Fox J E, Daniel E E, Jury J, Fox A E, Collins S M
Life Sci. 1983 Aug 29;33(9):817-25. doi: 10.1016/0024-3205(83)90619-7.
Motilin, pentagastrin and substance P (SP), injected intra-arterially into the canine gastric corpus in vivo increased the amplitude of contractions by an action dependent on activation of cholinergic nerves; i.e. atropine or tetrodotoxin (TTX) completely blocked the responses to motilin and pentagastrin and increased the ED50 of SP. TTX and atropine were not equally effective in increasing the ED50 for SP in vivo and the effect of combining them depended on the order of their addition. Both were much more effective than the SP analog D-Pro2, D-Trp7,9 SP (DSP) which appeared to be a weak antagonist of actions dependent on neural activity. In strips from the same region in vitro no receptors dependent on cholinergic nerve activation could be demonstrated for any peptide; i.e., all were atropine- and TTX-insensitive. Motilin, as expected in the absence of such receptors caused no contractile response in vitro. SP, also as predicted, caused contractions suggesting that a smooth muscle receptor, independent of nerve activation was present. However contrary to expectation pentagastrin induced an atropine and TTX-insensitive increase in the amplitude and frequency of contractions. These results show that 1) the most sensitive sites of action of a number of excitatory peptides depend on cholinergic nerve function in vivo; 2) such sites or the nerve activity on which they depend cannot be demonstrated in vitro; 3) SP has an additional site of action on smooth muscle demonstrable in vivo and in vitro, but motilin does not; 4) pentagastrin has only an action dependent on nerve function in vivo, but manifests an action independent of nerve function in vitro. We conclude that sites and mechanisms of action of peptides cannot be assumed to be identical in vivo and in vitro. Actions dependent on nerves are often lost in vitro and not all smooth muscle actions can be demonstrated in vivo.
在体内向犬胃体动脉内注射胃动素、五肽胃泌素和P物质（SP），通过依赖胆碱能神经激活的作用增加收缩幅度；即阿托品或河豚毒素（TTX）完全阻断对胃动素和五肽胃泌素的反应，并增加SP的半数有效剂量（ED50）。TTX和阿托品在增加体SP的ED50方面效果并不相同，联合使用它们的效果取决于添加顺序。两者都比SP类似物D-脯氨酸2、D-色氨酸7,9 SP（DSP）有效得多，DSP似乎是神经活动依赖性作用的弱拮抗剂。在体外取自同一区域的肌条中，未发现任何肽存在依赖胆碱能神经激活的受体；即所有肽对阿托品和TTX均不敏感。正如在不存在此类受体时所预期的那样，胃动素在体外未引起收缩反应。同样如预期的那样，SP引起收缩，表明存在一个独立于神经激活的平滑肌受体。然而，与预期相反，五肽胃泌素引起了对阿托品和TTX不敏感的收缩幅度和频率增加。这些结果表明：1）多种兴奋性肽最敏感的作用位点在体内依赖胆碱能神经功能；2）此类位点或它们所依赖的神经活动在体外无法证实；3）SP在体内和体外均可证明对平滑肌有额外的作用位点，但胃动素没有；4）五肽胃泌素在体内仅具有依赖神经功能的作用，但在体外表现出独立于神经功能的作用。我们得出结论，不能假定肽在体内和体外的作用位点和机制是相同的。依赖神经的作用在体外常常消失，并非所有平滑肌作用在体内都能得到证实。
