Vanilloid type 1 (VR-1) receptors are stimulated by capsaicin and hydrogen ions, the latter being a by-product of muscular contraction. We tested the hypothesis that activation of VR-1 receptors during static contraction contributes to the exercise pressor reflex. We established a dose of iodoresinaferatoxin (IRTX), a VR-1 receptor antagonist, that blocked the pressor response to capsaicin injected into the arterial supply of muscle. Specifically, in eight decerebrated cats, we compared pressor responses to capsaicin (10 μg) injected into the right popliteal artery, which was subsequently injected with IRTX (100 μg), with those to capsaicin injected into the left popliteal artery, which was not injected with IRTX. The pressor response to capsaicin injected into the right popliteal artery averaged 49 ± 9 mmHg before IRTX and 9 ± 2 mmHg after IRTX (P < 0.05). In contrast, the pressor response to capsaicin injected into the left popliteal artery averaged 46 ± 10 mmHg "before" and 43 ± 6 mmHg "after" (P > 0.05). We next determined whether VR-1 receptors mediated the pressor response to contraction of the triceps surae. During contraction without circulatory occlusion, the pressor response before IRTX (100 μg) averaged 26 ± 3 mmHg, whereas it averaged 22 ± 3 mmHg (P > 0.05) after IRTX (n = 8). In addition, during contraction with occlusion, the pressor responses averaged 35 ± 3 mmHg before IRTX injection and 49 ± 7 mmHg after IRTX injection (n = 7). We conclude that VR-1 receptors play little role in evoking the exercise pressor reflex.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|Issue number||4 57-4|
|State||Published - Apr 2005|
All Science Journal Classification (ASJC) codes
- Cardiology and Cardiovascular Medicine
- Physiology (medical)