Human Intestinal Amino Acid Absorption and the Role of a Local RAS

Inclusion Criteria: * Body Mass Index (BMI): 18-35 kg/m2 * cohort 1: therapy with an angiotensin II AT1 antagonist or ACE Inhibitor * cohort 2: no therapy with an angiotensin II AT1 antagonist or ACE Inhibitor * Carrying out a diagnostic gastroscopy, colonoscopy or a combined gastroscopy / colonoscopy * Existence of written consent after detailed information about the study Exclusion Criteria: * Severe pathological changes in the gastrointestinal tract (e.g. sprue, stomach ulcers, malignancies); (reflux esophagitis and gastritis are not Exclusion criteria) * History of gastrointestinal tract surgery (except for appendectomy and inguinal hernia surgery) * History of malignancy * Severe acute and chronic organ diseases requiring treatment (e.g. kidney replacement therapy) * Patients with an increased risk of bleeding (e.g. oral anticoagulation, coagulation disorders) * Drug or alcohol abuse * Mental impairment limiting the ability to meet all study requirements