In this study the effects of chronic administration of clonidine, an alpha-2-adrenergic agonist, on the growth rate and GH response to GHRH in 12 "slowly growing" children were reported. Clonidine was administered at the dose of 0.04 mg/m2 body surface twice daily along 12 months. The protocol of the study consisted in five periods of growth rate, insulin-like growth factor-1, basal and GHRH-stimulated GH level evaluation: 1) 6-month pretreatment (P1); 2) 6-month placebo administration (PO); 3) after 4 months of therapy (P1); 4) after 4 months of clonidine withdrawal (P2); 5) after 4 months of therapy reinstatement (P3). No difference was observed between P-1 and P0 when all the parameters were considered. During P1 a significant increase of linear growth (p < 0.05 vs P0 and P-1) was observed while standard deviation of height was not modified. At the end of P2, the growth rate and standard deviation of height were similar to those recorded in P0 and P-1. After reinstatement of clonidine therapy a new but less pronounced rise of the growth rate was found (p < 0.05 vs P1, p < 0.01 vs P0 and P-1). GH, insulin-like growth factor-1, GHRH-stimulated GH levels had significantly increased during P1 than P0 and P-1 (p < 0.05), while during P2 they were similar to P0 and P-1. During P3 a new increase of insulin-like growth factor-I baseline and GHRH-stimulated GH levels were observed. However, these were significantly lower than those observed during P1.(ABSTRACT TRUNCATED AT 250 WORDS)
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