Plasma and pituitary hormone changes and follicular development after unilateral ovariectomy in cyclic rats

After unilateral ovariectomy of 4-day-cyclic rats, plasma FSH increased over control values for 6--12 h after the surgery regardless of whether unilateral ovariectomy was performed before or after 08:00 h on the day of dioestrus, after which time compensatory ovulation did not occur at the next oestrus. Pituitary content of FSH also increased from 6 h after unilateral ovariectomy. In contrast, plasma and pituitary levels of LH and prolactin were generally within the range of values of sham-operated rats. Treatment with pentobarbitone between 13:00 and 14:00 h on the day of pro-oestrus in rats unilaterally ovariectomized after 08:00 h on dioestrus delayed the next spontaneous ovulation by 1 day and was accompanied by a rise in plasma FSH concentrations for 24 h and a doubling in the number of ovulations from the remaining ovary. Follicle counts showed an increase in large healthy follicles (greater than or equal to 501 micrometers diam.) and a decrease in atretic follicles in pentobarbitone-treated rats. It is suggested that the FSH rise induces compensatory follicular development and decreases follicular atresia when there is sufficient time for follicles to develop before the LH surge.