Human chorionic gonadotropin dilates uterine and mesenteric resistance arteries in pregnant and nonpregnant rats

Membrane receptors for human chorionic gonadotropin (hCG) are expressed in a variety of steroidongenic cells and also in extragonadal tissues such as vessels of the female genital tract. We examined the possible contribution of hCG to the endocrine control of prearteriolar mesenteric and uterine ves sels before and during pregnancy. Lumen diameters of isolated pressurized r esistance arteries from Sprague-Dawley rats were measured using a video-ele ctronic system. hCG produced marked and dose-dependent vasodilation. Uterin e radial arteries were found to be highly sensitive to hCG (EC(50)congruent to 60 mU/ml) before and throughout gestation. Second-order mesenteric arte ries from nonpregnant animals were even more sensitive (EC50=38 mU/ml), but , in these vessels, responsiveness to hCG was significantly attenuated by t he pregnant state. Mechanical removal of the vascular endothelium did not r educe the degree of vasodilation mediated by hCG. The expression of hCG rec eptor mRNA in intact vessels could be demonstrated using reverse transcript ase polymerase chain reaction (RT-PCR). hCG appears to be an important embr yonic signal, which could trigger adaptive cardiovascular changes in early pregnancy, simultaneously preserving a sufficient utero-placental perfusion during the entire gestation period by an endothelium-independent mechanism .