Effect of hysterectomy at different stages in the life cycle of the corpus luteum in the guinea-pig.

Hysterectomy on the 5th day of the luteal phase inhibited the dioestrous cycle for at least 8 months. The corpora lutea persisted throughout this period and, at the end, contained an appreciable amount of progesterone. Hysterectomy on the 10th day of the luteal phase caused the corpora lutea to enlarge as in pregnancy and to persist for a period about equal to that of gestation. Hysterectomy on the 15th day of the luteal phase prevented the impending ovulation and oestrus in 70 % (24/35) of animals. In these, the major effect was the arrest of the regressive changes in the corpora lutea, which became only slightly enlarged. In the remaining animals, ovulation and oestrus occurred shortly after the operation. The regres¬ sion of the corpora lutea occurred normally but the corpora lutea that formed post-operatively responded in the same way as those in animals operated on the 5th or 10th days of the luteal phase. The nature of the stimulus of hysterectomy on the corpus luteum of the guinea-pig is discussed briefly.