Comparing Physiological and Pharmacological Approaches to Assess Cutaneous Endothelium- and Nitric Oxide-Dependent Vasodilation in Young Adults

Cutaneous microvascular responses to local heating (LH) and perfusion of acetylcholine (ACh) are widely used to assess nitric oxide (NO)-mediated endothelium-dependent dilation (EDD) in human health and disease. Despite the increasingly common use of these various approaches, no studies have directly compared the magnitude of the responses to these different stimuli within an individual. We hypothesized that EDD and NO-dependent dilation would be greater in response to LH than to ACh, and that LH- and ACh-induced responses would not be correlated. We examined cutaneous EDD and NO-mediated EDD in response to: 1) LH to 39°C, 2) LH to 42°C, and 3) exogenous ACh using intradermal microdialysis coupled with laser-Doppler flowmetry in 24 young adults (12 women; 22±3 years). In two microdialysis sites, red cell flux was measured in response to a standard LH protocol to either 39°C or 42°C followed by perfusion of N(G)-nitro-l-arginine methyl ester (L-NAME; 15mM) to quantify NO-dependent dilation. In two separate sites, flux was measured in response to graded perfusion of ACh (10 -10 -10 -1 M) alone and co-perfusion with L-NAME. For all protocols, cutaneous vascular conductance was calculated (CVC=flux/mean arterial pressure) and normalized to maximum (%CVCmax; 28mM sodium nitroprusside+43°C). The relative proportion of the LH-induced plateau attributable to NO was calculated as [%NO=(LH plateau - L-NAME plateau)/LH plateau x 100]. The relative proportion of ACh-induced EDD attributable to NO was calculated as [%NO=(area under curve ACh - area under curve ACh+L-NAME)/area under curve ACh x 100]. Pearson correlations were used to evaluate the relations between the quantification of EDD and NO-mediated EDD for each stimulus. EDD in response to LH to 39°C was lower than both LH to 42°C (59±17 vs. 85±14%CVCmax; p<0.001) and the peak ACh-induced EDD (87±14%CVCmax; p<0.001). The NO-dependent contribution to LH-induced EDD was not different between 39°C and 42°C (74±9 vs. 77±1%NO; p=0.22); however, both were greater than the NO-dependent contribution to ACh-induced EDD (37±28%NO; both p<0.01). NO-mediated EDD in response to LH to 39°C was not related to the response to LH to 42°C (r=0.11, p=0.38). Similarly, NO-mediated EDD in response to ACh was not related to either the response to LH to 39°C (r=0.06, p=0.19) or to 42°C (r=0.09, p=0.13). These preliminary data suggest that cutaneous microvascular NO-mediated EDD in response to LH and exogenous ACh may not be comparable within an individual; thus, careful consideration is warranted when comparing results from studies utilizing differing physiological and pharmacological stimuli to elicit EDD. This work is supported by internal funds (A.E.S.) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.