Effect of volatile fatty acids on blood flow and oxygen uptake by the dog colon

The effects of volatile fatty acids on colonic hemodynamics and oxygen uptake were examined in a denervated autoperfused dog colon preparation. While measuring arterial pressure, colonic blood flow, venous pressure, and arteriovenous O2 difference, a Tyrode's solution containing acetic (75 mM), propionic (30 mM), and butyric acids (30 mM) was placed into the colon lumen. The volatile fatty acid mixture increased colonic blood flow (23.5%) and oxygen uptake (18.4%), yet did not affect oxygen extraction. Of the three fatty acids, only acetic acid (75 mM) could mimic the effects of the entire mixture on colonic hemodynamics and oxygen uptake. Butyric (30 mM) and propionic (30 mM) acids were without appreciable effects on colonic blood flow and oxygen uptake. The vehicle for the volatile fatty acids, Tyrode's did not alter blood flow, yet increased colonic oxygen uptake (18.7%) through an increase in oxygen extraction (18.3%). When compared with Tyrode's, acetic acid increased blood flow, yet did not alter oxygen uptake, while butyric and propionic acids did not alter colonic blood flow, yet inhibited colonic oxygen uptake. Close intraarterial infusion of acetic acid increased colonic blood flow and oxygen uptake. These data suggest that physiologic concentrations of volatile fatty acids (particularly acetic acid) significantly alter colonic flow.