Apocynin and Allopurinol Ameliorate Racial Differences in Cutaneous Microvascular Thermal Reactivity in Young Black Men but Not Black Women
Authors: Patik Jordan C. , Curtis Bryon M. , Akins John D. , Nasirian Aida , Olvera Guillermo , Brothers R. Matthew 
Published: June 2021

The black population is at a markedly elevated risk of hypertension and insulin resistance compared to all other major racial groups. Microvascular dysfunction is known to precede the development of these conditions and has been observed in otherwise healthy, young black adults compared to their white counterparts. The mechanisms responsible for this racial difference in microvascular function have not been elucidated; however there is evidence of greater oxidative stress in this population. With the use of intradermal microdialysis and laser Doppler flowmetry, the cutaneous microvasculature serves as a low‐risk vascular bed for the study of the underlying mechanisms of this dysfunction. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and xanthine oxidase are two potential sources of reactive oxygen species that could impair microvascular function in the black population. Therefore, we tested the hypothesis that inhibition of NADPH oxidase via apocynin and/or xanthine oxidase via allopurinol would augment cutaneous microvascular thermal reactivity in black individuals free of known disease. Skin blood flow (SkBF) responses to a standard 39°C local heating protocol were assessed in 30 healthy, young adult black and white individuals (8 men/7 women in each group). Three microdialysis membranes were placed in the skin of the forearm for infusion of apocynin (100 μM), allopurinol (10 μM), or lactated Ringer's solution (control site). After ~40 min of local heating, L‐NAME was infused at all sites to inhibit nitric oxide synthase (NOS) and thus quantify NO contribution to the SkBF response. Maximal SkBF at each site was determined via sodium nitroprusside (SNP) infusion (28 mM) and 43°C local heating. Cutaneous vascular conductance (CVC) was calculated as red blood cell flux/MAP and normalized to the site‐specific maximal CVC. The plateau response to continued local heating was blunted in the black group compared to the whites at the control site (45 ± 9 vs 68 ± 13 %CVCmax, P<0.001). Likewise, the NO‐dependent component was lower in blacks (29 ± 10 vs 48 ± 14 %CVCmax, P=0.002). Compared to the control site, the local heating plateau was augmented at both treatment sites in black men, (apocynin: 71 ± 10 %CVCmax, P<0.001 and allopurinol: 65 ± 16 %CVCmax, P=0.002). NO contribution was also augmented in the black men at both sites (both P<0.01 vs control site). However, there was no effect of either treatment plateau response in black women (apocynin: 51 ± 16 %CVCmax, P=0.61 and allopurinol: 49 ± 13 %CVCmax, P=0.84, each vs control site) or NO contribution: (apocynin: 27 ± 18 %CVCmax, allopurinol: 35 ± 12 %CVCmax, both P>0.55 vs control site). There was no effect of either treatment in the whites for any parameter. In conclusion, healthy college‐aged black men and women have attenuated cutaneous microvascular responses to local heating. Our results support our hypothesis that NADPH oxidase and xanthine oxidase activity contribute to blunted microvascular function in black men; however these enzymes do not appear to be the source of the impairment in black women. Future research is needed to clarify the mechanisms responsible for microvascular dysfunction in black women.Support or Funding InformationSupported by UTA College of Nursing and Health InnovationThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.