Pathogenesis of hemorrhage induced by rattlesnake venom. An electron microscopic study.

The pathogenesis of hemorrhage induced by rattlesnake (Crotalus atrox) venom was investigated at the electron microscopic level. Swiss-Webster white mice were injected intramuscularly with one-fifth the LD(50) dose of whole venom. Muscle samples were obtained by biopsy 2 minutes, 30 minutes and 3 hours after venom injection. Capillaries in the endomysium were in various stages of degeneration. Endothelial cells of damaged capillaries contained dilatated endoplasmic reticulum and perinuclear space, and, in many cases, swollen cytoplasm. Blebbing of endothelial cytoplasm of swollen and nonswollen cells was observed. These changes were followed by rupture of the plasma membrane which resulted in the subsequent extravasation of blood. Platelet aggregations plugged gaps in vessel walls and often completely occluded the lumina of capillaries. The experimental injection of rattlesnake venom induced hemorrhage by rhexis. The same or a similar pathogenesis is probably responsible for hemorrhage which occurs in actual snakebite cases.