1. We have recently shown that leukotriene B4 (LTB4), a product of the 5-lipoxygenase pathway of arachidonic acid metabolism, sensitizes nociceptors to mechanical stimuli. The present study examined whether LTB4 also induces a heat sensitization of cutaneous C-fiber nociceptors. The C-fiber nociceptors studied had von Frey hair thresholds greater than 5 g and were characterized according to their responses to noxious heat and chemical stimuli, including glacial acetic acid, bradykinin, and capsaicin. Thirty-four of the C-fibers that were activated by intense thermal stimulation were also activated by topical application of glacial acetic acid. They were classified as C-polymodal nociceptors (2, 28). Those that were activated by intense mechanical and thermal stimulation, but were unresponsive to acid, were classified as C-mechanoheat nociceptors (27). 2. Ninety-four percent of C-polymodal nociceptors and 60% of C-mechanoheat nociceptors were sensitized by LTB4. All C-fiber nociceptors that showed a decrease of their heat threshold also had a decrease of their mechanical threshold. LTB4 (75 ng) lowered the average heat threshold from 45 degrees C to 35 degrees C and produced an average decrease in the mechanical threshold of 86%. 3. The magnitude of the LTB4-evoked decrease in thermal threshold was similar to that produced by 75 ng of prostaglandin E2 (PGE2). These data demonstrate that LTB4 sensitizes C-mechanoheat nociceptors to both mechanical and thermal stimuli. 4. We conclude that LTB4 may contribute to the component of hyperalgesia that is resistant to nonsteroidal anti-inflammatory agents.
Effects of Reference Analgesics and Psychoactive Drugs on the Noxious Heat Threshold of Mice Measured by an Increasing-Temperature Water Bath