K Krawielitzki’s research while affiliated with University of Rostock and other places

Protein turnover, efficiency of growth and body composition were investigated in N balance experiments with growing male mice (26‐36 days of age) which were long‐time selected for high carcass protein amount (DU‐6P) or for high body weight (DU‐6) and in the unselected randomly bred control (DU‐Ks). In total 12 mice per line were housed singly in metabolic cages and had free access to a commercial stock diet (crude protein 267 g, gross energy 19 MJ/kg dry matter). N balance, whole body protein synthesis (PS, end‐product method, single dose of ¹⁵ N‐labelled amino‐acid mixture), fractional myofibrillar muscle breakdown rate (FBR, 3‐methylhistidine method) and N distribution in the body were measured. Additionally, the maintenance nitrogen requirement (MNR) and the maximum possible rate of N accretion (MNA) of the different lines was estimated after feeding semi‐synthetic diets with increasing protein levels. Body weight of both selection lines was about twice that of the control mice at the same age. The DU‐6P mice synthesized and deposited more protein and less fat per unit metabolic BW, than the DU‐6 mice did. However, scaled to the corresponding body protein pools, the rates of protein synthesis were not significantly different between both selection lines in contrast to the deposition rate. Selection for high body weight resulted in higher body fat content, higher muscle FBR and a lower proportion of carcass N compared to DU‐6P mice. The protein synthesis (13‐14 g protein/kg BW 0.75 per day) and MNR values (290‐305 mg N/kg BW 0.75 per day) of the selected mice were higher than those of control mice (11 g protein and 265 mg N/kg BW 0.75 , respectively) and may be due to selection‐linked enlargments of visceral organs. The MNA of DU‐6P and DU‐6 mice amounted to 6 and 5 g protein/kg BW 0.75 , respectively, and the MNA of the controls was between these values. Compared to DU‐6, the higher protein accretion rate of DU‐6P mice seems to be due more to a lower muscle protein breakdown rate than an increased protein synthesis rate. Zusammenfassung Proteinumsatz von Mäusen, die auf hohen Körperproteingehalt oder auf hohes Körpergewicht selektiert wurden An je 12 wachsenden männlichen Mäusen, die über 80 Generationen am 42. Lebenstag entweder auf hohen Proteingehalt im Schlachtkörper (DU‐6P) oder auf hohe Lebendmasse (DU‐6) selektiert worden waren, wurden Proteinstoffwechsel, Wachstumseffizienz und Körperzusammensetzung im Vergleich zur unselektierten Kontrollinie (DU‐Ks) untersucht. Die Tiere wurden einzeln in Stoffwechselkäfigen bei freiem Zugang zu Wasser und Altromin‐Zuchtfutter (Rohprotein 267 g/kg TS, Bruttoenergie 19 MJ/kg TS) gehalten. Neben der N‐Bilanz wurden Gesamtkörper‐Proteinsynthese (PS, Endproduktmethode, einmalige Gabe einer ¹⁵ N‐Aminosäurenmischung, Auswertung mittels Kompart‐mentmodell), fraktionelle Muskelprotein‐Abbaurate (FBR, 3‐Methylhistidin‐Methode), Verteilung des Körperstickstoffs, N‐Erhaltungsbedarf (MNR, regressiv nach Fütterung semi‐synthetischer Rationen mit steigenden Proteinniveaus) sowie maximales N‐Ansatzvermögen (MNA) der Mauslinien gemessen. Die mittleren Lebendmassen (LM) der selektierten Tiere waren bei gleichem Alter etwa doppelt so hoch wie die der unselektierten Kontrolle. Pro kg metabolischer LM synthetisierten und deponierten DU‐6P‐Mäuse täglich mehr Protein als DU‐6‐Mäuse. Bei Bezug auf die entsprechenden Körperprotein‐gehalte waren die Unterschiede in den täglichen Proteinsyntheseraten beider Selektionslinien im Gegensatz zur Proteinansatzrate nicht mehr signifikant. Die Selektion auf hohe LM (DU‐6) führte zu höheren Körper‐Fettgehalten, zu höheren FBR und damit zu niedrigeren Körper‐N‐Gehalten im Vergleich zur Selektion auf hohen Proteingehalt (DU‐6P). Proteinsynthese (13–14 g Protein/kg LM 0.75 .d) und MNR (290–305 mg N/kg LM 0.75 .d) der selektierten Mäuse waren höher als die der Kontrolltiere (11 g Protein bzw. 265 mg N/kg LM 0.75 .d) und können mit den selektionsbedingten Vergrößerungen der relativen Organgewichte zusammenhängen. Die MNA‐Werte lagen zwischen 5 (DU‐6) und 6 g (DU‐6P) Protein/kg LM 0.75 .d. Der im Vergleich zur Linie DU‐6 höhere Proteinansatz der DU‐6P‐Tiere scheint mehr durch eine verminderte Muskelprotein‐Abbaurate als durch eine höhere Proteinsyntheserate bedingt zu sein.

In an experiment with 3 pigs (initial live weight 30 kg, each fitted with 2 re-entrant fistulas in duodenum and ileum, one labelled with 15N), the duodenal and ileum digesta was exchanged. The N and 15N contents were estimated in faeces, urine, duodenal and ileum digesta of all experimental animals as well as in special organs and in the contents of different tract sections. The 15N excess (15N') of N compounds secreted into the gut lumen was determined using the 15N' in pancreas, gut mucosa and TCA-soluble blood serum. From measuring the digesta passage through the 3 sections of the digestive tract: 1. mouth ... duodenum, 2. duodenum ... ileum, 3. ileum ... after (Krawielitzki et al., 1989) the absorption and secretion rates of nitrogen were calculated. Secretion into the 1st section amounted to 5.3 g N/d (= 15% of intake) and the absorption to approximately 1% of intake. In the 2nd section the corresponding dates were 8.9 resp. 38.6 g N/d (= 25 resp. 110% of N intake), and in the 3rd one 1.9 resp. 8.4 g N/d (= 5.6 resp. 24% of N intake). Total absorption amounted to 134% of N intake and the over all re-absorption of endogenous N compounds secreted into the gut lumen to about 90%. During the passage the amount of endogenous N (g/d) decreased from 5.3 at the duodenum to 3.8 at the ileum to 1.6 in the faeces, but the relative portion increased (13 resp. 35 resp. 39%). An incorporation into body proteins occurred only from N compounds absorbed in the 1st and in the 2nd section. N (or 15N) absorbed in the large intestine was almost quantitatively excreted by urine. The method of digesta exchange between cannulated labelled and unlabelled pigs seems to be a suitable method to estimate absorption and secretion of exogenous and endogenous N portions in various sections of the digestive tract.

An experiment was carried out using pigs weighing approximately 30 kg. The animals were fitted with two re-entrant cannulas in duodenum and ileum. During a 5 day period the passage of digesta through duodenum and ileum as well as the excretion by urine and faeces was estimated, taking an aliquot of 5% for N analysis. Transit of digesta amounted to 12.4 ... 13.2. kg/d in the duodenum and 2.7 ... 3.6 kg/d in the ileum. The appertaining N passage rates were 36.8 ... 42.4 resp. 8.7 ... 11.2 g N/d, corresponding to 108 ... 120% and 27 ... 32% of the N intake. The transit rate of duodenal digesta was highest immediately after feeding (1.4 ... 1.5 kg/h), decreased thereafter strongly, reaching a second lower maximum of 0.85 ... 1.0 kg/h 2 ... 3 h after feeding and then going down to 0.3 ... 0.4 kg/h just before the next feeding. The daily mean value was about 500 g/h. Endogenous N content of duodenal digesta varied between 10% after feeding and 50% 6 ... 12 h after feeding, with an average of 18.1%. In contrast the endogenous N content of ileal digesta was relatively constant amounting about 42% during the whole day. These findings correspond with those found by other authors using other rations and other live weights of the pigs. They refer to a clear diurnal rhythm of digesta transit and to the enormous dynamics of absorption and secretion processes in the intestinal tract of pigs during digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Es werden an einigen Beispielen des Einsatzes von radioaktiv (H bzw. C) und stabilisotop (N) markierten Traceraminosāuren für in vivo-Untersuchungen verschiedene Probleme der Untersuchungsmethodik und kritische Punkte bei der Interpretation der Ergebnisse erörtert.Bei Einsatz radioaktiver oder stabilisotop markierter Verbindungen zur Untersuchung des Eiweißstoffwechsels ist stets die Berücksichtigung und Messung verschiedener physikalischer und physiologischer Parameter notwendig, um Interpretationsirrtūmer zu minimieren.

Using 15N labelled amino acids the amount of nitrogen in amino acid fractions, resulting from the impurity of the applied chemicals of the Kjeldahl method, was estimated. The study shows that the measured 15N values are dependent on the nitrogen content of the sample and the level of 15N labelling. Within the range of 250 μg … 1000 μg nitrogen in the sample and in the case of 15N-excess >1 Atom% a correction of the measured 15N excess values is recommended