Further observations on the pathological responses of rat skeletal muscle to toxins isolated from the venom of the Australian tiger snake, Notechis scutatus scutatus.

1. Some aspects of the response of mammalian skeletal muscle following the injection of purified toxins from the venom of the Australian tiger snake, Notechis scutatus scutatus, are described. 2. The toxins used were notexin, notechis II-5, notechis II-1 and a modified form of notexin (PBP-notexin). They were injected into the dorso-lateral aspect of one himd limb so that the soleus muscle would be exposed to the toxins. 3. Within 1 h after the injection of notexin, the soleus muscles were oedematous and by 3--6 h, polymorphonuclear leucocytes had entered the interstitial spaces. The invasion of necrotic muscle fibers was extensive by this time. Muscle spindles appeared relatively unaffected by the toxin. 4. The muscle regenerated via myoblasts at 2--3 days to myotubes at 3--5 days, immature muscle fibers at 7--14 days and fully differentiated muscle fibers by 21--28 days. Even after 6 months, however, the nuclei of many muscle fibres remained in a central position. 5. A second component of Australian tiger snake venom was also found to be myotoxic. It was slightly less potent than notexin, but caused qualitatively similar damage to that caused by notexin. It was identified as notechis II-5. A third fraction, notechis II-1, was found to be inactive. 6. Notexin could be neutralized by incubation with tiger snake antivenene; the simultaneous injection of antivenene with notexin did not afford complete protection against muscle damage.