THE INFLUENCE OF THE UTERUS ON THE CORPUS LUTEUM-PITUITARY RELATIONSHIP IN THE RAT

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Abstract
The mechanism through which hysterectomy increases the duration of pseudopregnancy in the rat was studied. The operation resulted in a mean increase in diestrous length of 8.8 days, and an incidence of such prolongations of about 78% when it was done before the late afternoon of the 9th diestrous day; from this time until the 12th diestrous day, the incidence of prolonged pseudo-pregnancies fell to 40%. Normal estrous cycles were resumed following the pseudopregnant cycle, and cervical stimulation of such rats resulted in pseudopregnancies, of which 77% were prolonged. Sham operations involving only a mild degree of uterine trauma resulted in a 29% incidence of prolonged pseudopregnancies, while increase in the amount of uterine tissue removed (up to one entire horn) increased the incidence to 60%. The homotransplantation of a pituitary to psuedopregnant rats at the time of hysterectomy did not increase the incidence of prolonged pseudopregnancies in the first postoperative cycle, but did increase the degree of prolongation slightly. The cycles of hysterectomized rats bearing pituitary homotransplants, when compared with those of intact rats bearing such transplants, showed a 46% increase in the incidence of all pseudopregnant cycles; 10% of such cycles were prolonged in the intact rats, and 44% in the hysterectomized rats. Ovarian compensatory hypertrophy occurred at a slightly slower rate in cyclic hysterectomized rats than in rats with intact uteri; in pseudopregnant rats, hysterectomy delayed the onset of ovarian compensatory hypertrophy until after the 15th diestrous day, while in rats with intact uteri, the increase in weight of the remaining ovary began on the 9th diestrous day. The pituitary folliculotrophic potency (measured by mouse uterine weight increase) of pseudopregnant hysterectomized rats did not increase until the 15th day, while in pseudopregnant rats with intact uteri this increase was seen by the 7th day, and was of greater extent. These results were discussed in terms of whether hysterectomy increased LTH secretion, or decreased the secretion of a pituitary luteolytic factor, probably LH; it was suggested that the results could be more readily accounted for by the second possibility.