Effects of Acute Capsaicin on the Central and Peripheral Hemodynamic Response to Passive Leg Movement

Abstract

Previous work in vitro and animal models suggests, capsaicin, the pungent ingredient in peppers, which acts on transient receptor potential vanilloid type 1 channels improves vascular function, in an endothelium and nitric oxide (NO) dependent manner. Recently, topical capsaicin has also been shown to attenuate the metaboreflex in humans. Thus, whether acute oral capsaicin improves an NO-dependent measure of vascular function, or the mechanoreflex response to PLM, remains elusive. PURPOSE: to determine the effects of capsaicin on the vascular and mechanoreflex responses to continuous PLM. METHODS: In a single blind crossover design, 13 young healthy men (21±3 yr, 177±7cm, and 73±12kg) underwent continuous PLM at 1 hz for 2 min after taking placebo (800 mg fiber) or capsaicin (780 mg pepper extract, ~2mg Capsaicin). At baseline and during PLM, Near-infrared spectroscopy (NIRS) of v. lateralis continuously measured tissue oxygen saturation (StO2), total hemoglobin concentration (THb), oxyhemoglobin concentration (HbO), and deoxyhemoglobin concentration (Hb), as estimates of microvascular function. Central hemodynamic responses (stroke volume, SV; heart rate, HR; cardiac output, CO; and mean arterial pressure, MAP) were measured using finger photoplethysmography. RESULTS: The individual absolute peak change in StO2 (4.9 ± 1.2 vs 4.0 ± 0.7%), THb (22 ± 15 vs 11 ± 4 ∆μM), HbO (22 ± 16 vs 10 ± 4 ∆μM), and Hb (-2.5 ± 1.3 vs -1.2 ± 1.1 ∆μM), were all unaffected by capsaicin (p>0.05, placebo vs. capsaicin, respectively). Exploring the area under the curve (AUC) in StO2 (301 ± 128 vs 155 ± 85), THb (1491 ± 1032 vs 758 ± 386 μM), HbO (1549 ± 1102 vs 707 ± 318 μM), and Hb (-59 ± 89 vs 51 ± 129 μM) were not different between placebo and capsaicin (all, p> 0.05). Peak changes in CO (1.3 ± 0.5 vs 1.1 ± 0.2 ∆L/min), and HR (10 ± 4 vs 8 ± 3 ∆beats/min), tended to be lower, while SV and MAP were not different between conditions (p>0.05). Post hoc analysis of potential racial differences, people of color and Caucasian’s elicited similar individual absolute peak change in StO2 (3.0 ± 1 vs 3.4 ± 1%), but tended to have lower AUC (108 ± 68 vs. 251 ± 83, p=0.09). CONCLUSION: In the current model, using a modest acute dose in young healthy males, capsaicin does not alter the central or peripheral hemodynamic responses to PLM, but warrants further work with aging or disease.