Endocrine Abstracts

This study was aimed to test our hypothesis that the brain-derived gonadotropin-releasing hormone (GnRH) and dopamine (DA) are delivered to the general circulation in fetal and neonatal rats, i.e. before the establishment of the blood-brain barrier, that is in contrast to adult rats. The GnRH and DA concentrations were measured in plasma and in the brain on the 18th embryonic day (E18), E21, 3rd postnatal day (P3), i.e. before the establishment of the blood-brain barrier, and on P30–36 after the establishment of the barrier. Moreover, the concentrations of GnRH and DA were measured in fetal plasma after microsurgical lesion of the brain regions containing most GnRH or DA neurons or after the inhibition of DA synthesis in the brain with sterotaxically injected α-methyl-p-tyrosine. According to our data, the concentrations of GnRH and DA in plasma on E18, E21 and P3 enormously exceeded those on P30–36 being as great as those in the hypophysial portal circulation in adult rats. Reverse was true for the ontogenetic dynamics of the GnRH and DA concentrations in the brain. The lesion of the local brain regions resulted in a drop of the GnRH and DA concentrations in fetal plasma. The DA concentration in plasma also decreased significantly after the inhibition of DA synthesis in the brain. The rest of circulating GnRH and DA was shown to be insufficient to provide the regulation of the respective adenohypophysial functions.

Thus, brain-derived GnRH and DA are delivered to the general circulation in fetal and neonatal rats in amounts sufficient to influence peripheral targets and the brain itself.