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Evaluation of techniques employed in the study of alanine metabolism in sheep Cooper, Donald Arthur

Abstract

In view of the importance of alanine as a gluconeogenic precursor in ruminants, the objective of the present study was to assess the effectiveness of three techniques in estimating the metabolic parameters surrounding alanine in wethers fed a maintenance diet of alfalfa hay. A preliminary experiment utilized a blood flow technique to study the net production and/or utilization of both alanine and glucose by the portal drained viscera. Such a method involved evaluating the arterio-venous concentration differences of alanine and glucose, in conjunction with determining the rate of portal vein blood flow. Radioactively labelled ¹⁴C - alanine was administered as a single injection in the second series of experiments to estimate the metabolic parameters of alanine as well as its contribution to glucose synthesis. The L-U-¹⁴C-alanine was given intravenously through previously implanted jugular catheters and the fall in the specific activity of plasma alanine with time was determined. The line of best fit for the decay curve of the specific activity of plasma alanine was constructed by means of a computer using a multi-term exponential function which enables the estimation of such parameters as the pool size, space, total entry rate, irreversible loss and recycling of alanine. The per cent conversion of alanine to glucose was determined by the corresponding peak of glucose specific activity following the single injection of ¹⁴C - alanine. The turnover of alanine was also studied using a continuous infusion of L-U-¹⁴C-alanine without a priming injection. The specific activity of plasma alanine reached a plateau five hours after the beginning of the infusion. It was from these plateau levels that the rate of irreversible loss of alanine as well as its percent conversion to glucose was estimated. The results indicated that the single injection technique was able to partition the total entry rate of alanine into irreversible loss and recycling and thus prove more informative than a continuous infusion method. The present study also suggested that under certain physiological stress conditions in ruminants, where recycling becomes prominent, a continuous infusion approach may overestimate the actual rate of irreversible loss of alanine.

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