Comparative histochemistry of the mucoproteic cells of the hypophysis from Rhamdia hilarii, Hypostomus punctatus, Prochilodus scrofa and Cyprinus carpio (Teleostei). Immunohistochemical identification of the gonadotropic cells.

Adenohypophyseal cells showing positive histochemical reactions for mucosubstances were classified as type I-IV in Hypostomus (Plecostomus) punctatus (Loricariidae), Rhamdia hilarii (Pimelolidae), Prochilodus scrofa (Prochilodontidae) and Cyprinus carpio (Cyprinidae) according to cell shape, size, cytological characteristics and adenohypophyseal distribution. Cell types I and II are common to the four species, with each cell type showing very similar cytological and histochemical characteristics, in spite of different adenohypophyseal distribution of cell type II, according to the teleost species. Type I cells are globular basophils located in the proximal pars ditalis and are positive to PAS and Alcian blue pH 2.5 (AB) reactions, showing cytoplasmic vacuoles and changes in granule concentration in the mature phase of the gonadal cycle. The smaller type II cells are fusiform or oval basophils exhibiting a strong AB reaction but also reacting to PAS. Type III cells are located in the pars intermedia showing PAS-positive reaction. Considering different teleost species, these cells exhibit some variations specially in relation to cell size and shape which are not detected in mature male C. carpio. Otherwise cell type IV is only present in the rostral pars distalis of P. scrofa. They are weakly basophilic and negative to PAS, reacting strongly to AB. Only cell type I showed unequivocally positive immunohistochemical results with anti-salmon gonadotropin.