Morphological study of lesions induced by snake venoms (Naja naja and Agkistrodon piscivorus) in the lung and cremaster vessels of rats.

The morphological effects of two snake venoms, N. naja and A. piscivorus, and of the Direct Lytic Factor and Phospholipase-A, compounds purified from N. naja crude venom, were investigated on lung and cremaster vessels of rats. The microcirculation of the rat reacts to these two venoms differently: N. naja produces congestion, haemolysis and increased vascular permeability, whereas A. piscivorus causes these alterations, plus haemorrhage and thrombosis. Direct Lytic Factor elicits reponses similar to the N. naja venom but Phopholipase-A has no effect on the vessels. Phospholipase-A does not seem to potentiate the effects of Direct Lytic Factor on the cremaster vessels. The colloidal carbon technique showed that intrathroacic administration of N. naja venom results in a generalised permeability increase of pleural and subpleural capillaries and A. piscivorus injections provoke only carbon retention in capillaries at sites of localised haemorrhage. In cremasters treated with N. naja venom the carbon blackened the venules predominantly but in cremasters in which A. piscivorus venom was administered the carbon particles labelled both venules and capillaries. There was evidence that the main vascular action of the venoms is local and not systemic, that the permeability factors involved in these lesions are different and that the cremaster vessels are much more sensitive to these snake venoms than the pulmonary vessels. Electron-microscopic studies showed mesothelial and epithelial lesions in lungs and an early inflammatory reaction in the cremaster vessels with both venoms. Erythrocyte fragmentation was a constant feature in all vessels. Endothelial degeneration and capillary disintegration in lung and cremaster vessels were observed in animals treated with A. piscivorus venom.