BOVINE PLACENTAL-LACTOGEN IS A POTENT STIMULATOR OF GROWTH AND DISPLAYS STRONG BINDING TO HEPATIC RECEPTOR-SITES OF COHO SALMON

Juvenile coho salmon were treated with bovine placental lactogen (bPL) and bovine growth hormone (bGH) to examine the growth promoting activ ities of these proteins in a lower vertebrate. Fish were intraperitone ally injected either with 0.5 or 5.0 mu g/g bPL or with 5.0 mu g/g bGH once a week for 5 weeks. After only a single injection and 1 week of growth, the high dose of bPL stimulated a significant increase in weig ht and length relative to untreated fish or fish treated with a contro l protein, bovine serum albumin. At the end of the experiment, all hor mone-treated groups were significantly larger than controls. Fish trea ted with 5 mu g/g bPL gained more than three times as much weight as c ontrols. The 5.0 mu g/g bGH group grew at the same rate as fish treate d with one-tenth this dose of bPL, indicating that bPL is a potent sti mulator of growth in this species. Radioreceptor assays performed on c oho salmon liver membrane preparations indicate that bPL binds with ap proximately 430-fold higher affinity than bGH, and some 8000-fold high er affinity than bovine prolactin. The action of bPL relative to the s tructure and function of salmonid pituitary hormones is discussed. (C) 1994 Academic Press, Inc.