Can reduced consumption of gonadotrophins account for ovarian compensation in unilaterally ovariectomized, immature mice injected with gonadotrophins?

The effect of unilateral ovariectomy on ovulation rates in immature mice was studied. Ovulations were induced by injecting PMSG and hCG and their number was determined by counting tubal oocytes. A 2--3-fold increase in number of ovulations per ovary was observed after unilateral ovariectomy, and daily injections of progesterone abolished this ovulatory compensation. No significant increase in serum concentrations of immunoreactive FSH and LH was observed at 4, 8, 32 and 51 h after unilateral ovariectomy. Progesterone treatment lowered FSH levels at all times, while LH was unaffected. In intact mice, ovarian sensitivity to PMSG and hCG was not substantially affected by progesterone. Ovulatory compensation in immature gonadotrophin-injected mice appears to arise through a negative feedback mechanism and transiently increased secretion of pituitary gonadotrophin rather than through a greater utilization of a fixed amount of gonadotrophin.