Lactulose or paromomycin do not affect ammonia generation in the isolated perfused rat small intestine

It has been hypothesized that the beneficial effect on hepatic encephalopathy of lactulose or neomycin might be exerted by their effect on intermediary glutamine metabolism and ammonia generation within enterocytes. We examined glutamine consumption and the production of alanine and ammonia (net substrate exchange in nmol min-1 g-1) in isolated vascularly and luminally perfused small intestine from rats with and without pretreatment with lactulose (2.0 g/kg) or paromomycin (60 mg/kg). Without pretreatment, 50 mM lactulose or 1 mM paromomycin were equally ineffective to significantly reduce the consumption of arterial glutamine (-92 +/- 5 vs. -80 +/- 6 vs. -71 +/- 6 for controls, lactulose, or paromomycin; mean +/- SEM, n = 6 each, n.s. by analysis of variance), and the production of alanine (41 +/- 3 vs. 44 +/- 3 vs. 61 +/- 7, n.s.) or ammonia (42 +/- 6 vs. 42 +/- 6 vs. 38 +/- 6, n.s.). Similarly, glutamine utilisation, and the release of alanine and ammonia were not different after pretreatment for 10 days. Also, both agents did not reduce glutamine absorption from the lumen (-170 +/- 9 vs. -171 +/- 6 vs. -219 +/- 25, n = 5 each) or the concomitant vascular release of metabolic products alanine (92 +/- 7 vs. 78 +/- 10 vs. 77 +/- 10 vs. 77 +/- 7, n.s.) and ammonia (73 +/- 6 vs. 69 +/- 7 vs. 65 +/- 8, n.s.). Our results do not support the hypothesis, that lactulose or paromomycin reduce ammonia generation by small intestinal mucosa through a specific effect on intermediary glutamine metabolism.