Effects of Anatomy and Diet on Gastrointestinal pH in Rodents KEVIN D. KOHL 1 *, ASHLEY STENGEL 1 , MICHAL SAMUNI‐BLANK 2 , AND M. DENISE DEARING 1 1 Department of Biology, University of Utah, Salt Lake City, Utah 2 Department of Biology, Technion‐Israel Institute of Technology, Haifa, Israel The gastrointestinal tract is a chemically complex mixture of macromolecules, electrolytes, and enzymes that interact to supply nutrients to the animal. However, certain physicochemical characteristics, such as pH, can alter digestive processes, including the efficiency of digestive enzymes (Cornish‐Bowden, '95), nutrient transporters (Thwaites and Anderson, 2007), and microbial fermentation (Erfle et al., '82). Therefore, vertebrates tightly regulate the pH of their gastrointestinal tract through the secretion of HCl from the stomach, and bicarbonate from the pancreas, intestine, and cecum (Schulz, '80; Hopfer and Liedtke, '87; Canfield, '91; Stevens and Hume, '95). However, variation in gastrointestinal anatomy may alter the pH of gut regions. For example, some species have gastric glands spread through the entirety of the stomach, while others have them reduced to the distal portion (Kararli, '95). Rodents tend to follow the latter condition, yet still exhibit variation in stomach anatomy. Some rodents, such as laboratory mice, exhibit a unilocular stomach, where the stomach exists as a single chamber (Stevens and Hume, '95). Others, such as New World mice (Peromyscus spp.), woodrats (Neotoma spp.), and voles (Microtus spp.) have a bilocular stomach, where a deep invagination near the ABSTRACT The pH of the gastrointestinal tract can have profound influences on digestive processes. Rodents exhibit wide variation in both stomach morphology and dietary strategies, both of which may influence gut pH. Various rodent species have evolved bilocular (or semi‐segmented) stomachs that may allow for more microbial growth compared to unilocular (single‐chambered) stomachs. Additionally, herbivory has evolved multiple times in rodents. The high dietary fiber typical of an herbivorous diet is known to induce secretion of bicarbonate in the gut. We predicted that stomach segmentation might facilitate the separation of contents in the proximal chamber from that of the gastric stomach, facilitating a chemical environment suitable to microbial growth. To investigate the effect of stomach anatomy and diet on gut pH, several species of rodent with varying stomach morphology were fed either a high or low‐fiber diet for 7 days, and pH of the proximal stomach, gastric stomach, small intestine, and cecum were measured. We discovered that rodents with bilocular stomach anatomy maintained a larger pH gradient between the proximal and gastric stomach compartments, and were able to achieve a lower absolute gastric pH compared to those with unilocular stomachs. Dietary fiber increased the pH of the small intestine, but not in any other gut regions. The stomach pH data supports the century old hypothesis that bilocular stomach anatomy creates an environment in the proximal stomach that is suitable for microbial growth. Additionally, the alkaline small intestinal pH on a high fiber diet may enhance digestion. J. Exp. Zool. 319A:225–229, 2013. © 2013 Wiley Periodicals, Inc. How to cite this article: Kohl KD, Stengel A, Samuni‐Blank M, Dearing MD. 2013. Effects of anatomy and diet on gastrointestinal pH in rodents. J. Exp. Zool. 319A:225–229. J. Exp. Zool. 319A:225–229, 2013 Grant sponsor: National Science Foundation; grant sponsor: IOS; grant number: 0817527; grant sponsor: DEB; grant number: 1210094. Additional Supporting Information may be found in the online version of this article.  Corresponding to: Kevin D. Kohl, Department of Biology, University of Utah, 257 S. 1400 East, Salt Lake City, UT 84112. E‐mail: kevin.kohl@utah.edu Received 6 November 2012; Revised 18 January 2013; Accepted 4 February 2013 Published online 4 March 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jez.1786 RESEARCH ARTICLE © 2013 WILEY PERIODICALS, INC.