Reflex renal vasoconstriction on portal vein distension.

The present experiments were designed to study effects of neural control mechanisms on renal sympathetic nerve activity during acute portal vein distension in anesthetized dogs. Following the inflation of a balloon placed into the main portal vein of animals with the neuraxis intact (intact group), portal vein pressure at a site of the splanchnic regions increased significantly. Mean blood pressure (MBP) fell significantly and then renal vascular resistance (RVR) increased significantly in parallel with changes in portal venous pressure. In animals with sinoaortic denervation (SAD group), changes in portal venous pressure during the inflation of a balloon did not differ from the intact group. However, decreases in MBP in the SAD group were greater than that in the intact group, and sinoaortic denervation did not alter increases in RVR. In animals with both sinoaortic denervation and cervical vagotomy (vagotomy group), portal vein distension produced more profound hypotension, and significant increases in RVR occurred. This increase in RVR, however, was abolished by renal nerve denervation. The results of the present study indicate that increases in RVR during the portal vein distension, which is associated with systemic hypotension, may be mediated by an activation of efferent sympathetic renal nerves and modified by at least two neural reflex mechanisms such as carotid sinus baroreceptors and cardiopulmonary baroreceptors. In addition, local reflex systems such as stretch receptors in the venous wall of the portal vein may be involved in excitatory response to renal sympathetic nerve, leading to renal vasoconstriction, during the portal vein distension.