[The passage, absorption and secretion of nitrogen during the postprandial period using 15N-labeled wheat and marker in growing rats].

After a 9 day preparation period 42 Wistar rats (live weight 100 g) were fed a diet of 15N labelled wheat supplemented with the marker TiO2 (impulse labelling). At 7 time intervals (0.5 to 6 h after feeding) 6 animals were killed and thereafter total N, 15N and TiO2 levels were estimated in the digesta of different intestinal sections. The following results were obtained: The transit rate of the marker amounted to 10.3 +/- 0.62% per hour of the intake. The endogenous part of N increased during passage from stomach (3.5%) to duodenum (38.6%), jejunum (59.1%), ileum (64.8%), large intestine (78.3%) and faeces (87.7%). The apparent N digestibility in the stomach increased with time reaching 26% 6 h after feeding. In the whole small intestine it was 66.3%, in the ileum 78.9% and in the large intestine 90.4%. The true digestibility (6 h after feeding) showed the same course, but was always some units higher (stomach 33.3%, whole small intestine 82.5%, ileum 92.2% and large intestine 93.5%). Apparent and true digestibility values in the ileum correspond best to the data of precaecal digestibility; those of the large intestine correspond to the postileal digestibility. The N disappearance rate in the stomach is the sum of absorption rate (16%/h) and transit rate into the small intestine (12.4 +/- 1.6 mg N/h). Most absorption occurred during passage through the small intestine (2/3 of total absorption). The absorption in the small intestine was about 80% of the N amount flowing from the stomach into the intestine. The amount lay between 18.2 and 26.1 mg N/h and half of this was of endogenous origin. The reabsorption rate of endogenous N for the whole intestinal tract was estimated to be 91.4%. The N secretion into the whole intestine increased during the 6 h after feeding up to 85.5 mg (64% of N intake), for which 77 +/- 5.5% was secreted into the small intestine. Secretion into the stomach was relatively small and up to 4 hours after feeding, amounted only to 3.0 ... 6.7 mg N.