Effects of wide variations in portal pressure on mesenteric blood flow and absorption from the canine colon.

Splanchnic blood flow was studied over a wide range of portal pressures in five dogs. An inverse linear relationship between flow and pressure was found in the range from 6 to 42 mmHg. The colonic absorption of ammonia, water, sodium, potassium, bicarbonate, and chloride was measured in four dogs over a similar range of portal pressures. Absorption of ammonia, water, sodium, and chloride was significantly reduced by increasing portal pressure, and this reduction was abolished when portal pressure was allowed to return to the basal level. It is suggested that splanchnic decompression by portasystemic shunt gives rise to increased mesenteric flow and increased colonic ammonia absorption, which may contribute to portasystemic encephalopathy.