Abstract
Horses are often subjected to short-term feed withdrawal (FW) pre- or post-surgery to reduce anesthetic complications. However, removing nutrients from the intestinal lumen may negatively impact intestinal health. Thirteen horses were used to determine the effects of a 24 h FW on gut barrier function, active nutrient transport, transporter gene expression, and intestinal morphology. Following 0 or 24 h FW (0FW or 24FW, respectively), horses were euthanized via overdose of sodium pentobarbital and sodium phenytoin, and segments of proximal jejunum (PJ), mid jejunum (MJ), ileum (Il), and right ventral colon (RVC) were harvested for histology (PJ and Il), gene expression, and active nutrient transport analysis. Active transport measurements were determined using modified Ussing chambers following the addition of glucose, phosphorus, glutamine, and Gly-Sar. Carbachol-induced chloride (Cl) ion secretion was measured to examine the diarrhetic response. Messenger RNA expression of the intestinal Na-dependent glucose cotransporter (SGLT1), fructose transporter (GLUT5), di- and tri-peptide transporter (PepT1), and neutral AA/glutamine transporter (ASCT2) were determined using RT-PCR. The GLM procedure of SAS was used to determine the effects of FW and responses among various intestinal sections. The horse served as the experimental unit. Villus heights (P < 0.002) and crypt depths (P < 0.02) in the Il were larger than in the PJ, though no differences were observed between 0FW and 24FW horses. Active glutamine absorption increased 82% in the PJ of 24FW horses compared to 0FW horses (P < 0.02). The mRNA expression of SGLT1 decreased (P < 0.05), moving aborally in the gastrointestinal tract. Horses subjected to 24FW had 82% less GLUT5 (P < 0.05) and 61% less PepT1 mRNA expression in the PJ, compared to 0FW horses. Interestingly, ASCT2 mRNA expression increased 164% from PJ to RVC (P = 0.05). However, a 36% decrease in ASCT2 mRNA expression was observed overall for 24FW horses. These data indicate that SGLT1, GLUT5, PepT1, and ASCT2 are expressed throughout the small intestine and RVC of the horse at varying concentrations and that they can be differentially regulated by a 24 h FW. Data from this experiment also indicate that a 24 h FW results in up regulation of active glutamine absorption, presumably in an effort to supply glutamine as an energy substrate for enterocytes.