AUTONOMIC CONTROL OF SUBMANDIBULAR PROTEIN SECRETION IN THE ANESTHETIZED CALF

The autonomic control of submandibular secretion has been investigated in fully weaned, anaesthetized calves 7 weeks after birth. Stimulatio n of the parasympathetic (chorda-lingual) innervation invariably produ ced a flow of saliva, the rate of which was frequency dependent over t he range 2-8 Hz continuously. Neither the rate of flow nor the output of protein was enhanced by stimulating in bursts at relatively high fr equencies. Stimulation of the sympathetic innervation (20 Hz for 1 s a t 10 s intervals) alone produced a much slower flow of saliva but with a considerably higher protein content. Stimulation of both together p roduced no greater flow of saliva than occurred with either alone at t he lower frequencies (2 and 4 Hz) but there was a pronounced synergy i n respect of the secretion of protein. Following pre-treatment with pr opranolol (1.0 mg kg(-1) I.V.), during on-going chorda-lingual stimula tion at 4 Hz, intra-arterial injections of 1 nmol of either vasoactive intestinal peptide (VIP) or pituitary adenylate cyclase activating pe ptide (PACAP) elicited an increase in the flow and protein output of a bout the same order of magnitude. Calcitonin gene-related peptide (CGR P) also produced these same effects with roughly half the efficacy of VIP and PACAP but substance P had no detectable effect. It is conclude d that VIP, PACAP and possibly CGRP are candidates for neurotransmitte rs with a role in the control of secretion in this gland.