Lyophilized bovine, porcine, and human choroid plexuses contain .02-.09 U of antidiuretic activity per milligram. The antidiuretic factor in bovine choroid plexus was concentrated 100 times by extraction with acetic acid, fractional precipitation with acetone and ethyl ether, gel filtration, and paper chromatography. Resulting choroid plexus fraction IIgammaB2 was eluted from Sephadex G-25 in position corresponding to molecular weight between 750 and 3,500; its antidiuretic activity was destroyed by trypsin, performic acid, and thioglycollic acid, but was not affected by leucine aminopeptidase, carboxypeptidase A or B, or cyanogen bromide. HgammaB2 possesses antidiuretic, pressor, and oxytocic potencies (measured in anesthetized-hydrated rat, anesthetized rat, and isolated rat uterus, respectively) of 1.9, 0.5, and 0.1 U/mg, respectively.
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