Sites of action of crystalline tetrodotoxin on sympathetic nervous systems

Vascular responsiveness to periarterial electrical nerve stimulation on canine ophthalmic arteries

Both periarterial electrical stimulation (ES) and intraluminal application of norepinephrine (NE) produced a vasoconstriction in the isolated canine ophthalmic artery (OA). The ES-induced vasoconstrictor response was markedly inhibited by treatment with tetrodotoxin and slightly but significantly depressed by xylazine, a selective alpha-2 adrenoceptor agonist. Moreover, the ES-induced response was enhanced by either DG-5128, a selective alpha-2 adrenoceptor antagonist, or angiotensin II. The inhibitory effect of bunazosin on the ES-induced response was significant, but it was rather small compared with that on the NE-induced response. The NE-induced constriction was not affected by xylazine and DG-5128, but significantly enhanced by angiotensin II. These results indicate that (1) the ES-induced response is mediated via sympathetic nerve activation, (2) there are inhibitory prejunctional alpha-2 adrenoceptors, (3) there are more postjunctional alpha-1 than postjunctional alpha-2 adrenoceptors in canine OAs, and (4) prejunctional angiotensin II receptors may exist in isolated OA preparations.

Effect of Clostridium perfringens beta toxin on blood pressure of rats

Guanethidine treatment or adrenal medullectomy significantly inhibited the elevation in blood pressure induced by Clostridium perfringens beta toxin, and the combination of the two drastically reduced the pressure rise, to less than 19% of that in control rats. When rats were pretreated with tetrodotoxin or hexamethonium, the toxin-evoked rise was significantly inhibited. Elevation in blood pressure induced by the toxin in spinal rats tended to be less than that in control rats. When investigated by a microscopical technique, arteriolar constriction in the mesenteric vasculature was observed after the blood pressure elevation induced by the toxin reached a maximum. Blood flow in the skin decreased with an increase in blood pressure following intravenous injection of the toxin. It is concluded that beta toxin acts on the autonomic nervous system and produces arterial constriction.