Pituitary adenylate cyclase activating peptide (PACAP) in salivary glands of the rat: origin, and secretory and vascular effects.

Abstract

Pituitary adenylate cyclase activating peptide (PACAP)-38, injected i.v. to the anaesthetized rat, evoked secretion of saliva from the three major salivary glands, the submandibular glands responding with the greatest and the sublingual glands with the smallest volumes. The parotid saliva was rich in amylase and protein. In vitro, pieces of parotid and submandibular gland tissues released K+ and protein in response to PACAP-38, with atropine and adrenoceptor antagonists present. The blood flow in the submandibular gland increased in response to PACAP-38, despite a marked fall in mean aortic blood pressure. PACAP is a vasoactive intestinal peptide (VIP)-like neuropeptide. A comparison between the two peptides showed PACAP-38 to be more effective than VIP with respect to vascular responses and less or equi-effective with VIP with respect to the secretory responses, thus suggesting the involvement of PACAP type I and type II receptors, respectively PACAP-38 and -27 were present in the parotid gland as judged by radioimmunoassay, the concentration of the former being about twice that of the latter. Parasympathetic denervation, by cutting the auriculo-temporal nerve, reduced the total parotid gland contents of PACAP-38 and -27 by 23 and 44%, respectively (compared with a previously demonstrated 95% reduction of VIP). Sympathetic denervation, section of the facial nerve or treatment with the sensory neurotoxin capsaicin did not affect the content of PACAP. The difference in efficacy between PACAP and VIP in the vascular and secretory responses as well as the difference in localization suggest that the two peptides play different physiological roles in the salivary glands.