Effects induced by exercise on lymphocyte β-adrenergic receptors and plasma catecholamine levels in performance horses

The effect of dynamic exercise on complete blood cell count, lymphocyte β-adrenergic receptor and plasma catecholamine (adrenaline and noradrenaline) levels in horses performing different disciplines were investigated during rest and after exercise.Blood samples were collected from jumping horses (n = 6), Arabian Endurance horses (n = 6) and Standardbred trotters (n = 6) before and immediately after competition. Dynamic exercise caused a significant increase in red blood cell count (Standardbred trotters: P = 0.0012), haemoglobin concentration (jumping horses: P = 0.001; Standardbred trotters: P = 0.01), haematocrit percentage (Standardbred trotters: P = 0.005), neutrophil percentage (jumping horses: P = 0.0003), lymphocyte percentage (jumping horses: P = 0.0003), monocyte percentage (Standardbred trotters: P = 0.0008), lymphocyte β-AR numbers (jumping horses: P = 0.01; Arabian Endurance horses: P = 0.016; Standardbred trotters: P = 0.05), plasma adrenaline concentration (Standardbred trotters: P = 0.0001) and plasma noradrenaline levels (Standardbred trotters: P = 0.003). It is concluded that acute increases in plasma catecholamine concentrations depended on the exercise performed and may induce up-regulation of β-AR in equine lymphocytes. However, the exact mechanism of β-AR up-regulation still remains unclear.