Partition and absorption of valatile fatty acids in the alimentary canal of the rat.

The partition and absorption of volatile fatty acids (VFA) have been studied in the rat using a non purified diet comprising mainly a mixture of cereals and soya-bean meal. 2. The concentration of acetic and lactic acid was compared in non secretory (cul-de-sac) and secretory regions of the stomach. The greatest concentrations of both acids were found in the cul-de-sac region where the pH was highest (pH 5.0). 3. Concentration and absorption of VFA were negligible in the small intestine. 4. High VFA concentrations were found in the caecal contents, while lactic acid concentrations were lower. The volume and concentrations of the caecum contents varied little during the day and decreased rapidly during the first 24 h of fasting. 5. The concentrations of VFA, particularly that of butyric acid, were lower in the proximal colon than in the caecum. Caecumectomy caused a considerable decrease in VFA concentrations in the colon. 6. Arteriovenous differences in VFA and detone bodies were studied for the caecal and colon veins in rats. A close parallel between VFA concentration in the caecal contents and the arteriovenous differences was observed. In rat, ketogenesis was weak in the caecal wall (12 p. 100 of butyric acid absorption) and negligible in the colon wall. VFA are absorbed entirely in ionized form when caecal PH attains 7.5 in fasted rats. Special mechanism for caecal absorption should therefore be considered, perhaps linked with the large sodium transport in the caecum. 7. The relatively high VFA concentrations measured in the portal vein suggested that they are important in the digestive processes.