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 3 h, 3 and 30 days af ter intramuscular injection of ACL. hemorrhagic toxin I (ACLHT-1, 5 mg/kg), partially purified from the venom of Agkistrodon contortrix laticinctus. C ontralateral muscles were injected with saline, Three hours after ACLHT-1 i njection: presence of hemorrhagic areas and myonecrotic muscle fibers. Thre e days: injured muscles showed areas in regeneration, some regions with del ay of regeneration and bundles of normal fibers. An increased TA muscle wei ght was found when compared with the contralateral (0.45 +/- 0.03 g versus 0.36 +/- 0.04 g, p = 0.04). Thirty days: areas of regenerated muscle fibers presented splits and centralized nuclei. Some regions were replaced by con nective 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). Regene rated areas of muscles were exclusively composed by fiber types Il and IIC. Regenerated muscles decreased the muscle weight (0.49 +/- 0.1 g versus 0.6 6 +/- 0.05 g, p = 0.03). In conclusion, ACLHT-I: (a) caused hemorrhage and muscle fiber injury; (b) injured both fiber types I and II; (c) increased t he incidence of fiber type IIC and: (d) some muscle regions were replaced b y connective tissue. (C) 2000 Elsevier Science Ltd. All rights reserved.