Monti-Bloch L, Eyzaguirre C
Brain Res. 1985 Jul 15;338(2):297-307. doi: 10.1016/0006-8993(85)90160-x.
The effects of methionine enkephalin (ME) and substance P (SP) were tested on the chemosensory discharge of the cat carotid body-nerve preparation in vitro. ME superfused in concentrations of 10(-8) to 10(-5) M depressed the sensory discharge, an effect followed by receptor excitation (rebound). Bolus applications of ME (30 ng to 3.0 microgram) induced variable effects (excitation or depression) on the discharge, excitation being more pronounced with the smaller doses. Superfusions with SP (10(-8) to 10(-5) M) either excited or depressed the discharge, excitation being more pronounced with higher SP concentrations (i.e. 10(-6) M). Bolus applications of SP (43 ng to 0.5 micrograms) also excited or depressed the sensory discharge. These variations may be dose-dependent. Superfused ME (10(-6) M) significantly depressed the chemoreceptor response to hypoxia (100% N2) and hypercapnia (6% CO2, pH 7.43). The responses to NaCN and acidity (pH 6.0) were marginally depressed. Superfused SP (10(-6) M) clearly depressed the responses to hypoxia, those to hypercapnia and NaCN were marginally affected but the effects of acidity were not altered. When the peptides were tested against the receptor responses to exogenously applied putative neurotransmitters (ACh, dopamine--DA), it was found that ME tended to depress both the ACh and DA actions whereas SP (10(-6) M) tended to increase their effects. Superfusions with naloxone (10(-6) M) increased the basal chemosensory discharge and this enkephalin blocker partially relieved the depressant effect of ME on the ACh-induced response. It is concluded that carotid body chemoreceptors have excitatory and inhibitory reactive sites to both ME and SP although their precise location is still unknown.
在体外对猫颈动脉体 - 神经制备物的化学感受性放电测试了甲硫氨酸脑啡肽（ME）和P物质（SP）的作用。以10⁻⁸至10⁻⁵M的浓度灌流ME会抑制感觉放电，随后会出现受体兴奋（反弹）。推注ME（30 ng至3.0微克）对放电产生可变作用（兴奋或抑制），较小剂量时兴奋作用更明显。用SP（10⁻⁸至10⁻⁵M）灌流会兴奋或抑制放电，较高SP浓度（即10⁻⁶M）时兴奋作用更明显。推注SP（43 ng至0.5微克）也会兴奋或抑制感觉放电。这些变化可能是剂量依赖性的。灌流ME（10⁻⁶M）显著抑制化学感受器对低氧（100% N₂）和高碳酸血症（6% CO₂，pH 7.43）的反应。对NaCN和酸度（pH 6.0）的反应略有抑制。灌流SP（10⁻⁶M）明显抑制对低氧的反应，对高碳酸血症和NaCN的反应略有影响，但对酸度的作用未改变。当测试这些肽对外源性应用的假定神经递质（乙酰胆碱 - ACh、多巴胺 - DA）的受体反应时，发现ME倾向于抑制ACh和DA的作用，而SP（10⁻⁶M）倾向于增强它们的作用。用纳洛酮（10⁻⁶M）灌流会增加基础化学感受性放电，这种脑啡肽阻断剂部分缓解了ME对ACh诱导反应的抑制作用。结论是，尽管颈动脉体化学感受器上ME和SP的确切反应位点位置尚不清楚，但它们对两者都有兴奋和抑制反应位点。
