Effect of l-NAME on oxygen uptake kinetics during heavy-intensity exercise in the horse.
Kindig, Casey A., Paul McDonough, Howard H. Erickson, and David C. Poole.
Departments of Anatomy and Physiology and Kinesiology, Kansas State University, Manhattan, Kansas 66506"hyphen"5602
APStracts 8:0284A, 2001.
There is evidence that oxidative enzyme inertia plays a major role in limiting/setting the O2 uptake ("vo2") response at the transition to higher metabolic rates and also that nitric oxide (NO) competitively inhibits "vo2" within the electron transport chain. To investigate whether NO is important in setting the dynamic response of "vo2" at the onset of high-intensity (heavy-domain) running in horses, five geldings were run on a treadmill across speed transitions from 3 m/s to speeds corresponding to 80% of peak "vo2" with and without "lname" (l-NAME), an NO synthase inhibitor (20 mg/kg; order randomized). l-NAME did not alter (both P > 0.05) baseline (3 m/s, 15.4 ± 0.3 and 16.2 ± 0.5 l/min for control and l-NAME, respectively) or end-exercise "vo2" (56.9 ± 5.1 and 55.2 ± 5.8 l/min for control and l-NAME, respectively). However, in the l-NAME trial, the primary on-kinetic response was significantly (P < 0.05) faster (i.e., reduced time constant, 27.0 ± 2.7 and 18.7 ± 3.0 s for control and l-NAME, respectively), despite no change in the gain of "vo2" (P > 0.05). The faster on-kinetic response was confirmed independent of modeling by reduced time to 50, 63, and 75% of overall "vo2" response (all P < 0.05). In addition, onset of the "vo2" slow component occurred earlier (124.6 ± 11.2 and 65.0 ± 6.6 s for control and l-NAME, respectively), and the magnitude of the O2 deficit was attenuated (both P < 0.05) in the l-NAME compared with the control trial. Acceleration of the "vo2" kinetics by l-NAME suggests that NO inhibition of mitochondrial "vo2" may contribute, in part, to the intrinsic metabolic inertia evidenced at the transition to higher metabolic rates in the horse.
Received 8 December 2000; accepted in final form 15 March 2001
APS Manuscript Number A1188-0.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 18 June 2001