INFLUENCE OF GONADOLIBERIN ON THE DIFFERENTIATION OF RAT GONADOTROPHS - AN INVIVO AND INVITRO STUDY

The influence of gonadoliberin (GnRH) on the differentiation of rat gonadotrophs in early fetal life was studied both in vivo and in vitro by immunocytology with anti-porcine luteinizing hormone .beta. (pLH.beta.) serum. Adenohypophyseal primordia explanted from 11 to 13 days of gestation were maintained in organ culture in synthetic Parker''s 199 medium enriched with insulin (0.5 .mu.g/ml) and transferrin (5 .mu.g/ml). Cultures lasted to approximate the usual gestation period (21 days). Synthetic GnRH (10-9 or 10-12 M) was added to the culture medium during the 1st day of culture only. In contrast to a previous report, immunoreactive cells were detected in the primordia explanted either at 11 or 12 days of gestation only when cultured in the presence of GnRH. The appearance of positive localization was seen by 17 days. No differences due to GnRH dosage were observed in the mean cytoplasmic area of the cells in the different experimental groups as seen at the equivalent of 21 days. GnRH was not effective in a medium deprived of insulin. GnRH, added 6 h before the end of the culture, could also release the secretory product of gonadotrophs which recently developed the presence of immunoreactivity pLH.beta. material. In these conditions, GnRH was shown to enter the cells as observed by immunocytochemistry on sections obtained after cryoultramicrotomy. Endogenous GnRH was also detected by the same technique in fetal pituitary glands removed from 14 to 21 days of gestation. It was always localized in agranular cells and from 18 days in some granular cells considered as gonadotrophs. In the early fetal life transfer of GnRH from the maternal to the fetal side is very unlikely since very small amounts of radioactivity were detected in 11-day-old fetuses after injection of [125I]-GnRH into pregnant rats. Apparently GnRH can stimulate the differentiation of gonadotrophs in early fetal life in synergy with insulin. This is supported by the intracellular presence of GnRH which is most likely of fetal origin, the possibility of the existence of a placental GnRH-like substance being not completely excluded.