Baroreceptor heart rate reflex in rabbits after reversal of renal hypertension.

The baroreceptor heart rate reflex was studied in 26 renal hypertensive and 17 normotensive rabbits and in 13 rabbits after reversal of hypertension. Blood pressure and heart rate were varied by bolus injections of methoxamine or nitroglycerine in conscious rabbits, and a logistic sigmoid function was fitted to the pressure-heart rate data to estimate upper and lower heart rate plateaus, median blood pressure, and reflex sensitivity. In hypertensive rabbits, resetting of the blood pressure-heart rate curves to higher pressures was associated with reduced reflex sensitivity, increased lower heart rate plateau, and operating pressures significantly greater than the region of maximum reflex sensitivity, resulting in substantial attenuation of reflex bradycardia in response to hypertension. Reflex bradycardia after smoke inhalation was normal. Reversing the hypertension completely reversed the abnormalities in baroreflex control of heart rate. Renal hypertension in the rabbit produces functional changes that are completely reversible in the baroreceptor-heart rate reflex, probably in the afferent limb.