Abstract
The purpose of these experiments was to learn something of the nature of the pressor action of renin. Renin was prepared from pig's kidneys in such concentration that an amount containing less than 2 mg of nitrogen produced a sharp, sustained rise (30 mm Hg. or more) of blood pressure in an unanesthetized dog. Its vasoconstrictor action was studied on perfused dogs′ tails (40 experiments), so eliminating all factors causing vasoconstriction other than peripheral ones.
It was found that undialyzed renin (0.2 cc) caused moderate vasoconstriction, contrariwise dialyzed renin (1 cc) was inactive. Normal heparinized dog's whole blood (dilution of 1 to 3 parts Ringer's solution) was inactive but if dialyzed renin (1 cc) were mixed with dog's blood (1 cc 1:3 dilution) marked vasoconstriction occurred. The undialyzed renin could be potentiated by addition of dog's blood.
Heparinized plasma in doses of 0.5 cc was vaso-inactive but strongly activated dialyzed renin just as whole blood had done. But protein-free ultrafiltrate of plasma no longer exhibited activating capacity while the colloid residue on resuspension was active.
The vasoconstrictor action of undialyzed renin appears to be due in part to non-protein materials contained in it, for the protein-free fluid obtained by boiling the renin produced vasoconstriction, but it was not potentiated by blood as was renin. Dialysis removes these substances. Boiled dialyzed renin with added plasma or protein-free nitrate of boiled plasma was vaso-inactive.
These results suggest that renin is an enzyme-like substance which is activated by a kinase-like material contained in the protein fraction of plasma and whole blood.
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