THE BARORECEPTOR-HEART RATE REFLEX IN RENAL HYPERTENSION IN THE RABBIT

SUMMARY 1. The 'steady-state' properties of the baroreceptor-heart rate reflex were studied in twenty-one renal hypertensive and twenty-eight normotensive unanaesthetized rabbits. In each animal, intravascular pressures were varied by inflating balloons previously placed around the aorta and inferior vena cava. An average curve relating mean arterial pressure (MAP) to heart period (HP; pulse interval) was constructed for each group.
2. The average resting MAP was 134 mmHg (s. e. m. = 5.7) in hypertensive and 91 mmHg (s. e. m. = 4.0) in normotensive rabbits. The mean values for resting HP in the two groups were 254 ms (s. e. m. = 13.4) and 258 ms (s. e. m. = 3.2), respectively. The baroreflex-dependent heart period range (HPR) between the lower and upper plateau levels of the MAP-HP curve of hypertensive rabbits was about 80% of the normotensive value. The average gain (change in HP per unit change in MAP) in hypertensives was about 50% of the normotensive value. The threshold pressure for evoking an increase in HP during a rise in MAP, and the median blood pressure (i. e. MAP corresponding to half HPR), were both about 40 mmHg higher in the hypertensive group than in normotensive rabbits.
3. The parameter changes in the MAP-HP curve in renal hypertension are closely similar to those previously observed in patients with essential hypertension of the same severity. The baroreflex changes in essential hypertension are thus probably non-specific accompaniments of chronic blood pressure elevation.