The aim of this study was to investigate how oxytocin (OXT) influences plasma 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 contrast, 1 mg/kg OXT (but not 10-100 microg/kg) decreased corticosterone, but not ACTH levels, 6 h after the injection. OXT (1 mg/kg s.c.) administered once a day for 5 days, decreased cortiocosterone for 10 days after the last injection. An acute challenge with ACTH increased corticosterone to the same level in rats pretreated with OXT and controls. Dexamethasone decreased corticosterone to equal levels in both groups. Thus, OXT seems to be able to stimulate as well as to inhibit the activity within the HPA-axis within a short- and a long-term perspective, respectively.