Some biochemical responses of rat skeletal muscle to a single subcutaneous injection of a toxin (notexin) isolated from the venom of the Australian tiger snake Notechis scutatus scutatus.

1. Some biochemical responses of mammalian skeletal muscle to a single subcutaneous injection of a purified toxin from the venom of the Australian tiger snake, Notechis scutatus scutatus, have been investigated to determine the role of changes in peptide hydrolase enzymes in the muscle wasting caused by notexin administration. 2. Within 6 h of injection, serum creatine kinase activity was increased by five- to ten-fold, and remained elevated for at least 24 h. 3. There was an initial inflammatory response in the muscle adjacent to the site of injection; by 12 h after injection, muscle wet weight increased by 60%. 4. After the initial increase, wet weight fell to about 50% of normal at 7 days. Normal wet weight was achieved by 20 days after the injection. Over the period 1-20 days after the injection of the toxin, the changes in wet weight were mirrored by changes in non-collagen protein content. 5. The activities of cathepsin B and acid proteinase were increased following the injection of the toxin. By 2 days after injection, there was a ten-fold increase in the activity of cathepsin B, and a seven-fold increase in the activity of acid proteinase. The activity of both enzymes become normal by 20 days. 6. Experiments utilizing a variety of cytotoxic drugs suggested that the acid proteinase and cathespin B are primarily located within invading phagocytic cells. 7. The results are discussed with reference to the previously described pathology of toxin-damaged skeletal muscle.