MULTIFACTORIAL CONTROL OF LH AND TSH PHENOTYPE EXPRESSION IN FETAL-RAT ADENOHYPOPHYSIS

Previous studies have demonstrated that the neuropeptides GnRH, DSIP a nd TRH induce LH and TSH differentiation in a dose-dependent manner. T hese studies have shown that a single hypothalamic hormone can induce the differentiation of more than one cell type, and conversely that on e pituitary cell can differentiate under the influence of more than on e hypothalamic factor. In the present study, our experimental in vitro model was used to demonstrate that these hypothalamic factors are abl e to influence LH and TSH cell appearance by a synergistic action. Pit uitary primordia of 11 day-old rat embryo were cultured in a synthetic medium. Four different combinations were tested by adding either DSIP , GnRH and TRH together, or any combination of two of them in the cult ure medium, each at a concentration of 10(-15) M. The expression of di fferent pituitary phenotypes was estimated as the percentage of immuno reactive area per section of cultured pituitary. The medium supplement ed with the three peptides at 10(-15) M was more efficient for the dif ferentiation of LH and TSH than the other media combinations including only two peptides. These results confirm that the LH and TSH cell dif ferentiation can be induced by a synergistic mechanism involving sever al neuropeptides. Such a mechanism, already demonstrated for somatotro pes, could prevail in in vivo pituitary cell differentiation.