Co-release of PHI and VIP in dog stomach by peripheral and central vagal stimulation

1. The purpose of this investigation was to examine the outputs of peptide histidine isoleucine (PHI) and vasoactive intestinal peptide (VIP) from the gastric corpus in response to stimulation of the peripheral (PVS) and central (CVS) ends of the vagus nerve and to compare the effects of PHI on gastric motility and blood flow with those of VIP in atropine-treated dogs. 2. PVS and CVS caused parallel increases in gastric venous plasma concentrations of VIP and PHI. The molar ratios of the peptides (VIP/PHI) appearing in the gastric venous plasma were about 1.5 for PVS at 10 Hz, 0.65 for PVS at 40 Hz and about 0.7 for CVS at 10 Hz. 3. The molar ratio of peptide concentration extracted from the gastric corpus was about 1.5 in the muscle layer and 2.7 in the mucosal layer. 4. Intra-arterially-injected PHI was about 5 fold and 50 fold less effective in producing gastric relaxation and vasodilatation, respectively, than VIP. 5. These results indicate that PHI is co-released with VIP by peripheral vagal stimulation and by initiation of the vago-vagal reflex, and that PHI seems to have an important role in the regulation of gastric motility but not gastric blood flow in the dog.