Assessment of growth hormone secretion in children

Growth hormone (GH) is secreted in a pulsatile way during the whole life under the reciprocal influence of somatostatin and GH-releasing hormone (GHRH). It mediates many effects by stimulating production of insulin like growth factor I (IGF I) in liver and other tissues, but IGF I is also regulated by the nutritional state. Women secrete more GH than men, and older men and women less than young women. This suggests importance of estradiol in regulating secretion. Sex hormone effects are also demonstrated by the increment of GH and IGF I at puberty, which is an amplitude-modulated phenomenon. Classic metabolic studies have shown that patients with GH-deficiency retain more nitrogen in response to a given dose of exogenous hGH than normal subjects. The use of the stable isotope 15N has simplified such studies. In GH-deficient patients, there was with this technique a marked positive hGH-induced balance change. In girls with Turner syndrome (as example of subjects with normal GH-secretion), balance change was less marked with the same dose. Girls with Turner syndrome, who were given a double hGH-dose showed a response in the same range as that in the GH-deficient patients with the lower dose. A conclusion from this is that patients with normal GH-secretion need higher doses to obtain a similar response, than patients with GH-deficiency. The dosage in such patients will have to be selected individually, and needs to be about twice or three times as high as in GH-deficient patients.