Bradykinin, digital blood flow, and the arteriovenous anastomoses.

• During studies on the anticoagulating properties of snake venom, Rocha e Silva and associates discovered the vasoactive polypeptide, bradykinin. The substance was called bradykinin because, in contrast to histamine and acetylcholine, it stimulated smooth muscle to contract after a latent period and because the contraction was gradual. The substance received little attention until recently when it was isolated in the pure state, synthesized, and its chemical structure confirmed." Animal experimentation subsequently showed that bradykinin had five important pharmacological properties, namely, smooth muscle stimulation, vasodilatation, increase in capillary permeability, migration of leukocytes, and stimulation of pain fibers. Only a few studies of this interesting substance have been carried out in man. Fox and Hilton" showed that the perfusate from the subcutaneous space of the forearm of human subjects contained much larger amounts of bradykinin after reflex induction of sweating than prior to the onset of sweating. They concluded that the sweat glands contain a bradykiniu-releasing enzyme and that the vasodilatation associated with sweating may be due to bradykinin. Herxheimer and Schachter have shown that the intracutaneous injection of bradykinin in man increases capillary permeability to dyes of high molecular weight. Studies in this laboratory (G. E. Bureh and N. P. DePasquale, unpublished observations) have indicated that bradykinin results in an increase in the volume of an intracutaneous bleb, but not in erythema. Recently, Fox et al. published an abstract in which they reported that bradykinin in-