Effects of adrenergic drugs injected into the nucleus tractus solitarius region on the baroreceptor reflex in rabbits.

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  • ウサギ孤束核注入によるアドレナリン作動性薬物の圧受容器反射におよぼす影響
  • ウサギ コソク カク チュウニュウ ニ ヨル アドレナリン サドウセイ ヤクブ

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Abstract

It has been presumed that a primary site of termination of the baroreceptor afferent was in the nucleus tractus solitarii (NTS). The intermediate region of the nucleus, located at the level of the obex, contains a large number of catecholamine neurons. The principal noradrenergic innervation of the NTS appears to arise from neurons of the so-called A2 group. It has been proposed that catecholamines released by A2 neurons serve to lower blood pressure and heart rate. We performed experiments to determine the effects of α-adrenoceptor agonists and antagonists on the baroreceptor reflex and alpha-adrenoceptor. Rabbits anesthetized with chloralose-urethane were injected with an alpha-adrenoceptor agonist, such as noradrenaline, phenylephrine or clonidine, into the NTS. An adrenoceptor-antagonist, such as yohimbine, phentolamine, prazosin or corynanthine was injected into the NTS of other anesthetized rabbits. Clonidine markedly lowered the blood pressure and heart rate, and it inhibited the baroreceptor reflex responses. Noradrenaline or phenylephrine did not lower the blood pressure and heart rate and scarcely inhibited the baroreceptor reflex. Yohimbine remarkedly inhibited the baroreceptor reflex responses; on the other hand, prazosin, corynanthine and phentolamine produced little inhibition of the responses. It is concluded that there are α1 and α2-receptors in the NTS of the rabbits, and the α2-receptors play an important role in the neurotransmission in the NTS.

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