Growth hormone increases plasma levels of insulin-like growth factor (IGF-I) in a teleost, the gilthead seabream (sparus aurata).

A heterologous radioimmunoassay (RIA) was applied for the determination of immunoreactive (IR)--insulin-like growth factor (IGF-I) in a teleost, the gilthead seabream (Sparus aurata). Serial dilutions of the fish plasma gave a linear curve when added to constant amounts of 125I-labelled human IGF-I(53-70) and antiserum prepared against this fragment. The RIA was used to study the effect of GH on plasma levels of IR-IGF-I in S. aurata. A single injection of human recombinant GH (1 micrograms/g) resulted in a significant increase in IR-IGF-I at 29, 48 and 72 h, when compared with saline-injected fish. This novel observation suggests that in fish, as in mammals, circulating IGF-I levels are modulated by GH.