Splanchnic clearance of plasma vasopressin in the dog: evidence for prehepatic extraction

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Abstract
It is generally considered that the liver is primarily responsible for the extraction of vasopressin from the circulating blood by the splanchnic viscera. To investigate this matter further, measurements were made in the anesthetized dog of the concentrations of vasopressin in arterial, portal venous and hepatic venous plasma and of total splanchnic plasma flow and hepatic arterial plasma flow. The total splanchnic vasopressin extraction ratio was 12.9 .+-. 1.0%. The concentration of vasopressin in portal venous plasma was consistently lower than in arterial plasma, and there was a substantial prehepatic extraction of vasopressin, averaging 10.5 .+-. 0.8%. A quantitative evaluation of the contribution of the prehepatic viscera, i.e., viscera with venous drainage into the portal vein, is provided by the relevant clearances of vasopressin. The prehepatic and total splanchnic vasopressin clearances were 1.58 .+-. 0.20 and 3.04 .+-. 0.31 ml .cntdot. min-1 .cntdot. kg-1, respectively. The splanchnic viscera other than the liver were responsible for .apprx. 1/2 of the splanchnic clearance of vasopressin; the remainder could be attributed to the liver. Immunoreactive vasopressin was not found in the bile. In splenectomized dogs, in which venous blood was collected from the superior mesenteric vein, the vasopressin extraction ratio was 14.6 .+-. 2.3%, suggesting that the prehepatic clearance of vasopressin occurs largely in the mesenteric bed. A more specific localization of the prehepatic clearance sites has not as yet been made.