Expression of vasoactive intestinal polypeptide receptor mRNA and secretory regulation by vasoactive intestinal polypeptide in rat submandibular and sublingual salivary glands

Abstract

Vasoactive intestinal polypeptide (VIP)-receptor mRNA was strongly expressed in the acinar cells in the submandibular gland but not in the sublingual gland. VIP-containing nerve fibres were richly distributed around acini in the submandibular gland but were rare around acini of the sublingual gland. In the submandibular gland, the chorda was stimulated at various frequencies (1-40 Hz) together with an infusion of (N-Ac-Tyr1, D-Phe2)-GRF(1-29)-NH2 (109 M), VIP antagonist, which reduced salivary flow from the submandibular gland only at high-frequency stimulation (> 20 Hz), and more markedly reduced the salivary protein concentration. When the chorda was continuously stimulated the antagonist reduced the salivary flow only during the initial 5 min. Exogenous VIP 10(-12) - 10(-8) M) infusion at the same time as chorda stimulation caused no increase in salivary flow, but the salivary protein concentration was increased in a dose-dependent manner. In the sublingual gland, neither VIP nor the VIP antagonist affected chorda-evoked salivary flow and protein concentration. Thus, endogenous VIP may play a part in the regulation of both fluid and protein secretion, especially of protein, evoked by chorda stimulation at high frequency in the submandibular gland. These phenomena occurred only in the initial phase of secretion. In the sublingual gland, it seems likely that VIP plays no part in the regulatory mechanism, at least with regard to salivary fluid secretion in the acinar cells.