A Rise in Tonic Luteinizing Hormone Secretion Occurs during Photoperiod-Stimulated Sexual Maturation of the Female Ferret*

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Abstract
Whether a rise in tonic secretion of LH [luteinizing hormone] occurred before long day-induced precocious puberty of the female ferret was determined. Twenty immature females were assigned to 1 of 2 photoperiods at 15 wk of age. Ten ferrets were placed in a long day, stimulatory photoperiod (16 h of light, 8 h of darkness) to induce sexual maturation and 10 remained in the nonstimulatory photoperiod (8 h of light, 16 h of darkness) for the duration of the study. Intensive blood sampling regimens (every 10 min for 8 h) were conducted at selected times after the onset of long days to permit definition of detailed secretory patterns of plasma LH. Females in each photoperiod were sampled from chronic jugular venous catheters .apprx. twice weekly until puberty was evident in females housed in long days. The end point for determination of the pubertal onset of adult ovarian function was the appearance of estrogen-sensitive vulvar edema. A marked increase in frequency of episodes of LH secretion per 8 h interval in females undergoing sexual maturation was seen. No such change in frequency occurred in unstimulated females housed continuously in short days, nor did the short day females exhibit vulvar edema. Further, the increment in LH secretion occurred before either vulvar edema or a significant increase in plasma estradiol levels was observed. Therefore, the rise in LH secretion that occurs after several weeks of exposure to a long day photoperiod may well be an important drive to maturational changes in ovarian function.