Evaluation of baroreflex function in young spontaneously hypertensive rats.

BACKGROUND The literature describes contradictory data regarding the onset of the baroreflex reduction in spontaneously hypertensive rats. OBJECTIVE This investigation was undertaken to evaluate the baroreflex function in 13-week-old spontaneously hypertensive rats. METHODS Male Wistar Kyoto (n=15) and spontaneously hypertensive rats (n=15) aged 13 weeks were studied. Cannulas were inserted in the abdominal aortic artery through the right femoral artery to measure mean arterial pressure and heart rate. Baroreflex function was calculated as the derivative of the variation of HR in function of the MAP variation (Delta heart rate/Delta mean arterial pressure) tested with a depressor dose of sodium nitroprusside (50microg/kg) and with a pressor dose of phenylephrine (8microg/kg) in the right femoral venous approach through an inserted cannula in awake spontaneously hypertensive rats and Wistar-Kyoto. Differences with p values < 0.05 were considered statistically significant. RESULTS Spontaneously hypertensive rats: Delta mean arterial pressure=43.5mmHg+/-5.2, Delta heart rate=-59.7ppm+/-17.9 and Delta heart rate/Delta mean arterial pressure=1.3ppm/mmHg+/-0.1 tested with phenylephrine; Wistar Kyoto: Delta mean arterial pressure=&56mmHg+/-3, Delta heart rate=*-114.9ppm+/-11.3 and Deltaheart rate/Delta mean arterial pressure=#1.9ppm/mmHg+/-0.3 tested with phenylephrine; spontaneously hypertensive rats: Delta mean arterial pressure=-45.6mmHg+/-8.1, Delta heart rate=40.1ppm+/-11.6 and Delta heart rate/Delta mean arterial pressure=0.9ppm/mmHg+/-0.5 tested with sodium nitroprusside; Wistar Kyoto: Delta mean arterial pressure=-39.8mmHg+/-6.2, Delta heart rate=51.9ppm+/-21.8 and Delta heart rate/Delta mean arterial pressure=1.4ppm/mmHg+/-0.7 tested with sodium nitroprusside (*p<0.05; #p<0.01; &<0.001). CONCLUSION Our results showed that 13-week-old spontaneously hypertensive rats presented reduced baroreflex function when tested with phenylephrine.