Bradykinin-induced Nociceptive Responses Are More Potent Than Capsaicin-Induced Responses in Rat Models

Background: Peripheral blood vessels are concerned with sensing the perivascular nociceptive information and signaling it to the higher centers through ipsilateral somatic nerves, thereby regulating the cardiorespiratory parameters by means of vasosensory reflex responses. Aims and Objectives: The present study was conducted to compare the potency of nociceptive responses elicited by bradykinin (BK) with the capsaicin-induced responses. Materials and Methods: Charles-Foster rats were anesthetized with urethane and injected intraperitoneally. After tracheostomy, the right femoral artery was cannulated with a 24G, double ported cannula for administering the chemicals/saline through vertical port and to record the blood pressure (BP) through horizontal port. BP, Electrocardiogram, and respiratory movements were recorded. Results: Injection of capsaicin into a segment of femoral artery evoked instantaneous transient tachypnoeic, hyperventilatory, and hypotensive responses. BK also produced similar pattern of nociceptive responses along with a transient fall in heart rate. In addition, the vasosensory responses produced by BK are of greater magnitude as compared to the capsaicin. Conclusions: BK is more potent in eliciting reflex nociceptive responses as compared to capsaicin. Further, BK has an additional cardioprotective role by slowing the heart, in the events of acute inflammation.