Capsaicin-Based Analgesic Balm Decreases Pressor Responses Evoked by Muscle Afferents

Capsaicin-based analgesic balm decreases pressor responses evoked by muscle afferents. Physically active individuals use countless analgesic balm (AB) products with various active ingredients daily. Despite this, few studies have investigated the mechanism of action and efficacy of AB. Purpose: We examined the effects of capsaicin (CAP) application on pressor responses evoked by muscle contraction (MC), which are mediated by group III and IV muscle afferents. Methods: Heart rate (HR), blood pressure, and end-tidal CO ₂ were monitored in cats (N = 12) decerebrated under halothane. Decerebration eliminated anesthesia use and effects from the higher brain. Electrical stimulation of L7 and S1 ventral roots evoked static hindlimb MC (30 s). After control runs, a commercial CAP (4.95% Oleoresin Capsicum) AB was applied to the skin over the contracting muscles of one hindlimb. MC were evoked every 10 min, alternating between hindlimbs. Data were analyzed with RM ANOVA and Tukey post hoc test. Results: Changes in peak mean arterial pressure (MAP) induced by static ipsilateral MC were significantly attenuated at 20 min and tended to approach baseline levels at 40 min after CAP application. The mean (±SEM) of the peak MAP for the ipsilateral side just before application (T = 0), at 20 min (T+20), and 40 min (T+40) were 28.3 mm Hg ± 6.4, 13.8 mm Hg ± 2.9, and 22.6 mm Hg ± 5.2, respectively. There were no significant changes in HR. Conclusions: Cardiovascular effects due to activation of group III and IV afferent fibers were significantly attenuated by the application of CAP. The time course of the effects appeared to support the need for repeated CAP application for pain relief. Central nervous system circuitry responsible for this effect awaits elucidation.