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

¹ Department of Agricultural Food and Nutritional Science, University of Alberta, Edmonton, Canada, T6G 2P5

^* To whom correspondence should be addressed. E-mail: masahito.oba{at}ualberta.ca.

	Abstract

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 BW) fed diets differing in CP content; high (19.4%) vs. low (13.1%). Ammonia concentration in the duodenal digesta fluid was higher for sheep fed a high CP diet compared to 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 non-essential 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 to a high CP diet (1.22 ± 0.05 vs. 1.04 ± 0.02 mUnit/mg 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

Key Words: ovine, duodenal mucosal cells, ammonia, glucose, non-essential amino acids