Metabolism of [U-¹⁴C; 2, 3-³H]-L-valine by the isolated perfused goat udder

Abstract

TWO lactating mammary glands excised from 2 goats were perfused for several hours in the presence of [U-14 C; 2,3-3 H]-L-valine and received adequate quantities of glucose, acetate and amino acids. In the synthesized milk 96 and 89 % respectively of the casein valine was derived from free plasma valine. Valine was extensively catabolized by mammary tissue, resulting in a considerable 14 CO 2 production and in the incorporation of 14 C into milk citric acid and to a lesser extent into casein aspartic acid and glutamic acid. About 30 % of the valine molecules which were taken up by the mammary gland were oxidized to CO 2 and 70 % were incorporated in casein as valine residues. About 10 % of the plasma valine molecules were reversibly transaminated during one passage through the udder. An important amount of radioactivity of plasma was present in unknown metabolites. Only 7 % of this activity was localized in isobutyrate. The radioactivity of total milk fat was very low. Mainly iso-14:0, iso-16:0 and 15:0 were labelled.

Effects of the standardized ileal digestible valine : lysine ratio on performance, milk composition and plasma indices of lactating sows

“…With increasing dietary SID valine : lysine ratio, we observed a linear decrease in plasma glucose levels in sows and a trend for a quadratic increase in urea nitrogen in piglets, which suggests that these metabolites were used to synthesize nutrients, including an energy source (Roets et al ) and a source of N for non‐essential amino acid synthesis (Nissen et al ). However, plasma urea N of sows was not influenced by dietary valine, indicating little change in muscle catabolism which was verified by the low body weight loss observed for sows in this experiment (Richert et al ).…”

“…body weight loss) is reduced, valine becomes more limiting than threonine and lysine for lactating sows (Kim et al 2001). Research with lactating sows (Linzell et al 1969;Trottier et al 1994) and goats (Annison & Linzell 1964;Roets et al 1979;Bequette et al 1994) suggest that valine showed the highest oxidation rate of any amino acid in the mammary gland to deliver energy for the synthesis of lactose and fatty acid in milk (Spires et al 1975). Oxidation of branched-chain keto-acid results in formation of acetyl-Co A and succinyl-Co A (Harper et al 1984) which ultimately leads to energy generation and provides carbon skeletons for the de novo synthesis of nonessential amino acids and fatty acids (Shimomura et al 2001).…”

Extracorporeal perfusion of isolated organs of large animals – Bridging the gap between in vitro and in vivo studies

“…For specific recipes, compounds and additives to optimize the fluid's performance, refer to the respective publications. Cowie et al, 1951;Verbeke et al, 1959;Lauryssens et al, 1959Lauryssens et al, , 1960Lauryssens et al, , 1961Wood et al, 1965 Caprine Physiology Hebb and Linzell, 1951;Hardwick and Linzell, 1960;Hardwick et al, 1961Hardwick et al, , 1963Hardwick, 1965Hardwick, , 1966Linzell et al, 1967;Verbeke et al, 1957Verbeke et al, , 1968Verbeke et al, , 1972Roets et al, 1974Roets et al, , 1979a Udder Bovine Pharmacology Kietzmann et al, 1993Kietzmann et al, , 1995Kietzmann et al, , 2008Kietzmann et al, , 2010Forster et al, 1999;Kietzmann, 1999, 2001;Ehinger and Kietzmann, 2000a,b;Ehinger et al, 2006;Schumacher et al, 2011 One of the advantages associated with the use of cell free solutions is their relatively easy handling in a perfusion set-up compared with blood. The solution is readily available, even in large volumes that might be needed if an open system is the set-up of choice and variability in perfusate composition is not a concern.…”

“…Especially in udder perfusion studies, when aspects of milk production are at the center of interest and relatively high flow rates are required, blockage of 5-hydroxytryptamine induced vasoconstriction has been shown to be advantageous (Roets et al, 1974(Roets et al, , 1979a. Improving flow rates, especially when using whole blood perfusates, alters the perfusate's rheological properties.…”

“…Nevertheless most secretory cells appeared normal in histology upon completion of the experiment (Hardwick and Linzell, 1960). Addition of an artificial kidney to the perfusion system allowed maintenance of high flow rates for a longer perfusion time (Hardwick et al, 1961(Hardwick et al, , 1963Hardwick, 1965Hardwick, , 1966Linzell et al, 1967;Verbeke et al, 1968Verbeke et al, , 1972Roets et al, 1974Roets et al, , 1979a.…”