Effect of gender and jumping exercise on leukocyte number, dopamine and prolactin levels in horses

Physical exercise is one of the most physiologically stressful stimuli which cause animal to experience reversible alterations in various homeostatic variables. The aim of this study was to evaluate the effect of gender and jumping exercise on leukocyte, dopamine and prolactin values and the correlation among these parameters in 20 clinically healthy and regularly trained horses. The horses took part in a three-day jumping competition. Blood sampling was performed before the first day of competition (T0), within 10 minutes from the end of each race (J1, J2, J3) and 24 h after the end of J3 race (T24) in order to assess dopamine, prolactin and leukocyte values. Two-way repeated measures analysis of variance showed significant effect of gender (P < 0.05) on dopamine and prolactin levels and of exercise (P < 0.0001) on all studied parameters in the geldings and mares. Dopamine values negatively correlated with prolactin and leukocyte values in the mares and geldings throughout the monitoring period, whereas a significant positive correlation between prolactin and leukocyte values was found in the mares and geldings. The findings of this study suggest that the gonads likely influence the activity of dopaminergic system and the degree of prolactin secretion. The exercise-induced changes in the studied parameters are probably related to the dynamic physiological adaptations to exercise that allow re-establishment of the homeostatic equilibrium of the organism. The correlation found among the studied parameters suggests a possible interaction among immune cells and these hormones, supporting the existence of intercommunication between the endocrine and immune systems.