The contractile effect of short-chain fatty acids on proximal, middle and distal segments of the rat colon was studied in vitro. A single contraction of the longitudinal muscle of the everted preparation of the middle and distal but not the proximal colon was induced by mucosal application of propionate, butyrate or valerate. Sigmoid dose-responses were observed between contraction and log dose of propionate, butyrate and valerate. The threshold concentration of short-chain fatty acids was between 0.02 and 0.04 mM. A maximal contraction was induced with 0.1 mM-propionate, butyrate and valerate. While acetate (up to 10 mM) and lactate (up to 30 mM) had no contractile effect at all. Serosal application of short-chain fatty acids was without effect, while the contractile response with up to 10 mM-propionate was abolished in both the middle and distal colon by scraping away the mucosa. Cumulative addition of short-chain fatty acids to the organ bath (without wash-out of the first dose) caused adaptation of the contractile response; thus, the effect of propionate (1 mM) was abolished by prior addition of acetate (10 mM) or lactate (30 mM) or propionate (1 mM) or butyrate (1 mM) or valerate (1 mM). The contractile effect of propionate was also inhibited by atropine (1 microM), procaine (0.4 mM) and tetrodotoxin (3 microM); was unaffected by hexamethonium (0.1 mM) and enhanced by eserine (10 nM). The results suggest that short-chain fatty acids, which are normal constituents of the colon, have the ability to stimulate colonic contractions, probably via an enteric reflex involving local sensory and cholinergic nerves.