Vasoactive Intestinal Peptide (VIP)
It is a peptide having 28 amino acids. It is formed from its precursor prepro-VIP. Prepro-VIP has VIP and another peptide resembling VIP called PHM-27.
VIP is found in the nerves in the GIT, blood (where its T1/2 is 2 minutes), brain and autonomic nerves. In the brain and autonomic nerves, VIP is often found along with acetylcholine.
- markedly increases the intestinal secretion of electrolytes and water
- relaxes the intestinal smooth muscle, including the sphincters
- inhibits gastric acid secretion
- increases action of acetylcholine on salivary glands. VIP and acetylcholine co-exist in the nerves to the salivary glands; they do not exist together in other nerves of the GIT.
- dilates peripheral blood vessels
- VIP secreting tumours (called as VIPomas) cause severe diarrhea