Development of radioimmunoassay for eel growth hormone.

Abstract

A highly specific and homologous radioimmunoassay (RIA) for the measurement of growth hormone (GH) in the plasma and the pituitary of the eel was developed using a rabbit antiserum to eel GH. Two forms of eel GH: eGHI and II, were purified from the media from organ-cultures of pituitaries of the Japanese eel Anguilla japonica. An antiserum against eGH I, which does not distinguish between the two forms, was used to measure total GH levels. Pituitary extracts from the Japanese eel and the European eel A. anguilla exhibited displacement curves parallel to the eGHI standard, whereas extracts from chum salmon, rainbow trout, Japanese charr, carp, goldfish and tilapia pituitaries showed no cross-reactivity. GH or prolactin preparations from sheep, whale, chum salmon and tilapia also did not cross-react with the antibody. RIA sensitivity was 0.2ng/ml of plasma when 50μl of plasma were employed. Most of the plasma GH levels were low or undetectable in starved eels either in fresh water or in seawater, or in fed eels in fresh water. On the other hand, plasma samples from seawater-adapted male eels receiving injections of human chorionic gonadotropin showed high GH levels. Apparent plasma half-life of eGH I injected intravascularly through a cannula into the pneumogastric artery was about 15 min.