Altered Negative Feedback Response to Ovariectomy and Estrogen in Prepubertal Restricted-diet Rats 1

Abstract

Studies were conducted to explore the hypothesis that the delayed sexual maturation of female rats induced by reduced food intake (R) may result partially from an altered negative feedback response to estrogen. Animals were placed on 60% of normal food intake at 20 days of age. Controls (C) were fed ad libitum. Rats were used for three different experiments at 31-32 days of age. In Experiment I, rats were ovariectomized (OVX) and injected subcutaneously for 4 days with varying doses of estradiol benzoate (EB). They were killed the day after the last injection. In Experiment II, rats were ovariectomized and killed in groups at 4, 12, 24, 48, 72, and 120 h after OVX. In Experiment III, they were castrated and 1 wk later received a single injection of 0.5 microgram EB. Groups were killed at 1, 2, 4, 8, and 24 h after injection. Sera from all experiments were assayed for follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. Results of Experiment I indicate that the efficacy of EB for suppressing LH, but not FSH, secretion is increased significantly in R rats. In Experiment II, OVX resulted in a delayed increase in serum LH, but not FSH, concentrations of R rats when compared to C animals. Results of Experiment III indicate a delayed, but more prolonged, suppression of LH secretion by EB in R rats when compared to C rats. Prolactin secretion, on the other hand, increased earlier in R rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of short-term starvation on reproductive hormone gene expression, secretion and receptor levels in male rats

“…There is evidence for increased sensitivity of the hypothalamic-pituitary level to negative feedback of steroids (Howland & Ibrahim, 1973;Pirke & Spyra, 1981;Piasek, 1985), but attempts to demonstrate altered hypothalamic response to catecholamines, prostaglandins, opioid peptides and androgen as the reason for the altered gonadotrophin secretion have yielded inconclusive results Küderling, Dorsch, Warnhoff & Pirke, 1984). Also the stress-induced increase of the corticotrophinreleasing hormone, and its inhibitory effect on GnRH secretion (Rivier, Rivier & Vale, 1986), may be involved in the present observations.…”

Opioid modulation of luteinizing hormone, progesterone, and cortisol secretion in the prepubertal zebu heifer

“…Further, estradiol treatment of both ovariectomized, control-diet-and low-energy diet fed heifers attenuated the postovariectomy increase in LH pulse frequency and LH mean concentration, but these parameters were significantly (p<.001) lower in the low-energy group. This study suggests that the effect of dietary energy on LH secretion is mediated by both an ovary-or steroid dependent, and an ovary-independent pathways as previously reported in the rat (Piacsek, 1985;Bronson, 1988) and in the ewe lamb (Foster and Olster, 1985;Foster et al, 1989).…”

Underfeeding Alters the Effect of Low Levels of Estradiol on Luteinizing Hormone Pulsatility in Ovariectomized Female Rats

“…Direct effects (not dependent on ovarian steroid hormone feedback) of reduced food intake on luteinizing hormone (LH) release have been shown in the prepubertal female rat [24] and in the lamb [25], Altered gonadal steroid feedback may be, at least partly, re sponsible for the effect of underfeeding. Although underfeeding in adult rats does not alter the ability to exhibit a postovariec tomy increase in LH secretion [3], the response to postovariec tomy administration of 17(3-estradiol (E2) is a greater decrease in serum LH concentrations in underfed rats (UR) than in ad libitum fed controls (CR) [4,5], Similar results have been ob tained using different doses of testosterone following castration in adult [6] and immature [7] male rats, and with E2 in ovariec tomized immature female rats [8], It is not clear, however, if the increased efficacy of E2 in the underfed rat is mediated through the central nervous system (CNS), the pituitary, or both. The research presented here attempts to resolve this question through an analysis of the pulsatile pattern of in vivo LH secre tion in chronically underfed rats.…”

“…In the case of the 2.4 and 4.8 ug doses of E2, this was at least partly due to the failure of all CR to show pulsatility. Previous studies in mature female rats [5], immature female rats [8] and in mature male rats [27] indicate a biphasic rise in the postcastration levels of circu lating LH. Studies in the male [27] suggest that the initial rise represents removal of direct inhibition at the pituitary level, while the second, and much greater, increase is dependent on hypothalamic input.…”

“…The present study indicates that the UR were more sensitive to the negative feedback effect of E2 than CR, supporting the theory that underfeeding causes an al teration in LH secretion by a steroid-dependent mechanism [4-6] acting on the CNS to suppress LHRH secretion. Evidence for a steroid dependent mechanism has been suggested by re sults of studies in the adult male rat [6], adult female rat [4,5], immature male rat [7] and immature female rat [8,24]. Studies in the lamb [25] indicate that a similar mechanism may operate in that species to mediate the delayed puberty in underfed animals.…”