Da. Maclean et al., Interstitial pH, K+, lactate, and phosphate determined with MSNA during exercise in humans, AM J P-REG, 278(3), 2000, pp. R563-R571
Citations number
49
Categorie Soggetti
Physiology
Journal title
AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY
The purpose of the present study was to use the microdialysis technique to
simultaneously measure the interstitial concentrations of several putative
stimulators of the exercise presser reflex during 5 min of intermittent sta
tic quadriceps exercise in humans (n = 7). Exercise resulted in approximate
ly a threefold (P < 0.05) increase in muscle sympathetic nerve activity (MS
NA) and 13 +/- 3 beats/min (P < 0.05) and 20 +/- 2 mmHg (P < 0.05) increase
s in heart rate and blood pressure;respectively. During recovery, all refle
x responses quickly returned to baseline. Interstitial lactate levels were
increased (P < 0.05) from rest (1.1 +/- 0.1 mM) to exercise (1.6 +/- 0.2 mM
) and were further increased (P < 0.05) during recovery (2.0 +/- 0.2 mM). D
ialysate phosphate concentrations were 0.55 +/- 0.04, 0.71 +/- 0.05, and 0.
48 +/- 0.03 mM during rest, exercise, and recovery, respectively, and were
significantly elevated during exercise. At the onset of exercise, dialysate
K+ levels rose rapidly above resting values (4.2 +/- 0.1 meq/l) and contin
ued to increase during the exercise bout. After 5 min of contractions, dial
ysate K+ levels had peaked with an increase (P < 0.05) of 0.6 +/- 0.1 meq/l
and subsequently decreased during recovery, not being different from rest
after 3 min. In contrast, H+ concentrations rapidly decreased (P < 0.05) fr
om resting levels (69.4 +/- 3.7 nM) during quadriceps exercise and continue
d to decrease with a mean decline (P < 0.05) of 16.7 +/- 3.8 nM being achie
ved after 5 min. During recovery, H+ concentrations rapidly increased and w
ere not significantly different from baseline after 1 min. This study repre
sents the first time that skeletal muscle interstitial pH, K+, lactate, and
phosphate have been measured in conjunction with MSNA, heart rate, and blo
od pressure during intermittent static quadriceps exercise in humans. These
data suggest that interstitial K+ and phosphate, but not lactate and H+, m
ay contribute to the stimulation of the exercise presser reflex.