Plasma ADH in normal Long-Evans rats and in Long-Evans rats heterozygous and homozygous for hypothalamic diabetes insipidus.

A radioimmunoassay for the measurement of arginine-vasopressin (AVP) in rat plasma is described. By precipitating plasma proteins with acetone prior to the assay, a blanc value of zero was obtained for plasma of rats with hypothalamic diabetes insipidus (DI). Under $\text{ad lib}$. water intake as well as after 48 hrs of dehydration, AVP concentrations in plasma of rats heterozygous for DI were by roughly 50 % lower than in plasma of normal control rats. In plasma of DI rats no AVP was measurable 24 hrs after withdrawal of water. These data support the notion that DI rats do not produce any AVP and that the heterozygous animals have partial ADH deficiency. - In normal and heterozygous rats, AVP concentrations in plasma obtained at 5 p.m. were lower than in plasma collected at 10 a.m. This might indicate a diurnal fluctuation of plasma AVP concentrations in the rat.