Evidence against the involvement of vasoactive intestinal peptide in ovine parotid secretion and blood flow

1. The proposition that stimulation of the secretomotor nerve to the ovine parotid gland might involve co-release of vasoactive intestinal peptide (VIP) was tested by studying responses to infusion of VIP directly into the gland's arterial blood supply and by assay of VIP in parotid venous blood. 2. In unstimulated glands, an arterial blood concentration of 1.5 - 2.5 X 10(-9) mol/L VIP did not evoke fluid secretion but it increased K+ and phosphate secretion and glandular blood flow. The same blood concentration of VIP potentiated the stimulation of salivary flow rate caused by intraarterial infusion of bethanechol but nerve stimulation was not potentiated. VIP increased glandular blood flow in both conditions of stimulation. 3. Atropine blocked neurally stimulated salivary secretion but an increase in glandular blood flow was still detectable. There was therefore no evidence for a non-cholinergic neural mechanism for salivary secretion. 4. Furthermore, VIP concentrations in glandular venous blood were not increased by nerve stimulation. 5. The results indicate that exogenous VIP can affect the flow and composition of ovine parotid secretion but was not involved in the response to secretomotor nerve stimulation.