Effect of different workload and hydrocortisone in vitro on platelet aggregation in athletic horse.

The objective of the present study was to evaluate the platelet response to different workload in athletic horse and the influence of hydrocortisone on this response. For this purpose, six Sella Italiana gelding athletic horses, ranging in age from 8 to 10 years and clinically healthy, were subjected to four different exercises: horse-walker, treadmill, obstacle course of 1.00 m and obstacle course of 1.25 m. From all the horses, citrated plasma samples were collected at rest, immediately after exercise and 30 min after the end of the exercise to assess the maximum degree of platelet aggregation and the initial velocity of aggregation (slope) after platelet activation with 10 microM ADP and 20 microM ADP. Successively, the effect of 20 minutes pre-incubation with hydrocortisone in ADP-induced aggregation was determined. One-way repeated measures analysis of variance (ANOVA) was applied to determine significant differences due to experimental conditions (P < 0.05) and, for each sampling time, one-way analysis of variance was applied to determine significant differences due to workload (P < 0.05). Bonferroni's test was applied for post-hoc comparison. Our results revealed a statistically significant effect of experimental conditions only after obstacle course of 1.00 m and 1.25 m. These findings showed an inhibition of platelet aggregation during different workload in athletic horses that probably represents a protective endothelial mechanism through the production of nitrix oxide, and a kinetic measurement of the reaction that changes in relation to percentage of aggregation. The mechanism of hydrocortisone had no effect on platelet receptor expression in vitro in athletic horses, so it might be useful to evaluate the effect of different anti-inflammatory steroids in order to confirm, or note any differences, with drugs that have the same mechanism of action.