Effects of pregnancy on femoral microvascular responses in the rat

OBJECTIVE: Our purpose was to test the hypothesis that augmented basal and vasodilator agonist-stimulated synthesis of endothelium-derived nitric oxide would blunt vasoconstrictor-induced contraction and enhance relaxation in isolated femoral resistance vessels from pregnant rats. STUDY DESIGN: Potassium chloride–, phenylephrine–, and angiotensin II–induced contraction and acetylcholine-induced relaxation were assessed in small (~240 μm diameter) femoral resistance arteries from gravid and virgin animals studied under isometric conditions; the effects of potassium chloride, phenylephrine, and acetylcholine were also studied in the presence of nitroarginine. RESULTS: Maximal vasoconstriction was similar in vessels from virgin and pregnant rats, whereas phenylephrine potency was slightly enhanced in vessels from gravid animals. Nitroarginine augmented contraction in both groups but with greater effect on phenylephrine potency and on submaximal potassium chloride contractions in virgins. Acetylcholine-induced relaxation did not differ between groups and was similarly, but only partially, inhibited by nitroarginine. CONCLUSIONS: Pregnancy does not result in vasoconstrictor resistance, increased basal nitric oxide synthesis, or augmented agonist-stimulated endothelium-dependent relaxation in this particular isolated rat microvascular preparation. Further, endothelium-dependent relaxation of these vessels depends only partly on nitric oxide. (Am J Obstet Gynecol 1996;175:730-6.)