Study of the Renal Perfusion in Healthy Volunteers and Renal Transplant Recipients During an Orthostatic Stress

Inclusion Criteria: \- Healthy volunteers Male or female, within 18 and 50 year old Caucasian type No cardiovascular risk factor: Body mass index below 25 kg/m2 No smoking No dyslipidemia No diabetes No kidney disease or chronic renal failure No medication Electrocardiogram: normal Arterial blood pressure: normal Plasma creatinine clearance equivalent to 50mL/min or more (Cockroft formula) No proteinuria and no hematuria Able to understand the purpose of the study and sign the informed consent \- Renal graft recipients Male or female, within 18 and 50 year old Caucasian type About a year after the first renal allograft Body mass index below 25 kg/m2 No smoking No dylipidemia No diabetes Arterial blood pressure controlled Electrocardiogram: normal Plasma creatinine clearance equivalent to 50mL/min or more (Cockroft formula) Able to understand the purpose of the study and sign the informed consent Exclusion Criteria: * Healthy volunteers Creatinine clearance \< 50 mL/min (Cockroft formula) More than 2 syncopes a year Pregnancy * Renal graft recipients Creatinine clearance \< 50 mL/min (Cockroft formula) Second renal allograft or more More than 3 antihypertensive treatments Beta adrenoreceptors blockers Acute rejection More than 2 syncopes a year