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Gonadotropin-releasing hormone sensitivity in underfed prepubertal female rats
1Department of Biology, Marquette University, Milwaukee, Wisconsin 53233.
Insights
Reduced food intake alters pituitary gonadotropin-releasing hormone (GnRH) sensitivity in female rats. This effect on GnRH sensitivity is dose-dependent and influenced by gonadal hormones, impacting puberty onset.
Area of Science:
- Reproductive Endocrinology
- Neuroendocrinology
Background:
- Underfeeding is linked to delayed puberty.
- The role of pituitary gonadotropin-releasing hormone (GnRH) sensitivity in this delay requires further investigation.
Purpose of the Study:
- To investigate the impact of reduced food intake on pituitary GnRH sensitivity in immature female rats.
- To determine if altered GnRH sensitivity mediates the pubertal delay associated with underfeeding.
Main Methods:
- Immature female rats were fed 60% of normal intake (R) or ad libitum (C).
- Rats were ovariectomized (OVX) and treated with steroids, or remained intact.
- Intravenous GnRH challenges at varying doses were administered, and serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured.
Main Results:
- In OVX-steroid treated rats, low-dose GnRH elicited higher LH in R rats, while high-dose GnRH response was reduced.
- No significant difference in FSH response was observed between R and C rats.
- In intact R rats, GnRH induced higher LH concentrations at both low and high doses compared to controls.
Conclusions:
- Reduced caloric intake significantly affects pituitary GnRH sensitivity.
- The observed changes in GnRH sensitivity are dependent on the GnRH dose administered.
- The internal gonadal steroid hormone milieu critically modulates the effect of reduced food intake on GnRH sensitivity.
Abstract:
Studies were conducted to investigate the effect of reduced food intake on pituitary gonadotropin-releasing hormone (GnRH) sensitivity as a possible link in the delay of puberty by underfeeding. Immature female rats (30-32 days old at the start of each experiment) were used throughout the study. Rats on reduced food intake (R) received 60% of normal food intake beginning at the age of 21 days, whereas control (C) animals were fed ad libitum. In ovariectomized (OVX), estradiol benzoate-progesterone-treated R rats, low doses (less than 5 ng/100 g body wt) of GnRH injected intravenously produced higher serum luteinizing hormone (LH) concentration than in comparable C rats. No difference was found at 5 ng GnRH but response to high doses (15 and 45 ng/100 g body wt) was sharply reduced in R rats. No difference in serum follicle-stimulating hormone concentrations was found. In contrast to the OVX-steroid treated animals, in intact R rats, GnRH evoked higher serum LH concentrations at both low and high doses. These studies indicate that reduced caloric intake can affect pituitary GnRH sensitivity and that the effect depends on both the dose of GnRH and the internal, gonadal steroid hormone milieu.