Ontogeny of hypothalamic GnRH and pituitary GnRH recepotors in fetal rats

Abstract

In order to clarify the different roles of GnRH during fetal life, the first appearance of GnRH in the fetal brain, the expression of GnRH receptors on the fetal pituitary gland, and the presence of GnRH within the fetal gonadotrophs have been investigated. GnRH was present in the earliest brain examined (12 days of gestation). From 12 to 17 days, GnRH content of fetal brain remained low and then increased markedly by the end of gestation. No immunoreactive GnRH-like material could be detected in placental tissue throughout gestation. Binding sites for GnRH were detected as early as 12 days of gestation in fetal pituitary gland. At 17 days, Scatchard analysis indicated the presence of high affinity, low capacity binding sites. Intracellular presence of GnRH as seen by immunocytochemistry was first visible at 14 days and started to increase at 16 days. LH was first detectable in the fetal pituitary at 17 days, and FSH, at 21 days. In summary, hypothalamic GnRH appears very early in fetal life and potentially can induce differentiation of the pituitary anlage. Conversely, the presence at 15 days of gestation of specific binding sites for GnRH and of intracellular GnRH immunoreactivity in gonadotrophs indicates that the hypophysiotropic action of GnRH clearly precedes the start of LH biosynthesis.