ACUTE EXERCISE STRESS MODULATES IMMUNE FUNCTION IN UNFIT HORSES

Since exercise stress is associated with multiple changes in immune pa rameters, we evaluated the effect of acute exercise on 3 indices of im mune function in the horse. Six unconditioned thoroughbred horses were subjected to a tread-mill-based exercise challenge. Exercise intensit y was determined by monitoring each horse's heart rate, plasma lactate , and cortisol levels. Concurrently, peripheral blood mono-nuclear cel ls were used to assess pokeweed mitogen (PWM) -induced blastogenesis, influenza-specific proliferation, and lymphokine activated killer (LAK ) cell activity. Heart rate peaked during the gallop on an incline whi le lactate was highest at the end of the stress test (T0) with values of 200 bpm and 9 mM/L respectively. Average plasma cortisol was greate st at T0 and T+20 with values 76% higher than unstressed horses. Signi ficantly (P<.05) lower PWM and influenza-associated proliferation of c ells collected at T0 and T+20 were observed. These results illustrate the complexity of changes in immune function that accompany intense ex ercise.