Effect of lactate and H+ on structure and function of rat intestine.

Segments of rat ileum and colon were infused in vivo to test if 0.1 M lactate, 10(-4) M H+, or both altered mucosal structure and function. In the first series of experiments, lactate concentration was kept at 0.1 M while H+ was varied from 10(-4) to 10(-7) M. Lactate and 10(-4) M H+ in the colon, and lactate and 10(-5) M H+ in the ileum depressed net water transport and caused sloughing of superficial absorptive cells. In the second series of experiments, H+ concentration was kept at 10(-4) by using carboxymethylcellulose, rather than organic acids, to buffer the infusion mixture; the concentration of lactate was varied from 0 to 0.1 M. Mucosa remained normal after infusions of 10(-4) M H+ alone. Addition to the 10(-4) M H+ infusion of 0.1 M lactate in the colon or 0.075 M lactate in the ileum caused increased mucosal sloughing. Thus lactate plus H+ (or unionized lactic acid) alters colonic and ileal mucosa. Because such high concentrations of lactate and H+ are found in subjects malabsorbing carbohydrates, the present experiments support the contention that H+ and organic acids are etiological factors in some cases of chronic fermentative diarrhea.