EFFECTS OF GONADOTROPIN-RELEASING-HORMONE (GNRH) ON THE CYTODIFFERENTIATION OF GONADOTROPES IN RAT ADENOHYPOPHYSEAL PRIMORDIA IN ORGAN-CULTURE

The effects of gonadotropin-releasing hormone (GnRH) on the developmen t of gonadotropes were investigated by the use of organ culture and by means of immunocytochemistry and radioimmunoassay. Pituitary primordi a from rat fetuses were cultured in a medium with or without 10(-9) M GnRH during the first 24 h of culture. The ratio of the number of immu noreactive LH cells to the total number of cells in the explants deriv ed from 13.5-day fetuses was increased by the GnRH treatment after 6 o r 8 days of culture, while the total number of cells was not altered. LH released into the medium and LH content of explants were not affect ed by the GnRH treatment. Subsequent treatment with 10(-9) M GnRH for 4 h after 7 days of culture resulted in a marked release of LH, accomp anying a significant decline in LH content, in both explants exposed o r unexposed to the first GnRH treatment. However, the former explants contained a lower amount of LH than the latter explants. The present r esults indicate that pituitary primordia at 13.5 days of gestation are capable to respond to GnRH, and that GnRH is effective in stimulating the responsiveness of gonadotropes to GnRH during early pituitary cyt odifferentiation.