Neurovascular Transduction During Exercise in Chronic Kidney Disease

Inclusion Criteria for Chronic Kidney Disease Patients: * Stage III or IV Chronic Kidney Disease, defined as reduction in estimated glomerular filtration rate (eGFR) to 15-59 cc/minute as calculated by the modified Modification of Diet in Renal Disease (MDRD) Study equation or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation * Stable renal function, with no greater than a 30% reduction in eGFR over the prior 3 months * Does not exercise regularly (defined as exercising less than 20 minutes twice per week) * Willing and able to cooperate with the study protocol Inclusion Criteria for Control Study Participants: * Does not exercise regularly (defined as exercising less than 20 minutes twice per week) * Willing and able to cooperate with the study protocol Exclusion Criteria: * severe CKD (eGFR\<15 cc/minute) * ongoing drug or alcohol abuse * diabetic neuropathy * any serious systemic disease that might influence survival * severe anemia with hgb level \<9 g/dL * clinical evidence of congestive heart failure or ejection fraction below 35% * symptomatic heart disease determined by prior electrocardiogram, stress test, and/or history * treatment with central alpha agonists (clonidine) * uncontrolled hypertension with BP greater than 170/100 mm Hg * low blood pressure with BP less than 100/50 * pregnancy or plans to become pregnant * current treatment with monoamine oxidase (MAO) inhibitors * inability to exercise on a stationary bicycle