Lomholt M, Nedergaard O A
Department of Pharmacology, School of Medicine, Odense University, Denmark.
Pharmacol Toxicol. 2000 Jun;86(6):264-9. doi: 10.1111/j.0901-9928.2000.860604.x.
The prejunctional muscarinic modulation of stimulation-evoked release of 3H-noradrenaline from sympathetic neurones in rabbit aorta was examined. The role of transmitter uptake, alpha-adrenoceptor blockade, stimulation frequency and endothelium on the modulation was investigated. Rings of aorta were incubated with (-)-3H-noradrenaline and subsequently subjected to electrical-field stimulation. Fractional 3H-overflow was determined by liquid scintillation counting. Acetylcholine (10(-8)-3 x 10(-6) M) added cumulatively, reduced the stimulation-evoked 3H-overflow up to 80%. The effect of acetylcholine was the same in intact and endothelium-free aorta. The inhibitory effect of acetylcholine was inversely related to the frequency of stimulation (1-10 Hz). The maximal inhibition (%) was 80 (1 Hz), 53 (3 Hz) and 14 (10 Hz). The inhibitory effect of acetylcholine (10(-6) M) and carbachol (10(-5) M) reached a maximum 15 min. after addition and then remained almost constant. Cocaine (3 x 10(-5) M) did not alter the effect of acetylcholine. Desipramine (10(-6) M) and corticosterone (4 x 10(-5) M) attenuated the inhibition seen with low concentrations (10(-8)-10(-7) M) of acetylcholine. The acetylcholine-induced inhibition was antagonized by desipramine. Cocaine plus corticosterone attenuated the inhibition seen with high concentrations (10(-6)-3 x 10(-6) M) of acetylcholine. Rauwolscine (10(-6) M) enhanced the maximal inhibitory effect of acetylcholine. We conclude that the inhibitory effect of acetylcholine on 3H-overflow from rabbit aorta preloaded with 3H-noradrenaline is (1) inversely related to stimulation frequency; (2) independent of endothelium; (3) unaffected by neuronal and extraneuronal transmitter uptake; (4) that cocaine is not a prejunctional muscarinic antagonist; (5) that cocaine, but not desipramine, is suited as a neuronal uptake inhibitor in studies of prejunctional muscarinic receptor subtypes; and (6) and that there is an inverse interaction between prejunctional alpha2-adrenoceptors and muscarinic receptors.
研究了家兔主动脉交感神经中，刺激诱发的3H-去甲肾上腺素释放的节前毒蕈碱调节作用。研究了递质摄取、α-肾上腺素能受体阻断、刺激频率和内皮对该调节作用的影响。将主动脉环与（-）-3H-去甲肾上腺素一起孵育，随后进行电场刺激。通过液体闪烁计数法测定3H-溢出分数。累积添加乙酰胆碱（10^(-8)-3×10^(-6)M）可使刺激诱发的3H-溢出减少高达80%。在完整主动脉和无内皮主动脉中，乙酰胆碱的作用相同。乙酰胆碱的抑制作用与刺激频率（1-10Hz）呈负相关。最大抑制率（%）分别为80（1Hz）、53（3Hz）和14（10Hz）。乙酰胆碱（10^(-6)M）和卡巴胆碱（10^(-5)M）的抑制作用在添加后15分钟达到最大值，然后几乎保持不变。可卡因（3×10^(-5)M）不改变乙酰胆碱的作用。地昔帕明（10^(-6)M）和皮质酮（4×10^(-5)M）减弱了低浓度（10^(-8)-10^(-7)M）乙酰胆碱的抑制作用。地昔帕明可拮抗乙酰胆碱诱导的抑制作用。可卡因加皮质酮减弱了高浓度（10^(-6)-3×10^(-6)M）乙酰胆碱的抑制作用。育亨宾（10^(-6)M）增强了乙酰胆碱的最大抑制作用。我们得出结论，乙酰胆碱对预先加载3H-去甲肾上腺素的家兔主动脉3H-溢出的抑制作用：（1）与刺激频率呈负相关；（2）与内皮无关；（3）不受神经元和非神经元递质摄取的影响；（4）可卡因不是节前毒蕈碱拮抗剂；（5）在节前毒蕈碱受体亚型研究中，可卡因适合作为神经元摄取抑制剂，而地昔帕明不适合；（6）节前α2-肾上腺素能受体和毒蕈碱受体之间存在反向相互作用。
