OBJECTIVE: Glucocorticoids seem to modify the release and effects of plasma vasopressin (pAVP). However, underlying processes are not well understood. This study aimed to evaluate the mechanism of the modulating effects of glucocorticoids on pAVP and renal water reabsorption. DESIGN: Fluid deprivation tests were performed without (d0) and after one (d1) and five days (d5) of oral prednisolone (Pred) pretreatment in a dosage relevant to drug therapy (30 mg/day). PATIENTS: Twelve healthy male volunteers participated in this trial. MEASUREMENTS: Plasma and urinary osmolality, pAVP, renin, aldosterone, plasma atrial natriuretic peptide (ANP) as well as urinary secretion of aquaporine-2 (AQP2) and prostaglandin E(2) (PGE2) were analysed. RESULTS: An appropriate rise of pAVP was observable during thirsting (p
