Lb. Gladden et al., EFFECT OF LACTATE CONCENTRATION AND METABOLIC-RATE ON NET LACTATE UPTAKE BY CANINE SKELETAL-MUSCLE, The American journal of physiology, 266(4), 1994, pp. 180001095-180001101
This study addressed two questions: 1) Does net lactate uptake (L) by
muscle approach a saturation limit with increasing blood lactate conce
ntration ([La])? 2) Is the muscle net L; response to increasing blood
[La] affected by metabolic rate (VO2)? The gastrocnemius plantaris mus
cle group (GP) was isolated in situ in 20 anesthetized dogs. In three
series of experiments, a lactate-lactic acid solution was infused into
the arterial inflow of the GP to produce five different plasma [La] v
alues: similar to 3, 9, 16, 22, and 30 mM, each of them maintained for
30 min. In one series, the GP remained at rest, whereas in the second
series it contracted at 1 Hz and in the third series at 4 Hz. VO2 ave
raged similar to 3, 43, and 100 ml.kg(-1).min(-1) at rest and at 1 and
4 Hz, respectively. Within each of the three metabolic rates, increas
ing plasma [La] resulted in an increase in net L, which was well descr
ibed (R > 0.98) by exponential equations. These equations predicted ne
t L asymptotic values of 0.80, 0.72, and 1.09 mmol.kg(-1).min(-1) for
rest and for 1 and 4 Hz, respectively. The corresponding plasma [La]s
for half-maximal net L from the exponential equations were 16, 10, and
12 mM. Glucose uptake, pyruvate uptake/output, and alanine output by
the muscles were not affected by the increasing [La] (and concomitant
increases in net L) at any of the metabolic rates. Neither net glycoge
n synthesis nor depletion was changed by increasing [La]. These result
s answer the two questions posed: net L by skeletal muscle does approa
ch a saturation limit as plasma [La] increases, and this relationship
is altered by changing metabolic rate.