Stoffwechselorientierte Lysinbedarfsbestimmung bei Ausgewachsenen Ratten Anhand Der Katabolisierungsrate von¹⁴C- und¹⁵N-Markiertem Lysin

Abstract

Mature male albino rats (ca. 300 g body mass) received 10 diets with a varying lysine content (1.6 to 8.4 g/16 g N). In one partial test the animals were fed ad libitum and in another partial test they were kept in the state of maintenance by limiting the amount of the diet. After 7 feeding days the catabolisation of 14C-lysine into 14CO2 was measured and after 8 feeding days the 15N-excretion in urine after 15N-lysine doses was ascertained. Based on these characteristics typical of metabolism, which show increased catabolisation of the amino acid after the lysine requirement was met, the lysine requirement of a mature rat was determined as 3.5 to 4.0 g/16 g N in the diet. In conclusion, this shows that the lysine requirement in the state of maintenenace and of mature animals is considerably lower than during the period of growth.

Dynamics of human whole body amino acid metabolism: Use of stable isotope probes and relevance to nutritional requirements.

“…However, it is significant that the responses of whole body lysine and leucine metabolism that we have obtained with healthy adult humans are similar to those reported from studies in growing and adult rats (44)(45)(46)(47). Furthermore, these dynamic responses of amino acid metabolism in rats have been used to estimate the dietary requirement for specific indispensable amino acids.…”

Protein metabolism and nutritional state in man

“…For example, studies in rats show that the change in the oxidation rate of methionine is linear throughout a broad range of methionine intake, both above and below the requirement level (Aguilar et al 1974). This contrasts with the 'breakpoint' type of response observed for the oxidation of lysine, histidine and threonine (Brookes et al 1972;Kang-Lee & Harper, 1977Simon, Adam et al 1978), to graded intakes of these specific amino acids over this same range. Therefore, the relationship between methionine intake, whole body amino acid dynamics and the methionine requirement of human subjects might be explored more usefully by studying changes in whole body protein synthesis or breakdown rates or methionine flux.…”

“…A summary of the responses of the components of leucine flux (oxidation, outflow of leucine from the metabolic pool into proteins and inflow via protein Tanaka & Ogura, 1980) or for maintenance in adult rats (Simon, Adam et al 1978). They also suggest that more than one mechanism is responsible for the adaptive responses of whole-body leucine metabolism and of body N balance to changes in dietary protein intakes.…”

Metabolism of lysine and tryptophan in growing rats at various dietary protein levels.

“…To evaluate 14CO2produc-tion for estimating the requirement of the amino acids in the rat, Brookes et al25) reported that the oxidation of lysine did not increase markedly until the dietary lysine intake was increased above that level at which average daily gain and gain/feed were maximal. Simon et al 28) also reported that an estimation of lysine requirement on the basis of CO2 production data may be a very exact and sensitive method, especially in the maintenance requirement for mature rats. Patterson and Harper32'33) reported that after the tryptophan requirement for growth is met, the amount of tryptophan oxidized was directly proportional to the amountof tryptophan consumed.…”