NEUROPHYSIOLOGICAL BASIS OF MYOCARDIAL ISCHEMIC PAIN-INDUCED RECTAL REFLEX IN THE ANESTHETIZED CAT: AN EXPERIMENTAL STUDY
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Keywords
Cardiogenic reflex, Algesic agent-induced rectal response, Cardiac ischemic pain, and Gastro Intestinal movement
Abstract
Background: Clinically it has been observed that heart failure due to cardiac ischemia is often associated with different reflexes like bradycardia, hypotension, urge of urination, and stool. It is also well documented that different chemical mediators e.g.; bradykinin, prostaglandins, lactic acid, etc. are released during myocardial ischemia which takes part in the genesis of cardiac pain to initiate different visceral and somatic reflexes. The present set of investigations is designed to study the afferent and efferent pathways responsible for this cardiogenic defecatory reflex by studying rectal movement.
Methods; Experiments were carried out on 54 lightly anesthetized, artificially ventilated cats of either sex after an overnight fast with water ad libitum. Cardiac nociceptors are stimulated by epicardial application of nicotine or lactic acid or capsaicin and its effect on rectal motility was studied along with its neurophysiological mechanism.
Results; Epicardial application of nicotine, lactic acid, or prostaglandin induced the biphasic rectal response which was abolished after sectioning of the Left inferior cardiac sympathetic nerve (LICN) but not by cardiac vagotomy. The same response was also abolished by pelvic nerve sectioning but not by sectioning of the gastric vagus or splanchnic nerve.
Conclusions; Thus the present study reveals that epicardial application of algesic agents like nicotine, lactic acid, and prostaglandin excites the cardiac nociceptors to initiate a biphasic rectal response that might be the causative factor of defecation during cardiac ischemia-induced heart failure. It also indicates that the afferent and efferent limb for such reflex is the cardiac sympathetic and the pelvic nerve respectively.
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Dr Asim Kumar Basak
Professor, Department of Allied Health Sciences, Brainware University, Barasat, Kolkata, West Bengal-700125