Bestimmung von kinetischen Parametern des Proteinmetabolismus bei wachsenden Ratten in Verbindung mit Energieumsatzmessungen. 1. Mitteilung. Bestimmung von kinetischen Parametern des Proteinmetabolismus in Abhängigkeit von der Lebendmasse und dem Proteingehalt des Futters

Abstract

The digestibility, the N balance, the rate of protein synthesis and other parameters, characterising the protein metabolism in dependence on live weight, protein- and energy supply are estimated on Wistar rats (4-5 animals/group). These experiments were done in 5 alternating consecutive growth and energy maintenance periods at 4 different levels of protein (6, 10, 17, 26% CP) during the live weight period of 70 to 230 g. The rate of protein synthesis was calculated from the course of renale 15N excretion by means of the end product method after giving a single dose of a mixture of 17 15N labelled amino acids. N deposition, rate of protein synthesis and flux rate increased with the protein level of the ration. During maintenance these data were much lower, but showed the same dependence on the protein level. The absolute protein synthesis (g/d) increased up to the live weight of 130... 180 g and decreased afterwards according to the age. The reutilization rate varied between 44 and 87% and decreased with increasing dietary protein level by 27% and during proceeding age by 8 ... 12%. In contrast to the absolute metabolism rates (g/d) the fractional rates (%/d) clearly decreased with the age of the animals. The stimulation of these rates by the dietary protein level resembled that for the absolute rates of synthesis. The protein deposition showed the typical course of a growing curve according to the N intake and the protein synthesis showed practically the same course but on a higher level. The break down remained constantly (approximately 140 mg N/d) up to an N intake of about 360 mg and afterwards it increased too.

Estimation of protein and amino acid metabolism using [¹⁵N] and [¹⁴C] labeled tracer amino acids

“…Table 2 shows the influence of age and live weight demonstrated on rats, summarized from different experiments (Millward, 1978;Krawielitzki et al, 1991). The data show that both synthesis and breakdown decrease with age or live weight, but synthesis more than break-down.…”