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Isolated mesenteric arteries from pregnant rats show enhanced flow‐mediated relaxation but normal myogenic tone.
Author(s) -
Cockell A P,
Poston L
Publication year - 1996
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1996.sp021614
Subject(s) - mesenteric arteries , medicine , endocrinology , nitric oxide , incubation , nitric oxide synthase , pregnancy , chemistry , anatomy , artery , biology , biochemistry , genetics
1. The mechanisms of vascular adaptation to pregnancy remain to be fully elucidated. In this study we have compared flow‐induced dilatation and myogenic responses in fifth generation mesenteric arteries from late pregnant and non‐pregnant Wistar rats. 2. Myogenic tone, assessed as the difference between internal diameter (i.d.) in the presence and absence of external calcium, at each of six transmural pressure steps (40‐90 mmHg) was no different in arteries from pregnant and non‐pregnant animals (90 mmHg; pregnant animals, 20.5 +/‐ 3.2% change in i.d., n = 13; non‐pregnant animals, 14.4 +/‐ 4.4% change in i.d., n = 13; n.s.). 3. Flow‐induced dilatation was significantly increased in arteries from pregnant animals when compared with that in non‐pregnant animals (pregnant, 11.2 +/‐ 3.7% increase in i.d., n = 12; non‐pregnant, 1.2 +/‐ 1.0%, n = 8; P < 0.02; at the maximal flow rate of 1.46 microliters s‐1). 4. Flow‐induced dilatation was significantly reduced in arteries from pregnant rats after incubation with the nitric oxide synthase inhibitor N omega‐nitro‐L‐arginine methyl ester (11.2 +/‐ 3.7% increase in i.d. vs. 0.8 +/‐ 1.5% with L‐NAME, n = 12, at a flow rate of 1.46 microliters s‐1; P < 0.02), but not altered in non‐pregnant rats (1.2 +/‐ 1.0% vs. 1.4 +/‐ 1.5% with L‐NAME, n = 8; n.s.). This was also reflected in a greater response to shear stress in the arteries from pregnant animals. 5. We conclude that myogenic tone is not significantly different in pregnant and non‐pregnant resistance sized mesenteric arteries of Wistar rats. However, flow‐induced dilatation, mediated by nitric oxide release, may play a major role in lowering vascular resistance during pregnancy.