The isolation of a renally active substance from arterial blood.

1. A substance (Art. HS) which resembles the 18-monoacetate of D-aldosterone (18 MA) in its biological actions is found in arterial blood of cats and sheep: Art. HS is assayed in terms of antidiuretic activity equivalent to synthetic 18 MA.2. In cats under chloralose anaesthesia, dialysis of arterial blood (2-3 ml./min) in a small external circuit (8-15 ml.) without disturbance of heart rate, blood pressure or respiration, predicts a physiological concentration of Art. HS equivalent to 31.5-51.9 ng 18 MA/100 ml. Efficiency of dialysis assumed in this calculation is 100%.3. Art. HS is almost evenly distributed throughout the plasma and formed elements of blood.4. Concentrations of Art. HS found during severe arterial haemorrhage are equivalent to 188 +/- 6.7 and 151 +/- 9.2 ng 18 MA/100 ml. in cats and sheep respectively.5. Art. HS has been isolated from 27.6 l. sheep arterial blood by ethyl acetate: chloroform 1:1 extraction, defatting by partitioning between methanol and petroleum ether and purifying by seven-stage thin layer chromatography on MN Kieselgel UV(254). Final yield was equivalent in activity to 21.6 mug 18 MA. Synthetic 18 MA was used as R(F) marker. Spots of 2 mug 18 MA are visible on MN Kieselgel UV under U.V. Art. HS activity equivalent to 21.6 mug 18 MA cannot be seen.6. Art. HS was not detectable in IVC blood of cats under chloralose anaesthesia during haemorrhage. The threshold for detection was the equivalent of 15-20 ng 18 MA/100 ml.7. Art. HS resembles a substance liberated by the heart (Lockett & Retallack, 1970a, b, 1971) in chromatographic properties, biological properties and stability in aqueous solution. Art. HS is very much more stable in aqueous solution than 18 MA.