Fox J E, Daniel E E
Am J Physiol. 1987 Aug;253(2 Pt 1):G189-94. doi: 10.1152/ajpgi.1987.253.2.G189.
Field stimulation of intrinsic nerves (40 V, 0.5 ms, 1-5 pps for 3-10 min) or intraarterial administration of motilin (10(-11)-10(-8 mol) caused contractions of the canine small intestine that were partially resistant to atropine and abolished by tetrodotoxin. Naloxone (10 micrograms ia or 200 micrograms/kg iv) in selective doses (10(-10)-10(-9) mol) that left responses to intra-arterial acetylcholine unaffected reduced responses to field stimulation or motilin in the ileum in the absence of atropine or residual responses in the presence of atropine. Results in the jejunum were similar except that selective doses of naloxone (10 micrograms ia or 200 micrograms/kg iv) increased the sensitivity to motilin in the absence of atropine. Higher doses of naloxone decreased these responses. In common with naloxone, tachyphylaxis to methionine-enkephalin (Met-Enk) reduced the responses to field stimulation or motilin before or after atropine but did not affect the responses to acetylcholine before or the responses to field stimulation of muscle after atropine. These findings are consistent with the hypothesis that Met-Enk may be a noncholinergic, excitatory transmitter released by field stimulation of nerves or intra-arterial motilin in the canine intestine.
对内脏神经进行场刺激（40伏，0.5毫秒，1 - 5次/秒，持续3 - 10分钟）或动脉内注射胃动素（10⁻¹¹ - 10⁻⁸摩尔）可引起犬小肠收缩，这种收缩对阿托品有部分抗性，且可被河豚毒素消除。选择性剂量（10⁻¹⁰ - 10⁻⁹摩尔）的纳洛酮（动脉内注射10微克或静脉注射200微克/千克）在不影响对动脉内乙酰胆碱反应的情况下，可降低在无阿托品时回肠对场刺激或胃动素的反应，或在有阿托品时的残余反应。空肠的结果相似，只是在无阿托品时，选择性剂量的纳洛酮（动脉内注射10微克或静脉注射200微克/千克）会增加对胃动素的敏感性。更高剂量的纳洛酮会降低这些反应。与纳洛酮一样，对甲硫氨酸脑啡肽（Met - Enk）的快速耐受性会降低在阿托品给药前后对场刺激或胃动素的反应，但不影响给药前对乙酰胆碱的反应或给药后对肌肉场刺激的反应。这些发现与以下假设一致，即Met - Enk可能是一种非胆碱能兴奋性递质，由犬肠道神经的场刺激或动脉内注射胃动素释放。
