The inhibitory effects of ACTH and adrenalectomy on reproductive maturation in female rats

Abstract

The purpose of this study was to compare hormonally the delay of sexual maturation resulting from ACTH treatment and adrenalectomy in female rats. ACTH (4 IU/100 g body weight) was administered daily to intact and adrenalectomized female Sprague-Dawley rats beginning on the day of weaning (Day 21) and continuing until Day 40. Animals were decapitated at 1600 h on Days 25, 30, 35, 40 and on the day of vaginal opening; blood samples collected were assayed for progesterone, corticosterone, LH and prolactin. Animals were also sacrificed on first estrus and the Fallopian tubes were examined for the number of ova present. Either chronic ACTH treatment of intact animals or adrenalectomy delayed vaginal opening by four days. Our studies indicate that the inhibitory action of ACTH on vaginal opening is mediated by the adrenal glands, since ACTH-injected adrenalectomized rats failed to show a delay in vaginal patency. However, these animals exhibited a significant reduction in the number of ova present on first estrus as well as significantly lower body weights at vaginal opening. Plasma progesterone and corticosterone levels were elevated in ACTH-treated intact rats that exhibited delayed vaginal opening. Only plasma corticosterone was elevated in vehicle-injected rats that did not show retarded sexual maturation. Although our data suggest that chronically elevated levels of plasma progesterone in ACTH-treated rats inhibits sexual maturation by interfering with LH secretion, attempts to demonstrate a suppression of plasma LH concentrations in these animals were unsuccessful.