Metabolism of Valine and the Exchange of Amino Acids across the Hind-limb Muscles of Fed and Starved Sheep

Abstract

A combination of the isotope-dilution and arterio-venous (A V) difference techniques was used to study simultaneously the metabolism of valine in the whole body and in the hind-limb muscles of fed and starved (40 h) sheep. The net exchange of gluconeogenic amino acids across hind-limb muscles was also studied.Valine entry rate was unaffected by nutritional status. There was significant extraction of valine by hind-limb muscles in both fed and starved sheep. The percentage of valine uptake decarboxylated was higher (P < 0'05) in fed sheep but the amount of valine decarboxylated was not significantly different. The proportion of valine uptake that was transaminated was about 30 times higher in starved sheep. About 54% of valine taken up by hind-limb muscle of starved sheep was metabolized.The corresponding value for fed sheep was 21 %. The contribution of CO2 from valine decarboxylation to total hind-limb muscle C02 output was about 0·2%.The output of alanine in both fed and starved sheep was low but the output of glutamine was relatively high and roughly equivalent to the amounts of aspartate, glutamate and branched-chain amino acids that were catabolized. This study has confirmed that valine is catabolized in sheep skeletal muscle, and shown that glutamine is a major carrier of amino nitrogen out of muscle.

Identification of amino acids associated with skeletal muscle growth in late gestation and at weaning in lambs of well-nourished sheep1

“…However, it may also indicate an increased uptake of BCAA in females muscle to generate glutamine and alanine (Teleni et al, 1986), which is supported by the lesser concentration of both glutamine and alanine in female muscle. The increased concentration of the BCAA isoleucine, leucine, and valine in females compared to males could be associated with an increased BCAA deamination in males.…”

“…It was therefore hypothesized that reduced muscle growth in twins compared to singletons is associated with decreased intracellular concentration of FAA, especially those associated with mTOR activation (e.g., leucine, arginine, and glutamine; Wu, 2009). Valine is the only glucogenic BCAA (Teleni et al, 1986) and might have been the first BCAA to be used as a glucogenic precursor, which may explain in part the reduced concentration of valine in twins. Valine has been associated with activation of downstream targets of mTOR (Xu et al, 2001).…”

Energy metabolism reactions in ruminant muscle: responses to age, nutrition and hormonal status

“…Between fasting and ad libitum intake milk fed lambs increased the fractional rate of protein synthesis across the hind leg from 0.071-0.115/d (Oddy et al, 1987). In growing ruminants increases in feed intake from 0.6 to 1.8 x maintenance caused corresponding increases in hind limb protein synthesis from 2.3 to 5.2 g/h in cattle (Boisclair et al, 1988) and from 0.2 to 0.59 g/h in lambs (Harris et al, 1989 (Teleni et al, 1986) but fasting for 3 days (Pell et al, 1986) caused a marked decline in both whole body (-28%) (Oddy et al, 1987); the latter observation is in contrast to findings in the fasted rat (Garlick et al, 1983;Reeds et al, 1985 (Eisemann et al, 1989) and lambs (Pell and Bates, 1987). Epinephrine increases both whole body and muscle oxygen consumption (Lundholm and Svedmyr, 1965).…”

Amino acid profiles of muscle and liver tissues of Australian Merino, Damara and Dorper lambs under restricted feeding

“…During fasting, sheep are reported to mobilize muscle protein to increase the availability of amino acids (AA's) for gluconeogenesis in the liver (Ballard, Filsell, & Jarrett, ; Teleni, Annison, & Lindsay, ). Interestingly, the glucogenic potential of AA is low in the hepatic tissue of fed sheep, but it increases in fasted individuals (Demigné, Yacoub, Morand, & Rémésy, ).…”

“…Interestingly, the glucogenic potential of AA is low in the hepatic tissue of fed sheep, but it increases in fasted individuals (Demigné, Yacoub, Morand, & Rémésy, ). Sheep have been compared regarding the exchange of amino acids in hindlimb muscles, as affected by fasting (Teleni et al, ). There was a general trend for circulating amino acids to increase due to starvation, for 40 hr.…”