02910naa a2200229 a 450000100080000000500110000800800410001902400850006010000220014524501880016726000090035552021450036465000160250965000120252565000180253765000120255565000100256765000140257770000150259170000160260677300580262215177972026-01-15       1997    bl uuuu     u00u1 u    #d7 ahttps://doi-org.ez103.periodicos.capes.gov.br/10.1016/S0921-4488(96)00937-62DOI1 aRUBERT-ALEMAN, X.  aIsotopic enrichment kinetics of milk niteogenous fractions in goats receiving a single intravenous injection of either L-(U-14C) -leucine or L-(1-13C) -leucine.h[electronic resource]  c1997  aAbstract: Enrichment levels and kinetics of the milk nitrogenous fractions in eight goats receiving a single intravenous injection of either l-(1-13C)-LEU (500 mg/goat, 90% atom 13C) or l-(U-14C)-LEU (0.045 mg/goat, 3.6 × 106 Bq) were studied. After tracer injection, the goats were milked out at 3, 5, 7, 9, 24, 32, 48, 56 and 72 h for 13C and 14C enrichment measurements. In both experiments, a labelling peak was observed in all nitrogenous fractions [casein (CN), whey protein (WP), non protein (NP) fraction] three hours after the tracer injection, and after the peak an exponential decreasing curve was noticed. In the first experiment, the maximal 13C enrichment of CN and WP was −7.27 ± 2.23 δ%. 13C vs. PDB (Pee Dee Belemnite) and −4.63 ± 2.53 δ%. vs. PDB, respectively. In the second experiment, the radioactivity values measured at the peak were 60.3 ± 3.4 Bq/mg C in CN and 55.3 ± 9.9 Bq/mg C in WP. In spite of the difference between the LEU doses in both experiments, the labelling kinetics of CN and WP were similar. The overall recovery of the tracer in milk proteins was similar in both experiments: 9.8% vs. 11.6% for 13C and 14C, respectively. In contrast, a substantial difference in the 13C and 14C skim milk labelling kinetics was observed. The overall 13C recovery in the NP fraction averaged 8% while it was close to 1% in the 14C experiment. These observations indicate that a high dose of intravenously injected 13C-LEU may induce modifications in the mammary utilisation of free plasma LEU. The level of 14C enrichment in casein (at peak time point) was tested in monogastric animals. The radioactivity recovery in stomach contents of the rats was between 32% and 69% and in ileum contents between 0.2% and 0.4% of the ingested dose. In portal plasma, radioactivity was between 10 and 40 Bq/ml. In all animals, radioactivity in the liver was approximately 20% and total radioactivity recovered in stomach contents, ileum contents and liver was between 53% and 93%. This study shows the possible utilization of these radioactive goat milk proteins for further nutritional studies in monogastric animals.  aDairy goats  aLeucine  aMilk proteins  aCaprino  aLeite  aProteína1 aRYCHEN, G.1 aLAURENT, F.  tSmall Ruminant Researchgv. 25, n. 1, p. 23-31, 1997.