Human chorionic gonadotropin directly and indirectly alters uterine arteriolar diameters in cycling rats

Objective: Our purpose was to investigate whether uterine microvascular responses to human chorionic gonadotropin application depend on route of administration and estrous cycle day. Study Design: One uterine horn was exteriorized in pentobarbital-anesthetized cycling and ovariectomized rats and superfused with Krebs solution. Uterine arterioles (64±2.1 μm) were viewed by videomicroscopy. Diameters were measured during a 20-minute baselline period and for 60 minutes during human chorionic gonadotropin suffusion (20 IU/60 ml) or 60 minutes after intraperitoneal injection of 50 IU of human chorionic gonadotropin. Papaverine (100 μmol/L) suffusion maximally dilated the uterine arterioles (80±2.6 μm). Results: Suffusion of human chorionic gonadotropin-dilated arterioles on diestrus-1 (122%±2% baseline) and diestrus-2 (118%±4% baseline) but constricted arterioles on proestrus (78%±7% baseline). Intraperitoneal injection of human chorionic gonadotropin resulted in arteriolar constriction on diestrus-2 (76%±5% baseline) and proestrus (82%±3% baseline). Ovariectomy eliminated the effects of injected but not suffused human chorionic gonadotropin. All results are significant at p<0.05. Conclusions: Results indicate estrous cycle day-dependent direct and indirect effects of human chorionic gonadotropin on the resistance of uterine arterioles.