Lactate Turnover and Oxidation in Normal and Adrenal-Demedullated Dogs during Cold Exposure

Abstract

Plasma lactate turnover and oxidation rates have been measured by primed continuous infusion of L-¹⁴C-lactate in normal and adrenal-demedullated dogs shivering in a cold environment. In normal dogs, oxygen consumption due to shivering in the cold increased by a factor of 5.2 relative to the resting state in a thermoneutral environment. Plasma lactate concentration did not change but the rates of production and utilization of this metabolite were more than doubled. The increase in turnover of lactate in the cold was accompanied by an increase in its rate of oxidation. Over two-thirds of the lactate produced was promptly oxidized accounting for 12% of the expired CO₂. Relative to normal dogs exposed to cold, cold-exposed adrenal-demedullated dogs showed increases of 40–60% of plasma lactate concentration, turnover rate, and conversion to respiratory CO₂.