Some Observations on the Role of LH Receptor Binding Inhibitor of Ovine Corpora Lutea in Ovarian Processes

Preliminary studies, both in vitro and in vivo were carried out to understand the physiological significance of LH receptor binding inhibitors isolated from ovine corpora lutea. Among the four active fractions tested, while UM-2R-III administered intraperitoneally suppressed both hMG and hCG-induced stimulation of uterine weights in immature mice, UM-2R-IX reduced the hCG-induced uterine weight. Fraction UM-2R-III inhibited both FSH and LH-stimulated cyclic AMP production by rat granulosa cells. Intraperitoneal injections of UM-2R-III and IX to adult cycling rats on the day of proestrus partially blocked ovulation. Similar i.p. treatment of cycling rats in 2 doses on day 1 of diestrus, prevented implantation/or early pregnancy (on 10th day of pregnancy) in 70 to 80% of rats. As the plasma levels of progesterone were low in the treated animals compared to the control, the decrease was attributed to the inadequate development of the corpus luteum. Of these fractions, UM-2R-IX was more effective at 5 to 10 times less doses compared to UM-2R-III. Further studies are needed to assess the route and dose of administering the active LHRBR components.