Effect of unilateral ovariectomy on follicular growth in hypophysectomized rats treated with pregnant mare serum gonadotrophin

Unilateral ovariectomy results in compensatory follicular growth and doubling of the number of ovulations in the remaining ovary. It has been suggested that this is (at least partly) due to the increased availability of circulating gonadotrophins to the remaining ovary (McLaren, 1966). If this view is correct, it could be expected that in hypophysectomized rats treated with fixed regimens of pregnant mare serum gonadotrophin (PMS), follicular development in one ovary would be stimulated by removal of the other ovary. Wistar rats (180-200 g) which had had at least three consecutive 5-day cycles were used. In a first experiment (Table 1) the effect of unilateral ovariectomy on follicular growth in rats with an intact hypophysis was determined. The animals were unilaterally ovariectomized during oestrus or 2 days later (dioestrus 2). They were killed 1, 2, 3 or 4 days thereafter. In these rats a significant increase of follicular growth in the remaining ovary was seen on the 2nd postoperative day after removal of one ovary during oestrus and on the 1st postoperative day after removal of one ovary during dioestrus 2. In a second experiment rats were hypophysectomize