Fate of soluble carbohydrate in the colon of rats and man.

Abstract

A B S T R A CT The fate of glucose in the colon of rats and man was investigated by measuring breath '4CO0 and fecal '4C after direct instillation of '4C-labeled glucose, acetate, and lactate into the cecum. For the 6 h after administration of as much as 400 mg of [U-14C]-glucose to the rat and 12.5 g to man, 1CO2 excretion was as rapid after intracecal as after intragastric instillation. Less than 20% of 14C instilled into the cecum as glucose was recovered in feces and only about 15% of this fecal "4C was in a dialyzable form. The conversion of intracecally administered glucose to C02 was dependent upon the presence of the colonic flora, as evidenced by the minimal excretion of "CO2 after administration of ['4C]glucose to germ-free rats. In contrast, acetate and lactate, fermentation products of glucose, were converted to C02 as rapidly in germ-free rats as in their conventional counterparts. Measurement of 02 availability in the colonic lumen indicated that insufficient 02 was available for the aerobic metabolism of glucose by the colonic bacteria. These experiments suggest that the colon bacteria anaerobically metabolize most of the glucose to short-chain fatty acids, which are absorbed and oxidized by the host. Most of the remaining fecal glucose is converted to a larger molecular form that has limited osmotic activity. Thus, the colonic flora benefits the host by reducing the osmotic load of nonabsorbed carbohydrate and by making possible the salvage of a large percentage of the calories of carbohydrate, which is not absorbed in the small bowel.

Effects of Butyrate on Intestinal Barrier Function in a Caco-2 Cell Monolayer Model of Intestinal Barrier

“…TER of Caco-2 monolayers treated with media alone showed a spontaneous increase with time and reached a maximum of 200 Ϯ 21 ⍀ · cm 2 by 72 h. Butyrate at 2 mM stimulated a significant increase of TER in Caco-2 cell monolayers after 24-h of butyrate treatment (p Ͻ 0.01, compared with the untreated cells). The TER continued to increase for an additional 24 h and remained constant from 48 h to 96 h with an average of 297 Ϯ 28 ⍀ · cm 2 . In monolayers treated with a high concentration (8 mM) of butyrate, no significant change in resistance was observed during first 24 h compared with the control cells.…”

“…SCFA, mainly acetic acid, butyric acid, and propionic acid, are the products of the bacterial fermentation of undigested carbohydrates and proteins in the intestine. SCFA are normally absorbed by the colonocyte and are either locally used as fuel for the colonic mucosal epithelial cells or enter the portal bloodstream (2,3). Production of SCFA in the bowel is important for normal intestinal biology such as water and salt absorption in the colon and energy salvation, and may also play important role in the maintenance of the intestinal barrier (4,5).…”

Toxins, Butyric Acid, and Other Short-Chain Fatty Acids Are Coordinately Expressed and Down-Regulated by Cysteine in Clostridium difficile

“…Our finding that the addition of butanol suppressed toxin production was intriguing and further indicates that toxin and butyric acid and butanol production share the same regulatory control. The large intestine is a milieu essentially lacking free glucose (2), and the availability of amino acids is likely to be crucial to the growth of C. difficile and other bacteria in vivo. In continuous cultures containing human feces, significant competition for amino acids between C. difficile and other microorganisms of the biota was shown (26).…”

Carbohydrate fermentation in the human colon and its relation to acetate concentrations in venous blood.

“…The gases methane, hydrogen, and carbon dioxide are also produced. Hydrogen and methane are not formed by human tissues and their excretion both in breath and per rectum has been used to monitor colonic carbohydrate metabolism in man (13)(14)(15). Fermentation is also the way in which the microflora of the large intestine obtain energy for maintenance of cellular function and growth (16,17).…”