Reduced Sensory Nerve Function and Nitric Oxide Sensitivity in Non‐Hispanic Blacks Compared to Non‐Hispanic Whites

Abstract

Microvascular function is known to be impaired in healthy non‐Hispanic Blacks (NHB) compared to non‐Hispanic Whites (NHW), but it remains unknown if sensory nerve function is also impaired in NHB. Mechanisms of reduced bioavailable nitric oxide (NO) or sensitivity to NO may play a role in this racial discrepancy. The purpose of this study was to assess sensory nerve activation and sensitivity to NO in young, healthy NHB and NHW. Eight participants who self‐identified as NHB (n=4) or NHW (n=4) were instrumented with three microdialysis fibers in the skin of the forearm: 1) lactated Ringer's (control), 2) 20 mM NG‐nitro‐L‐arginine methyl ester (L‐NAME)to inhibit NO synthase (NOS), and 3) 1μM low‐dose sodium nitroprusside (SNP). A slow local heating protocol was used to heat the skin from 33°C to 40°C at a rate of 0.1°C per minute. Maximal vasodilation was elicited by heating the skin to 43°C and infusion of 54 mM SNP. An index of skin blood flow was assessed using laser‐Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated (LDF/MAP) and normalized to maximum (%CVCmax). At control sites, sensory nerve activation was shifted to a higher local temperature in NHB (39.4 ± 0.4°C) compared to NHW (38.1 ± 0.3°C). L‐NAME did not alter the temperature threshold for sensory nerve activation in either NHB (39.8 ± 0.2°C) or NHW (38.8 ± 0.6°C) compared to control. Low‐dose SNP did not alter the temperature threshold (38.7 ± 0.7°C) relative to control sites in NHB but did reduce the temperature threshold in NHB to a value similar to that observed at control sites in NHW (P > 0.99). In NHW, low dose SNP reduced the temperature threshold (37.4 ± 0.6°C) compared to L‐NAME (P< 0.001) but not control sites. The magnitude of vasodilation was significantly reduced in NHB (23 ± 9 %CVCmax) compared to NHW (45 ± 9 %CVCmax) at control sites. L‐NAME did not alter %CVCmax in NHB (21 ± 5) or NHW (32 ± 5) compared to control. Low‐dose SNP increased the magnitude of vasodilation in NHB (45 ± 1 %CVCmax) compared to both control and L‐NAME sites. Low‐dose SNP in NHB also increased the magnitude of vasodilation to a value similar to that observed at all sites in NHW. Conversely, low‐dose SNP did not affect the magnitude of vasodilation (49 ± 5 %CVCmax) compared to control or L‐NAME sites in NHW. These data suggest increasing bioavailable NO results in greater sensory nerve sensitivity and increased skin blood flow in NHB. Low‐dose SNP improved sensory nerve sensitivity and cutaneous microvascular vasodilation in NHB to comparable levels as that observed in NHW. As increasing bioavailable NO did not fully reduce the temperature threshold for sensory nerve activation in NHB, it appears other mechanisms may contribute to the differences in sensory nerve sensitivity between these racial groups and that other NO‐independent mechanisms help to increase skin blood flow in response to heat.Support or Funding InformationNIH R01HL141205This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.