Regeneration and change of muscle fiber types after injury induced by a hemorrhagic fraction isolated from Agkistrodon contortrix laticinctus venom.

Tibialis anterior (TA) muscles of rats were evaluated 3h, 3 and 30days after intramuscular injection of ACL hemorrhagic toxin I (ACLHT-I, 5mg/kg), partially purified from the venom of Agkistrodon contortrix laticinctus. Contralateral muscles were injected with saline. Three hours after ACLHT-1 injection: presence of hemorrhagic areas and myonecrotic muscle fibers. Three days: injured muscles showed areas in regeneration, some regions with delay of regeneration and bundles of normal fibers. An increased TA muscle weight was found when compared with the contralateral (0.45+/-0.03g versus 0.36+/-0.04g, p=0.04). Thirty days: areas of regenerated muscle fibers presented splits and centralized nuclei. Some regions were replaced by connective tissue. All muscle fiber types were injured but only the incidence of type IIC increased (3.4+/-2.0% versus 0.2+/-0.2%, p=0.0005). Regenerated areas of muscles were exclusively composed by fiber types II and IIC. Regenerated muscles decreased the muscle weight (0.49+/-0.1g versus 0.66+/-0.05g, p=0. 03). In conclusion, ACLHT-I: (a) caused hemorrhage and muscle fiber injury; (b) injured both fiber types I and II; (c) increased the incidence of fiber type IIC and; (d) some muscle regions were replaced by connective tissue.