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Nitric oxide and thermoregulation during exercise in the horse
P C Mills1, D J Marlin, C M Scott
1Equine Centre, The Animal Health Trust, Newmarket, Suffolk, United Kingdom.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|April 1, 1997
Summary
Inhibiting nitric oxide production in horses significantly reduced sweating rate (SR) and increased body temperature during exercise, impairing thermoregulation. This suggests nitric oxide is crucial for equine heat dissipation.
Area of Science:
- Equine physiology
- Exercise science
- Thermoregulation
Background:
- Nitric oxide (NO) plays a role in physiological processes, including vasodilation and neurotransmission.
- Understanding thermoregulatory mechanisms in exercising horses is vital for athletic performance and welfare.
Purpose of the Study:
- To investigate the effect of inhibiting nitric oxide production on sweating rate (SR) and body temperature in Thoroughbred horses during exercise.
- To determine the role of nitric oxide synthase (NOS) in equine thermoregulation.
Main Methods:
- Five Thoroughbred horses underwent a standardized exercise test on a treadmill, performed twice: once with a placebo and once with N(G)-nitro-L-arginine methyl ester (L-NAME).
- L-NAME, a nitric oxide synthase inhibitor, was infused intravenously.
- Sweating rate and core, rectal, and tail skin temperatures were monitored during exercise.
Main Results:
- L-NAME administration significantly reduced SR on the neck and rump by approximately 67% during canter.
- Core, rectal, and tail skin temperatures significantly increased in horses treated with L-NAME.
- L-arginine partially reversed the SR reduction but did not prevent continued temperature increases, indicating heat accumulation.
Conclusions:
- Inhibition of nitric oxide production diminishes sweating rate in horses during exercise.
- Reduced SR due to nitric oxide synthase inhibition leads to elevated core and peripheral temperatures, impairing thermoregulation.
- The findings suggest nitric oxide is essential for effective heat dissipation in exercising horses, potentially through mechanisms involving peripheral vasodilation and neurogenic sweating control.