Immunochemical comparisons between a low molecular weight adenohypophyseal constituent and the gonadotrophins

A biologically active peptide (called sperm-releasing substance, abbreviated SRS) with a molecular weight of about 5000, prepared from bovine adenohypophyses, has been compared with the known adenohypophyseal glycoprotein hormones using immunological methods. By means of immunofluorescence it can be seen that antisera against SRS have an affinity for the gonadotrophic cells in the anterior pituitary. Using complement fixation assay and immunodiffusion, no similarity between SRS and FSH can be found, while there are great resemblances between the reactions of LH and those of SRS. From the radioimmunoassay studies, it can be seen that the alpha-subunit of LH reacts in the same way as SRS in the different systems. However, using immunofluorescence, the antiserum against SRS has an affinity for the gonadotrophic cells only, like anti-LHbeta, and not for the thyrotrophic cells, as has anti-LHalpha. The reasons for these different results are discussed.