Contribution of vanilloid receptors to the overt nociception induced by B2 kinin receptor activation in mice

1 The vanilloid receptor (TRPV1) is viewed as a molecular integrator of several nociceptive stimuli. In the present study, we have investigated the role played by TRPV1 in the nociceptive response induced by the peripheral activation of kinin B-2 receptor in mice. 2 The intraplantar (i.pl.) administration of bradykinin (BK) and the selective B-2 agonist Tyr(8)-BK, or the vanilloid agonists resiniferatoxin and capsaicin, into the mouse paw induced a dose-related overt nociception of short duration. The B-2 receptor antagonist Hoe 140 inhibited BK-induced, but not capsaicin-induced, nociceptive response. On the other hand, the TRPV1 antagonist capsazepine inhibited both capsaicin- and BK-mediated nociception. 3 Repeated injections of BK or capsaicin produced desensitization to their nociceptive response. Capsaicin desensitization greatly reduced BK-induced nociception, but in contrast, the desensitization to BK increased the capsaicin response. 4 Administration of low doses of capsaicin or acidified saline did not produce nociception when administered alone, but caused a pronounced effect when administered in association with a subthreshold dose of BK. Moreover, the degeneration of the subset of primary afferent fibers, sensitive to capsaicin, abolished both capsaicin- and BK-induced nociception. 5 The inhibition of phospholipase C ( PLC), protein kinase C or phospholipase A(2) markedly decreased the nociception caused by BK, but not that of capsaicin. BK administration increased leukotriene B-4 levels in the injected paw. Likewise, BK-induced overt nociception was decreased by lipoxygenase (LOX) inhibition. 6 These results demonstrate that BK produces overt nociception mediated by TRPV1 receptor stimulation, via PLC pathway activation and LOX product formation.