The effect of autonomic agonists and nerve stimulation on protein secretion from the rat submandibular gland

Saliva samples were obtained from the cannulated duct of the rat submandibular gland following intravenous administration of the autonomic agonists, acetyl beta-methyl choline (methacholine), phenylephrine and isoprenaline and by stimulating sympathetically at 5 and 20 Hz. Phenylephrine and isoprenaline produced a saliva approximately 50-fold richer in protein than that induced by methacholine. Protease activity was greatest in saliva induced by phenylephrine. Methacholine, phenylephrine and isoprenaline caused the secretion of markedly different protein populations, determined by separation on SDS-polyacrylamide gradient gels followed by staining with Coomassie Brilliant Blue R250. Many species in the molecular weight range 10000-40000 were secreted in response to phenylephrine and isoprenaline. Methacholine produced a saliva poor in protein and the resulting electrophoretic banding patterns were faint. Staining with periodic acid-Schiff's reagent showed that the largest protein species (mol. wt. 150000) secreted in response to isoprenaline was glycosylated and that small quantities of a similar protein were present in saliva produced by methacholine and phenylephrine but were not visualized by staining with Coomassie Brilliant Blue R250. Phosphorylated proteins of molecular weights 30000-35000 and 38000-45000 were detected in saliva produced by isoprenaline but not in saliva produced by methacholine or phenylephrine. Stimulation of the cervical sympathetic trunk at 5 Hz yielded a population of salivary proteins, many of which behaved similarly on electrophoresis to proteins secreted in response to isoprenaline. At 20 Hz a different population was secreted, resembling that present in phenylephrine-induced saliva.