TRAINING SUPPRESSES HEPATIC LACTATE-DEHYDROGENASE ACTIVITY WITHOUT ALTERING THE ISOENZYME PROFILE

A decrease in hepatic lactate dehydrogenase (LDH) activity following e ndurance training has been a consistent observation. In the present st udy, we sought to determine whether the training-induced decrease in h epatic LDH activity (pyruvate = substrate) was associated with a shift in the isoenzyme profile and/or alteration in other kinetic parameter s. Animals (rats) were randomly assigned to either an endurance traine d group (running 90 min at 30 m . min(-1), 10% grade) or sedentary con trol group. Eight weeks of endurance training resulted in a significan t decrease in maximal hepatic LDH activity for the forward reaction (p yruvate double right arrow lactate), 107.3 +/- 5.5 mu mol . min(-1). g (-1) when compared with control animals, 147.3 +/- 5.6 mu mol . min(-1 ). g(-1) A similar decrease was observed for maximal LDH activity in t he reverse reaction (lactate double right arrow pyruvate), 49.8 +/- 2. 1 vs 66.7 +/- 2.9 mu mol . min(-1). g(-1), trained and controls, respe ctively. Training was also observed to decrease the Km for the reverse reaction, 5.18 +/- 0.78 mM vs 6.94 +/- 0.55 mM, for trained and contr ols, respectively. Km for the forward reaction was unaffected by train ing. Gel electrophoresis with densitometric evaluation revealed no shi ft in the isoenzyme pattern following endurance training. LDH(5) accou nted for 89% +/- 2%, whereas 6% +/- 0.5% was observed in LDH(4), and 4 % +/- 0.3% was observed in LDH, for both groups. The densitometric are a was similar to 34% lower from trained liver homogenates, a fractiona l decrease similar to that observed for maximal LDH activity. The decr ease in hepatic LDH activity with endurance training appears attributa ble to a down regulation of enzyme content, with no significant altera tion in isoenzyme distribution.