Effects of ammonia load on glucose metabolism by isolated ovine duodenal mucosa

To determine the effects of ammonia load on glucose metabolism in ruminant small intestinal tissues, duodenal mucosal cells (DMC) were isolated from growing female sheep (n = 10; 46. 0 ± 0. 8 kg of BW) fed diets differing in CP content: high (19. 4%) vs. low (13. 1%). Ammonia concentration in the duodenal digesta fluid was greater for sheep fed a high CP diet compared with those fed a low CP diet (16. 4 ± 1. 0 vs. 9. 1 ± 1. 8 mM). The isolated primary mucosal cells were incubated for 90 min with [2-¹³C] glucose (3 mM) and ammonium chloride (0, 0. 1, 1, 5, 10, 20, or 50 mM) in Krebs-Ringer HEPES buffer. It was hypothesized that DMC would increase glucose carbon utilization for the synthesis of nonessential AA when the ammonia concentration in the incubation media increased. However, utilization of glucose carbon for alanine synthesis decreased linearly (P = 0. 03) as the ammonia concentration in the incubation media increased. Furthermore, glucose disappearance and utilization of glucose carbon for aspartate synthesis were not affected (P > 0. 47) by the ammonia concentration. Contrarily, in vitro glucose disappearance was greater (P = 0. 03) for DMC isolated from sheep fed a low CP diet vs. a high CP diet [14. 6 ± 1. 6 vs. 8. 6 ± 1. 3 nmol·(10⁶ cells)⁻¹·(90 min) ⁻¹], and hexokinase activity was greater (P = 0. 01) in the mucosa of sheep fed a low CP diet compared with a high CP diet (1. 22 ± 0. 05 vs. 1. 04 ± 0. 02 mUnit/mg of protein). These observations indicate that ammonia load does not affect the extent of glucose utilization by DMC, and that glucose carbon may not play a significant role for the synthesis of alanine, aspartate, or glutamate when DMC are exposed to increased concentrations of ammonia.