Local changes in immunoreactive gonadotropin releasing hormone in the rat median eminence during the estrous cycle. Correlation with the pituitary luteinizing hormone.

The immunocytochemical approach was used to explore the possibility of local changes in immunoreactive gonadotropin releasing hormone (GnRH) of the median eminence (ME) during the estrous cycle in rats, and an attempt was made to correlate these changes with immunoreactive luteinizing hormone (LH) content in gonadotropic cells. On the day of proestrus, between 9:00 and 18:00 h, a severe depletion of GnRH from the medial palisade zone (MPZ) of the rostral part of the ME was observed whenever any marked changes in the density of GnRH present in the lateral palisade zone and in organum vasculosum of the lamina terminalis (OVLT) were visible. The depletion of GnRH from the MPZ was accompanied by a degranulation of LH-cells (stained with anti-pLH-beta) in the pituitary which occurred over the same period. It is postulated that the MPZ of the rostral part of the ME contains the majority of nerve endings originating from the perikaya responsible for the cyclic surge of LH.