title: Non-opiate and peripheral-opiate cardiovascular effects of morphine in conscious dogs.
abstract: Morphine is generally regarded as having a centrally mediated depressant effect upon the cardiovascular system. We report here that in chronically instrumented conscious dogs, morphine produces a biphasic response; heart rate and mean arterial pressure initially increase followed by a reduction to below baseline levels. Differential inhibition by naloxone (NAL) and methylnaloxone (MRZ), a quaternary opiate antagonist which does not readily enter the CNS, suggests that the initial pressor response is mediated peripherally, while the latter occurring vasodepressor and bradycardic responses are mediated centrally. The initial tachycardia was not inhibited by NAL or MRZ, suggesting that this response is mediated by a non-opiate mechanism.
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002320:Cardiovascular Physiological Phenomena; D002319:Cardiovascular System / Q000187:drug effects*; D004285:Dogs; D004743:Enkephalin, Leucine / Q000494:pharmacology; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D007700:Kinetics; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D010111:Oxymorphone / Q000494:pharmacology
chemical_list: D009270:Naloxone; D004743:Enkephalin, Leucine; D009020:Morphine; D010111:Oxymorphone