Baroreflex sensitivity and pressor responses in a rat model of uraemia.

Baroreflex sensitivity and pressor responsiveness to exogenous noradrenaline, angiotensin II and arginine vasopressin were determined in a rat model of uraemia. The slope of the regression line relating delta heart rate to delta blood pressure after phenylephrine administration was significantly less in the renal failure group than the normal control group, indicating a reduction of baroreflex sensitivity in the setting of uraemia. The pressor response to noradrenaline and angiotensin II was significantly less in the renal failure group whereas there was no difference in delta blood pressure on administration of arginine vasopressin. It is concluded that diminished baroreflex sensitivity does not contribute to the pathogenesis of hypertension in uraemia by the hypothesized mechanism of allowing the pressor effect of endogenous pressor substances to go unbuffered.