“…Intact GH3 cells have been shown to posses specific binding sites for [3H]-TRH [Gourdji et al, 1973; Hinkle and Tashjian, 1973], The binding is time dependent, reaching a plateau after the first [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] min, at the same lime as the TRH-induced stimulation of Prl release. Two classes of TRH binding sites have been detected on intact G H 3 cells in suspension, one of high affinity (Kr>: 4 x I0~sm) for physiological doses and the other of low affinity (3 x 10~7m for high doses (front 150 up to 1080 nM) [Tixier-Vidal et at., 1975], Two binding constants of similar values were observed in cultured mouse TSH-secreting tumor cells [Grant et at., 1973], A previous autoradiographic study together with a chemical analysis of intact GH3 cells previously incubated for 30 min at 37 C with ['H]-TRH and then thoroughly washed at 4 C. have demonstrated the presence of chemically unmodified TRH associated to subcellular fractions: nucleus (17%), cytoplasmic organelles (26%) and cytosol (57%) [Gourdji et ah, 1973: Brunet et a/., 1974. It was.…”