Forearm muscle metabolism studied using (31)P-MRS during progressive exercise to fatigue after Acz administration.
The effects of acetazolamide (Acz)-induced carbonic anhydrase inhibition (CAI) on muscle intracellular thresholds (T) for intracellular pH (pH(i)) and inorganic phosphate-to-phosphate creatine ratio (P(i)/PCr) and the plasma lactate (La(-)) threshold were examined in nine adult male subjects performing forearm wrist flexion exercise to fatigue. Exercise consisted of raising and lowering (1-s contraction, 1-s relaxation) a cylinder whose volume increased at a rate of 200 ml/min. The protocol was performed during control (Con) and after 45 min of CAI with Acz (10 mg/kg body wt iv). T(pH(i)) and T(P(i)/PCr), determined using (31)P-labeled magnetic resonance spectroscopy (MRS), were similar in Acz (722 +/- 50 and 796 +/- 75 mW, respectively) and Con (855 +/- 211 and 835 +/- 235 mW, respectively). The pH(i) was similar at end-exercise (6.38 +/- 0.10 Acz and 6.43 +/- 0.22 Con), but pH(i) recovery was slowed in Acz. In a separate experiment, blood was sampled from a deep arm vein at the elbow for determination of plasma lactate concentration ([La(-)](pl)) and T(La(-)). [La(-)](pl) was lower (P < 0.05) in Acz than Con (3.7 +/- 1.7 vs. 5.0 +/- 1.7 mmol/l) at end-exercise and in early recovery, but T(La(-)) was higher (1,433 +/- 243 vs. 1,041 +/- 414 mW, respectively). These data suggest that the lower [La(-)](pl) seen with CAI was not due to a delayed onset or rate of muscle La(-) accumulation but may be related to impaired La(-) removal from muscle.
Kowalchuk
J M
JM
The Centre for Activity and Ageing, School of Kinesiology, University of Western Ontario, London, Ontario N6A 3K7. jkowalch@julian.uwo.ca
Smith
S A
SA
Weening
B S
BS
Marsh
G D
GD
Paterson
D H
DH
D000086:Acetazolamide / Q000008:administration & dosage*; D000136:Acid-Base Equilibrium / Q000187:drug effects / Q000502:physiology; D000328:Adult; D002245:Carbon Dioxide / Q000097:blood; D002257:Carbonic Anhydrase Inhibitors / Q000008:administration & dosage*; D002256:Carbonic Anhydrases / Q000378:metabolism; D005542:Forearm / Q000502:physiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000097:blood; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000201:enzymology; D018482:Muscle, Skeletal / Q000378:metabolism*; D010759:Phosphorus Isotopes; D005082:Physical Exertion / Q000187:drug effects / Q000502:physiology*
D002257:Carbonic Anhydrase Inhibitors; D007773:Lactates; D010759:Phosphorus Isotopes; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases; D000086:Acetazolamide