Effect of Glyceroltrinitrate on Human Energy Expenditure and Brown Adipose Tissue Thermogenesis

Inclusion Criteria: * BMI 18.5 to 25 kg/m2 or 30 to 35kg/m2 * Able to give informed consent as documented by signature * Age 18 to 40 years Exclusion Criteria: * Contraindications to glyceroltrinitrate, e.g. known hypersensitivity or allergy * Concomitant medication: Non-steroidal anti-inflammatory drugs (NSAID), glucocorticoids, diuretics, antihypertensives, fibrates or statins, metformin, PDE-5-inhibitors * Clinically significant concomitant disease states (e.g. renal failure, hepatic dysfunction, cardiovascular disease, diabetes mellitus) * Hypersensitivity to cold (e.g. Raynaud Syndrome) * Orthostatic hypotension: systolic blood pressure decreases min. 20mmHg or diastolic blood pressure decreases min 10mmHg within 3-5min after standing up (Schellong Test at screening visit) * History of orthostatic syncope or pre-syncope * Blood pressure values below 100 mmHg systolic and 60 mmHg diastolic * Allergy to local anesthetic * Hypothyroidism without sufficient substitution * Hyperthyroidism * Claustrophobia * Smoker / habitual tobacco use * Habitual excessive alcohol use * Weight change of \>5% within 3 months prior to inclusion * Known or suspected non-compliance, drug or alcohol abuse * Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant * Enrolment of the investigator, his/her family members, employees and other dependent persons * Enrolment into another study using ionizing radiation w…