Serum gonadotropins in rats fed a low-valine diet

Female rats fed a low-valine diet from the time of weaning have been shown to have delayed puberty compared to growth-matched controls. To explore the mechanism of this delay, serum LH and FSH were measured in rats fed the low-valine diet and in growth-matched control rats at several ages prior to puberty. Hormonal determinations at each time point were made both in the basal state and after LHRH administration or castration. After age 27 days, the mean basal serum FSH was lower in the low-valine group than in the control group. The mean serum levels of LH and FSH after oophorectomy were significantly lower in the low-valine group than in the control group, although the mean serum levels of LH and FSH after LHRH administration to intact animals were similar in both groups. The combination of impaired response to castration with unimpaired pituitary response to LHRH suggests that the low-valine group had a hypothalamic defect which accounts for their delayed sexual maturation when compared to growth-matched animals.