INCREASES IN GILL CYTOSOLIC CORTICOSTEROID RECEPTOR ABUNDANCE AND SALTWATER TOLERANCE IN JUVENILE COHO SALMON (ONCORHYNCHUS-KISUTCH) TREATED WITH GROWTH-HORMONE AND PLACENTAL-LACTOGEN

Juvenile coho salmon (Oncorhynchus kisutch) were injected with one of two recombinant bovine hormones, growth hormone (bGH; 5.0 and 0.5 mu g . g(-1) body wt) or placental lactogen (bPL; 5.0, 0.5, and 0.05 mu g . g(-1) body wt) to determine the effect on growth, plasma cortisol co ncentration, cytosolic corticosteroid receptors (CR) in the gills, and the development of hypoosmoregulatory ability. One week following a s ingle injection or six weekly injections of bGH or bPL, the fish were measured and sampled for CR concentration and Na+,K+-ATPase activity i n the gills. Fish were also challenged with salt water (salinity 25%) for 24 hr to determine saltwater tolerance at the end of the 6-week tr eatment. Treatment with bPL and bGH significantly increased weight and length of the fish. The 0.05-mu g bPL dose significantly elevated pla sma cortisol concentration, whereas all other hormone treatments did n ot affect cortisol levels. bPL and bGH also significantly increased CR concentration and Na+,K+-ATPase activity in the gills. The perturbati on in plasma sodium concentration was least in animals receiving the h ighest dose of bPL and the bGH-treated animals following transfer to s eawater. An increase in cytosolic CR by bGH and bPL may increase respo nsiveness of the gills to cortisol and partially account for the incre ase in Na+,K+-ATPase activity and greater ability to regulate plasma s odium in seawater as exhibited by the experimental groups. (c) 1995 Ac ademic Press, Inc.