Effect of human chorionic gonadotropin on reproductive organ blood flow in cycling rats

Recent characterization of luteinizing hormone++ (LH)/human chorionic gonadotropin (hCG) receptors in uterine vascular tissue, evidence that expression of these receptors is cyclic in nature, and demonstration of a correlation between hCG level and uterine vascular resistance lead us to investigate the effect of hCG administration on blood flow in reproductive organs of cycling and ovariectomized Sprague-Dawley rats. Blood flow (ml/min/g dry wt/cardiac output +/- SEM) was determined by microsphere spectroscopy (57Co, 113Sn, 95Nb, 141Ce). Baseline uterine (0.5842 +/- 0.1037) and cervical (0.7785 +/- 0.1199) blood flows were greater in diestrus-2 rats than in every other group. Diestrus-2 (0.4530 +/- 0.0584) and estrus (0.4692 +/- 0.0848) rats had greater baseline ovarian blood flow than proestrus rats (0.2521 +/- 0.0279). A single intraperitoneal injection of 50 IU hCG on each day of the 4-day estrus cycle decreased uterine flow by more than 30% within 20 min (P<0.05), but did not alter uterine flow in ovariectomized rats. This dose of hCG also decreased ovarian flow in diestrus-2 rats (0.5219 +/- 0.0857 to 0.4207 +/- 0.0753), decreased liver flow in diestrus-2 (0.0282 +/- 0.0060 to 0.0231 +/- 0.0051) and estrus (0.0301 +/- 0.0029 to 0.0203 +/- 0.0038 rats, and increased liver flow in ovariectomized rats (0.0279 +/- 0.0054 to 0.0325 +/- 0.0050). Injection of 0.10 IU hCG did not alter blood flow to reproductive organs in any group, but decreased liver flow in estrus rats (0.0469 +/- 0.0121 to 0.0326 +/- 0.0088). Neither dose of hCG altered cervical, kidney, or skeletal muscle flow in any group. Our results indicate an organ specific, dose-dependent blood flow response to hCG in cycling rats, which appears, in the case of uterine flow, to be attenuated by removal of the ovaries. The present findings suggest high doses of hCG given clinically may decrease uterine flow and potentially lead to implantation failure.