Influence of alpha-linked glucose on sodium-glucose cotransport activity along the small intestine in cattle

Thirteen steers (378 +/- 23 kg) were used in a split-plot experimental desi gn to evaluate the effect of small intestinal carbohydrate on sodium-glucos e cotransport in brush border membrane vesicles prepared from five equidist ant sites along the small intestine. The steers consumed 7.2 +/- 0.4 kg/d g round fescue hay and soybean meal-based supplement and were infused ruminal ly or postruminally with a partial cr-amylase starch hydrolysate (914.5 +/- 8.3 g/d) for 7 d. On d 7, five equidistant l-m small intestinal sections w ere harvested and frozen in liquid N for later preparation of brush-border membrane vesicles. Maltase activity of the homogenate and vesicle preparati ons changed (P < 0.001; lowest in the duodenum, highest in the jejunum) and alkaline phosphatase decreased (P < 0.001) along the small intestine. With respect to the original homogenates, the vesicle preparations were enriche d 9.80 +/- 0.83- and 7.64 + 0.67-fold for alkaline phosphatase and maltase, respectively; enrichments were not different between treatments (P = 0.76 and 0.39, respectively). However, alkaline phosphatase and maltase enrichme nt changed (P < 0.001) along the small intestine. Recoveries of alkaline ph osphatase and maltase activities (25.0 <plus/minus> 0.2% and 19.5 +/- 0.2%, respectively) in the vesicle preparation were not affected (P = 0.29 and 0 .21, respectively) by treatment but changed (P < 0.001) along the intestine . Recovery of protein in the vesicle preparation was 2.60 <plus/minus> 0.01 % and was not affected by treatment or intestinal site. Sodium-glucose cotr ansport activity (220 +/- 44 pmol(.)mg(-1.)s(-1)) was not affected (P = 0.3 4) by treatment but did change (P < 0.001; lowest in the ileum, highest in the proximal and mid-jejunum) along the small intestine. Apparent K-m of th e sodium-glucose cotransporter for glucose was 62.8 +/- 5.8 muM. The specif ic activity of maltase was highest in the jejunum, and sodium-glucose cotra nsport was highest in the first two jejunal sites. However, duodenal maltas e activity was lowest and ileal sodium-glucose cotransport activity was low est. Sodium-glucose cotransport activity may limit small intestinal starch assimilation in the distal small intestine. It does not seem that glucose a rising from carbohydrate hydrolysis regulates activity of sodium-dependent glucose transport in cattle.