Effects of Absorption of Large Amounts of Volatile Fatty Acids on Rat Liver Metabolism

Abstract

The effects of large amounts of volatile fatty acids (VFA) on hepatic metabolism have been investigated in vivo, with rats adapted to a high fiber (HF) diet, or in vitro with isolated hepatocytes. Net absorption of glucose was negligible and lactate production was lower in rats fed the HF diet than in those fed a fiber-free basal diet. VFA (particularly acetate and propionate) were absorbed in very large amounts in rats fed the HF diet. Propionate and butyrate were completely removed by the liver in both groups of rats; the efficiency of acetate uptake was higher in rats fed the HF diet than in those fed the basal diet. Gluconeogenesis was active in rats fed the HF diet, but lactate uptake was very limited in spite of high portal concentrations. Hepatocytes from rats fed the HF diet utilized VFA at different rates: acetate was poorly utilized, propionate utilization plateaued at about 1 mM external propionate, whereas butyrate utilization was utilized about twice as efficiently. Propionate and butyrate displayed opposite effects on lactate utilization. The stimulating effect of butyrate prevailed over the inhibitory effects of propionate, at high concentrations (2 mM). However, the results at lower concentrations (less than or equal to 0.5 mM) suggest that, owing to its higher portal concentrations, the effects of propionate on lactate uptake might prevail in vivo. The effects of acetate in vivo might be greater than on isolated hepatocytes.

The effect of dietary fibre fractions from different cereals and microbial enzyme supplementation on performance, ileal viscosity and short-chain fatty acid concentrations in the caeca of broiler chickens

“…In rats, SCFA concentrations in the portal vein were closely dependent on the inclusion of fermentable carbohydrates into the diet (Demigné et al, 1986). Liver size may depend on the GIT microfl ora and/or its fermentation end products.…”

Short- and medium-chain fatty acids in energy metabolism: the cellular perspective

“…Thus, it seems likely that the transport across the basolateral membrane is based on the anionic form of SCFAs against HCO 3  (57). Butyrate, as well as other SCFAs and MCFAs, that has not been utilized by enterocytes is transported by the portal vein to the liver (40,58) and metabolized by hepatocytes. In contrast to LCFAs, which are esterified to triglycerides in enterocytes, incorporated into chylomicrons, and then enter the lymphatic system, SCFAs and MCFAs from the intestinal tract enter the portal vein as free acids.…”

Colonic Acetate in the Circulating Acetate Pool of the Infant Pig

“…Acetate metabolism by the liver is variable, species-specific, and depends on numerous factors; for example, acetate uptake is low in the ruminant liver but is believed to be much greater in humans, perhaps because the human liver is capable of lipogenesis (12,32). In rats and pigs, acetate is taken up by the liver in proportion to the acetate concentration in the portal vein (12,28,33).…”