors were present in rat lacrimal and saliv ary glands and were located predominantly in the cytoplasm and plasma membr ane. Functional studies demonstrated that insulin induced a dose-dependent phosphorylation of the insulin receptor, IGF-1R, insulin receptor substrate s-1 and -2, Shc, and STAT-1. In rats with streptozotocin-induced diabetes m ellitus there was a significant reduction in insulin-induced insulin recept or and STAT-1 phosphorylation in the lacrimal gland but not in the salivary gland; there was no influence on Shc phosphorylation in either tissue. Conclusions. The present results indicate that insulin and IGF-1 receptors are expressed in lacrimal and salivary glands, and that insulin can induce the phosphorylation of its receptor and activate elements involved in the e arly steps of insulin signaling in both tissues.