IN-VITRO MODULATION BY STEROIDS AND GROWTH-HORMONE OF THE SPECIFIC BINDING OF GONADOTROPIN-II IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) FOLLICULAR LAYERS

A procedure of incubation of thecal layers from rainbow trout (Oncorhy nchus mykiss) has been developed, in order to study the in vitro bindi ng of salmon gonadotropin II (sGtH II) during the periovulatory period . The effects of two steroids and growth hormone (GH) on SGtH II bindi ng on thecal layers were investigated in vitro to determine if these h ormones are involved in GtH II binding regulation, Steroids alone had no action on GtH II binding, Oestradiol-17 beta with sGtH II had littl e effect on GtH II binding on thecal layers at the end of vitellogenes is. In contrast, testosterone in combination with GtH II modulated GtH II binding on, thecal layers, being either inhibitory at the end of v itellogenesis, or stimulatory at the peripheral-GV stage, GH, without action alone, induced, in synergy with sGtH II, a significant decrease in GtH II binding on thecal layers at the end of vitellogenesis. Thus , GtH II binding on thecal tissues may be modulated in vitro by steroi ds, especially testosterone, and by GH, which act through synergism wi th GtH II.