THE USE OF RECOMBINANT GILTHEAD SEA BREAM (SPARUS-AURATA) GROWTH-HORMONE FOR RADIOIODINATION AND STANDARD PREPARATION IN RADIOIMMUNOASSAY

A gilthead sea bream growth hormone (sbGH) obtained by cloning and exp ression of sbGH cDNA was used to develop a sensitive and specific radi oimmunoassay (RIA). Iodination of recombinant sbGH (rsbGH) was perform ed by the classical Chloramine-T method. Specific antiserum, raised in rabbits, was added in a final dilution of 1/36,000. The minimum detec table dose was 30 pg, and the midrange of the assay (ED(50)) was 275 p g. Intra- and inter-assay coefficients of variation (CV) were 3.3 and 5.8% at ED(50) levels. Human GH (hGH), ovine GH (oGH), carp gonadotrop in (cGtH), chinook salmon gonadotropin (sGtH), ovine prolactin (oPRL) and recombinant tilapia prolactin (rtiPRL) did not show cross-reactivi ty. Serial dilutions of chinook salmon GH (sGH) and recombinant rainbo w trout GH (rtGH) showed a low but significant cross-reactivity. A goo d parallelism between rsbGH standard and serial dilutions of native sb GH, plasma and pituitary extracts was observed. In addition, when plas ma and pituitary samples were analyzed for GH quantification, non-sign ificant differences were observed within this and previous RIA for nat ive sbGH. Therefore, it appears conclusive that our rsbGH dan be used successfully as a standard and radioiodinated hormone in GH assays for gilthead sea bream, which is extensively cultured in the Mediterranea n area.