A Sensitive Hydroosmotic Toad Bladder Assay A nity and intrinsic activity of neurohypophyseal peptides

I N T R O D U C T I O N T h e m a m m a l i a n ant id iure t ic ho rmone , vasopressin, modif ies the p e r m e a b i l i t y to wa t e r of the distal n e p h r o n and t he r eby accelera tes osmotic equ i l ib ra t ion of the fo rming ur ine wi th the renal interst i t ial fluid (4). Similar ly , neu ro hypophysea l pept ides increase the ra te of wa t e r m o v e m e n t a long an osmot ic g rad ien t across the skins and b ladders f rom frogs and toads. In these t a rge t tissues the h o r m o n e in teracts wi th a r ecep to r moie ty in the epi thel ial cell