EVIDENCE FOR GROWTH-HORMONE INSULIN-LIKE-GROWTH-FACTOR-I AXIS REGULATION OF SEAWATER ACCLIMATION IN THE EURYHALINE TELEOST FUNDULUS-HETEROCLITUS

The ability of ovine growth hormone (oGH), recombinant bovine insulin- like growth factor I (rbIGF-I), recombinant human insulin-like growth factor II (rhIGF-II), and bovine insulin to increase hypoosmoregulator y capacity in the euryhaline teleost Fundulus heteroclitus was examine d. Fish acclimated to brackish water (BW, 10 ppt salinity, 320 mOsm/kg H2O) were injected with a single dose of hormone and transferred to s eawater (SW, 35 ppt salinity, 1120 mOsm/kg H2O) 2 days later. Fish wer e sampled 24 h after transfer and plasma osmolality, plasma glucose, a nd gill Na+,K+-ATPase activity were examined. Transfer from BW to SW i ncreased plasma osmolality and gill Na+,K+-ATPase activity. Transfer f rom BW to BW had no effect on these parameters. rbIGF-I (0.05, 0.1, an d 0.2 mu g/g) improved the ability to maintain plasma osmolality and t o increase gill Na+, K+-ATPase activity in a dose-dependent manner, oG H (0.5, 1, and 2 mu g/g) also increased hypoosmoregulatory ability but only the higher doses (2 mu g/g) significantly increased gill Na+,K+- ATPase activity. oGH (1 mu g/g) and rbIGF-I (0.1 mu g/g) had a signifi cantly greater effect on plasma osmolality and gill Na+,K+-ATPase acti vity than either hormone alone, rhIGF-II (0.05, 0.1, and 0.2 mu g/g) a nd bovine insulin (0.01 and 0.05 mu g/g) were without effect. The resu lts suggest a role of GH and insulin-like growth factor I (IGF-I) in s eawater acclimation of F. heteroclitus. Based on these findings and pr evious studies, it is concluded that the capacity of the GH/GF-I axis to increase hypoosmoregulatory ability may be a common feature of eury halinity in teleosts. (C) 1998 Academic Press.