Injection of Mesobuthus tamulus venom in distal segment of femoral artery evokes hyperventilatory and hypertensive responses in anaesthetised rats.

Intra-arterial (i.a.) injection of Indian red scorpion (Mesobuthus tamulus; BT) venom produces cardiorespiratory changes by involving perivascular receptors. The afferents involved in mediating these reflex responses are not known. The present investigation was conducted to examine the afferents mediating the vasosensory reflexes evoked by i.a. injection of BT venom in the peripheral end of femoral artery in urethane anaesthetised rats. Blood pressure (BP), ECG (for heart rate), and respiratory movements (for rate and depth) were recorded for 30min after the i.a. injection of venom. Minute ventilation (MV) was computed by using appropriate calibrations for depth and rate of respiration. After the injection of venom, there was immediate hyperventilatory, intermediate hypertensive and delayed bradycardiac response. Equal volume of saline (0.10ml, i.a.) did not produce any cardiorespiratory changes thus, eliminating the possibility of stretch mediated responses. Sectioning of ipsilateral sciatic and femoral nerves attenuated the hyperventilatory and hypertensive responses produced by venom significantly. After the neurotomy, the latency of bradycardiac response was shortened significantly. Even the time to reach the peak bradycardiac response was also shortened. The data provide evidences for the partial involvement of somatic nerves in mediating the vascular reflexes.