ISOLATION AND CULTURE OF SOMATOTROPHS FROM THE PITUITARY OF THE RAINBOW-TROUT - IMMUNOLOGICAL AND PHYSIOLOGICAL CHARACTERIZATION

The aim of the present paper was to obtain somatotroph- and gonadotrop h-enriched populations from collagenase dispersed pituitaries of male rainbow trout. Inasmuch as the percentage of immunoreactive gonadotrop hs and somatotrophs present in pituitaries was higher at spermiation t han at the beginning of spermatogenesis, we tried such a cell separati on with fish at this stage of spermatogenesis. Cells were fractionated using their differences in buoyant density with centrifugation in Per coll solutions. The use of Percoll linear gradients (1.110 to 1.027 g/ ml) showed that somatotroph cells have a density of between 1.102 and 1.064 g/ml whereas gonadotrophs are spread over the range of the gradi ent. It was thus possible, by using linear or discontinuous Percoll gr adients, to obtain 95 to 67% (mean 80%) enriched somatotropic cell fra ctions while no enriched gonadotropic cell fractions were collected. T he fractionated cells kept their ability to be cultured and to be resp onsive to specific secretagogues. Somatostatine induced a 80 to 85% de crease in growth hormone release per somatotroph in the initial cell s uspension as well as in the different cell fractions. On the other han d, the basal growth hormone release per cell was lower in the fraction s containing cells with a density lower than 1.062 g/ml. Inversely, th e gonadotrophs have a basal release per cell independent of their dens ity, and this is also available for their responsiveness to salmon gon adotropin-releasing hormone.