Ultrafilterability of endogenous antidiuretic hormone from plasma of dogs

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Abstract
External jugular blood removed during the last half of a fatal hemorrhage in pentobarbital-anesthetized dogs given hypertonic saline into the ipsilateral carotid artery was rich in antidiuretic activity when assayed by intravenous injection in conscious, hydrated female dogs or ethanol-anesthetized rats. The antidiuretic activity in this plasma was in all probability due to neurohypophysial vasopressin: a) its renal effects were qualitatively the same as those of bovine Pitressin and purified arginine vasopressin; b) the antidiuresis resulting from injection of such plasma was not due to histamine or ferritin; c) the activity was destroyed by thioglycollate, trypsin and chymotrypsin but was resistant to pepsin and carboxypeptidase. Practically all of the antidiuretic activity in hemorrhaged dog blood was contained in the plasma; none was adsorbed by or permeated into erythrocytes. About three-fourths of the ADH in this plasma circulated in a form permitting it to be ultrafiltered through cellulose tubing at 4°C under pressure supplied by 5% carbon dioxide in oxygen. These data and those of others indicate that there is a marked species difference between the dog and rat with respect to the extent that endogenous vasopressin is bound to plasma proteins.