BARORECEPTOR REFLEX IN HIGH-VOLUME EXPANDED RATS

We have studied cardiovascular parameters and the baroreflex system in conscious rats following extracellular volume expansion by saline loa ding. An infusion of isotonic saline solution at a rate of 0.05 ml/min for 50 min was given to stabilize haemodynamic parameters (baseline). Then the animals were divided in four experimental groups and respect ively expanded at 2, 5, 10 or 15% body weight with isotonic saline ove r 30 min. In all groups, the baroreceptor reflex was evaluated by incr easing arterial pressure with a bolus injection of phenylephrine hydro chloride (6 mu g/kg). After sigmoid curves relating systolic blood pre ssure and heart period were obtained, gain and the threshold were calc ulated. Acute Volume expansion did not induce changes in arterial bloo d pressure or heart rate at any of the levels studied, but the higher (10 and 15%) volume expansion did appear to reset the baroreceptor-hea rt rate reflex: there was a smaller decrease in heart rate when blood pressure was raised. (C) 1998 Chapman & Hall Ltd.