SHORT-CHAIN FATTY-ACID AND GLUCOSE-METABOLISM IN ISOLATED PIG COLONOCYTES - MODULATION BY NH4+

Short chain fatty acids (SCFA) from bacterial origin, as well as gluco se from vascular origin, are among fuel substrates available to the co lonic mucosa. The present work investigated the possible modulation by another bacterial metabolite, i.e, ammonia, of the capacities of colo nic epithelial cells to metabolize these substrates. Viable colonocyte s were isolated from the proximal colon of 40-50 kg pigs fed a standar d diet and were incubated (30 min, 37 degrees C) in the presence of a concentration range of C-14-labeled n-butyrate or acetate, or C-14-lab eled glucose (5 mM), with or without NH4Cl (10 mM) addition. (CO2)-C-1 4 and metabolites generated were measured. Butyrate utilization result ed in a high generation of ketone bodies (acetoacetate and beta-OH-but yrate), in addition to (CO2)-C-14 production. However, the net ketone body generation was significantly decreased for butyrate concentration s higher than 10 mM. In contrast to n-butyrate, acetate when given as the sole substrate got preferentially metabolized in the oxidation pat hway. Acetate metabolism was not affected by NH4Cl, thus indicating th at the tricarboxylic acid cycle was unchanged. Conversely, (CO2)-C-14 and ketone body production from butyrate were decreased by 30% in the presence of NH4Cl, suggesting that butyrate activation or beta-oxidati on was diminished. Glucose utilization rate was increased by 20%, due to an increased glycolytic capacity in the presence of NH4Cl. A dose-d ependent stimulation of phosphofructokinase activity by NH4+ could acc ount for this effect. It is concluded that ammonia, whose physiologica l concentration is high in the colonic lumen, can modulate the metabol ism of two major substrates, n-butyrate and glucose, in colonic epithe lial cells.