This study investigates stimulation of the posterior pituitary gland by oral Macimorelin (a ghrelin receptor Agonist) to be a novel diagnostic test in the polyuria-polydipsia syndrome.

Copeptin measurements upon intravenous arginine stimulation discriminate patients with diabetes insipidus versus patients with primary polydipsia with a high diagnostic accuracy. An oral test would be easier to perform, causes less risks and discomfort for the patients and would require less resources in clinical practice. This study investigates stimulation of the posterior pituitary gland by oral Macimorelin (a ghrelin receptor Agonist) to be a novel diagnostic test in the polyuria-polydipsia syndrome.

Inclusion Criteria:

• No medication except hormonal contraception

Exclusion Criteria:

• Body Mass Index (BMI) > 40kg/m2 or BMI < 18.5 kg/m2
• participation in a trial with investigational drugs within 30 days
• vigorous physical exercise within 24 hours before the study participation
• Alcohol intake within 24 hours before study participation
• pregnancy and breastfeeding
• Evidence of disordered drinking habits and diuresis defined as polyuria >50ml/kg body weight/24h and polydipsia >3l /24h
• a prolonged QT interval (QTc >500 ms) or concomitant treatment with drugs that prolong the QT/QTc.
• Intention to become pregnant during the course of the study
• Known allergy towards Macimorelin