Aim of the study is to assess the impact of the factors ´bed rest´ and ´hypocaloric nutrition´ on endothelium-dependent vasoreactivity in healthy volunteers.

In a randomized, four-phase cross-over study the effect of simulated microgravity (13 days of bed rest), energetic restriction (-25%, fat reduced), and their combination on endothelium-dependent and -independent vasodilation will be compared with ambulatory control conditions. Using venous occlusion plethysmography cumulative intraarterial dose-response curves to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) vasodilators will be constructed in 10 healthy male volunteers before and on day 13 of each of the four intervention periods.

Inclusion Criteria:´

• Healthy, male volunteers, age: 18-40
• Able and willing to give written informed consent

Exclusion Criteria:

• Known condition causing endothelial dysfunction (e.g. diabetes, hyperlipidaemia, arterial hypertension, smoking, hyperhomocysteinaemia)
• Regular medication and/or treatment with drugs within the last 4-6 weeks (exclusion has to be decided in each case)
• Acute or chronic illness
• Participation in clinical trial/blood donation within 2 month before the study
• Nicotine during 1 year before the study; drug and/or alcohol abuse.