Vasopressin contamination as a cause of some apparent renal actions of prolactin.

The injection or infusion of NIAMDD prolactin (NIH P-S-10) into unanesthetized rats resulted in water and electrolyte retention with a large increase in urine osmolality but no effect on glomerular filtration rate. Since these effects on urine output were also observed in homozygous Brattleboro rats, the antidiuretic activity could not have caused by the release of endogenous antidiuretic hormone. Radioimmunoassay of NIH prolactin showed that it was contaminated with vasopressin (20 ng/mg of prolactin). By comparison, Sigma prolactin had no observed effect on urine excretion and contained very little vasopressin (2.5 ng/mg). It is concluded that some of the renal effects of prolactin have been reported in the literature may have been caused by the contaminating vasopressin.