[Inhibition of renal sympathetic efferent activities induced by stimulation of the paraventricular nucleus of the hypothalamus(PVH) in rabbits].

Experiments were performed on rabbits anesthetized with chloralose-urethane mixture, paralyzed with gallamine triethiodide, and ventilated artificially. Bilateral vagi, aortic and carotid sinus nerves were severed. Renal sympathetic efferent discharge (RSED) and its histogram were recorded, while the blood pressure (BP) of the femoral artery was monitored. When PVH was strongly stimulated, a transient increase of RSED was observed, which was followed by an inhibition of RSED. The inhibition of RSED was divided into two phases: the initial inhibitory phase without change in BP and the late inhibitory phase with an increase of BP. It was found that both the duration of total inhibition and the late, but not initial, inhibitory phase were positively correlated with the alterations of BP. When PVH was weakly stimulated, no change in BP was observed, but the inhibition of RSED still appeared. The inhibition duration was shortened remarkably following cutting of baroreceptor nerves. In some experiments, the RSED inhibition was not accompanied by a definite excitatory response. The present results indicate that 1) an inhibitory mechanism of PVH-renal sympathetic efferent system is present in the central nervous system; 2) the initial inhibitory phase of RSED originates from central mechanisms, while the late inhibitory phase is associated with the baroreceptor reflex and a direct action of the central nervous system; 3) the inhibition of RSED seems not to be a post-excitation depression, but an active inhibition exerted by the PVH on the spinal sympathetic preganglionic neurons.