A single high-fat meal impairs functional sympatholysis in young healthy adults
Authors: Teixeira André , Gangat Ayesha , Millar Philip 
Published: May 2023

Introduction: A high-fat diet increases the risk of cardiovascular disease and mortality, but the underlying mechanisms remain incompletely understood. During exercise, sympathetically mediated vasoconstriction is dampened in active skeletal muscle due to the counteracting vasodilatory effects of metabolic by-products from muscle contraction. This phenomenon, termed functional sympatholysis, plays a critical role in the redistribution of cardiac output to contracting skeletal muscles to meet the metabolic demands of exercise. Whether a high-fat meal modulates the magnitude of sympatholysis is currently unknown. Herein, we tested the hypothesis that a high-fat meal would acutely impair functional sympatholysis in young healthy adults. Methods: In a randomized, controlled, and cross-over design, 14 healthy adults (8 women, 26±4 years), consumed either a high- (1030kcals, 91g fat) or a low-fat (1006kcals, 1g fat) meal on two separate days. Forearm blood flow (FBF; Doppler ultrasound) and beat-to-beat mean arterial pressure (MAP; finger photoplethysmography) were measured during sympathetic activation induced by -20 mmHg lower-body negative pressure (LBNP) applied at rest and simultaneously during rhythmic handgrip exercise at 15% and 30% maximum voluntary contraction (MVC). Measurements were taken pre-meal and at 1-, 2-, and 3-hours post-prandial. Forearm vascular conductance (FVC) was calculated as FBF/MAP and the magnitude of sympatholysis as the difference of LBNP-induced changes in FVC between handgrip and rest. Results: Prior to the high-fat meal, LBNP decreased resting FVC (Δ-57±10%), and this response was attenuated during exercise at 15% (Δ-18±8%) and 30% MVC (Δ-9±7%). After the high-fat meal, LBNP induced smaller decreases in resting FVC (1h: Δ-43±12%, 2h: Δ-45±12%, 3h: Δ-49±8%, all P≤0.01 vs. pre), but during exercise greater decreases in FVC were observed at both 15% (1h: Δ-22±10%, 2h: Δ-23±8%, 3h: Δ-25±8%, all P≤0.04 vs. pre) and 30% MVC (1h: Δ-15±8%, 2h: Δ-15±6%, 3h: Δ-16±6%, all P≤0.04 vs. pre). As a result, the high-fat meal decreased the magnitude of sympatholysis during rhythmic handgrip exercise at 15% (pre-prandial: 39±8%, 1h: 20±10%, 2h: 21±8%, 3h: 24±7%, all P≤0.001) and 30% MVC (pre-prandial: 48±11%, 1h: 28±10%, 2h: 30±11%, 3h: 33±8%, all P≤0.001). The low-fat meal did not change the magnitude of sympatholysis at either 15% (pre-prandial: 37±6%, 1h: 39±6%, 2h: 38±7%, 3h: 37±8%, all P≥0.07) or 30% MVC (pre-prandial: 45±10%, 1h: 47±8%, 2h: 47±9%, 3h: 46±7%, all P≥0.39). Conclusion: These findings demonstrate the capacity of a high-fat meal to acutely impair the ability of contracting skeletal muscle to offset the vascular responsiveness to α1-adrenoreceptor activation during low- and moderate-intensity rhythmic handgrip exercise. Natural Science and Engineering Research Council (NSERC) of Canada Discovery Grant (P.J.M) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.