Fox J E, Daniel E E
Am J Physiol. 1987 Aug;253(2 Pt 1):G179-88. doi: 10.1152/ajpgi.1987.253.2.G179.
Methionine-enkephalin (Met-Enk) and dynorphin were injected intra-arterially into the distal stomach and small intestine of the anesthetized dog during quiescence and phasic activity initiated by field stimulation or intra-arterially administered motilin. The effects of morphine, [D-Ala2, N-Me-Phe4, Met(O)5-ol]enkephalin (Met-ol), and [D-Ala2, D-Leu5]enkephalin (DADLE) were also examined. Opiates had no effect on the quiescent stomach but produced inhibition of phasic contractions (potencies: dynorphin greater than Met-Enk greater than Met-ol greater than DADLE greater than morphine). In the quiescent small intestine, low doses of each opiate, except dynorphin, produced excitation (potencies: Met-Enk congruent to Met-ol congruent to DADLE greater than morphine). Excitation apparently occurred via release of acetylcholine and a partially naloxone-sensitive direct stimulation of smooth muscle. During phasic activity all opiates produced inhibition of phasic muscular contractions (relative potencies as in the stomach). Inhibition by dynorphin in both the stomach and small intestine was shown to occur via naloxone-sensitive inhibition of release of acetylcholine from nerves. Thus inhibition by opiates appears common to the stomach and small intestine, and excitation is a function of opiate action only in the small intestine. Dynorphin may be a natural neuropeptide causing inhibition, and Met-Enk may be a natural neuropeptide causing excitation.
在麻醉犬处于静息状态以及由场刺激或动脉内注射胃动素引发的相性活动期间，将甲硫氨酸脑啡肽（Met-Enk）和强啡肽动脉内注射到犬的远端胃和小肠中。还研究了吗啡、[D-丙氨酸2，N-甲基苯丙氨酸4，甲硫氨酸（O）5-醇]脑啡肽（Met-ol）和[D-丙氨酸2，D-亮氨酸5]脑啡肽（DADLE）的作用。阿片类药物对静息状态的胃无影响，但可抑制相性收缩（效力：强啡肽＞甲硫氨酸脑啡肽＞Met-ol＞DADLE＞吗啡）。在静息状态的小肠中，除强啡肽外，每种阿片类药物的低剂量均可产生兴奋作用（效力：甲硫氨酸脑啡肽≈Met-ol≈DADLE＞吗啡）。兴奋显然是通过乙酰胆碱的释放以及对平滑肌的部分纳洛酮敏感的直接刺激而发生的。在相性活动期间，所有阿片类药物均抑制相性肌肉收缩（相对效力与在胃中相同）。强啡肽在胃和小肠中的抑制作用均通过对神经释放乙酰胆碱的纳洛酮敏感抑制而发生。因此，阿片类药物的抑制作用在胃和小肠中似乎是常见的，而兴奋作用仅是阿片类药物在小肠中的作用。强啡肽可能是一种引起抑制的天然神经肽，而甲硫氨酸脑啡肽可能是一种引起兴奋的天然神经肽。
