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The putative somatostatin antagonist cyclo-somatostatin has opioid agonist effects in gastrointestinal preparations

机译：推定的生长抑素拮抗剂环生长抑素在胃肠道制剂中具有阿片样物质激动剂作用

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Aims: Specificity of receptor antagonists used is crucial for clarifying physiological/pathophysiological roles of the respective endogenous agonist. We studied the effects (somatostatin antagonist and possibly other actions) of cyclo-somatostatin (CSST), a putative somatostatin receptor antagonist on the guinea-pig small intestine, a preparation where somatostatin causes inhibition of nerve-mediated contractions. Main methods: In isolated organ experiments, half-maximal cholinergic "twitch" contractions of the guinea-pig small intestine were evoked or tonic contractions of the rat stomach fundus strip (in the presence of physostigmine) were elicited by electrical field stimulation. The effects of somatostatin (somatostatin-14), CSST, naloxone, as well as of direct smooth muscle stimulants were examined. Key findings: Somatostatin (10 nM-1 μM) caused transient inhibition of the twitch contraction, in a naloxone-insensitive manner. Surprisingly, CSST (0.3-1 μM) also inhibited twitch contractions (more than 50% reduction at 1 μM). This effect was prevented by the opioid receptor antagonist naloxone. Responses to acetylcholine or histamine were not or only minimally inhibited by CSST (up to 3 μM). CSST (0.3 μM in the absence or 1-10 μM in the presence of naloxone) failed to inhibit the effect of somatostatin. The SST 2 receptor antagonist CYN-154806 (3 μM) attenuated the effect of somatostatin and failed to evoke naloxone-sensitive inhibition of the twitch response. The naloxone-sensitive inhibitory effect of CSST on cholinergic contractions was also confirmed in the rat stomach fundus preparation. Significance: Cyclo-somatostatin exerts opioid agonist activity in the two preparations tested, while it does not behave as a somatostatin-receptor antagonist in the guinea-pig intestine.
机译：目的：所用受体拮抗剂的特异性对于阐明各自内源性激动剂的生理/病理生理作用至关重要。我们研究了环生长抑素（CSST）（一种推定的生长抑素受体拮抗剂）对豚鼠小肠的作用（生长抑素拮抗剂和其他作用），该制剂可抑制生长抑素抑制神经介导的收缩。主要方法：在孤立的器官实验中，诱发豚鼠小肠的最大胆碱能“抽搐”收缩，或通过电场刺激引起大鼠胃底条的强直收缩（在有毒扁豆碱存在下）。检查了生长抑素（somatostatin-14），CSST，纳洛酮以及直接平滑肌兴奋剂的作用。主要发现：生长抑素（10 nM-1μM）以纳洛酮不敏感的方式引起了抽搐收缩的短暂抑制。出乎意料的是，CSST（0.3-1μM）还抑制了抽搐收缩（在1μM时降低了50％以上）。阿片受体拮抗剂纳洛酮阻止了该作用。 CSST对乙酰胆碱或组胺的反应没有或仅有极少的抑制作用（最高3μM）。 CSST（不存在时为0.3μM，在纳洛酮存在时为1-10μM）未能抑制生长抑素的作用。 SST 2受体拮抗剂CYN-154806（3μM）减弱了生长抑素的作用，并且未能引起纳洛酮敏感的抽搐反应抑制。在大鼠胃底制剂中也证实了CSST对纳洛酮敏感的胆碱能收缩抑制作用。意义：环-他汀类药物在两种测试制剂中均发挥阿片样物质激动剂的活性，而在豚鼠肠道中却不充当生长抑素受体拮抗剂。

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