Identification and Clinical Relevance of an Oxytocin Deficient State (Melatonin Study)

Inclusion Criteria: * Patients with hypopituitarism (HYPO) (\>1 pituitary hormone deficiency) and stable hormone replacement for the prior three months * At least one clinical sign of hypothalamic damage Exclusion Criteria: * uncorrected hormone deficiency * creatinine \>1.5mg/dL * alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \>2.5x upper limit of normal * hematocrit less than 30% * suicidality or active psychosis * participation in a trial with investigational drugs within 30 days * using a high glucocorticoid dose * vigorous physical exercise * alcohol intake within 24 hours before the study participation * evidence of any acute illness or any illness that the Investigator determines could interfere with study participation or safety * pregnancy or breastfeeding for last 8 weeks * known allergies towards melatonin * patients refusing or unable to give written informed consent * patients receiving fluvoxamine and/or impossibility to stop hypnotics 48 hours prior to the study visit. * Additionally for healthy controls: the presence of brain or pituitary tumor, radiation involving the hypothalamus or pituitary, history of hypopituitarism or receiving testosterone or glucocorticoids esters.