Large Intestinal pH and Ammonia in Rats: Dietary Fat and Protein Interactions

Abstract

Mature male Sprague-Dawley rats were assigned to a 3 x 3 factorial experiment in which they were fed AIN-76A diets supplying 8, 16 and 32% of energy as protein and 12, 24 and 48% of energy as fat. During the 5 mo of feeding, 10 in vivo measurements of intracolonic pH were recorded on each rat with a flexible electrode. The pH ranged from 7.8 to 8.0 near the anus and declined to 7.4 to 7.5 at 12 cm from the anus. The mean percentages of dry matter in the contents of the colon, divided into three approximately equal segments, were as follows: proximal colon, 35; middle colon, 45; distal colon, 58. Ammonia concentrations in luminal fluid rose significantly with higher protein intake in the cecum, proximal colon and distal colon. The concentrations in the distal colon ranged from 39 to 74 mmol/L, depending upon protein intake. Thymidine incorporation by distal colon mucosal cells was higher in rats fed 32% of energy as protein and 48% of energy as fat compared with rats fed 8% of energy as protein and 12% as fat. The evidence suggests that increased intestinal cell proliferation in rats fed the high protein, high fat diet was due to greater concentrations of ammonia in the large intestine resulting from the high protein intake and greater concentrations of non-ionized ammonia resulting from the higher pH associated with increased fat intake. The actual determinations and calculations of ionized to non-ionized ammonia concentrations were compatible with the assumption that the large intestinal cells absorbed more ammonia at higher fat intakes.

Segregation of Na/H exchanger-3 and Cl/HCO3exchanger SLC26A3 (DRA) in rodent cecum and colon

“…Similar results were obtained in a subset of experiments by using a miniature glass pH combination electrode with a 0.75-mm-diameter tip and internal reference (MI-415, Microelectrodes). In some experiments, the external reference electrode was anchored subcutaneously in the inguinal region with a suture, without correction for transmucosal potential differences (6 -12 mV) (30), to allow comparison to previous data obtained in the same manner (56). Electrodes were connected to a pH meter (Orion 720A) and calibrated against phosphate pH buffer standards (4.0 -10.0) or [Na ϩ ] standards (0 -100 mM in 20 mM K-acetate).…”

Ammonia inhibits cAMP-regulated intestinal Cl- transport. Asymmetric effects of apical and basolateral exposure and implications for epithelial barrier function.

“…The mammalian colon represents an interesting and important exception. Ammonia is formed in the gut lumen by bacterial action upon nitrogen-containing substances such as urea, and is a major component of colonic lumenal fluid, with concentrations in human and rat fecal dialysates reported to range between 4-70 mM depending upon dietary protein intake (7)(8)(9). Thus, the apical surface of colonocytes is normally bathed by a remarkably high concentration of ammonia.…”

Low-molecular Weight Amines Have Marked Potential to Promote Colitis in a Mouse Experimental Model: A Possible Proposal of in vivo Formation of Their Chloramines

“…22) Several studies have reported that the level of NH 3 is approximately 10 mM in rat feces 23) and that an excessive intake of dietary protein by rats also leads to a significant increase in fecal NH 3 . 23,24) Intrarectal administration of NH 2 Cl, which is prepared by the reaction of NH 3 and HOCl, into rats induced intense inflammatory responses in the large intestine, 13) although the concentration of NH 2 Cl used (3.2 mg, 250 mM/0.25 ml, 62.5 µmol/rat) was much higher than that of chloramines estimated in human phagocytes. 25) Since it has been reported that the concentration of fecal NH 3 in humans is approximately 0.2 mM (mmol/kg), 26) which is similar to that of CH 3 NH 2 in feces, 27) experiments performed using biological levels are needed to further elucidate the possible mechanism(s) of inflammatory re- sponses due to the formation of low-molecular chloramines.…”