GROWTH-HORMONE AS AN IN-VITRO PHAGOCYTE-ACTIVATING FACTOR IN THE GILTHEAD SEA BREAM (SPARUS-AURATA)

The stimulatory action of growth hormone on gilthead sea bream phagocy te-enriched cultures was demonstrated in vitro for the first time in a fish species. Phagocytes consisted mainly of macrophages, with a smal l number of neutrophils and eosinophils. Macrophages were unequivocall y identified by their esterase staining and the lack of myeloperoxidas e staining. Cells primed with recombinant rainbow trout GH showed clea r morphological (light- and scanning electron-microscopic) and functio nal differences from non-primed cells. Stimulated phagocytes exhibited numerous branched lamellipodia, abundant membrane ruffles, increased spreading, and cell size. When incubated with sheep red blood cells, t he phagocytic index and phagocytic capacity was also enhanced in prime d cells. A bell-shaped dose-response curve (1.5-500 nM) was obtained w hen the metabolic activity of growth-hormone-activated cells was measu red. This finding suggests that the homodimerization of the growth hor mone receptor is a characteristic feature both in mammals and fish.