Oxytocin causes a sustained decrease in plasma levels of corticosterone inrats

The aim of this study was to investigate how oxytocin (OXT) influences plas ma levels of ACTH and corticosterone in rats. A single injection of OXT (1 mg/kg s.c.) caused a transient increase in ACTH and corticosterone. In cont rast, 1 mg/kg OXT (but not 10-100 mu g/kg) decreased corticosterone, but no t ACTH levels, 6 h after the injection. OXT (1 mg/kg s.c.) administered onc e a day for 5 days, decreased cortiocosterone for 10 days after the last in jection. An acute challenge with ACTH increased corticosterone to the same level in rats pretreated with OXT and controls, Dexamethasone decreased cor ticosterone to equal levels in both groups. Thus, OXT seems to be able to s timulate as well as to inhibit the activity within the HPA-axis within a sh ort-and a long-term perspective, respectively. (C) 1999 Elsevier Science Ir eland Ltd. All rights reserved.