Mehta A K, Kulkarni S K
Arch Int Pharmacodyn Ther. 1983 Aug;264(2):187-94.
Adenosine, 2-chloroadenosine, adenosine triphosphate (ATP) and adenosine tetraphosphate induced concentration-dependent relaxation of rat caecum. Caffeine as well as theophylline, at concentrations (25-100 microM) lower than that known to produce significant phosphodiesterase inhibition, shifted the concentration-response curve for adenosine to the right in a parallel fashion without diminishing the maximal response. The pA2 values for caffeine and theophylline against adenosine were found to be 4.6 +/- 0.26 (slope = 0.97 +/- 0.05) and 4.9 +/- 0.28 (slope = 0.98 +/- 0.07), respectively. Though the relaxant effect of adenosine tetraphosphate was blocked in a non-competitive manner by quinidine (5 microM) and phenoxybenzamine (25 microM), theophylline or caffeine (50 microM) failed to block this response. Similarly, quinidine also blocked the relaxant effect of ATP in a non-competitive manner. Besides, the relaxant effect due to adensine was rapid in onset as compared to a slow relaxant effect of ATP. These observations suggest the presence of P1- and P2-purinoceptors in the caecum. The activation of these receptors by adenosine and ATP, respectively, leads to relaxation of the tissue.
腺苷、2-氯腺苷、三磷酸腺苷（ATP）和四磷酸腺苷可引起大鼠盲肠浓度依赖性舒张。咖啡因以及茶碱，在低于已知能产生显著磷酸二酯酶抑制作用的浓度（25 - 100微摩尔）时，使腺苷的浓度 - 反应曲线平行右移，而不降低最大反应。咖啡因和茶碱对腺苷的pA2值分别为4.6±0.26（斜率 = 0.97±0.05）和4.9±0.28（斜率 = 0.98±0.07）。虽然四磷酸腺苷的舒张作用被奎尼丁（5微摩尔）和酚苄明（25微摩尔）以非竞争性方式阻断，但茶碱或咖啡因（50微摩尔）未能阻断此反应。同样，奎尼丁也以非竞争性方式阻断ATP的舒张作用。此外，与ATP缓慢的舒张作用相比，腺苷引起的舒张作用起效迅速。这些观察结果提示盲肠中存在P1和P2嘌呤受体。腺苷和ATP分别激活这些受体导致组织舒张。
