Metabolomics Profiling in Response to a Cold Pressor Test
Authors: Clarke Holly Elizabeth , Kluess Heidi , Adams Sean , Kim Do-Houn , Hickner Robert 
Published: April 2020

The cold pressor test (CPT) has been widely used to assess both cardiovascular and hemodynamic responses to stress. Despite the broad utilization of the CPT, there have been few if any studies in which metabolomic profiling was used to study the metabolic response to such a stimulus. Metabolomics allows insight into varying chemical processes, displaying detailed profiles of metabolites, small molecule substrates, intermediates and products of metabolism. The purpose of this study was to investigate the influence of sympathetic activation induced by a 1‐minute cold‐water immersion CPT, upon muscle metabolic responses, through metabolomics profiling of muscle interstitial fluid in adults. Five healthy adults (2 males, 3 females; 29.4 ± 9.4 yrs.; 77.6 ± 19.3 kg) were recruited for this pilot study. Three microdialysis probes (CMA 20, CMA/Microdialysis, Stockholm, Sweden) were percutaneously inserted into the vastus lateralis muscle of the dominant leg using sterile technique. Probes were then perfused with sterile saline containing 5 mM ethanol through the inlet tubing at a rate of 2.0 μL/min, and dialysate from the outlet tubing was collected in 150 μL polyethylene collection vials. One hour (3 × 20‐minute collections) of basal dialysates were collected and pooled. Participants then completed, in a seated position, a CPT in which the right hand was immersed up to the wrist in ice water for 1 minute. A 20‐min dialysate sample was collected during and immediately following the CPT. Microdialysis samples were sent to the West Coast Metabolomics Center (UC Davis Genome Center, Davis, CA, USA) for metabolomic profiling. Enzymatic‐fluorometric ethanol assay was also used to measure ethanol outflow: inflow (O:I) ratio to determine microvascular blood flow. The percent change from pre‐CPT to the CPT sample was calculated for every metabolite found. Data were then sorted on a magnitude basis, from smallest to largest change from basal levels. From the 413 metabolites detected, 207 were found to increase and 206 were found to decrease from baseline to post‐CPT. Nine metabolites were found within the 95th to 100th percentile of positive change from baseline to CPT, including: 1‐monostearin (median: 50.4%; range: 10.0–183.1), 3‐aminoisobutyric acid (median: 52.5%; range: 39.2–95.4), palmitoleic acid (median: 92.2%; range: 35.4–204.5); and 6 “unknown metabolites.” Furthermore, 5 “unknown metabolites” were also detected within the 95th to 100th percentile of negative change (decrease from baseline). Ethanol O:I ratio increased baseline to CPT, indicating decreased blood flow (0.483 ± 0.088 to 0.547 ± 0.027, mean ± SEM). These results indicate that the CPT can elicit both vasoconstriction and a notable metabolic response in muscle tissue, identifiable by the use of ethanol analysis and metabolomics of dialysate from microdialysis of skeletal muscle. Of specific interest, 1‐monostearin and palmitoleic acid were found to be in the group of molecules that increased the most in response to CPT. Although speculative, increased adrenergic stimulation resulting from CPT‐induced sympathetic activation may have resulted in liberation of 1‐monostearin and palmitoleic acid from membranes or other locations, or from increases in desaturase activities.