SITE AND SUBSTRATES FOR METHANE PRODUCTION IN HUMAN COLON

On two occasions separated by seven days, 22 g mucin (hog gastric mucin) was infused into right and left colon of 12 healthy volunteers (6 CH4 producers and 6 non-producers) maintained on a controlled diet. In the six CH4 producers, excess volumes of H-2 excreted in breath were 73.4 +/- 11.9 and 35.1 +/- 14.1 (SE) ml/8 h (P < 0.05) in response to right and left colonic infusion of mucin, respectively; excess volumes of CH4 were, respectively, 6.7 +/- 1.7 and 38.9 +/- 11.1 ml/8 h (P < 0.05). In the six CH4 nonproducers, excess volumes of H-2 excreted in breath were 76.6 +/- 17.6 and 30.8 +/- 6.3 ml/8 h (P < 0.02) in response to right and left colonic infusion of mucin, respectively; excess volumes of CH4 were, respectively, 0.0 +/- 0.0 and 0.1 +/- 0.1 ml/8 h (not significant). In a further experiment, 17 healthy volunteers (10 CH4 producers and 7 nonproducers) were given on 2 consecutive days an oral load and an enema of 10 g lactulose. In the 10 CH4 producers, excess volumes of H-2 excreted in breath were 74.6 +/- 15.1 and 32.3 +/- 11.5 ml/6 h (P < 0.001) in response to oral ingestion and lactulose enema, respectively; excess volumes of CH4 were, respectively, 7.7 +/- 3.0 and 38.2 +/- 7.2 ml/6 h (P < 0.001). In the seven CH4 nonproducers, excess volumes of H-2 excreted in breath were 94.0 +/- 21.8 and 43.0 +/- 16.4 ml/6 h (P < 0.01) in response to oral ingestion and lactulose enema, respectively; excess volumes of CH4 were, respectively, 0.0 +/- 0.0 and 2.1 +/- 1.2 ml/6 h (not significant). These results show that 1) H-2 production occurs in both right and left colon, whereas CH4 production occurs in CH4 producers mainly in distal large intestine; 2) both exogenous and endogenous substrates promote CH4 production, but in usual dietary situations the latter might provide the bulk of the fuel for methanogenesis.