Temporal aspects of the involvement of the uterus and prolactin in the establishment of luteinizing hormones-dependent progesterone secretion in the rat.

This paper deals with some of the temporal aspects of the inhibition by PRL and the promotion by the uterus of the development of a crucial need for LH (LH dependency) in the maintenance of progesterone secretion by the rat corpus luteum. A severe and permanent fall in the concentration of progesterone in the serum and a shortening of the duration of the vaginal diestrus in response to 0.5 ml of a specific antiserum to LH, injected sc on the morning of day 9 of pseudopregnancy (day 1 = ovulation), confirmed the presence of LH dependency. In rats hysterectomized before the induction of pseudopregnancy or on days 2, 3, or 4 of pseudopregnancy, LH antiserum did not induce luteolysis, but in rats hysterectomized on day 5, it did. In rats subjected to chronic PRL treatment (through the homotransplantation of a rat pituitary beneath the kidney capsule) from day 2 onward, LH antiserum did not induce luteolysis if the uterus was removed on day 5, 6, or 7; if the uterus remained in place until at least day 8, however, LH antiserum induced luteolysis. In rats hysterectomized on day 5, the presence of a pituitary homotransplant only between 2 and 5 or only from day 5 onward prevented the luteolytic response to LH antiserum; if the pituitary was not transplanted until day 8, however, LH antiserum induced luteolysis. These results imply that there probably is a quantitative relationship between the duration (as well as time of onset) of the mutually opposing effects of PRL and the uterus on the appearance of LH dependency.