Induction of localized differences in rat uterine radial artery behavior and structure during gestation.

Objectives: The objectives of this study were to investigate differences in diameter and vasoconstriction of premyometrial versus uteroplacental radial arteries and to evaluate the contribution of nitric oxide (NO) to myogenic tone as a function of vessel location.

Study Design: Radial arteries supplying either the myometrium or placenta were dissected from the uterus of pregnant rats. Constrictor responses to pressure elevation were studied before and after inhibition of endothelial NO synthase (eNOS).

Results: Passive lumen diameters of premyometrial and proximal uteroplacental arteries were comparable and significantly smaller than those of distal uteroplacental vessels. High potassium- and pressure-induced responses were also similar in premyometrial and proximal but were virtually absent in distal uteroplacental segments. L-NNA enhanced pressure-induced tone, but was without effect in distal uteroplacental segments.

Conclusion: Gestational remodeling alters arterial structure and reactivity in a highly localized manner. During pregnancy, enhanced basal production of NO may be an important local mechanism for uterine blood flow regulation.