Effect of immunological deprivation of endogenous LHRH on the course of pregnancy in rats

Specific and well characterized sheep anti-LHRH gamma globulin (A-LHRHrG) was administered to pregnant rats and the effect was investigated. Daily injection of A-LHRHrG (1 ml) from day 7 through day 11 led to the total resorption of embryonal ampullae when autopsied on day 14. On the other hand, animals receiving normal sheep gamma globulin (NGS) exhibited normal size of implantation sites and had what could be considered an uneventful pregnancy. Mean ovarian weight from NSG treated and from A-LHRHrG treated rats were 107.5±12.3 mg and 67.5±7.0 mg, respectively. Some of the corpora lutea from A-LHRHrG treated rats had undergone cystic degenerative change. Critical period was also determined by checking the effect of single injection of A-LHRHrG (1 ml) performed on various days of pregnancy. Rats receiving A-LHRHrG on day 9 or 10 underwent total resorption of implantation sites and serum progesterone levels abruptly declined to the level of less than 20 ng/ml. On the other hand, rats injected on day 8 or 11 exhibited partial resorption and injection on day 7 or 12 failed to affect either biological change or the levels of serum progesterone concentration. Administration of synthetic LHRH (1 μg, twice (4 mg, or progesterone (4mg, once daily) from day 9 through day 12, could overcome the effect of A-LHRHrG given on day 9. The results clearly indicate that hypothalamic control is indispensable for the maintenance of early pregnancy in rats, especially around day 9 and 10, by way of progesterone secretion.