Metabolic Interfaces between Growth and Reproduction. I. Nutritional Modulation of Gonadotropin, Prolactin, and Growth Hormone Secretion in the Growth-Limited Female Lamb*

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Abstract
The acute and long term effects of dietary restrictions on gonadotropin secretion were studied in ovariectomized female lambs. Nutritionally growth-restricted lambs which were chronically maintained at a body weight comparable to that at weaning (.apprx. 20 kg) became hypogonadotropic, exhibiting a low frequency of episodic LH discharges. Repeated administration of physiological doses of GnRH to these females at hourly intervals produced corresponding LH pulses, leading to the hypothesis that the dietary-induced hypogonadotropism arises from a deficiency in endogenous GnRH release, rather than an inability of the pituitary gland to secrete gonadotropins in response to hypothalamic stimulation. In such growth-restricted females receiving a single meal daily, initiation of ad libitum feeding led to a spontaneous LH pulse within 1 h. After 14 days of increased food intake, hourly LH pulses were evident; a marked reduction in LH pulse frequency was associated with the return to limited nutrition. No effects on pulse amplitude were evident. Changes in circulating FSH followed a pattern similar to that for LH, namely an increase in concentration with improved nutrition and a decrease with reduced nutrition. The rate of response of FSH secretion to these alterations in nutrition was slower than that for LH. PRL levels were not altered by changes in nutrition, and a clear annual rhythm of secretion was observed. GH concentrations changes inversely with the level of nutrition; high secretion was associated with periods of restricted feeding, and low secretion with increased nutrition. These findings indicate that dietary restriction in the developing female lamb depresses gonadotropin secretion withou reducing other anterior pituitary gland secretions, such as PRL and GH. That these changes occur in the absence of the ovaries implies that metabolic and growth-related modulation of neuroendocrine function can occur independently of changes in sensitivity to the feedback actions of ovarian steroids and polypeptides.

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