In vitro incorporation of [14C]glycine into muscle protein of gulf killifish (Fundulus grandis) in response to insulin-like growth factor-I.

The effect of recombinant human insulin-like growth factor I (rhIGF-I) on protein synthesis was studied in vitro in the muscle of a teleost fish. Protein synthesis was assessed by the incorporation of [14C]glycine into protein. rhIGF-I stimulated [14C]glycine incorporation in a dose-dependent manner. The minimal effective dose was 0.1 ng/ml and maximal stimulation was obtained with 1 ng/ml. A high concentration (100 ng/ml) was ineffective. Treatment with 1 ng/ml rhIGF-I produced a significant response after 3 hr of incubation and the greatest stimulation was observed after 6 hr. Responsiveness of muscle tissue to IGF-I examined at three different times (0, 6, and 12 hr after light onset, LD 12:12) was greatest at light onset. These results provide evidence that IGF-I may have a role in the regulation of growth in fish and that its activities are dose and time-of-day dependent.