ORAL-ADMINISTRATION OF RECOMBINANT SALMON GROWTH-HORMONE TO RAINBOW-TROUT, ONCORHYNCHUS-MYKISS

Recombinant chum salmon growth hormone (rsGH) was incorporated into a polymer matrix that remains intact in acidic conditions of the stomach, but decays at higher pHs in the intestine, in an attempt to protect the hormone from proteolytic cleavage in the stomach. The GH enteric polymer matrix (GH-EPM) and free rsGH were administered to rainbow trout by admixing in food. Changes in plasma GH levels were subsequently measured by a radioimmunoassay specific for chum salmon GH. Feeding of GH-EPM in a wet food pellet resulted in significantly higher and longer elevations in plasma GH levels than that of free GH. Moreover, the GH-EPM group exhibited greater increases in length and body weight than controls. These results strongly suggest that the enteric polymer matrix protected the hormone from proteolytic enzymes in the gastrointestinal tract, allowing immunoreactive and bioactive hormone to enter the circulation and subsequently stimulate growth.