Destruction of the nucleus tractus solitarii in the dog: comparison with sinoaortic denervation

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Abstract
In anesthetized dogs, the acute hemodynamic effects of bilateral lesions of the nucleus tractus soltarii (NTS) are similar to those seen after sinoarotic denervation. Bilateral lesions of NTS abolished the baroreceptor reflexes and induced a marked increase in blood pressure and heart rate without any change in cardiac output. Left ventricular end-diastolic pressure was elevated and (dP/dt)max [maximum change in pressure/time] was increased. These hemodynamic efffects resulted from increased sympathetic tone because blood pressure and heart rate were decreased by the central sympathetic depressants, clonidine (10 .mu.g/kg i.v.) and fentanyl (20 .mu.g/kg i.v.) and by ganglionic or .alpha.- and .beta.-adrenergic blockade. The hypotension and the bradycardia induced by injection of veratridine into the left ventricle or by injection of capsaicin into the right ventricle were abolished by destruction of the NTS. The bradycardia induced by i.v. administered ouabain was also abolished. Destruction of NTS interrupts cardiopulmonary and baroreceptor reflexes. In conscious dogs, destruction of NTS induced an immediate and sustained hypertension and tachycardia. Sinoarortic denervation in conscious dogs induced a gradual increase in blood pressure, and after 3 mo. all the dogs exhibited a very marked hypertension. The chronic hypertension and tachycardia seen in NTS-lesioned dogs and in sinoaortic-denervated dogs resulted from a sustained increase in sympathetic tone.