Does sex influence near-infrared spectroscopy-derived indicators of microvascular reactivity and the response to acute dietary capsaicin.

Abstract

Endothelial dysfunction is associated with cardiovascular disease development, nitric oxide (NO) deficiencies, and may be limb or sex-specific. Prior in vitro work indicated that the transient receptor potential vanilloid channel-1 (TRPV1) is expressed in human arteries and the TRPV1 agonist capsaicin alters vasodilation in an endothelium-dependent manner; however, it is unknown if this translates in vivo or is limb or sex-dependent. Therefore, we sought to determine if there was limb or sex-specificity in the effect of capsaicin on microvascular function using near-infrared spectroscopy (NIRS)-derived tissue oxygen saturation (StO2) reperfusion slope. In a blinded placebo-controlled crossover design, 45 young males (M: n=25) and females (F: n=20), the reperfusion slopes of the forearm and quadriceps were assessed, and a urine sample obtained to assay for nitrate/nitrite (NOx) concentrations and antioxidant capacity after acutely ingesting placebo or capsaicin. Under placebo, females had greater reperfusion rates in both the forearm (M: 0.44±0.24 vs. F: 0.98±0.46%/sec; p=0.002, d=-1.50) and quadricep (M: 0.86±0.31 vs. F: 1.17±0.43%/sec; p=0.010, d=-0.85). Capsaicin decreased microvascular responsiveness in the forearm of females (placebo: 0.98±0.45 vs. capsaicin: 0.84±0.45%/sec) as compared to males (placebo: 0.45±0.24 vs. capsaicin: 0.38±0.16%/sec, interaction p<0.001, η2=0.475). There was a sex*treatment interaction for NOx concentrations, where males increased (placebo: 21.13±12.83 vs. capsaicin: 23.82±13.34μM), while females decreased (placebo: 22.78±14.40 vs. capsaicin: 14.43±10.01μM; p=0.037, η2=0.042). Using NIRS to assess microvascular function, there is apparent limb and sex-specificity, and, for the first-time, document that acute oral capsaicin alters reperfusion slope in a sexually divergent manner.