Pregnancy-induced alterations of uterine arteriolar reactivity in the rat:Observations with a new in vivo microcirculatory preparation

OBJECTIVE: The aim of this study was to compare reactivity of uterine arter ioles in vivo between virgin and gravid rats. STUDY DESIGN: In anesthetized gravid and virgin rats circumferential arteri oles were observed by videomicroscopy while vasoactive agonists were suffus ed over the uterus. Arteriolar diameter changes were compared. RESULTS: Resting and maximum diameters of circumferential arterioles were s ignificantly larger in pregnant animals. Sensitivity to acetylcholine was g reater in pregnant animals than in virgin animals (50% effective concentrat ion, 7.1 +/- 0.17 negative log mol/L vs 6.1 +/- 0.32 negative log mol/L), w hereas that to phenylephrine was less (50% effective concentration, 5.3 +/- 0.11 negative log mol/L vs 6.0 +/- 0.17 negative log mol/L). Angiotensin I t-induced constriction was significantly reduced in pregnant rats only at l ower concentrations. Serotonin significantly dilated arterioles in virgin r ats (76% +/- 3% of maximum) but caused significant arteriolar constriction in pregnant animals (65% +/- 4% of maximum). CONCLUSION: The in vivo uterine microcirculatory preparation allows measure ment of resistance vessels in the intact animal. Although these results dif fer from some previous reports, differences may be attributable to vessel l ocation or to in vivo versus in vitro conditions.