The Dialyzability of the Pressor and Antidiuretic Activities of Pitressin.

According to the present extent of our knowledge it appears that the pressor and the antidiuretic activities of Pitressin 1 both reside in the same substance. Since Kamm (1) showed that the pressor activity dialyzes from aqueous solution, the antidiuretic activity should dialyze also. But Ralli (2) found that when Pitressin mixed with normal urine was dialyzed against water the full antidiuretic activity for rats remained in 'the non-dialyzable fraction. This suggested that urine might in some way inhibit the dialysis of Pitressin. On the other hand, if pressor activity dialyzes and antidiuretic does not, dialysis would provide a means of separating the 2 activities. Others (3) have reported that antidiuretic activity does not dialyze. However, Smith (4) early showed that all 3 posterior pituitary activities dialyzed, and Walker (5) demonstrated the presence of antidiuretic activity in the dialysate. The purpose of the present experiment is to report the pressor activity for dogs and the antidiuretic activity for humans of the non-dialyzable residue following dialysis of Pitressin mixed with water and mixed with normal urine. The results suggest that both the pressor and the antidiuretic activities do dialyze, whether mixed with water or with urine.