Secretory dose-response curves were obtained with both acetylcholine and phenylephrine treatment in rat parotid and submandibular glands. Vasoactive intestinal peptide (VIP), which produced relatively low volumes of protein-rich saliva in rat salivary glands, also enhanced acetylcholine-, phenylephrine-, and substance-P-mediated fluid and protein secretion when administered in combination with these agents. The specific mechanisms involved in the synergistic actions of VIP with substances such as acetylcholine, phenylephrine, and substance P, which are primarily linked to the production of fluid secretion in rat salivary glands, have yet to be determined.
5-Hydroxytryptamine (5-HT) has been reported to produce significant responses in blowfly salivary glands, but little information is available concerning its action on mammalian salivary glands. When 5-HT (0.1 mumol/L to 10 mumol/L) is infused i.a. into anesthetized rats, no salivary secretion is obtained from either parotid or submandibular glands. However, when 5-HT is infused along with a threshold concentration of acetylcholine (0.1 mmol/L), potentiation of parotid secretory response is seen with 5-HT (1 mumol/L, 260% increase; 10 mumol/L, 146% increase). Substance P (0.3 mumol/L) combined with 5-HT (1 mumol/L) also resulted in a potentiation of parotid secretion (160% increase). Protein and calcium concentrations were not altered during such treatments. No potentiation of submandibular secretion was noted. Experiments in vitro with parotid cell aggregates exhibited no potentiation associated with the combined use of 5-HT and carbachol, as measured by amylase secretion and inositol trisphosphate accumulation. The experiments indicate that 5-HT substantially modulates parotid salivary secretion in vivo; however, the in vitro findings suggest that 5-HT does not act directly on surface glandular receptors. The magnitude of the in vivo potentiation could very well implicate circulating or released 5-HT as a physiological modulator of endogenous neurotransmitter action.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.