Acute cold exposure and the metabolism of blood glucose, lactate and pyruvate, and plasma amino acids in the hind leg of the fed and fasted young ox

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Abstract
1. Young steers were fed either 3–4 or 20 h before exposure to a thermoneutral or a moderately cold environment. Measurements were made of total oxygen consumption (totalVo2), respiratory quotient (RQ), blood packed cell volume (PCV), and hind-leg blood flow (leg Q) and oxygen uptake (legVo2). The arteriovenous differences in whole blood glucose, lactate and pyruvate, and individual plasma amino acid and urea concentrations across the leg were also measured. Net exchange and fractional uptake of these metabolites by the leg were calculated from these results2. Cold exposure doubled totalVo2, significantly decreased RQ and significantly increased PCV. LegQand legVo2increased 3- to 5-fold and 4- to 13-fold respectively in both feeding groups. Arterial blood glucose increased slightly but significantly in both 20 h- and 3 h-fed steers. There was a substantial increase in mean net leg uptake of glucose in both feeding groups. This was much greater in the 20 h-fed group because of the significant increase in fractional uptake occurring only in this group. Cold did not significantly affect arterial blood lactate or pyruvate levels, but the net leg output of lactate found in both feeding groups in thermoneutrality was increased in the 20 h-fed steers, and reversed to a net uptake in the 3 h-fed animals. Cold caused a small but significant decrease in the total plasma amino acid level in the 20 h-fed but not in the 3 h-fed group; individual amino acid levels or leg uptakes were not affected3. Feeding before the experiment caused a significant increase in RQ. LegQ, leg uptake of glucose and leg output of lactate increased after feeding in the thermoneutral environment only. Arterial pyruvate increased significantly, but net leg output was not significantly affected by feeding. Arterial plasma concentration of several individual, but not of total amino acids, increased significantly in both environments, and the net output of many individual amino acids in the 20 h-fed steers was decreased or reversed to a net uptake in the 3 h-fed group in thermoneutrality only4. The results suggest that blood glucose could be a significant fuel for oxidation in shivering skeletal muscle in young steers, and that output of amino acids from skeletal muscle could not contribute significantly to this increased glucose supply by hepatic gluconeogenesis.