Investigation of arginine and NO metabolism in healthy subjects is important as a reference for alterations in arginine-NO metabolism in patients. Moreover, this study will indicate the changes during aging and gender-related differences. Although data on arginine metabolism exist in literature, data are limited to young healthy male subjects. Since patients with suspected changes in arginine metabolism, e.g. sepsis and cancer patients are often elderly and also women, knowledge of arginine metabolism in these groups is needed.

Inclusion Criteria:

• Written informed consent
• Age 18-25 years (young); 50-70 years (middle aged/elderly)

Exclusion Criteria:

• Diabetes mellitus type I
• Livercirrhosis, pancreatitis, malignancies
• Hypertension (diastolic blood pressure >95 mmHg or systolic blood pressure >160 mmHg)
• History of gastrointestinal complaints
• Recent involuntary weight loss (more than 10 % in 6 months or more than 5 % in one month)
• Pregnancy (pregnancy test is done in female subjects)
• Use of medication that can affect arginine metabolism (nitrovasodilators and corticosteroids)
• Subjects with "high activity level"