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SUMMARY. Intestinal transcapillary water and total protein flux were determined in dogs with chronic extrahepatic portal hypertension after construction of an aortic-portal shunt combined with hilar portal vein constriction and compared to acute portal vein constriction. Measurements were made of thoracic duct lymph flow, portal venous pressure, and total protein concentration in plasma, thoracic duct lymph, intestinal and liver lymph. From these data and calculations based on the dual visceral origin of thoracic duct lymph from liver and intestine, intestinal transcapillary water flux in chronic extrahepatic portal hypertension (portal venous pressure = 21.4 ± 2 mm Hg; mean ± SEM), increased 5-fold (93 ± 12 from 17 ± 4 /il/min/kg, P < 0.001), while intestinal total protein flux expressed as protein clearance (intestinal transcapillary water flux X intestinal lymph/plasma total protein concentration) was unchanged (13 ± 3 from 10 ± 2 jil/min per kg; P > 0.4), a finding supported by unaltered whole body plasma albumin 'leak rate" (83 ± 1 6 from 80 ± 2 /il/min per kg; P > 0.9). In acute portal vein constriction (portal venous pressure = 26 ± 1 mm Hg) intestinal transcapillary water flux was similarly increased (58 ± 16 from 9 ± 2; P < 0.014) but intestinal total protein flux was increased 3-fold (16 ± 4 from 5 ± 2; P < 0.032). Calculated permeability surface area product and protein reflection coefficient (crosspoint method) increased similarly in both preparations. In accord with earlier findings in patients with hepatic cirrhosis, chronic elevation in portal pressure increased intestinal transcapillary water flux but not total protein flux. (Circ Res 53: 622-629, 1983)

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