[Effects of adrenergic drugs injected into the nucleus tractus solitarius region on the baroreceptor reflex in rabbits].
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 alpha-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 alpha 1- and alpha 2-receptors in the NTS of the rabbits, and the alpha 2-receptors play an important role in the neurotransmission in the NTS.
Sato
C
C
Department of Internal Medicine III, School of Medicine, Chiba University, Japan.
Tamagawa
M
M
Suzuki
T
T
Murayama
S
S
D000818:Animals; D005260:Female; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects*; D011311:Pressoreceptors / Q000187:drug effects*; D011817:Rabbits; D012018:Reflex / Q000187:drug effects*; D013566:Sympathomimetics / Q000008:administration & dosage / Q000494:pharmacology*
D013566:Sympathomimetics