IMMUNOCYTOCHEMICAL LOCALIZATION OF GONADOTROPIN, ITS SUBUNITS, AND THYROTROPIN IN THE TELEOST, XIPHOPHORUS-MACULATUS

An immunoperoxidase method has permitted the identification of gonadotropin (GtH)- and thyrotropin (TSH)-producing (containing) cells in the caudal pars distalis of the pituitary gland of mature platyfish (Xiphophorus maculatus). The results corroborate earlier reports where the locations of these cells were determined by the use of basic staining methods. The immunoreactivity of antisera generated against a number of teleostean gonadotropins and their subunits and against human TSH was examined. To verify the specificity of the response, controls were employed which included the substitution of normal rabbit serum for the specific antiserum and/or the absorption of the final dilution of antiserum with corresponding homologous or heterologous antigens. Antiserum to carp GtH (anti-cGtH) displayed the highest degree of specificity when compared to other preparations (trout and salmon) produced against the intact GtH molecule. Antiserum against the α subunit of carp GtH (anti-cGtH-α) cross-reacted with both thyrotrops and gonadotrops whereas the β subunit antiserum (anti-cGtH-β) displayed immunoreactivity with gonadotrops but not with thyrotrops. Antiserum against human TSH (anti-hTSH) cross-reacted only with thyrotrops. Our results indicate that the use of suitable antisera permits the localization of thyrotrops and gonadotrops. This report is presumably the first to show that the α subunit of carp GtH is a chain common to both TSH and GtH in fish. It is also the first demonstration of antigenic similarity between human and fish TSH. © 1979.