Exercise Study for Chronic Kidney Disease Patients

Inclusion Criteria: * patients with CKD (Stages III and IV), kidney transplant recipients with varying degrees of kidney function, or persons without kidney disease as matched study controls * sedentary and do not regularly exercise (defined as exercising \< 20 minutes twice per week) * CKD patients must have stable renal function (no greater than a decline of estimated glomerular filtration (eGFR) of 1 cc/min/1.73 m2 per month over the prior 6 months) and baseline serum bicarbonate 22-24 mmol/L * comorbid hypertension Exclusion Criteria: * severe CKD (eGFR\<15 cc/min) * metabolic alkalosis * current treatment with bicarbonate * ongoing drug or alcohol abuse * diabetic neuropathy, autonomic dysfunction * any serious disease that might influence survival * anemia with hemoglobin \<10 g/dL * clinical evidence of heart failure * volume overload or ejection fraction below 45% * symptomatic heart disease by EKG, stress test, and/or history * treatment with central α-agonists (clonidine) * myocardial infarction or cerebrovascular accident within the past six months * uncontrolled hypertension (BP\>170/100 mm Hg) * low BP\<100/50 mm Hg * surgery within the past 3 months * pregnancy or plans to become pregnant * inability to exercise on a stationary bicycle * contraindication to temporary withdrawal of α- and β-blockers * peripheral arterial disease * class 3 obesity (BMI\>40) * hypo- or hyperkalemia (K\<3.5meq/L, K\>5.0 meq/L) * current use of immunosuppressive medications (including but not limited to steroids, cyclophosphamide, calcineurin inhibitors, mycophenolate, biologics, methotrexate, etc) * arteriovenous (AV) fistula/graft * any contraindication to MR scanning including cardiac pacemaker, cochlear implants, neurostimulators, implanted devices with metal, any metal in the body that could pose a hazard during scanning, history of claustrophobia