The fact that the secretion of growth hormone (GH) is markedly stimulated during sleep has been recognized for more than three decades. Early studies using the first available radioimmunoassays for GH demonstrated that the peripheral levels of this hormone increased rapidly following sleep onset (1-5). In normal adult subjects, the 24-h profile of plasma GH levels consists of stable low levels abruptly interrupted by bursts of secretion. The most reproducible pulse occurs shortly after sleep onset (3,4). This relationship between sleep onset and GH secretion appears to be most consistent in the human species, because it is more difficult to evidence in other mammals, although elevated blood GH levels have been observed during sleep in baboons, rhesus monkeys, dogs, lambs, and both immature and adult rats (6-12). Species differences could be
From: Human Growth Hormone: Research and Clinical Practice Edited by: R. G. Smith and M. O. Thorner © Humana Press Inc., Totowa, NJ
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