Renal Response to Isotonic Saline Infusions into Portal and Jugular Vein in Sodium-Loaded, Conscious Rats

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Abstract
Evidence for the participation of the liver in the control of Na excretion is controversial. In the present study, Sprague-Dawley rats were fed either a low Na diet or regular chow plus saline drinking for at least 1 wk. The day of the experiment, the unanesthetized, undisturbed animals received infusions of isotonic saline (2% of body wt.; 0.2 ml/min) either in a branch of the portal vein or in the jugular vein via chronically implanted catheters. There were no differences in renal Na handling between portal and systemic infusions in Na-restricted animals. Both absolute and fractional Na excretion in Na-loaded animals receiving portal infusions exceeded those of systemically infused animals at 30 and 60 min. There were no significant differences in hematocrit, serum Na or K concentration, filtered load of Na, or inulin clearances between groups of animals receiving portal and jugular infusions on either diet. The results provide evidence for a role of the liver in the control of the Na excretion.