Effects of central infusion of ANG II and losartan on the cardiac baroreflex in rabbits

The effect of chronic activation or inhibition of central ANG II receptors on cardiac baroreflex function in conscious normotensive rabbits was examin ed. Animals received a fourth ventricular (4V) infusion of ANG II (30 and 1 00 ng/h), losartan (3 and 30 mu g/h), or Ringer solution (2 mu l/h) for 2 w k. After 1 and 2 wk, ANG II (100 ng/h) decreased cardiac baroreflex gain by 20 and 37%, respectively (P = 0.015), whereas losartan (30 mu g/h) increas ed baroreflex gain by 24 and 58%, respectively (P = 0.02). Within 1 wk of t he end of the infusions, cardiac baroreflex gain had returned to control. R inger solution or the lower doses of ANG II or losartan did not modify the cardiac baroreflex function. Blood pressure and heart rate were not altered by any treatment, nor was their variability affected. These data demonstra te a novel long-term modulation of cardiac baroreflexes by endogenous ANG I I that is independent of blood pressure level.