Aguilar María J, Estañ Luis, Martínez-Mir Inocencia, Martínez-Abad Manuel, Rubio Elena, Morales-Olivas Francisco J
Departamento de Farmacología, Universidad de Valencia, Valencia, España.
Can J Physiol Pharmacol. 2005 Jun;83(6):447-52. doi: 10.1139/y05-031.
The aim of the present work is to investigate the effects of dopamine on isolated rat colon strips, and whether dopamine receptors are involved in these effects. Experiments on spontaneous motility and under potassium contraction were performed with dopamine and isoprenaline, both in the absence and presence of antagonists (distal colon strips, isotonic recording, Tyrode solution, 31 degrees C, 1 g of resting tension). At higher concentration (10(-4) mol/L), dopamine abolished spontaneous motility of the rat colon and this effect was not modified by antagonists. In isolated rat colon strips that were depolarized with potassium, dopamine produced concentration-dependent relaxation, without significant differences in reserpinized rats. Preincubation with sulpiride or Sch 23390, dopamine antagonists, did not modify the effects of dopamine. Propranolol shifted the concentration-response curve to the right, though in a noncompetitive manner. Prazosin and yohimbine (alpha-antagonists) did not modify the response to dopamine. Isoprenaline produced a concentration-dependent relaxant response to the KCl-induced contraction antagonized by propranolol, but not by prazosin, in a noncompetitive manner. In conclusion, dopamine exhibits a relaxant effect on the isolated rat colon, which is not mediated by specific dopamine receptors or alpha-adrenoceptors but it may be mediated by atypical beta-adrenoceptors.
本研究的目的是探讨多巴胺对离体大鼠结肠条的作用，以及多巴胺受体是否参与这些作用。分别在有无拮抗剂的情况下，用多巴胺和异丙肾上腺素对大鼠结肠条进行了自发运动和钾离子收缩实验（远端结肠条，等张记录，台氏液，31℃，1g静息张力）。在较高浓度（10⁻⁴mol/L）时，多巴胺可消除大鼠结肠的自发运动，且这种作用不受拮抗剂的影响。在经钾离子去极化的离体大鼠结肠条中，多巴胺产生浓度依赖性舒张作用，利血平化大鼠无显著差异。预先用多巴胺拮抗剂舒必利或Sch 23390孵育，并不改变多巴胺的作用。普萘洛尔使浓度-反应曲线右移，但为非竞争性方式。哌唑嗪和育亨宾（α拮抗剂）不改变对多巴胺的反应。异丙肾上腺素对氯化钾诱导的收缩产生浓度依赖性舒张反应，普萘洛尔可拮抗该反应，但哌唑嗪不能，为非竞争性方式。总之，多巴胺对离体大鼠结肠具有舒张作用，该作用不是由特异性多巴胺受体或α肾上腺素能受体介导的，可能是由非典型β肾上腺素能受体介导的。
