Somatostatin excites canine ileum ex vivo: role for no?.
P., Vergara, Woskowska Z., Cipris S., Fox-Threlkeld J. E. T. and E. E.
Daniel.
Division of Physiology and Pharmacology, McMaster University, 1200
Main Street West, Hamilton, Ontario L8N 3Z5
APStracts 2:0021G, 1995.
Isolated perfused segments of canine ileum have no spontaneous motor
activity, and release large quantities of vasoactive intestinal
polypeptide (VIP) continuously. Somatostatin perfusion was shown to
decrease VIP release, accompanied by increased contractions and
amplification of responses to low frequency electrical field
stimulation. After perfusion of higher somatostatin concentrations,
the VIP output did not recover but quiescence returned. The actions
of somatostatin on motor activity were not modified by hexamethonium,
slightly reduced by atropine and markedly reduced by tetrodotoxin
(TTX). Inhibition of VIP output was not the major determinant of
motor activity in the ileum because: 1) a second infusion of
somatostatin had similar motor effects despite markedly reduced VIP
output; 2) abolition of tonic VIP output did not prevent induction of
motor activity by somatostatin; and 3) artificial restoration of VIP
levels did not prevent or antagonize somatostatin induced ileal
contractions. In contrast, the increment in motor responses induced
by somatostatin was not apparent after L-N_-arginine methyl ester, an
inhibitor of NO synthase, but recovered after reversal by L-arginine.
We conclude that the mode of somatostatin activation of intestinal
motor activity involves reduced nitric oxide output, enhanced
excitatory mediator action or release, a direct action on smooth
muscle and possibly inhibition of VIP output. Of these, reduced
nitric oxide output plays the most important role.
Received 15 October 1993; accepted in final form 1 February 1995.
APS Manuscript Number G412-3.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 February 1995.