Effects of VIP, PHM and substance P on blood vessels and secretory elements of the human submandibular gland.

The effects of the neuropeptides VIP, PHM and substance P (SP) on vascular smooth muscle tone, K+ secretion from exocrine elements and tissue content of cyclic AMP (cAMP) in the human submandibular gland were studied in vitro. All three peptides caused relaxation of noradrenaline contracted human submandibular arteries at nM concentrations. SP was slightly more active than VIP and PHM which had a similar potency as vasodilators. Only carbachol but not VIP, PHM or SP stimulated K+ secretion from exocrine elements of the human submandibular gland. Principally similar in vitro effects on K+ secretion were obtained on the cat submandibular gland, but in the rat not only carbachol but also SP stimulated K+ secretion. VIP and PHM increased cAMP production of exocrine elements in the human submandibular gland in nM concentrations. VIP was about 5-fold more potent than PHM with regards to cAMP production. In conclusion, VIP, PHM and SP relaxed human submandibular arteries in vitro. Both VIP and PHM stimulated cAMP production in glandular tissue but none of the three peptides induced K+ secretion from human submandibular gland tissue. This suggests that, in contrast to the situation in the rat, SP does not cause watery salivation in man, while VIP and PHM may modulate protein e.g. amylase content of the saliva.