Sex steroids, growth hormone, leptin and the pubertal growth spurt

A normal rate for the linear growth of a child or adolescent is a strong statement for the good general health of that child. Normal growth during childhood is primarily dependent on adequate nutrition, an adequate psychosocial environment, the absence of disease and adequate amounts thyroid hormone and growth hormone (and its downstream product, IGF-1). At adolescence there is the reawakening of the hypothalamic-pituitary-gonadal axis and its interaction with the GH/IGF-1 axis to subserve the pubertal growth spurt. The fat tissue-derived hormone, leptin and its receptor are likely involved in at least two aspects of pubertal development - sexual development itself and the alterations in body composition including the regional distribution of fat and bone mineralization. During the prepubertal years the male female differences in body composition are quite modest, but change remarkably during pubertal development with boys showing a relative decrement in fat percentage and girls a marked increase in concert with rising levels of circulating leptin. The boys show a much greater increase in lean body tissue and the relative proportions of water, muscle and bone. These may be observed as the differential growth of the shoulders and hips. The net effect of these pubertal changes is that the young adult woman has approximately 25% body fat in the 'gynoid' distribution while the male has much more muscle, especially in the shoulders and upper body but only approximately 13% body fat.