This study was designed to determine the reflex effects of renal nerve activity during acutely altered portal venous pressure in anesthetized dogs. Following inflation of a balloon in the main portal vein of animals with the neuraxis intact, mean blood pressure (MBP) fell significantly from 127 +/- 8 mm Hg to 101 +/- 7 mm Hg, while renal nerve activity (RNA) increased to 189 +/- 11%. This significant increase in RNA during inflation of the balloon was not entirely eliminated by either carotid sinus nerve (CSN) denervation (163 +/- 9% of the control level) or vagotomy (161 +/- 11% of the control level). The reflex increase in RNA observed with the combined denervation of the carotid sinus and vagal nerves (CSN + Va denervation) was 138 +/- 2% of the control level, and this level of RNA increase was significantly smaller compared to those in the other 3 groups (intact, CSN or Va denervated). Even when the portal venous pressure below caudal to the balloon was controlled at a pre-distension level by means of opening an artificial bypass constructed between the mesenteric vein and the femoral vein in the CSN + Va denervated group, the increased RNA response during inflation of the balloon remained. After hepatic denervation in the CSN + Va denervated group with the opening of the bypass, however, inflation of a balloon caused no significant changes in RNA, even when more profound hypotension existed during inflation of the balloon.(ABSTRACT TRUNCATED AT 250 WORDS)