Isolated mesenteric arteries from pregnant rats show enhanced flow-mediated relaxation but normal myogenic tone.
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.
Division of Obstetrics and Gynaecology, United Medical and Dental Schools of Guy's Hospitals, London, UK.
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Cockell
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Poston
D000403:Airway Resistance / Q000502:physiology; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000502:physiology*; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009129:Muscle Tonus / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D014655:Vascular Resistance / Q000187:drug effects
D004791:Enzyme Inhibitors; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester