Buthus tamulus venom-induced vasosensory reflexes are mediated through efferent pathways in sympathetic and vagal parasympathetics

Present study was conducted to identify the efferents mediating the vasosensory reflexes evoked by intra-arterial (i.a.) injection of Mesobuthus tamulus (BT; 1 mg/kg) venom in the distal segment of femoral artery. Blood pressure (BP), electrocardiogram (ECG) and respiratory movements were recorded for 60 min after the i.a. injection of venom in urethane anaesthetised rats. Intra-arterial injection of venom produces immediate-tachypnoeic, intermediate-hypertensive and delayed-bradycardiac responses. Respiratory changes manifested as immediate increase (by 40%) in respiratory frequency (RF) followed by a decrease (by 40%) within 1 min and subsequent sustained increase (50%) up to 60 min. Increase in BP began after the respiratory changes, peaked (50%) at 5 min and remained at that level throughout. The decrease in heart rate (HR) began after 5 min, peaked (60%) at 10 min and recovered subsequently (40%) but remained below the initial level. In terazosin pretreated animals, the venom-induced cardiorespiratory changes were attenuated significantly. Whereas in vagotomized group, venom-induced respiratory changes and HR changes were blocked but not the BP changes. The findings suggest that the venom-induced vasosensory responses involve α1-adrenoceptors for BP and vagal efferents for HR changes.