Jandhyala B S, Kivlighn S D
Fed Proc. 1987 Feb;46(2):276-80.
In the flow-regulated dog forelimb, electrical stimulation of the efferent median nerve produced frequency-dependent increases in perfusion pressure. These vasoconstrictor effects were attenuated by a large dose of phentolamine, an alpha 1 and alpha 2 blocking drug. Administration of methysergide after phentolamine completely reversed the vasoconstrictor responses to vasodilation at most frequencies of stimulation. In the absence of phentolamine pretreatment, even a lower dose of methysergide reversed or caused biphasic responses (attenuated constriction followed by dilatation) during the nerve stimulation at the lower frequencies (0.5-4.0 Hz). This lower dose of methysergide completely abolished vascular effects of exogenous 5-hydroxytryptamine (5-HT) and potentiated those of norepinephrine; hence, the antagonism by methysergide of neurally mediated vasoconstriction is not caused by an action on alpha-adrenergic receptors. Unlike methysergide, selective 5-HT2 antagonists ketanserin and ritanserin have no modifying effect on exogenous 5-HT responses. These studies have provided pharmacological evidence that suggests that 5-HT may be the neurotransmitter mediating neurogenic vasoconstriction in the dog forelimb, and that this effect does not involve activation of 5-HT2 receptors.
在流量调节的犬前肢中，电刺激正中神经传出支会使灌注压出现频率依赖性升高。这些血管收缩效应被大剂量酚妥拉明（一种α1和α2阻断药物）减弱。在酚妥拉明之后给予麦角新碱，在大多数刺激频率下，血管收缩反应完全逆转成血管舒张反应。在没有酚妥拉明预处理的情况下，即使是较低剂量的麦角新碱在较低频率（0.5 - 4.0 Hz）的神经刺激期间也会逆转或引起双相反应（收缩减弱随后舒张）。这种较低剂量的麦角新碱完全消除了外源性5-羟色胺（5-HT）的血管效应，并增强了去甲肾上腺素的血管效应；因此，麦角新碱对神经介导的血管收缩的拮抗作用不是由其对α-肾上腺素能受体的作用引起的。与麦角新碱不同，选择性5-HT2拮抗剂酮色林和利坦色林对外源性5-HT反应没有调节作用。这些研究提供了药理学证据，表明5-HT可能是介导犬前肢神经源性血管收缩的神经递质，并且这种效应不涉及5-HT2受体的激活。
