Effects of dietary energy on ovarian function, estrogen suppression of luteinizing hormone and follicle-stimulating hormone, and competency of the gonadotropin surge.

Fall-born ewe lambs were utilized to test the hypotheses that 1) inhibitory effects of increasing day length supersedes the stimulatory effects of increased nutrient intake on secretion of LH; 2) chronic undernutrition impairs ovarian function independent of changes in secretion of LH; and 3) undernutrition alters hypothalamic-pituitary responsiveness so as to influence feedback effects of estradiol on secretion of gonadotropins. Lambs were fed a low-energy diet (LE) from 14 to 26 wk of age to maintain a body weight of 24 kg during an inhibitory photoperiod. At 26 wk of age (experiment 1), lambs were either switched to a high-energy diet (HE; n = 10) or maintained on LE (n = 10). During increased nutrient intake, the frequency of pulses of LH remained at prepubertal levels, indicating that the inhibitory effects of photoperiod on tonic secretion of LH prevent the stimulatory effects of increased nutrition in chronically undernourished lambs. In experiment 2, lambs (33 wk of age) received hourly injections of ovine LH (15 micrograms; n = 6/diet group) or saline (n = 4/diet group) for 60 h during an inhibitory photoperiod. Chronically undernourished lambs were able to secrete estradiol, elicit a surge of LH, and form luteal tissue in the same manner as well-nourished lambs. After experiment 2, 4 lambs in each diet group were either bilaterally ovariectomized (OVX) or sham operated (INT) for experiment 3. At 36 wk of age, lambs were infused with estradiol-17 beta at a linearly increasing rate of 0.08 pg/ml for 56 h.(ABSTRACT TRUNCATED AT 250 WORDS)