A comparative study of vascular responsiveness of myometrial and omental small resistance arteries in late-gestation sheep

OBJECTIVE: We determined whether local regulation by vasoactive agents differs in the myometrial and omental vascular beds in the pregnant sheep. Specifically, we hypothesized that there would be blunting of in vitro responses to constrictor agonists, enhancement of sensitivity to dilator agonists, or both in myometrial compared with omental resistance arteries. STUDY DESIGN: We compared in vitro responsiveness of small resistance intramyometrial and omental arteries from near-term pregnant ewes to the vasoconstrictor agents norepinephrine, U46619 (a thromboxane sympathomimetic), and potassium and the vasodilator agents acetylcholine and bradykinin. RESULTS: The vascular sensitivity and the maximum response of intramyometrial small arteries to U46619 was attenuated compared with that of omental arteries. There were no significant differences between the intramyometrial and omental arteries in response to norepinephrine, potassium, acetylcholine, or bradykinin. CONCLUSIONS: These results support regional heterogeneity of regulation of function in different maternal vascular beds during pregnancy. The relative insensitivity of the myometrial arteries to the thromboxane mimetic indicates the existence of decreased constrictor function that may facilitate preservation of uterine blood flow in vivo.