title: Nitric oxide synthase inhibition speeds oxygen uptake kinetics in horses during moderate domain running.
abstract: Within the moderate exercise intensity domain, the speed of oxygen uptake (V(O(2))) kinetics at the transition to a higher metabolic rate is thought to be limited by an inertia of the oxidative machinery. Nitric oxide (NO)-induced inhibition of O(2) consumption within the electron transport chain may contribute to this inertia. This investigation tested the hypothesis that a reduction or removal of any such NO effect via infusion of N(omega)-nitro-L-arginine methyl ester (L-NAME; a NOS inhibitor) would speed V(O(2)) kinetics at the onset of moderate exercise. Five Thoroughbred geldings underwent four transitions to running speeds of 7 m sec(-1) (two control, C, 2 L-NAME [20 mg kg(-1)]) on an equine treadmill during which pulmonary gas exchange was determined using a bias flow system. Consistent with exercise in the moderate intensity domain, in none of the transitions was a V(O(2)) slow component elicited. The L-NAME treatment significantly accelerated V(O(2)) kinetics via a reduction of the primary amplitude time constant (C, 17.3 +/- 1.7; L-NAME, 11.8 +/- 1.5 sec, P < 0.05) concomitant with faster overall dynamics (i.e. T(50) and T(75) both P < 0.05) and a trend toward a decreased O(2) deficit (C, 6.4 +/- 0.7; L-NAME, 4.7 +/- 1.2 L; P = 0.06). These data support the notion that NO contributes prominently to the oxidative enzyme inertia and thus the speed of V(O(2)) kinetics at the onset of moderate intensity exercise in the horse.
authors.affiliation: Department of Anatomy, Kansas State University, 228 Coles Hall, 1600 Denison Avenue Manhattan, KS 66506-5802, USA. ckindig@ucsd.edu
authors.forename: Casey A
authors.initials: CA
authors.lastname: Kindig
authors.forename: Paul
authors.initials: P
authors.lastname: McDonough
authors.forename: Howard H
authors.initials: HH
authors.lastname: Erickson
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005080:Exercise Test; D006736:Horses / Q000502:physiology*; D019344:Lactic Acid / Q000097:blood; D008297:Male; D016555:Matched-Pair Analysis; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D010100:Oxygen / Q000493:pharmacokinetics*; D010101:Oxygen Consumption / Q000187:drug effects; D012119:Respiration / Q000187:drug effects; D012420:Running / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D019344:Lactic Acid; D019001:Nitric Oxide Synthase; D010100:Oxygen; D019331:NG-Nitroarginine Methyl Ester