BINDING OF 2-[I-125]MELATONIN BY RAT THYMUS MEMBRANES DURING POSTNATAL-DEVELOPMENT

Previously, we have demonstrated the presence of melatonin binding sites in thymus membranes of adult rats. In this paper, we show that the binding of melatonin by thymus membranes changes during postnatal development. Maximum binding was observed in newborn rats; thereafter, binding decreased progressively during the first weeks of life and exhibited the lowest values in adult animals. Stoichiometric studies showed that the decrease in melatonin binding was due to changes in the binding capacity (2.5-fold) rather than to changes in the affinity of the receptor for the ligand. The results suggest a physiological role of melatonin in regulating thymus activity early during postnatal development.