Nitric oxide modulates regional blood flow differences in the fetal
gastrointestinal tract.
Fan, Wq, Jj Smolich, J Wild, Vyh Yu, and Am Walker.
Institute of Reproduction and Development, Monash University,
Clayton, Victoria, 3168 Australia
APStracts 3:0070G, 1996.
We studied the role of endogenous nitric oxide (NO) in the regulation
of the gastrointestinal (GI) circulation in 11 chronically
instrumented and unanesthetised late- gestation fetal sheep. Systemic
and gastrointestinal blood flow was measured by the radiolabelled
microsphere technique. Mean arterial pressure (MAP), heart rate,
blood flows, oxygen delivery and vascular resistance were determined
before and after infusion of the specific NO synthase inhibitor, Nw
-nitro-L-arginine (L-NNA) to cumulative doses of 10 and 25 mg . kg-1.
At both L-NNA doses, MAP increased and combined ventricular output
and heart rate decreased. GI blood flow and oxygen delivery decreased
and vascular resistance increased for the stomach, all segments of
the small intestine and the proximal colon and cecum, but were
unchanged in the middle-distal colon and rectum. Because the blood
flow reduction in the small intestine was pronounced (from 176 to 107
ml . min-1 . 100 g-1, P < 0.001), and that in the large
intestine unchanged, distribution of intestinal blood flow became
more uniform. Overall, the blood flow reduction was proportionally
greater in the GI circulation than in the remainder of the fetal
circulation. In 3 additional animals we established that L-NNA
reduced blood flow to the mucosa-submucosal layer (P < 0.02),
but not to the muscularis-serosa of the small intestine. In the same
animals, L-arginine (250 mg . kg-1) restored systemic hemodynamics
and partially restored small intestine blood flow. Our results
suggest that NO is an important differential regulator of vascular
tone in the developing gastrointestinal circulation.
Received 10 July 1995; accepted in final form 15 March 1996.
APS Manuscript Number G286-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 April 96