Nitric oxide and thermoregulation during exercise in the horse.
Mills, Paul C., David J. Marlin, Caroline M. Scott, and Nicola C.
Smith.
Equine Centre, The Animal Health Trust, PO Box 5, Newmarket,
Suffolk, CB8 7DW, UK
APStracts 3:0564A, 1996.
The effect of inhibition of nitric oxide (NO) production on sweating
rate (SR) and core, rectal and tail skin temperatures was measured in
five Thoroughbred horses during exercise of variable intensity on a
high-speed treadmill. A standard exercise test (SET) consisting of
three canters (55%O2,max), with walking (9% O2,max) and trotting (22%
O2,max) between each canter, was performed twice (control or test),
in random order, by each horse. N-nitro-L-arginine methyl ester (L
-NAME; 20 mg kg-1), a competitive inhibitor of nitric oxide synthase
(NOS), was infused into the central circulation and induced a
significant reduction in the SR measured on the neck (31.6+/-6.4
versus 9.7+/-4.2 g min-1 (m2)-1 (69%)) and rump (14.7+/-5.2 versus
4.8+/-1.6 g min-1 (m2)-1 (67%)) of the horses during canter
(P<0.05). Significant increases in core, rectal and tail skin
temperatures were also measured (P<0.05). L-arginine (200 mg
kg-1 iv) partially reversed the inhibitory effects of L-NAME on SR
but core, rectal and tail skin temperatures continued to increase
(P<0.05) suggesting a cumulation of body heat. The results
support the contention that NOS inhibition diminishes SR resulting in
elevated core and peripheral temperatures leading to deranged
thermoregulation during exercise. The inhibition of sweating by L
-NAME may be related to peripheral vasoconstriction but may also
involve the neurogenic control of sweating.
Received 8 July 1996; accepted in final form 22 November 1996.
APS Manuscript Number A628-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996