A Spectrum of Pharmacological Activity in Some Biologically Active Peptides

The actions of bradykinin, angiotensin, oxytocin, vasopressin and substance P have been examined both on isolated smooth muscle preparations and in vivo. It was found that the isolated rat uterus and guinea-pig ileum can be used to distinguish between oxytocin and bradykinin and that the isolated rat colon and hen rectal caecum are almost specific test preparations for substance P. All the peptides were active on peripheral blood vessels, bradykinin, substance P and oxytocin causing vasodilatation and vasopressin and angiotensin vasoconstriction; bradykinin, substance P and angiotensin also caused an increase in capillary permeability in guinea-pigs. Only bradykinin and substance P were active in low concentrations in producing pain when applied to an exposed blister base. These two peptides were also active in causing bronchoconstriction. Oxytocin and vasopressin were the only peptides having milk-ejecting or antidiuretic activity which could be dissociated from cardiovascular effects. The spectrum of activity displayed by these peptides is in agreement with those functions which have been established for vasopressin and oxytocin and with those suggested, but not yet fully accepted, for bradykinin and angiotensin. It also indicates a possible function for substance P based on its vascular and permeability effects.