Role of the nongravid part of the uterus in the regulation of corpus luteum function in pregnant rats.

Abstract

The effect of the nongravid part of the uterus on corpus luteum (CL) activity was studied in rats bearing a single conceptus during midpregnancy. On day 7 (day 1 = insemination), the number of conceptuses was reduced to one by aspirating all but one conceptus (the aspiration group), by removing all of of the uterus except that containing a single conceptus (the hysterectomy group), or by aspirating conceptuses, as in the aspiration group, plus ligating the uterus, as in the hysterectomy group, but without removing the uterus (the sham hysterectomy group). Rats with a full complement of conceptuses (the intact control group) served as additional controls. Blood samples were obtained on days, 10, 12, and 15, to determine the effects of these procedures on the increase in serum progesterone that normally occurs between days 12 and 15 and to observe any related changes in serum LH between days 10 and 15. On day 15, the mean serum prgesterone concentrations and weights of the CL in the aspiration and sham hysterectomy groups were significantly lower than those in the intact control group. In the hysterectomy group, however, serum progesterone was even higher than in the intact control group, although the CL were significantly smaller than in the intact control group and were not different from those in the aspiration or sham hysterectomy groups. Serum LH on day 10 was significantly lower in the hysterectomy group than in any of the other groups; the latter were not significantly different from each other. By day 15, serum LH in the intact group had fallen to less than 50% of the value on day 10, while in the aspiration group, it remained as high as on day 10. In the hysterectomy group, there was no significant difference in serum LH concentrations between days 10 and 15. These results suggest that the nongravid part of the uterus inhibits progesterone secretion, and that in its absence, even a single conceptus can increase progesterone secretion after day 12 as much as can a full complement of conceptuses, but without also increasing the size of the CL. The uterus may exert this effect either through the pituitary or in cooperation with a pituitary factor, possibly LH.