Phenyldiguanide activates cardiac receptors to produce responses by involving three different efferent pathways in anaesthetized rats.
The present study was undertaken to determine the afferent and efferent pathways involved in the phenyldiguanide (PDG)-induced reflex response in rats. Intravenous (iv) injection of PDG (10 microg/kg), produced hypotension, bradycardia and apnea over a period of time. Bilateral vagotomy abolished the PDG-induced reflex changes. Atropine (2 mg/kg; iv) blocked only the bradycardiac response produced by PDG, while prazosin (0.5 mg/kg; iv) blocked the hypotensive response, and bilateral vagotomy in these animals abolished the apneic response. In separate series of experiments, intrapericardial injection of lignocaine abolished the hypotensive and bradycardiac responses evoked by PDG in artificially ventilated rats. The results reveal that the PDG-induced reflex is mediated through vagal afferents originating from the heart and efferents involve three different pathways. The bradycardiac response was through the muscarinic receptors, the hypotension is mediated through alpha1 adrenoceptors and the apnea presumably through the spinal motoneurones supplying the respiratory muscles.
Bagchi
S
S
Department of Physiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi 221005, India.
Deshpande
S B
SB
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000779:Anesthetics, Local; D000818:Animals; D001049:Apnea / Q000139:chemically induced; D001645:Biguanides / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000139:chemically induced; D005260:Female; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D007022:Hypotension / Q000139:chemically induced; D007267:Injections; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D009046:Motor Neurons / Q000378:metabolism; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D012018:Reflex / Q000187:drug effects*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D014628:Vagotomy
D000317:Adrenergic alpha-Antagonists; D000779:Anesthetics, Local; D001645:Biguanides; D018727:Muscarinic Antagonists; D018340:Receptors, Adrenergic, alpha-1; D011976:Receptors, Muscarinic; D017366:Serotonin Receptor Agonists; D008012:Lidocaine; C008846:phenyl biguanide