A RADIOIMMUNOASSAY FOR THE DETERMINATION OF ARGININE VASOTOCIN (AVT) - PLASMA AND PITUITARY CONCENTRATIONS IN FRESH-WATER AND SEAWATER FISH

A specific radioimmunoassay was developed and characterized for the me asurement of arginine vasotocin (AVT) in teleost fish. Specificity of the antibody for AVT was demonstrated by parallelism of a series of AV T standards with serially diluted pituitary and plasma extracts. Cross reactivity of the antibody with the other teleost neurohypophysial pep tide, isotocin, was less than 1% and the sensitivity of the assay was 0.24 fmol/assay tube. AVT was extracted from plasma by reverse-phase l iquid chromatography [efficiency of 87.6 +/- 9.3% (n = 5)] and demonst rated as an effective procedure for plasma volumes ranging from 0.4 to 1.2 mi. Plasma AVT concentrations measured in a range of euryhaline a nd stenohaline teleost fish were between 10(-12) and 2 x 10(-11) M (1- 20 pg/ml). There were no consistent differences between plasma AVT lev els in euryhaline fish (flounder, trout, and eel) adapted to fresh wat er (FW) and sea water (SW). In flounder, pituitary AVT levels in FW- a nd SW-adapted fish were also similar. (C) 1994 Academic Press, Inc.