Redistribution of ovarian blood flow after injection of human chorionic gonadotropin and luteinizing hormone in the adult pseudopregnant rat.

It is well known that LH and human CG (hCG) induce an increase in total ovarian blood flow. The effect of LH/hCG on luteal blood flow, however, is unknown. This work studies the effect of hCG on both luteal and ovarian blood flows at different stages of pseudopregnancy in adult female rats. Pseudopregnancy was induced by mating with sterile male rats. The length of pseudopregnancy was 13 +/- 1 days and, during this time, blood flow was measured by the injection of radioactive microspheres during anesthesia. At autopsy, the corpora lutea were identified and extirpated under a stereomicroscope. These, and the remaining ovary, were then counted for radioactivity and the blood flow was calculated. Progesterone levels were determined in plasma and ovarian tissues. Furthermore, the responsiveness of adenylate cyclase was tested in ovarian tissues at day 6 of pseudopregnancy. An intraarterial injection of hCG (50 IU) or vehicle (saline) was given 20 min before the blood flow determinations in anesthetized rats. The luteal blood flow was not changed by hCG on days 2, 6, and 11 of pseudopregnancy, whereas in the remaining ovary the blood flow increased more than 2-fold, thereby resulting in redistribution of the blood flow. Ten micrograms of NIH-LH-B9, tested at day 6 of pseudopregnancy, mimicked the effect of hCG. At day 6 of pseudopregnancy, hCG (50 IU) was given ip to conscious rats 200 min and 24 h before blood flow determinations. At 200 min after hCG there was a more pronounced redistribution of ovarian blood flow with a 45% reduction in luteal blood flow and a 4-fold increase in flow through the remaining ovary. LH as well as hCG doubled the progesterone content of the remaining ovary. In the corpora lutea an increased progesterone content was seen after 200 min of hCG exposure. At 24 h after hCG injection, all parameters had returned to control levels except that adenylate cyclase was nonresponsive. The increase in the total ovarian blood flow coincides with the increased steroidogenesis and these effects are likely due to release of metabolites and/or vasoactive substances. Despite this increase, the blood flow of the corpus luteum was not increased rendering vascular mechanisms unlikely as a part of the acute LH/hCG effects on corpus luteum of pseudopregnancy.