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 arterioles in vivo between virgin and gravid rats. STUDY DESIGN: In anesthetized gravid and virgin rats circumferential arterioles were observed by videomicroscopy while vasoactive agonists were suffused over the uterus. Arteriolar diameter changes were compared. RESULTS: Resting and maximum diameters of circumferential arterioles were significantly larger in pregnant animals. Sensitivity to acetylcholine was greater in pregnant animals than in virgin animals (50% effective concentration, 7.1 +/- 0.17 negative log mol/L vs 6.1 +/- 0.32 negative log mol/L), whereas 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 II-induced constriction was significantly reduced in pregnant rats only at lower concentrations. Serotonin significantly dilated arterioles in virgin rats (76% +/- 3% of maximum) but caused significant arteriolar constriction in pregnant animals (65% +/- 4% of maximum). CONCLUSION: The in vivo uterine microcirculatory preparation allows measurement of resistance vessels in the intact animal. Although these results differ from some previous reports, differences may be attributable to vessel location or to in vivo versus in vitro conditions.

A new technique for studying the uterine microvasculature in the rat.

OBJECTIVE: Our purpose was to develop a method for direct measurement of rat uterine microvessels and to test their viability. STUDY DESIGN: In anesthetized female Sprague-Dawley diestrus rats, one uterine hom was isolated from the body cavity with its nerve and blood supply intact. A small fiberoptic probe inserted into the lumen of the uterus served as a light source for transillumination of uterine vessels. Diameters of circumferential arterioles were observed while increasing concentrations of vasoactive agonists were suffused over the uterus. RESULTS: No significant diameter changes occurred in circumferential arterioles of the control group (100-minute suffusion of Krebs solution). Dilation with papaverine (100 mumol/L) demonstrated that vessels possessed basal tone. Circumferential arterioles showed concentration-dependent constriction to phenylephrine and angiotensin II and dilation to acetylcholine and serotonin. CONCLUSIONS: This uterine microcirculatory preparation provides a stable, reproducible model of a unique microcirculatory bed that responds to vasoactive agents in a manner similar to other microcirculatory beds.