Pain, wheal and flare in human forearm skin induced by bradykinin and 5-hydroxytryptamine

Pain was induced in 19 healthy individuals by double-blind injections into the forearm skin of 0.05 ml of physiological saline with or without active substances added. Bradykinin (0.5 nmol), 5-hydroxytryptamine (0.5 nmol) and a mixture of the two substances in half dosage (0.25 nmol + 0.25 nmol) caused significantly more pain than saline (p less than 0.05). The three test solutions also induced wheal and flare responses significantly more pronounced than saline. Bradykinin induced significantly more pain and more wheal than 5-hydroxytryptamine (p less than 0.05) but a significantly smaller flare (p less than 0.01). A dissociation between induced pain and flare was thus demonstrated.