Heart rate fluctuations in rabbits during different behavioural states

Heart rate fluctuations (HRF) were investigated in 18 adult female rabbits (Weisses Grosssilber) in chronical experiments at rest, during motor activity, passive and active avoidance. Pharmacological blockades of the neurovegetative transmission were used to determine the characteristics of neurovegetative mediation during the behavioural states examined. Mean heart rate was always increased during vagal blockade and decreased during beta-adrenergic blockade. At rest the HRF in rabbits are mainly vagally mediated. Vagal blockade reduced the overall heart rate variability by more than 50%. Vagal blockade did not abolish respiratory heart rate fluctuations. If the mean respiratory frequency is greater than half of the mean heart rate frequently occurring in rabbits, the respiratory HRF are generated not synchronously with respiration but in a slower frequency range according to the physiologic effect of "cardiac aliasing". The movement related heart rate increase was absent if the movements were performed during combined beta adrenergic and vagal blockade. The heart rate reaction during passive avoidance was characterized by a heart rate deceleration abolished by vagal blockade. Respiratory HR were increased. Furthermore, the heart rate was returned to the previous mean level and the slow HRF not induced by respiration increased, mediated by beta adrenergic activation. Vagal blockade and beta adrenergic blockade diminished the heart rate acceleration and reduced the overall heart rate variability by more than 50% during active avoidance. Combined vagal and beta-adrenergic blockade fully abolished the heart rate acceleration effect during active avoidance. The ratio of the vagal to sympathetic reaction components differed in behavioural types.