Effect of vip and pacap on the basal release of serotonin from
isolated vascularly and luminally perfused rat duodenum.
Fujimiya, Mineko, Hiroshi Yamamoto and Atsukazu Kuwahara#.
*Department of Anatomy, Shiga University of Medical Science, Otsu,
Shiga 520-21, #Laboratory of Environmental Physiology, Graduate
School of Nutritional and Environmental Sciences, University of
Shizuoka, Shizuoka 422, Japan
APStracts 5:0165G, 1998.
The effect of vasoactive intestinal polypeptide (VIP), pituitary
adenylate cyclase activating peptide (PACAP) 38 and PACAP 27 on the
release of serotonin (5HT) into the intestinal lumen and into the
portal circulation was studied by using in vivo isolated vascularly
and luminally perfused rat duodenum. The determination of 5HT was
performed by HPLC. VIP, PACAP 38 and 27 reduced the luminal release
of 5HT but did not affect the vascular release of 5HT. The inhibitory
effect caused by VIP, PACAP 38 and 27 was not affected by neither
atropine, hexamethonium, TTX nor TTX + acetylcholine, however
completely antagonized by nitric oxide (NO) synthase inhibitor, NG
-nitro-L-arginine (L-NA). VIP receptor antagonist, VIP(10-28) blocked
the effects of both VIP and PACAPs. These results suggest that VIP
and PACAPs exert a direct inhibitory effect on the luminal release of
5HT from the enterochromaffin (EC) cells via a common receptor site
on the EC cells and this effect is mediated by NO but not cholinergic
pathways. Single injection of TTX, atropine or hexamethonium reduced
the luminal release of 5HT, while single injection of VIP(10-28)
stimulated the luminal release of 5HT and this effect was antagonized
by either atropine, hexamethonium or TTX. These results suggest that
EC cells may receive the direct innervation of cholinergic neuron as
well as VIP and/or PACAPs neuron, the former exerts a tonic
stimulatory influence and the latter exerts a tonic inhibitory
influence on the release of 5HT into the intestinal lumen.
Received 11 March 1998; accepted in final form 12 June 1998.
APS Manuscript Number G78-8.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 30 July 1998