A RADIOIMMUNOASSAY FOR ONCORHYNCHID GROWTH-HORMONE TARGETED TO THE PHYSIOLOGICAL RANGE

This study describes the development of an oncorhynchid growth hormone (GH) radioimmunoassay using recombinant chum salmon GH (rsGH) and a r abbit antiserum (TJK-1) raised against this recombinant material. The assay was designed to measure the wide range of circulating immunoreac tive GH (IRGH) levels in Pacific salmonids, resulting in a standard cu rve capable of accurately determining plasma levels of IRGH from 0.5 t o 250 ng/mL without dilution. The assay ED(50) and ED(90) values avera ged 13.1 and 0.5 ng/mL, respectively. This radioimmunoassay specifical ly recognizes oncorhynchid IRGH, showing no cross-reactivity with reco mbinant porcine and bovine GH, or natural chum salmon prolactin at con centrations up to 10 mu g/mL. Curves approximately parallel to the sta ndard curve were obtained with purified natural coho salmon GH and pla sma from chinook salmon. Recovery of rsGH from plasma was complete ove r the full range of the standard curve. Intra- and inter-assay coeffic ients of variation were 6.0 and 12.9%, respectively. Plasma IRGH level s in fed coho salmon were 30.6 +/- 5.3 ng/mL, while those in fish star ved for 2 weeks were 132.9 +/- 53.9 ng/mL. Starvation for an additiona l 4 weeks had no significant effect. Plasma IRGH levels in control rai nbow trout injected with saline were significantly higher 45 min post- injection. In contrast, fish injected with recombinant porcine GH exhi bited no elevation in IRGH. It is speculated that exogenous GH inhibit s the production of endogenous GH.