PULMONARY VASCULAR PRESSURES OF STRENUOUSLY EXERCISING THOROUGHBRED HORSES AFTER ADMINISTRATION OF PHENYLBUTAZONE AND FRUSEMIDE

The present study was carried out to examine the effects of phenylbuta zone treatment on the pulmonary haemodynamic effects of frusemide in s trenuously exercising hones, Using catheter mounted manometers, whose in vivo signals were referenced at the point of the shoulder, heart ra te, right atrial, right ventricular and pulmonary vascular pressures w ere measured in 3 different sets of experiments. Seven Thoroughbreds w ere subjected to 1) control (no medications), 2) frusemide control and 3) phenylbutazone + frusemide, The experiments were carried out in ra ndom order and were separated by 7 days, Measurements were made at res t and during incremental exercise performed on a treadmill set at 3.5% uphill grade, In the frusemide control experiment, horses received fr usemide 250 mg i.v., 4 h pre-exercise. In the phenylbutazone + frusemi de experiment, horses received 4 i.v. injections of phenylbutazone (4. 4 mg/kg but) at 12 h intervals, Twenty-four hours after the last pheny lbutazone injection, horses received frusemide 250 mg i.v. and exercis e was performed 4 h later, This latter regimen mimics prevailing veter inary practice at Illinois racetracks, The highest work intensity (14. 2 m/s, 35% uphill grade) elicited maximal heart rate of horses, Signif icant right atrial, as well as pulmonary arterial, capillary and venou s hypertension occurred with exertion in all 3 experiments, However in the frusemide-control and the phenylbutazone + frusemide studies, the exercise induced rise in mean right atrial and pulmonary vascular pre ssures was significantly (P<0.05) attenuated in comparison with that i n the control experiments. Statistically significant differences were not found between the frusemide control study and the phenylbutazone frusemide study either at rest or during any level of exertion, There fore, it was concluded that the phenylbutazone treatment in our study did not mitigate the pulmonary haemodynamic effects of frusemide in st renuously exercising Thoroughbred horses.