The GH/IGF-I axis in puberty.

Puberty, either spontaneous, precocious or pharmacologically induced has profound effects on the physiology of the GH/IGF-I axis. Both spontaneous and stimulated GH secretion increase with puberty. The increase in spontaneous GH secretion is the result of increased GH pulse amplitude rather than frequency, and is probably an oestrogen-dependent effect. Parallel to the increase in GH secretion at puberty, circulating IGF-I and IGF binding protein-3 also increase. The pubertal increase in IGF-I correlates with stages of puberty as well as sex steroid levels. Circulating immunoreactive GHRH also increases with puberty, while circulating GH-binding protein levels are not affected by sexual maturation. Several data suggest an important role for the GH/IGF-I axis in the pubertal growth spurt. More recent data, however, have provided evidence of an important role for gonadal hormones in promoting adolescent growth independent of GH.