Gonadal Hormones

Awakening of the gonads at the onset of sexual maturation is accompanied by a dramatic acceleration of growth. The adolescent growth spurt, like other changes at puberty, is attributable to steroid hormones of the gonads and perhaps the adrenals. Because the development of pubic and axillary hair at the onset of puberty is a response to increased secretion of adrenal androgens, this initial stage of sexual maturation is called adrenarche. The physiological mechanisms that trigger increased secretion of adrenal androgens and the awakening of the gonadotropic secretory apparatus are poorly understood; they are considered further in Chapter 45. At the same time that gonadal steroids promote linear growth, they accelerate closure of the epiphyses and therefore limit the final height that can be attained. Children who undergo early puberty and hence experience their growth spurt while their contemporaries continue to grow at the slower prepubertal rate are likely to be the tallest and most physically developed in grade school or junior high but among the shortest in their high school graduating class. Deficiency of gonadal hormones, if left untreated, delays epiphyseal closure, and, despite the absence of a pubertal growth spurt, such hypogonadal individuals tend to be tall and have unusually long arms and legs.

In considering the relationship of the gonadal hormones to the pubertal growth spurt it is important to understand that:

• Androgens and estrogens are produced and secreted by both the ovaries and the testes.

• Androgens are precursors of estrogens and are aromatized to estrogens by a reaction catalyzed by P450 aromatase in the gonads and extragonadal tissues.

• Estrogens produce their biological effects at concentrations that are more than 1000 times lower than the concentrations at which androgens produce their effects.

Until recently it was generally accepted that andro-gens produce the adolescent growth spurt in both sexes. This idea was rooted in the observations that even at the

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