Brain is an important source of GnRH in general circulation in the rat during prenatal and early postnatal ontogenesis

This study was aimed to test our hypothesis that, in contrast to adult rats, in fetuses and neonates, a large amount of the brain-derived GnRH is delivered to the general circulation. The GnRH concentration and content were estimated in general circulation and in the forebrain in rats on the 18th embryonic day (E18), E21, 3rd postnatal day (P3) and P30-36. Moreover, the GnRH concentration was measured in general circulation on E21 following microsurgical lesion on E18 of the forebrain containing most GnRH neurons. The concentration and content of GnRH in plasma on E18, E21 and P3 enormously exceeded those on P30-36. Reverse was true for the ontogenetic dynamics of the GnRH concentration in the forebrain. The lesion of the forebrain resulted in a drop of the GnRH concentration in plasma. The above data strongly suggest that the forebrain is the principal source of GnRH in general circulation in fetal and neonatal rats. Thus, the brain-derived GnRH is delivered to the general circulation in fetal and neonatal rats in amounts likely sufficient to influence the potential peripheral targets.