EFFECTS OF A TOXIN ISOLATED FROM AUSTRALIAN TIGER SNAKE (NOTECHIS-SCUTATUS-SCUTATUS) VENOM ON AUTONOMIC NEUROMUSCULAR-TRANSMISSION

The effects on mammalian autonomic neuromuscular transmission of a purified toxin from the crude venom of the Australian tiger snake, Notechis scutatus scutatus, have been investigated. The toxin had no measurable effect on transmission in either the rat anococcygeus, the rat vas deferens, or the longitudinal muscle of the guinea‐pig ileum. The toxin induced a contraction of longitudinal smooth muscle of the ileum. The tissue relaxed in spite of the continued presence of the toxin, and remained insensitive to further doses. The contractile response was not mediated by either cholinergic or histaminergic mechanisms. The toxin caused an inhibition of the response to field stimulation of the guinea‐pig vas deferens and the guinea‐pig seminal vesicle. The inhibition was spontaneously reversible, and the preparations remained insensitive to further doses of the toxin. The effects of the toxin were not mediated by either prostaglandins or by noradrenaline. The inhibitory effects of a variety of compounds known to act at presynaptic sites were also blocked by exposure to the toxin; inhibition caused by postsynaptic activity was unaffected by the toxin. It is suggested that the toxin inhibits transmission in the guinea‐pig vas deferens and seminal vesicle by a presynaptic mechanism. The possibility that the mechanism involves phospholipase A2 activity is discussed. 1978 British Pharmacological Society