Effect of propranolol plus exercise on melatonin and growth hormone levelsin children with growth delay

The pineal gland in humans is under both alpha- and beta -adrenergic contro l, although it seems that beta (1)-adrenoceptors are mainly implicated in m elatonin secretion. In the present study, we evaluated the role of e-adrene rgic innervation on melatonin production and its relation with the producti on of growth hormone (GH). Thirty-four children (15 males and 19 females, m ean age 10.5 +/- 0.8 years) from the University of Granada Hospital were st udied. The children were included in a protocol For the evaluation of growt h delay using the propranolol + exercise test. This standardized test allow ed us to study simultaneously the role of an unspecific beta -adrenergic bl ocker such as propranolol and of an adrenergic stimulus such as exercise on the pineal production of melatonin. Changes in plasma levels of melatonin and GH were determined at basal, 120 and 140 min after the test was applied . Hormonal determinations were carried out by commercial radioimmunoassay k its previously standardized in our laboratory. The results show a significa nt decrease in plasma melatonin levels at 120 and 140 min after the test (P < 0.05), whereas GH levels increased significantly at 140 min (P < 0.001). The decrease of melatonin levels was a consequence of the test, since in a control group. the circadian decay of melatonin was significantly less pro nounced (P < 0.05). These data suggest an inverse relationship between mela tonin and GH after the propranolol + exercise test, and the reduction in me latonin may be related to its depletion by exercise-induced oxidative stres s.