Immunocytochemical identification of two distinct gonadotropic cells (GTH I and GTH II) in the pituitary of bluefin tuna, Thunnus thynnus

Immunocytochemical identification of GTH I and GTH II cells in the pituitary of the bluefin tuna (Thunnus thynnus) was performed using antisera specific for the common alpha-subunit and the two distinct beta-subunits of tuna (Thunnus obesus) GTH I and GTH II. Cells of the dorsal part of the proximal pars distalis (PPD), in close association with somatotrophs, displayed immunoreactivity of GTHI beta. GTH II beta immunoreactivity was present in cells of the central part of the PPD and the external border of the pars intermedia. Anti-GTH alpha immunostained both GTH I beta- and GTH II beta-immunoreactive cells and also thyrotrophs. Both GTH I beta- and GTH II beta-immunoreactive cells were observed in immature bluefin tuna, although there were greater numbers of GTH II beta immunoreactive cells. These results suggest that GTH I and GTH II are synthesized in separate cells in the pituitary of the bluefin tuna. The localization and appearance of the two distinct gonadotropic cells of the tuna are compared with the salmonid arrangement. (C) 1998 Academic Press.