Lactate-bicarbonate interrelationship during exercise and recovery in lean and obese Zucker rats

Abstract

OBJECTIVE: To determine the relationship between muscle-derived lactate at fatigue and earlier onset of fatigue in the obese rat subjected to intense exercise. DESIGN: Rats were subjected to a short, intense exercise protocol on a treadmill. Blood was drawn from hind leg vein and artery during exercise and up to 1 h afterwards. Assuming an exercise respiratory quotient of 1.0, the extra carbon dioxide released was computed and assumed to be displaced by equimolar amounts of lactic acid produced by the rat during exercise. SUBJECTS: Conscious female adult Zucker lean and Zucker obese rats. MEASUREMENTS: Oxygen consumption and carbon dioxide release. Lactate and bicarbonate levels in hind leg venous and arterial blood; balances were estimated by measuring blood¯ow with¯uorescent microspheres. Lactate levels in periovaric white adipose tissue were also measured. RESULTS: Muscle released, during exercise and post exercise roughly 2.3 mmol lactate in lean rats and 2.6 mmol in obese ones. Of these amounts, hind leg lactate release accounted for 0.40 mmol in lean rats and only 0.11 in the obese ones, which showed a release of acid (mainly lactate) elsewhere in the rats totalling about 19.9 mmol CO 2 in lean rats and 4.4% in the obese ones; that is both hind quarters accounted for only 17.2% of all lactate produced in the lean rats and 4.4% in the obese ones. The amount of lactate produced by the rats was roughly similar. White adipose tissue lactate levels (in the basal state and after exercise) were much higher than could be expected from blood sources alone, indicating an active production of lactate. CONCLUSION: Fatigue appears earlier in the obese rats than in lean ones because of loss of buffering ability caused by massive extra-muscular glycolysis (probably in adipose tissue) and lactate production triggered by exercise-induced adrenergic stimulation.

Diet-induced obesity accelerates blood lactate accumulation of rats in response to incremental exercise to maximum

“…Nevertheless, blood lactate increases during incremental exercise at high-intensity workloads (2,3). Similar to previous findings (1,23,36), we found exercise performance in the incremental exercise test to be lower in obese animals. Importantly, we found that the decreased exercise performance of obese rats in the incremental exercise test was strongly associated with their faster blood lactate accumulation.…”

Hind leg heat balance in obese Zucker rats during exercise

“…The increase in lactate levels in lean and to a greater extent in obese rats during exercise, but the relatively low lactate production by muscle, suggests massive extra-muscular lactate production [6]. This factor is probably more important than heat dissipation in the onset of fatigue.…”