Pulmonary vascular pressures of strenuously exercising thoroughbreds after administration of phenylbutazone.
OBJECTIVE
To determine the effects of phenylbutazone administration on heart rate and right atrial and pulmonary vascular pressures in Thoroughbreds during rest and during exercise performed at maximal heart rate.


METHODS
7 healthy, exercise-conditioned Thoroughbreds.


METHODS
Horses were studied on 3 occasions: without medication [control], after i.v. administration of phenylbutazone (4.4 mg/kg of body weight) at 12-hour intervals for 2 days and a final dose given 1 hour before exercise, and after i.v. administration of phenylbutazone for 2 days in the same manner, but with the final dose given 24 hours before exercise. Horses were studied at rest and during exercise performed at maximal heart rate on a treadmill. Right atrial and pulmonary vascular pressures were measured with catheter-tip manometers referenced at the point of the shoulder.


RESULTS
We did not detect significant differences in heart rate or right atrial and pulmonary vascular pressures among values recorded when horses were not given medication and values recorded when phenylbutazone was administered by either regimen. Exercise-induced pulmonary hemorrhage occurred in 6 of the 7 horses regardless of whether phenylbutazone was administered or the dosage regimen used.


CONCLUSIONS
In these Thoroughbreds, phenylbutazone treatment did not modify heart rate or right atrial and pulmonary vascular pressures at rest or during exercise capable of eliciting exercise-induced pulmonary hemorrhage. Thus, because phenylbutazone is a potent inhibitor of cyclooxygenase, prostaglandins probably do not play a role in mediating exercise-induced pulmonary hypertension in horses.


CONCLUSIONS
Phenylbutazone administration did not modify the pulmonary capillary hypertension in the strenuously exercising Thoroughbreds, and therefore, is unlikely to alter the prevalence or severity of exercise-induced pulmonary hemorrhage in Thoroughbred race-horses.
Manohar
M
M
Department of Veterinary Biosciences, College of Veterinary Medicine, University of Ilhnois, Urbana 61801, USA.
Goetz
T E
TE
Griffin
R
R
Sullivan
E
E
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006470:Hemorrhage / Q000209:etiology / Q000503:physiopathology / Q000662:veterinary*; D006734:Horse Diseases; D006736:Horses; D006976:Hypertension, Pulmonary / Q000209:etiology / Q000503:physiopathology / Q000662:veterinary*; D008297:Male; D009919:Orchiectomy; D010653:Phenylbutazone / Q000494:pharmacology*; D010805:Physical Conditioning, Animal / Q000009:adverse effects; D005082:Physical Exertion; D011651:Pulmonary Artery / Q000187:drug effects / Q000502:physiology*; D011652:Pulmonary Circulation / Q000187:drug effects / Q000502:physiology*; D012146:Rest
D010653:Phenylbutazone