BASAL AND STIMULATED ALPHA-MSH PLASMA LEVELS THROUGHOUT PUBERTY

Abstract

a-Melanocyte-stimulating-hormone (a-MSH) is a peptide derived from a two steps cleavage of Pro-opiomelanocortin (POMC) and produced in adults by a residual zona of the original intermediate lobe. It has recently been shown that a-MSH is not only detectable in healthy adult subjects, but also that plasma levels change during menstrual cycle, concomitantly with sex steroids modification. In addition it has been demonstrated that the peptide secretion is controlled by a dopaminergic inhibitory tore. In order to evaluate whether plasma a-MSH levels vary with advancing pubertal development and the dopaminergic tone influence the peptide release in children, 12 prepubertal and 15 pubertal subjects of both sexes underwent a domperidone stimulation (i.v. bolus dose of 0.3 mg/kg, max 10 mg). a-MSH and ACTH 1-13 plasma levels were determined before and after domperidone administration. Both peptides were measured by RIA after plasma extraction on Seppak Cartridges and reverse phase HPL-C fractionation. In prepubertal children basal a-MSH (2.8±0.8 fmol/ml) and ACTH 1-13 (6.0±1.6 fmol/ml) levels were lower, though not significantly, than those in pubertal subjects (4.8±0.9 and 8.2±1.4 respectively). After domperidone both a-MSH (8.1±2.5) and ACTH 1-13 (20.7±5.2) plasma levels significantly (p 0.05) increased in prepubertal subjects, whereas no changes were detected in pubertal ones. The results of the present study demonstrate that: 1) plasma a-MSH levels are detectable troughout childhood; 2) a functional activity of pituitary neurointermediate lobe is more evident in prepubertal than in pubertal subjects, suggesting a modified dopaminergic tone and/or anatomical changes during puberty.