Effects of food restriction and starvation-refeeding on volatile fatty acid concentrations in the rat

Adult male rats were fed either ad libitum or at levels of 19 or 15 g of nonpurified diet per rat daily or subjected to 48 h of starvation followed by 24 h of refeeding. Concentrations of total and individual volatile fatty acids (VFA) in cecal contents were higher in rats fed ad libitum than in those restricted to 19 or 15 g/d. Only butyrate concentration was lower in rats given 15 g/d than in those given 19 g/d. In starved animals all cecal VFA declined within 24 h of food removal, but the greatest change was in butyrate, which fell to less than 12% of the initial value. Acetate and propionate fell further after 48 h, but their concentrations were restored to control values within 24 h of refeeding while butyrate remained depressed by 50%. Cecal pH was closely related to total VFA concentration, although the highest degree of correlation was with butyrate. Hepatic portal venous plasma VFA concentrations generally reflected those in cecal digesta except that the proportion of butyrate was relatively lower in this blood vessel than in cecal contents. Under all conditions acetate was the only VFA found in arterial plasma and in the fully fed state was lower than in hepatic portal venous plasma. Food restriction and starvation did not alter arterial concentrations, indicating abolition of net uptake. We conclude that all VFA are affected by availability of fermentable material to the large bowel microflora but that the disproportionate changes in butyrate may reflect preferential use of this acid by cells of the large bowel wall.