Pituitary steroids in two teleost species: immunohistological and biochemical studies

Antisera raised against steroid hormones [estradiol-17 beta (E2), testosterone (T), 11 beta-hydroxyandrostenedione (OHA)] were used to localize immunoreactive material in fixed and paraffin-embedded pituitaries of the African catfish and the rainbow trout. Organic extracts of pituitary homogenates were analyzed for steroid hormones by radioimmunoassay and gas chromatography-mass spectrometry (E2 in female catfish only). With the exception of an E2-positive cell type in the catfish neurointermediate lobe, steroid immunoreactivity was found to be restricted to the cytoplasm of adenohypophyseal cells, which were also labeled after incubation with catfish alpha,beta-gonadotropin and salmon gonadotropin antisera, respectively. Steroid levels determined by radioimmunoassay in the catfish ranged between 85 and 628 pg/pituitary, while lower levels (2-8 pg/pituitary) were found in the rainbow trout. E2 was identified by gas chromatography-mass spectrometry at a level of 84 pg/pituitary. The observation that immunolabeling after steroid antiserum incubation is confined mainly to gonadotrops provides morphological evidence for direct steroid effects on this particular cell type.