Rhythms of Progesterone and Corticosterone After PMS-Induced Puberty: Effects of Ovariectomy

The purpose of these experiments was to determine the ovarian contribution to changes in peripheral progesterone (PROG) levels during normal maturation and after treatment with 25 IU pregnant mare's serum gonadotrophin (PMS) at 26 days of age. Sprague-Dawley derived rats were ovariectomized (OVX) at 22 days of age and given either saline or PMS at 9 AM at 26 days of age. Groups of animals were killed by decapitation every 4 hr on days 28–29 and days 33–34 (3 days and 7 days after PMS). There was a significant peak (p < 0.01) of PROG at 1600 on day 28 in both intact and OVX saline-treated rats. The lowest PROG levels were found at 0400. PROG values were higher on day 33 in both intact and OVX rats with a maximum at 1600. Peripheral values of corticosterone (B) were the same in intact and OVX saline-treated rats at 28 days of age with a peak at 1600 while B was higher in intact rats at 33 days of age than OVX rats (p = 0.01). PMS given on day 26 produced a marked elevation inserum progesterone and corticosterone in comparison to intact saline-treated controls and a longer period of peak blood concentration (1200 to 2000 us 1600 only in controls). Peak B values in PMS-treated rats were higher than in controls (p = 0.01). Ovariectomy prior to PMS administration prevented the increase in P and B on day 28, but resulted in higher than control values for P and B on day 33 (p = 0.05). It is concluded that the daily rhythm of progesterone in maturing rats persists after ovariectomy but that the increase seen in progesterone at ovulation is initiated in the presence of the ovaries. Peripheral progesterone and corticosterone rise and fall together in immature rats but become dissociated a week after PMS treatment when high levels of progesterone persist in association with suppression of adrenal corticosterone. (Endocrinology95: 1719 1974)