Effect of clonidine on plasma ACTH, cortisol and melatonin in children

An interaction between melatonin and adrenocorticotropin (ACTH) seems to oc cur in humans and both hormones respond to beta-adrenergic stimulation. As in lower animal species, human pineal gland also contains alpha(2)-adrenerg ic receptors as does the hypothalamus-pituitary axis. In this study the res ponse of the pineal gland and of the hypothalamus-pituitary-adrenal axis to alpha(2)-adrenergic stimulation was assessed, Twenty-nine children (21 mal es, mean age 11.2 +/- 0.6 yr and eight females, mean age 9.1 +/- 1.1 yr) fr om the University of Granada Hospital were studied. The children were diagn osed as having growth problems but with a normal response of growth hormone (GH) to clonidine test. Changes in plasma levels of ACTH, cortisol and mel atonin were evaluated in these children after oral administration of the al pha(2)-adrenoceptor agonist clonidine (100 mu g/m(2)) or a placebo. Plasma ACTH, cortisol and melatonin were measured before (basal) and at 30, 60 and 90 min after oral clonidine or placebo administration. Hormonal determinat ions were carried out by commercial radioimmunoassay kits, previously stand ardised in our laboratory. The results show a significant decrease in plasm a ACTH, cortisol and melatonin 30 min after clonidine administration (P < 0 .001), reaching lowest values at 90 min after the drug was administered. Th e reduction in the levels of these hormones is independent of their normal circadian decay since the control group showed a significantly different pa ttern of behaviour. These data support the existence of an inhibitory alpha (2)-adrenergic influence on both the pineal gland and the hypothalamus-pitu itary-ad renal in children and further support the presence of alpha(2)-adr enoceptors in the human pineal gland.