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Effect of Exercise on the Disposal of Infused Ketone Bodies in Humans^*

Laboratory of Experimental Medicine, Free University of Brussels Brussels, Belgium

Address all correspondence and requests for reprints to: Francoise Fery, Laboratory of Experimental Medicine, University of Brussels, 115 Boulevard de Waterloo, B-1000 Brussels, Belgium.

We previously reported that the stimulatory effect of exercise on the metabolic clearance of ketone bodies in postabsorptive subjects is abolished when plasma ketone body concentrations are elevated above 4 mmol/L by prior fasting. In this study we determined whether this process is related to fasting or to hyperketonemia itself. Eight normal postabsorptive subjects were rendered artificially hyperketonemic (6 mmol/ L) by a constant infusion of acetoacetate and exercised moderately for 2 h. The kinetics of ketone bodies were determined with [¹⁴C] acetoacetate or β[¹⁴C]hydroxybutyrate. The metabolic clearance was slightly increased (25%) at the beginning of exercise, but this phenomenon was subsequently amplified by the progressive fall in ketonemia, which decreased to about 4 mmol/L at the end of exercise. Taking into account the fact that the metabolic clearance of ketones is inversely related to their concentration, it could be estimated that the direct effect of exercise on the metabolic clearance is negligible. Thus, the inability of exercise to enhance the metabolic clearance of ketones at high physiological plasma ketone levels is a general phenomenon that applies to both endogenous and exogenous ketosis.

^* This work was supported by the Fonds de la Recherche Scientifique Medicale Beige (Grant 3.4541.84), la Loterie Nationale Beige, and the Fondation Erasme.

Received November 23, 1987.