Reproductive function in humans changes markedly during life and is usually divided into four stages. During the initial stage, which begins early in fetal life and ends in infancy, gonadotropins and gonadal steroids are secreted at levels similar to those seen in early and mid-adolescence. In the second stage, which lasts from infancy through the first decade of life, reproductive function first regresses and then becomes quiescent. Puberty, the third stage, is heralded by a nocturnal increase in the secretion of gonadotropins and sex steroids. This nocturnal predominance gradually diminishes and disappears during the fourth stage — adulthood. In men, . . .
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Flier et al. (1986) studied this question.