The Effect of Antioxidants on Skin Blood Flow-BH4

African Americans (AA) not only have a higher prevalence of hypertension but the severity of
the cardiovascular complications related to this condition are greater in this population
relative to other populations. While the underlying causes of this elevated risk are
multifactorial, vascular dysfunction (i.e. impaired vasodilation and/or augmented
vasoconstriction) is believed to be a key contributing factor. The investigators have
recently observed (UTA IRB 2016-0268) that the small blood vessels in the skin (the cutaneous
microvasculature) in AA, but otherwise healthy individuals, have an impaired blood flow
response in the cutaneous circulation to local heating when compared to age, body mass index
(BMI), and gender, matched Caucasians (CA). This blunted response is abolished in AA when the
sites are pre-treated with either Allopurinol or Apocynin which block the production of
xanthine oxidase and NADPH oxidase, respectively. In addition, Tetrahydrobiopterin (BH4) is
critically involved in vascular function. BH4 is a cofactor involved in the conversion of
L-Arginine into the potent vasodilator nitric oxide (NO) by the enzyme endothelial nitric
oxide synthase (eNOS). Reduced bioavailable BH4 leads to elevated oxidative stress and thus
impaired vascular function.

In addition to local heating another commonly utilized research approach to assess
microcirculatory vascular function is via local infusion of the potent vasodilator
methacholine (Mch). Mch is an acetylcholine analog that causes endothelial dependent
vasodilation primarily through stimulation of NO production. Much like the local heating data
mentioned above, our laboratory (data collected while at UT Austin) has demonstrated a
blunted response to Mch in AA relative to CA. However, the role of xanthine oxidase, NADPH
oxidase, and BH4 in this blunted response remains unknown.

Inclusion Criteria:

- Individuals (ages 18-35, both genders) will be recruited from the greater Arlington
area to participate in the study.

- Must self-report both parents as either African American or Caucasian American.

Exclusion Criteria:

- Individuals who have donated more than 550 ml of blood within the past 8 weeks will
not have blood drawn from them in this protocol. However, if they remain interested in
the study, and otherwise meet the inclusion criteria, than we may still opt to proceed
with data collection.

- Individuals with cardiovascular, neurological, and/or metabolic illnesses will be
excluded from participating as well as individuals with a history of various diseases
of the microvasculature including Reynaud's disease, cold-induced urticaria,
cryoglobulinemia, etc.

- Subjects currently taking any prescription medications and individuals with a body
mass index about 30 kg/m2) will be excluded.

- Pregnant subjects and children (i.e. younger than 18) will not be recruited for the
study. Eligible females will be scheduled for days 2-7 of their menstrual cycle to
account for hormonal effects on blood flow. A regular menstrual cycle is required to
identify and schedule the study for the low hormone period, therefore females who lack
a regular cycle will be excluded from the study. Females currently taking birth
control are eligible, as long as they can be scheduled during a low-hormone "placebo"
week. If their hormone do not contain a placebo week than these individuals will not
be eligible for data collection. Females who are breast-feeding will also be eligible
as there are no systemic or lasting effects of the proposed vasoactive agents.

- Given that smoking can affect the peripheral vasculature, current smokers and
individuals who regularly smoked (>1 pack per two weeks) within the prior 2 years will
be excluded