Pituitary Gonadotrophin-Releasing Hormone Responsiveness in the Prepubertal Period:Effect of Delayed Puberty Onset

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Abstract
Daily administration of 4% ethanol in the drinking water resulted in a significant delay in puberty onset. First ovulation occurred in controls at 35.4 ± 0.9 days and in ethanol-treated animals at 41.1 ± 1.2 days. Dietary controls failed to show a delay in puberty onset. The purpose of this study was to determine whether pubertal delay could be explained by delayed maturation of pituitary sensitivity to gonadotrophin-releasing hormone (GnRH). Basal LH values at 08.00 h were comparable in both groups at 23, 28, 32, and 36 days of age and first metestrus. FSH values were comparable at 23 and 36 days of age and first metestrus but were lower in ethanol-treated rats at 28 days of age and higher at 32 days of age. This difference appears to relate to a delay in the peripubertal rise and then fall of FSH in comparison to that which occurs in controls. 23-day-old controls were more sensitive to GnRH than were 28-day-old rats, as indicated by the serum FSH and LH response to increasing dosages of GnRH. In ethanol-treated animals, 28-day-old rats showed an LH response resembling 28-day-old controls but the FSH response was similar to that of the younger control animals. When the GnRH responses were measured as a function of age, the amplitude of the FSH response dropped sooner in controls than in ethanol-treated animals while the LH responses diminished in a linear fashion at the same rate over time in both groups. The difference in pituitary responsiveness to GnRH at 28 days of age in the two groups was not due to a difference in radioimmunoassayable FSH and LH in the pituitary. Over a 24-hour period at 28 days of age, ethanol-treated animals had lower estradiol levels at 08.00 h but not at other times of day. Progesterone values were comparable in the two groups. It is concluded that, by several criteria (basal FSH levels, FSH response to GnRH as a function of age, and the duration of the FSH response after GnRH), delayed puberty in response to ad libitum ethanol exposure is associated with a delay in the development of the pubertal pattern of FSH regulation. LH secretion is normal and is not obviously involved in the delay process.