Immunohistochemical study of the responsiveness of LH cells of fetal rats to synthetic LHRH in vitro.

Fetal rat pituitaries on days 17-19 of gestation were maintained in serum-free Medium 199 for 24 h in the presence of 1, 10 and 100 ng/ml of synthetic LHRH. Immunohistochemical examination of such stimulated tissue reveals a complete depletion of immunoreactive material in most of the LH cells, irrespective of the LHRH concentrations tested, though some cells remain weakly immunopositive in the pituitaries of later developmental stages. Once discharge has occurred, there is little reaccumulation of secretory material in LH cells during prolonged incubation for 48 h in LHRH-free medium containing 10% calf serum. The LHRH treatment causes no immunohistochemical change in TSH cells. It is concluded that in fetal rats recently differentiated LH cells can release the secretory product if they are stimulated by hypothalamic LHRH.