Radioimmunoassay for arginine-vasotocin (AVT) in serum of Pekin ducks: AVT concentrations after adaptation to fresh water and salt water.

A radioimmunoassay for arginine-vasotocin (AVT), the antidiuretic principle in birds, was developed using the high cross-reactivity of AVT with an AVP antiserum raised in rabbits. This assay is specific for the measurement of AVT in serum of birds. The sensitivity and precision is such that serum AVT concentrations above 0.5 fmol/ml can be measured quantitatively. A serum AVT concentration of 5.1 +/- 1.4 fmol/ml was found in normally hydrated, fresh water adapted ducks with a serum osmolality of 293.7 +/- 2.2 mosmol/kg. When the same animals were acutely hydrated, no or < 0.5 fmol/ml AVT was present at an osmolality of 289.8 +/- 2.4 mosmol/kg. In salt water adapted ducks with a serum osmolality of 333.0 +/- 7.6 mosmol/kg, a serum AVT of 22.7 +/- 3.0 fmol/ml was found. When fresh water adapted ducks were hydrated and infused with different doses of AVT, a linear relationship between serum AVT and the amount infused was obtained. During AVT infusions, serum osmolality and urine flow rate were negatively correlated and urine osmolality was positively correlated with serum AVT.