Effects of recombinant human growth hormone and insulin-like growth factor 1 on body growth and blood metabolites in brook trout (Salvelinus fontinalis).

Groups of juvenile brook trout (Salvelinus fontinalis) were acclimated to 12.0-13.0 degrees dechlorified water and a photoperiod of 12 hr light: 12 hr dark. Recombinant human growth hormone (hGH) (10.0 micrograms/g body wt) or insulin-like growth factor 1 (hIGF-1), used in a wide range of dosages (0.001-10.0 micrograms/g body wt), were given weekly as intramuscular injections. The fish receiving hGH were already significantly heavier and longer than the saline-injected control fish after 3 weeks of treatment. In addition, a liver specific growth promoting effect of hGH was found. In contrast, hIGF-1 did not stimulate body growth in any dosage tested. The fish receiving the highest dosages of hIGF-1 were all seriously affected with retarded body growth and high mortality. A possible insulin-like activity of hIGF-1 was verified by measuring the plasma glucose and amino acid levels in brook trout after a single injection of hIGF-1 (2.0 micrograms/g body wt) or bovine insulin (0.01 IU/g body wt). Both hormones caused a reduction in both glucose and amino acid levels to 35% of the control levels 24-72 hr after injection. The results strongly suggest that hIGF-1 does not stimulate growth, but that in high dosages causes profound insulin-like effects in brook trout resulting in hypoglycemia and hypoaminoacidemia.