Abstract
1 Some pharmacological properties of surugatoxin (SGTX), a purified toxic substance from the Japanese ivory mollusc (Babylonia japonica), have been investigated. SGTX (50 nmol/kg i.v.) produced a prolonged fall of blood pressure in anaesthetized cats. This hypotensive effect was neither blocked by atropine and propranolol nor by spinal cord transection. 2 SGTX (37-50 nmol/kg i.v.) inhibited the hypertensive and hypotensive response to 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) and to electrical stimulation of the splanchnic and vagal nerve, whereas it usually augmented the hypertensive response to adrenaline and to 4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride (McN-A-343) in anaesthetized cats. 3 Close intra-arterial injection of SGTX (6.2-12.3 nmol/kg) to the superior cervical ganglion blocked the contractile response of the nictitating membrane to preganglionic stimulation of cervical sympathetic nerve or injected DMPP, but not to postganglionic stimulation or to injected adrenaline and McN-A-343. 4 SGTX affected neither the indirectly nor the directly stimulated response of the rat isolated phrenic nerve-diaphragm at concentrations less than 12.3 mum. 5 The effect of SGTX on the contractile response to some agonists and on the twitch response to transmural stimulation in the guinea-pig isolated ileum was investigated. At less than 12.3 mumSGTX did not depress responses to acetylcholine or histamine. The curves for nicotine- and DMPP-induced contractions were shifted to the right and depressed gradually as the concentration of SGTX was increased (12.3 nm-1.23 mum). SGTX partially inhibited the contraction induced by 5-hyroxytryptamine and the transmurally-stimulated twitch response. 6 These results suggest that SGTX has a ganglion-blocking action. The mode of anti-nicotinic action of SGTX in the guinea-pig isolated ileum seems to differ from that of hexamethonium and tetraethylammonium and to resemble more closely that of mecamylamine.
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