Effects of vascular or luminal administration and of simultaneous glucose availability on glutamine utilization by isolated rat small intestine

This study examined whether the route of glutamine administration and the s imultaneous availability of glucose affect intestinal glutamine metabolism. We measured net substrate exchange rates of glutamine and its nitrogenous products in the isolated vascularly and luminally perfused rat small intest ine (a) as a function of glutamine provision from either the vascular or th e luminal or simultaneously from both sides and (b) as a function of simult aneous availability of glucose from various routes. When glutamine was prov ided from the lumen, only 19-32% of absorbed glutamine appeared intact in t he venous effluent, but the release of metabolic products was 170 +/- 5 nmo l N min(-1) g(-1). This measure of intestinal glutamine metabolism was unch anged when glutamine was available only in the vascular perfusate (164 +/- 6 nmol N min(-1) g(-1)). It increased, however, to 271 +/- 14 nmol N min(-1 ) g(-1) (P < 0.001) when glutamine was available simultaneously from both t he luminal and the vascular perfusate. Glutamine consumption (-110 +/- 6 vs . -70 +/- 5 or -91 +/- 5 vs. -73 +/- 7 nmol min(-1) g(-1); P < 0.05 each) a nd the production of citrulline (11.4 +/- 0.7 vs. 10.0 +/- 0.8 or 9.8 +/- 0 .5 vs. 7.8 +/- 0.4 nmol min(-1) g(-1); P < 0.05 each) or ammonia (124 +/- 7 vs. 88 +/- 4; P < 0.01 or 78 +/- 4 vs. 68 +/- 5 nmol min(-1) g(-1)) decrea sed when glucose (vascular or luminal perfusate) became available in additi on to glutamine. We conclude that glutamine is utilized by the small intest ine very efficiently regardless of the route of administration being entera l or parenteral. The two routes can be used interchangeably to provide the intestinal mucosa with glutamine. Glucose and glutamine may partially subst itute each other, most likely for the purpose as a metabolic fuel.