The Effect of Endothelin and L-Arginine on Racial Differences in Vasoconstriction

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 in…