[Evaluation of changes in hepatic energy metabolism during exercise by ketone body ratio in humans]

Abstract

Changes in the redox state of liver mitochondria were investigated by measuring the arterial ketone body ratio (acetoacetate/3-hydroxybutyrate: AKBR) in nine healthy volunteers (eight males and one female, mean age 38.4 +/- 5.0 years) during exercise. The correlation between the changes in AKBR and levels of various hormones controlling energy metabolism was also investigated. Subjects participated in symptom-limited exercise test using the ramping bicycle ergometer with expired gas analysis, blood pressure and 12 lead electrocardiogram monitoring. Anaerobic threshold by gas exchange parameters (ATge) was determined from the expired gas data with the v-slope method. AKBR, glucose, non-esterified fatty acid (NEFA) and lactate were measured in arterial plasma samples. Catecholamines (epinephrine, norepinephrine, dopamine), insulin, glucagon, antidiuretic hormone (ADH), growth hormone (GH), thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), human-atrial natriuretic peptide (hANP) and brain natriuretic peptide (BNP) were measured in venous plasma samples. AKBR was gradually decreased by exercise from the resting value of 1.82 +/- 0.20. AKBR reduction was potentiated after ATge to 0.93 +/- 0.18 (p < 0.01 vs rest) at peak exercise. AKBR was further decreased during recovery to the minimum value of 0.70 +/- 0.06 (p < 0.01) at 6 min in the recovery phase. AKBR then began to increase and reached 0.95 +/- 0.07 30 min after peak exercise. Epinephrine increased from 45.9 +/- 11.0 to 210 +/- 75 pg/ml (p < 0.01), norepinephrine increased from 348 +/- 52 to 1,277 +/- 111 pg/ml (p < 0.01), and dopamine increased from 13.0 +/- 1.9 to 25.0 +/- 2.5 pg/ml (p < 0.01) between rest and peak exercise, respectively. Insulin decreased from 22.0 +/- 3.5 to 14.2 +/- 2.1 pg/ml (p < 0.05). No significant change was observed in glucagon, ADH, GH, TSH, T3, T4, hANP or BNP. Glucose decreased from 124 +/- 9 to 84 +/- 8 mg/dl (p < 0.05), whereas NEFA increased from 94 +/- 10 to 190 +/- 66 mg/dl (p < 0.05). A negative correlation was observed between AKBR and lactate (r = -0.41, p < 0.001). These results indicate that hepatic adenosine triphosphate production is promoted as energy demand increases by exercise, and maximizes early in the recovery phase when hepatic energy demand is maximum due to active gluconeogenesis. The levels of catecholamines, insulin and lactate contribute to the control of liver energy metabolism.