Influence of environmental salinity on prolactin and corticotropic cells in the gilthead sea bream (Sparus aurata L.).

The influence of the environmental salinity on the prolactin (PRL) and corticotropic (ACTH) cells of the rostral pars distalis of the adenohypophysis of the gilthead sea bream (Sparus aurata) adapted to sea water (SW, 980 mOsm/kg) and brackish water (BW, 200 mOsm/kg) has been studied by immunocytochemical, morphometric, and electron-microscopic techniques. Prolactin (PRL) cells of fish adapted to BW occupied a greater hypophysial volume (about 24% of the total hypophysial volume in BW, 10% in SW) and had larger nuclear areas than those of SW-adapted fish (about 21 microns 2 in BW, 12 microns 2 in SW). Conversely, immunoreactivity against PRL antiserum was lower (mean optical density 117 in BW, 157 in SW). Characteristic ultrastructural features of PRL cells of BW-adapted fishes included a distended rough endoplasmic reticulum and large granules. Together the volumetric, densitometric, and ultrastructural evidences suggest an activation of synthesis and release of PRL in S. aurata adapted to hypoosmotic environments. ACTH cells occupied similar hypophysial volumes in both SW- and BW-adapted fishes (about 6.5%), but nuclear areas were higher (16 microns 2 in BW, 13 microns 2 in SW) and immunoreactivity against ACTH antiserum was lower in BW fishes (mean optical density 117 in BW, 139 in SW). Their ultrastructure suggested cell activation in BW-adapted fishes. Plasma levels of cortisol were eventually threefold greater in BW (about 142 ng/ml) than in SW fish (54 ng/ml). These data suggest activation of ACTH cells of S. aurata adapted to BW.