Pain and hyperalgesia after intradermal injection of bradykinin in humans.

Pain and hyperalgesia, the perceptual campanions of tissue injury and inflammation, are thought to be in part attributable to the sensitization of primary afferent nociceptors by endogenously released chemicals, such as bradykinin. Bradykinin (0.1 to 10 nmol in 10 microliters) evoked a dose-dependent pain, hyperalgesia to heat stimuli, and wheal and flare when injected in a double-blind manner into the volar forearm intradermally. Though hyperalgesia to mechanical stimuli is a conspicuous feature of inflammatory pain, none was measurable for any of the bradykinin doses in response to graded nylon monofilament probes. A second injection of bradykinin (5- or 30-minute intervals) at the same site produced markedly less pain and hyperalgesia to heat stimuli, indicating that the algesic and hyperalgesic effects of bradykinin undergo tachyphylaxis. These findings suggest that bradykinin alone cannot account for all aspects of the hyperalgesia that occurs after inflammation.