Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Acta Physiol (Oxf). 2010 Jun;199(2):231-41. doi: 10.1111/j.1748-1716.2010.02090.x. Epub 2010 Jan 30.
Adenosine modulates neurotransmission and in the intestine adenosine is continuously released both from nerves and from smooth muscle. The main effect is modulation of contractile activity by inhibition of neurotransmitter release and by direct smooth muscle relaxation. Estimation of adenosine concentration at the receptors is difficult due to metabolic inactivation. We hypothesized that endogenous adenosine concentrations can be calculated by using adenosine receptor antagonist and agonist and dose ratio (DR) equations.
Plexus-containing guinea-pig ileum longitudinal smooth muscle preparations were made to contract intermittently by electrical field stimulation in organ baths. Schild plot regressions were constructed with 2-chloroadenosine (agonist) and 8-(p-sulfophenyl)theophylline (8-PST; antagonist). In separate experiments the reversing or enhancing effect of 8-PST and the inhibiting effect of 2-chloroadenosine (CADO) were analysed in the absence or presence of an adenosine uptake inhibitor (dilazep), and nucleoside overflow was measured by HPLC.
Using the obtained DR, baseline adenosine concentration was calculated to 28 nm expressed as CADO activity, which increased dose dependently after addition of 10(-6) m dilazep to 150 nm (P < 0.05). HPLC measurements yielded a lower fractional increment (80%) in adenosine during dilazep, than found in the pharmacological determination (440%).
Endogenous adenosine is an important modulator of intestinal neuro-effector activity, operating in the linear part of the dose-response curve. Other adenosine-like agonists might contribute to neuromodulation and the derived formulas can be used to calculate endogenous agonist activity, which is markedly affected by nucleoside uptake inhibition. The method described should be suitable for other endogenous signalling molecules in many biological systems.
腺苷调节神经递质的释放，在肠道中，神经和平滑肌都会持续释放腺苷。其主要作用是通过抑制神经递质的释放和直接松弛平滑肌来调节收缩活性。由于代谢失活，估计受体部位的腺苷浓度很困难。我们假设可以使用腺苷受体激动剂和拮抗剂以及剂量比（DR）方程来计算内源性腺苷浓度。
在器官浴中，通过电场刺激使含有神经丛的豚鼠回肠纵向平滑肌制剂间歇性收缩。用 2-氯腺苷（激动剂）和 8-（对磺基苯）茶碱（8-PST；拮抗剂）构建 Schild 图回归。在单独的实验中，分析了 8-PST 的反转或增强作用以及 2-氯腺苷（CADO）的抑制作用在不存在或存在腺苷摄取抑制剂（地拉卓）的情况下，并用 HPLC 测量核苷溢出。
使用获得的 DR，将基线腺苷浓度计算为以 CADO 活性表示的 28nm，加入 10（-6）m 地拉卓后，浓度剂量依赖性地增加至 150nm（P < 0.05）。HPLC 测量结果显示，在地拉卓存在的情况下，核苷的分数增加（80%）低于药理学测定值（440%）。
内源性腺苷是肠道神经效应器活动的重要调节剂，作用于剂量反应曲线的线性部分。其他类似腺苷的激动剂可能有助于神经调节，所推导的公式可用于计算内源性激动剂活性，该活性受核苷摄取抑制的显著影响。所描述的方法应适用于许多生物系统中的其他内源性信号分子。
