ADENOSINE RECEPTOR AGONISTS AND ANTAGONISTS

腺苷通过以下途径调节广泛的生理功能 与至少两种主要的腺苷受体相互作用。 A1和A3类腺苷受体对血管生成有抑制作用 腺苷环化酶，而A2类对腺苷有刺激作用 循环酶。腺苷受体的亚类也会出现。其中一些 对钙通道有抑制作用，对钾离子有刺激作用 通道，有的激活鸟苷环化酶，有的调节磷脂 翻身和一些动作会导致肌肉松弛。可能的地点 咖啡因和茶碱除阻断A1-、A2a-和A2a-外的作用 A2B-腺苷受体的定义仍然不明确。抑制 磷酸二酯酶似乎与行为刺激剂无关 黄嘌呤中咖啡因和茶碱的活性 磷酸二酯酶抑制剂是一种行为抑制药。效应 在GABA/A受体上可能解释了咖啡因引起焦虑的特性， 而咖啡因对钙释放的调节作用 兰诺定敏感的细胞内池尚不清楚。抗焦虑药 吡唑并吡啶，如咔唑，与咖啡因有共同作用，作用 在以下位置：i)腺苷受体，ii) 磷酸二酯酶，iii)GABA/A受体，以及iv)钙释放。一个 黄嘌呤和吡唑并吡啶的范围正在研究中 关于这些不同的行动地点。两者都是 腺苷受体拮抗剂。黄嘌呤类化合物抑制 [~3H]安定结合，而吡唑并吡啶具有双相效应； 刺激，然后在较高浓度下抑制。慢性 黄嘌呤/吡唑并吡啶类化合物对中心密度的影响 受体和对不同介质的行为反应也在 比较一下。在肥大细胞系中，腺苷类似物似乎能引起 依赖IP3的A3-腺苷释放细胞内钙 受体。但是，IP2和IP1的总累积仅出现 部分依赖于A3-腺苷受体介导的途径。

Adenosine regulates a wide range of physiological functions through interaction with at least two major classes of adenosine receptors. The A1 and A3 classes of adenosine receptors are inhibitory to adenylate cyclase, while the A2 class is stimulatory to adenylate cyclase. Subclasses of adenosine receptors also occur. Some of these are inhibitory to calcium channels, some are stimulatory to potassium channels, some activate guanylate cyclase, some modulate phospholipid turn-over and some cause smooth muscle relaxation. Possible sites of action of caffeine and theophylline besides blockade of A1-, A2a- and A2b-adenosine receptors remain poorly defined. Inhibition of phosphodiesterase does not seem relevant to the behavioral stimulant activity of caffeine and theophylline since xanthines that are potent inhibitors of phosphodiesterases are behavioral depressants. Effects on GABA/A receptors may account for anxiogenic properties of caffeine, while a role for caffeine-elicited modulation of calcium-release from ryanodine-sensitive intracellular pools is unclear. The anxiolytic pyrazolopyridines, such as cartazolate, share with caffeine, actions at the following sites: i)adenosine receptors, ii) phosphodiesterases, iii) GABA/A-receptors, and iv) calcium release. A range of xanthines and of pyrazolopyridines are being investigated with respect to these different sites of action. Both are antagonists at adenosine receptors. The xanthines inhibit [3H]diazepam binding, while pyrazolopyridines have biphasic effects; stimulatory, and then at higher concentrations inhibitory. Chronic effects of xanthines/pyrazolopyridines on densities of central receptors and behavioral responses to different agents are also being compared. In a mast cell line, adenosine analogs appear to cause an IP3-dependent release of intracellular calcium through an A3-adenosine receptor. However, total accumulation of IP2 and IP1 appears only partly dependent on the A3-adenosine receptor-mediated pathway.