ACUTE CLONIDINE ADMINISTRATION POTENTIATES SPONTANEOUS DIURNAL, BUT NOT NOCTURNAL, GROWTH-HORMONE SECRETION IN NORMAL SHORT CHILDREN

It has been shown that α2-adrenoreceptor activation induced by clonidine (CLON) increases plasma GH levels in both adults and children. In this study the effects of CLON (150 μg/m2, orally) on GH secretion were studied both in the morning (from 0800–1100 h) and at night (from 2300–0200 h) in nine short children previously shown to have normal spontaneous nocturnal GH secretion. In the morning, CLON induced a GH increase higher than placebo [peak (mean ± sem), 23.8 ± 4.3 vs. 3.4 ± 1.4 μg/L; P = 0.0001; area under curve (AUC), 624.4 ± 62.7 vs. 135.6 ± 33.3 μg/·h; P < 0.00001]. In the night, no difference was observed between GH secretion after CLON (peak, 15.4 ± 3.2 μg/L; AUC, 562.2 ± 57.5 μg/·h) and placebo (peak, 13.1 ± 4.7 μg/L; AUC, 497.2 ± 83.5 μg/·h). Spontaneous GH secretion was higher during the night than in the morning (P = 0.0001), whereas nocturnal GH secretion overlapped with that in the morning after CLON. The data presented show that α2-adrenoreceptor activation is probably mediated by increased endogenous GHRH release; our results suggest that the endogenous GHRH secretion is maximally stimulated at night. © 1990 by The Endocrine Society.