Sex differences in nutritional modulation of gonadotropin secretion during development: studies in the growth-retarded lamb

This study determined whether changes in nutrition during development alter LH secretion in males in a manner similar to that in females; sheep were used as an experimental model. Studies were conducted in the absence of gonadal steroid negative feedback. First, we compared the effect of chronic growth restriction on LH secretion in male and female lambs, Second, we determined whether the gonadotropic response to acute increases and decreases in nutrition is sexually differentiated, Seven male and 8 female Suffolk lambs, gonadectomized, and weaned by 8 wk of age were maintained at a target weight of 20 kg by level of nutrition. After 7 wk of chronic low nutrition (15 wk of age), LH pulse frequency, was equally low in males (2.0 +/- 0.7 pulses/4 h) and females (2.0 +/- 0. pulses/4 h) relative to that (ca. hourly pulses) in normally growing gonadectomized lambs. Seven weeks later, at 22 wk of age, LH pulse frequency dropped further (males 0.9 +/- 0.3/4 h: females 0.9 +/- 0.4 pulses/4 h). The results of this first experiment, in which we observed no sex difference in gonadotropin secretion under chronic growth restriction, imply equal neuroendocrine sensitivity in males and females to long-term low nutrition. in the second experiment, however, a sex difference was evident in the response to increased and decreased nutrition. Both sexes responded to feeding ad libitum with a rapid increase in LH pulse frequency but the response was greater in the males than in the females. For example, after 2 wk on increased nutrition, the LH pulse frequency, in males had increased 450%, from 0.9 +/- 0.3 to 3.9 +/- 0.5 pulses/4 h, whereas the number of LH pulses in females increased by 300% from 0.9 +/- 0.4 to 2.6 +/- 0.5 pulses/4 h. Upon return to low nutrition, a similar sex difference was revealed. LH pulses decreased to 0.1 +/- 0.1 pulses/4 h for males and to 1.1 +/- 0.3 pulses/4 h for females. These acute responses reveal a sex difference in gonadotropin secretion, one in which males art somewhat more responsive than females to increased and decreased nutrition. Together, the results of the two experiments suggest that, in the absence of steroid negative feedback, the reproductive neuroendocrine system of the male is at least as sensitive as that of the female to changes in the level of nutrition.