Human Reproduction, Vol 12, 1805-1809, Copyright © 1997 by Oxford University Press
A Jovanovic, S Jovanovic and L Grbovic
Recently, strong evidence has suggested that nitric oxide (NO) synthesis is
significantly increased in the uterine artery during pregnancy, which may
mediate the increased blood flow to the uterus that is characteristic of
pregnancy. We therefore investigated the nature of the mediators of
acetylcholine (ACh)-induced relaxation in pregnant guinea-pig uterine
arterial rings. ACh (0.1 nM to 60 microM) induced endothelium-dependent
relaxation of phenylephrine-precontracted pregnant guinea-pig uterine
artery. N(G)-monomethyl-L-arginine (3-30 microM) antagonized the effect of
ACh, with suppression of maximal ACh- induced relaxation, in a
concentration-dependent manner. The inhibition of relaxation by
N(G)-monomethyl-L-arginine (10 microM) was significantly overcome by
L-arginine (10 microM), but not by D-arginine (100 microM). On the
contrary, the administration of indomethacin (10 microM) and
diethylcarbamazine (100 microM) did not modify the relaxation of guinea-pig
uterine artery induced by ACh. The ACh-evoked relaxation was unaltered when
K+-rich Krebs-Ringer bicarbonate solution was used to induce tone instead
of phenylephrine, or when a nonselective blocker of K+ channels,
4-aminopyridine (6 mM), was applied to phenylephrine-precontracted
segments. It is concluded that the relaxation induced by ACh in pregnant
guinea-pig uterine artery can be explained entirely by the release of NO
from vascular endothelial cells, without involvement of other
endothelium-derived relaxing factors, similar to that previously reported
for non-pregnant guinea- pig uterine artery. Thus, it seems that increased
activity of NO synthase during pregnancy is without significant influence
on the ACh action on uterine artery.
ARTICLES
Endothelium-dependent relaxation in response to acetylcholine in pregnant guinea-pig uterine artery
Department of Clinical Pharmacology, Pharmacology and Toxicology, School of Medicine, Belgrade, Yugoslavia.
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