Variations of plasma growth hormone (GH)-releasing factor levels during GH stimulation tests in children.
GH-releasing factor (GHRH) was measured by RIA in the plasma of 22 constitutionally short children given an ornithine infusion or an oral dose of L-dopa. After an overnight fast and 1 h of rest, plasma GHRH levels were 49.7 +/- 7.3 pg/ml (+/- SEM). In 5 children, L-dopa induced an increase in mean GH levels from 1.8 to 12 ng/ml at 60 min. Mean plasma GHRH levels increased from 47 pg/ml to a peak of 96 pg/ml at 15 min (P less than 0.02). In 4 other children, no increase in either GH or GHRH occurred after L-dopa treatment. In these 9 children, a significant correlation was found between the peak GH and GHRH concentrations (r = 0.841; P less than 0.001). On the contrary, ornithine-induced GH release was not preceded by a GHRH rise, but was followed by a GHRH decrease, from 51 to 27 pg/ml (P less than 0.02). We conclude that the 2 tests stimulate GH release in different ways, and that GH levels may be involved in the feedback control of GHRH secretion.
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone / Q000097:blood*; D006801:Humans; D007457:Iodine Radioisotopes; D007980:Levodopa / Q000494:pharmacology; D008297:Male; D009952:Ornithine
D007457:Iodine Radioisotopes; D007980:Levodopa; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D009952:Ornithine