The total amount and the temporal distribution of GH secretion is strongly dependent on age. Spontaneous GH secretion is detectable in term infants who appear to have a high level of tonic, i.e., non pulsatile, secretion (60). As the infant matures, GH pulse frequency and amplitude decrease and tonic secretion diminishes (60). A pulsatile pattern of GH release, with increased pulse amplitude during sleep, is present in prepubertal boys and girls (61). During puberty, the amplitude of the pulses but not the frequency is increased, particularly at night (62,63). Maximal overall GH concentrations are reached in early puberty in girls and in late puberty in boys (63). Because of the robust nature of the relationship between sleep and GH release in both prepubertal and pubertal children, it has been proposed that a "sleep test", i.e., repeated measurements of plasma GH during overnight sleep, may provide a reliable index of GH secretion and a useful test of GH deficiency (64,65). A number of reports examining the relationship between nocturnal GH secretion and SW sleep in children have indicated that the temporal association observed in adult is already present both in prepubertal and pubertal children and remains detectable in growth retarded children without growth hormone deficiency and in hyperactive children of small stature (66-69).

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