Portal and peripheral blood short chain fatty acid concentrations after caecal lactulose instillation at surgery.

The major end products of fermentation, short chain fatty acids (acetate, propionate, butyrate) were measured in portal and peripheral venous blood after the caecal instillation of lactulose at surgery in patients undergoing elective cholecystectomy. Blood samples for short chain fatty acid measurement were taken before and at 15 minute intervals up to 60 minutes after caecal instillation of either 20 ml sterile saline or 6.7 g or 10 g lactulose. Fasting concentrations (n = 28) were (mumol/l, mean (SD)); portal acetate 128.0 (70.8), propionate 34.4 (23.3), butyrate 17.6 (18.4); peripheral acetate 67.0 (23.0), propionate 3.7 (1.2), butyrate traces only. After lactulose there was a rapid rise in portal short chain fatty acids with peak concentrations being reached in 15 to 45 minutes. Mean peak concentrations (mumol/l (SD)) after 10 g lactulose were acetate 240.9 (142.2), propionate 39.0 (17.8) and butyrate 26.9 (17.6). The changes in acetate concentrations seen in portal blood were reflected in peripheral blood acetate measurements. In contrast with portal blood, only small amounts of propionate and traces of butyrate were found in peripheral blood.