Precocious puberty: the effect of adrenalectomy on PMS-induced ovulation and progesterone secretion

Female Sprague-Dawley derived rats were received at 21 days of age and either sham-operated or adrenalectomized on that day. Half of the animals received either 25 IU pregnant mare's serum gonadotrophin (PMS) or 0.9 saline at 9 AM on the next day; the other half were injected at 26 days of age. On the day of expected ovulation (days 24-25 and days 28-29) the rats were killed at 4-hr intervals and the incidence of ovulation determined. Serum progesterone and corticosterone were measured with the intent of comparing the pattern of these steroids with the timing and incidence of ovulation. Twenty-two-day-old rats given PMS ovulated later (at 0400 on day 25) than did the 26-day-old rats (at 2400 on day 28). Adrenalectomized ADRX rats ovulated later than intact controls at both ages (ovulation complete at 1600 on days 25 and 29, respectively). There was a reduced ovarian weight response to PMS in ADRX rats but uterine weights were not consistently different from intact PMS-treated rats. Associated with the different timing of ovulation and organ weight response in the ADRX rats there was a lower serum progesterone response on days 24-25. In intact PMS-treated rats, the rhythm of the serum corticosterone was different in the two age groups. It is concluded that adrenalectomy alters the normal response to PMS resulting in a delay in the time of ovulation. It is possible that the adrenal normally participates in the induction of ovulation after PMS, possibly by acting as an internal priming agent to facilitate gonadotrophin release in the young rat.