Dynamics of GH Secretion in Children

Abstract

Growth and development during fetal and early postnatal life proceeds at a normal or near normal rate in the absence of growth hormone (GH) both in experimental animals and in man. Later on, somatic growth progressively becomes dependent upon GH. In contrast to other hormones, GH is the only hormone known to produce a dose-dependent stimulation of proportional body growth: in man, excess of growth hormone (GH) is known to cause gigantism and deficiency of GH leads to hypophyseal dwarfism. However, it is not known whether differences in growth rates among normal children are due to differences in endogenous secretion of GH. There is also insufficient knowledge about the influence of age and sex during the prepubertal period, as well as the influence of puberty on spontaneous GH secretion in children. In normal humans, serum levels of GH fluctuate in a pulsatile pattern, with great inter-individual variations in terms of pulse height and pulse frequency. Surges of GH secretion from the pituitary are spontaneous, with no apparent relationship to external stimuli. The release of pituitary GH is controlled by growth hormone releasing factor (GHRH) and growth hormone inhibitory factor, somatostatin. Each secretory episode of GH is initiated by changes in the concentration of these two hypothalamic peptides in the hypophyseal portal blood. The hypothalamic neuronal cell bodies producing GHRH or somatostatin interact with suprahypothalamic brain regions. Clearly, higher brain centers are involved in the control of GH secretion and, consequently, by affecting the secretory pattern of GH, the brain participates in the regulation of body growth.