The Importance of EDHF in Functional Sympatholysis in Healthy Young Adults

Abstract

Functional Sympatholysis allows for the matching of increased demands in skeletal muscle oxygenation by increasing exercise hyperemia despite elevated sympathetic outflow. Endothelial-Derived Hyperpolarizing Factor (EDHF) may be involved in functional sympatholysis although its role is not clear. Purpose: The purpose of the present study was to determine the importance of EDHF in functional sympatholysis in healthy young adults. Methods: 14 participants (8 Females) participated in three study visits (2 experimental visits). Experimental visits were identical with the exception of ingestion of a placebo (PLA) (250 mg microcrystalline cellulose) or 150 mg of fluconazole (FLZ) 120 minutes before testing (randomized and counter-balanced). Forearm blood flow, (FBF, doppler and echo ultrasound), mean arterial pressure (MAP, finger photoplethysmography), vascular conductance (FVC, FBF/MAP x100mmHg), and muscle oxygenation (near-infrared spectroscopy) were compared during rest, -20mmHg of lower body negative pressure (LBNP), rhythmic forearm exercise at 20% maximum voluntary contraction (MVC) for 5 minutes, and forearm exercise with LBNP for 2 minutes Results: Data are percent change (Δ%) ± SD. FVC declined from rest to LBNP but did not differ between PLA and FLZ (Δ -32.02 ± 18.99% vsΔ -38.16 ± 15.97, p=0.35). During exercise, FVC was unaltered in PLA with the addition of LBNP (Δ 2.92 ± 12.69%, p=0.81), however, declined in FLZ (Δ –11.58 ± 15.06%, p=0.01). exercise within FLZ, exercise + LBNP between PLA vs FLZ, (p = 0.0003). Conclusion: Our results indicate that young, healthy adults were able to maintain FVC with the addition of LBNP induced sympathetic stress during exercise in the PLA, however, when EDHF was inhibited with FLZ, FVC declined. Therefore, EDHF may have an important role in functional sympatholysis.