Characterization of urea transport mechanisms in the intestinal tract of growing pigs

Abstract

Pigs are capable of nitrogen salvage via urea recycling, which involves the movement of urea in the gastrointestinal tract. Aquaporins (AQP) and urea transporter B (UT-B) are involved in urea recycling in ruminants; however, their contribution to urea flux in the intestinal tract of the pig is not known. The objective of this study was to characterize the presence and relative contribution of known urea transporters to urea flux in the growing pig. Intestinal tissue samples (duodenum, jejunum, ileum, cecum, and colon) were obtained from nine barrows (50.8 ± 0.9 kg) and analyzed for mRNA abundance of UT-B and AQP-3, -7, and -10. Immediately after tissue collection, samples from the jejunum and cecum were placed in Ussing chambers for analysis of the serosal-to-mucosal urea flux ( Jsm-urea) with no inhibition or when incubated in the presence of phloretin to inhibit UT-B-mediated transport, NiCl2 to inhibit AQP-mediated transport, or both inhibitors. UT-B expression was greatest ( P < 0.05) in the cecum, whereas AQP-3, -7, and -10 expression was greatest ( P < 0.05) in the jejunum. The Jsm-urea was greater in the cecum than the jejunum (67.8 . 42.7 ± 5.01 µmol·cm−2·h−1; P < 0.05), confirming the capacity for urea recycling in the gut in pigs; however, flux rate was not influenced ( P > 0.05) by urea transporter inhibitors. The results of this study suggest that, although known urea transporters are expressed in the gastrointestinal tract of pigs, they may not play a significant functional role in transepithelial urea transport. NEW & NOTEWORTHY We characterized the location and contribution of known urea transporters to urea flux in the pig. Aquaporins are located throughout the intestinal tract, and urea transporter B is expressed only in the cecum. Urea flux occurred in both the jejunum and cecum. Transporter inhibitors had no affect on urea flux, suggesting that their contribution to urea transport in the intestinal tract is limited. Further work is required to determine which factors contribute to urea flux in swine.

Protein Level and Infantile Diarrhea in a Postweaning Piglet Model

“…Generally speaking, the water transport through the epithelium across the small intestine is regulated by all these AQPs. However, under stress and bacterial infection (e.g., Fusobacterium) conditions, AQP1, AQP3, AQP8, and AQP10 are mainly responsible for the maintaining of water homeostasis in the gastrointestinal tract [48]. Also, under a high protein level diet, AQP1, AQP3, AQP8, and AQP10 in the ileum were downregulated, thus interrupting the intestinal permeability during diarrhea.…”

Aquaporin: targets for dietary nutrients to regulate intestinal health

“…AQP8 is expressed on the apex of the human colonic villi and crypt epithelial cells. AQP3, AQP7 and AQP10 were found in pig jejunum (Crone et al, 2019). AQP10 staining was seen in epithelial cells on the luminal villus side (Ansar et al, 2013).…”

Ammonia volatilization from manure mixed with biochar

“…the negligible fraction of the total urea produced in these ruminants and mongastric animals (Getahun, et al, 2019;Krone et al, 2019). Poultry that ingest biochar might have lower NH 3 volatilization from their manure, based on the fact that urine and feces are combined in the digestive tract before they are excreted together through the cloaca, but inconsistent results were reported after feeding biochar to broilers and laying hens (Kalus et al, 2020;Parasai et al, 2018).…”