Effects of picric acid-formaldehyde fixation on the LH(HCG) receptors' binding activity in the rat testis. A histochemichal model for qualitative and quantitative studies.

PAF (picric acid-formaldehyde) fixation of rat testis for a short time at 0-4 degrees C was found to give satisfactory histological results and to preserve most of the specific binding activity of LH(HCG) receptors. Investigations of the characteristics of the hormone-receptor reaction after mild PAF fixation indicated that this reaction was not substantially affected in hormne receptor affinity and its own specificity; only the capacity of the receptors was lowered by about 20%. A histochemical model is presented whose main features are: fixation of testis tissue in PAF; freezing in liquid nitrogen and cutting in the cryostat; radiolabelled hormone-receptor binding reaction performed on the sections; autoradiography to reveal the binding reaction. The utility of the method for qualitative and quantitative receptor studies and its possible application to biopsy and surgical specimens, are discussed.