Males, Females, and Behavior: Toward Biological Understanding

By Lee Ellis; Linda Ebertz | Go to book overview
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Chapter 8
Developmental Significance of the Postnatal Testosterone "Surge" in Male Primates

Alan F. Dixson, Gillian R. Brown, and Claire M. Nevison

In man, activation of the hypothalamic-pituitary-testicular axis during early infancy results in a "surge" of gonadotrophin and testosterone secretion beginning in the second postnatal week, peaking in months 2 through 4, and returning to baseline levels by approximately six months of age ( Forest, Deperetti, & Bertrand, 1976; Forest, 1990). The significance of this postnatal hormone surge remains enigmatic. Much of the testosterone is thought to be bound to sex-hormone binding globulin and unavailable to target tissues. Salivary levels of testosterone in baby boys have been reported to decline progressively from birth until six months of age ( Huhtaniemi, Dunkel, & Perheentupa, 1986), and salivary testosterone measurements are usually indicative of the levels of "free" (i.e., unbound) hormone in the bloodstream ( Quissell, 1993). It is not known whether the genitalia or the brain of the developing human male are exposed to an increase in androgenic stimulation during the first six months of infancy. However, there are at least three reasons to believe that the postnatal testosterone surge is a significant developmental event rather than an epiphenomenon. First, important changes in testicular development occur at this time. Numbers of germ cells in the human testis increase postnatally, peaking at approximately 100 days of age; that is, at the height of the postnatal testosterone surge ( Muller & Skakkeback, 1984). Second, a reversible blockade of the pituitary-testicular axis using LHRH analogues in infant male monkeys leads to a transitory suppression of LH and testosterone secretion during puberty (for rhesus monkey, see Mann,

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