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Augmentation of Growth Hormone Secretion in Children With Constitutional Growth Delay by Short Term Clonidine Administration: A Pulse Amplitude-Modulated Phenomenon^*

Department of Pediatrics, Chair of Pediatric Endocrinology, University of Cagliari Cagliari, Italy
the Department of Pharmacology, University of Milan (S.G.C., E.E.M.) Milan, Italy

Address all correspondence and requests for reprints to: Prof. Carlo Pintor, Cattedra di Endocrinologia Pediatrica, Ospedale Microcitemico, Via Jenner, 09100 Cagliari, Italy.

We evaluated the effect of chronic clonidine administration on 24-h integrated GH secretion (IC-GH) in eight children (six boys and two girls; age, 6.0–13.0 yr) with constitutional growth delay (CGD). Clonidine was given orally in a daily dose of 0.1 mg/m² at bedtime for 6 months; 24-h secretion studies were performed before and after 2 months of treatment. Clonidine caused a significant augmentation (P < 0.02) of mean IC-GH from 2.6 ± 0.4 (±SE) to 4.6 ± 0.6 µg/L. The increase in IC-GH was mainly the result of increased GH pulse amplitude, which rose from 12.3 ± 1.3 to 18.2 ± 2.1 µg/L (P < 0.01). The mean GH pulse amplitude was significantly higher (P < 0.02) during sleep (15.9 ± 2.4 µg/L) than during the awake hours (8.4 ± 1.5 µg/L) before treatment. During clonidine treatment the mean GH pulse amplitude during the awake hours (15.0 ± 3.8 µg/L) was similar to that during sleep (20.3 ± 3.1 µg/L). GH pulse frequency was not altered by treatment during either the awake or sleep hours. The mean insulin-like growth factor I levels after 2 (1400 ± 300 U/L) and 6 (1760 ± 430 U/L) months of treatment were significantly higher (P < 0.02 and P < 0.05, respectively) than the pretreatment value (920 ± 240 U/L). After 2 months of clonidine treatment, growth velocity increased from 3.1 ± 0.5 to 10.2 ± 1.0 cm/yr (P < 0.001), and after 6 months of treatment is was still significantly higher (7.0 ± 0.7 cm/yr; P < 0.02) than that before treatment. These results confirm the ability of clonidine to accelerate growth in children with CGD and indicate that clonidine is capable of increasing IC-GH levels. They also reinforce the view that many children with CGD have decreased endogenous GH secretion

^* Presented in part at the 69th Annual Meeting of The Endocrine Society, Indianapolis, IN, June 10–12, 1987.

Received December 14, 1987.