Journal of Applied Physiology, Vol 81, Issue 1 312-317, Copyright © 1996 by American Physiological Society
Phenylbutazone increases right atrial pressure and heart rate of running horses
L. A. Mitten, K. W. Hinchcliff and J. L. Pate
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University, Columbus 43210-1089, USA.
The effect of inhibition of cyclooxygenase activity on the hemodynamic
response to exertion was examined in 6 horses. Rates of O2 consumption and
CO2 production and carotid, pulmonary arterial, and right atrial pressures
were measured while the horses performed a standardized exercise test on a
treadmill after treatment with phenylbutazone or a placebo. Phenylbutazone
(8.8 mg/kg p.o. for 2 days and 4.4 mg/kg i.v. 60 min before exertion)
abolished the exertion-induced increases in plasma 6-ketoprostaglandin F1
alpha and thromboxane B2 concentrations, confirming inhibition of
cyclooxygenase activity. Phenylbutazone treatment resulted in significantly
(P < 0.05) higher heart rates and right atrial pressures during exertion
than did treatment with placebo, which may have been due to increased
myocardial sensitivity to sympathetic stimulation and/or decreased venous
compliance. There was not a detectable effect of phenylbutazone on carotid
or pulmonary arterial pressures, O2 consumption, CO2 production, or blood
lactate concentration. Changes in plasma volume during exertion were not
influenced by phenylbutazone. These results demonstrate that cyclooxygenase
products likely mediate or modulate some of the systemic hemodynamic
responses to exertion in horses.
