DISSIMILARITY BETWEEN ARGININE- AND LYSINE VASOPRESSIN IN RAT PRESSOR ASSAYS

Abstract

Two preparations of hog posterior pituitary: (1) acetone dried hog posterior pituitary and (2) purified lysine vasopressin were assayed for pressor activity against two different preparations of beef posterior pituitary: (1) the International Posterior Pituitary Standard and (2) the USP Posterior Pituitary Reference Standard, batch G. Three slightly different rat pressor methods were used: I: pithed rat under pentobarbitone + urethane, II: rat under chlorbutol + phenoxybenzamine, III: rat under urethane + phenoxybenzamine. In male rats the index of discrimination: arginine- against lysine vasopressin on method II over method I ranged from 1.15-1.19. Within the particular methods a significant heterogeneity among replicates was demonstrated. It was concluded, that neither the antidiuretic nor the pressor activity of lysine vasopressin could be definitely expressed in international (beef posterior pituitary-) units. An international standard for lysine vasopressin (hog posterior) seems essential.