Aim of this trial is to investigate the expression and localisation of different amino acid transporters and their regulatory proteins derived from the regulatory proteins of the local renin angiotensin system (RAS) in the intestine. This is investigated on one hand in patients who do not take any drugs interfering with RAS. On the other hand expression analysis is done in patients taking daily RAS-active drugs, like ACE inhibitors or sartanes.

After obtaining informed consent of patients attending the hospital for clarification of gastrointestinal symptoms by gastroduodenoscopy or colonoscopy, 2 biopsies (in addition to biopsies needed for clinical diagnostics) will be taken from each duodenum, jejunum, ileum and descending colon.

Biopsies are investigated anonymously at the Institute of Physiology of the University of Zurich. The mRNA content of amino acid transporters and regulatory proteins, respectively, in the biopsies is analyzed by quantitative PCR. Transport proteins are in addition analyzed with immunohistochemistry.

Furthermore amino acid concentration in plasma and urine samples are analyzed by HPLC. From plasma and serum samples RAS parameters like renin, aldosterone, ACE and angiotensin(1-7) are measured.

Inclusion criteria:

• Men and women aged 18-80 years
• BMI 18-35 kg/m2
• Group 1: patients taking daily RAS-active drugs, like ACE inhibitors or sartanes (treatment indication outside of this study)
• Group 2: no therapy with RAS-active drugs, like ACE inhibitors or sartanes Gastroduodenoscopy and/or colonoscopy with a treatment indication outside of this study
• Informed consent

Exclusion criteria:

• Severe pathologic alterations in the gastrointestinal tract (ulcers, tumors, celiac disease; GERD and gastritis are no exclusion criteria)
• Status after operations of the gastrointestinal tract (except uncomplicated appendectomy or inguinal hernia repair)
• Patients with malignant diseases
• Severe acute or chronic diseases which require treatment (e.g. renal replacement therapy)
• Patients with increased bleeding risk (e.g. oral anticoagulation, coagulopathy)
• Drug or alcohol abuse
• Mental disorders which limits the ability to fulfil all study requirements

Patients attending the hospital for clarification of gastrointestinal symptoms by gastroduodenoscopy or colonoscopy