A histochemical approach to the study of human chorionic gonadotrophin receptors in the rat testis.

Standard suspensions of interstitial cells in PBS were exposed to the action of various fixatives, solvents (clearing agents), temperatures and U. V. light, in order to establish the effects of such chemical and physical agents on the HCG receptors. After exposure to the various agents, the interstitial cells were incubated with [125I]HCG for 2 h at 37 degrees C. To check the specificity of the reaction, competitive tests were performed with added excess non-iodinated HCG. Only formaldehyde fixation for short periods of time, preserved satisfactorily the specific binding activity of the receptors. A different degree of thermolability of the receptors was demonstrated, in relation to 37, 45, 54 and 60 degrees C, while freezing in liquid nitrogen had no effect on the receptors binding activity. After the binding reaction, solvents had a significant solubilizing effect on the HCG-receptor complexes. U. V. light had no significant damaging effect on the receptors. The application of the results for a histochemical approach to the study of the HCG receptors is discussed.