Chronic administration of
capsiate is known to accelerate whole-body basal energy metabolism, but the consequences in exercising skeletal muscle remain very poorly documented. In order to clarify this issue, the effect of 2-week daily administration of either vehicle (control) or purified
capsiate (
at 10- or 100-mg/kg
body weight) on skeletal muscle function and energetics were investigated throughout a multidisciplinary approach combining in vivo and in vitro measurements in mice. Mechanical performance and energy metabolism were assessed strictly non-invasively in contracting gastrocnemius muscle using magnetic resonance (MR) imaging and 31-phosphorus MR spectroscopy (31P-MRS). Regardless of the dose,
capsiate treatments markedly disturbed basal bioenergetics in vivo including intracellular pH
alkalosis and decreased
phosphocreatine content. Besides,
capsiate administration did affect neither mitochondrial
uncoupling protein-3 gene expression nor both basal and maximal oxygen consumption in isolated
saponin-permeabilized fibers, but decreased by about twofold the Km of mitochondrial respiration for
ADP. During a standardized in vivo fatiguing protocol (6-min of repeated maximal isometric contractions electrically induced at a frequency of 1.7 Hz), both
capsiate treatments reduced oxidative cost of contraction by 30-40%, whereas force-generating capacity and fatigability were not changed. Moreover, the rate of
phosphocreatine resynthesis during the post-electrostimulation recovery period remained unaffected by
capsiate. Both
capsiate treatments further promoted muscle mass gain, and the higher dose also reduced
body weight gain and abdominal fat content. These findings demonstrate that, in addition to its anti-
obesity effect,
capsiate supplementation improves oxidative metabolism in exercising muscle, which strengthen this compound as a natural compound for improving health.