Morphine enhances nitric oxide release in the mammalian gastrointestinal tract via the micro(3) opiate receptor subtype: a hormonal role for endogenous morphine.
Studies from our laboratory have revealed a novel micro opiate receptor, micro(3), which is expressed in both human vascular tissues and leukocytes. The micro(3) receptor is selective for opiate alkaloids, insensitive to opioid peptides and is coupled to constitutive nitric oxide (cNO) release. We now identify the micro(3) receptor characteristics in mammalian gut tissues. It appears that the various regions of the mouse gut release low levels of NO (0.02 to 4.6 nM ) in a pulsatile manner. We demonstrate that morphine stimulates cNO release (peak level 17 nM) in the mouse stomach, small intestine and large intestine in a naloxone and L-NAME antagonizable manner. Opioid peptides do not exhibit cNO-stimulating capabilities in these tissues. Taken together, we surmise morphine acts as a hormone to limit gut activity via micro(3) coupled to NO release since micro opiate receptors are found in the gut and endogenous morphine is not but is found in blood.
Stefano
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Neuroscience Research Institute, State University of New York / College at Old Westbury, Old Westbury, New York 11568, USA. gstefano@sunynri.org
Zhu
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Cadet
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Bilfinger
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Mantione
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D000818:Animals; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000502:physiology*; D041981:Gastrointestinal Tract / Q000187:drug effects* / Q000378:metabolism*; D015870:Gene Expression / Q000502:physiology; D008322:Mammals / Q000033:anatomy & histology / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D004723:Endorphins; D017450:Receptors, Opioid, mu; D009569:Nitric Oxide; D009270:Naloxone; D009020:Morphine; D019331:NG-Nitroarginine Methyl Ester