Centrally induced cardiovascular and sympathetic responses to hydrocortisone in rats

Central effects of hydrocortisone were investigated by injecting it intracerebroventricularly (icv) while recording blood pressure and heart rate in awake rats. Dose-dependent increases in both blood pressure and heart rate occurred following injections of hydrocortisone. Pretreatment by icv injections of the angiotensin II antagonist, [Sar1-Ile8]angiotensin II, completely abolished vasopressor responses to subsequent injections of hydrocortisone. When rats were later anesthetized with urethan to allow recording of abdominal sympathetic nerve activity, hydrocortisone produced vasopressor responses accompanied by corresponding increases in sympathetic nerve firing, which were also abolished by central pretreatment with either [Sar1-Ile8]angiotensin II or angiotensin I converting-enzyme inhibitor, captopril. These results indicate that centrally administered hydrocortisone stimulates the brain renin-angiotensin system to produce vasopressor responses by increasing sympathetic nerve firing.