This study is to find out what role a local intestinal RAS (renin angiotensin system) plays in the context of amino acid absorption in the human intestinal tract and how this RAS and thus the amino acid absorption is influenced by the RAS-active drugs (angiotensin II AT1 receptor blockers (sartans) or ACE inhibitors).

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

Patients undertaking a gastroscopy and / or colonoscopy for a medical indication