Observation On The Micro-structure And Ultra-structure Of The Venom Gland Of G. Intermedius

G intermedius subordinates to the Genus Gloydius, the subfamily Crotalinae of Viperidae, which distributes in a wide geographical area from the western desert subregion of Mongolian-Xinjiang region, Tian-shan Mountain subregion to western Loess Plateau subregion. It is the most toxic pit-viper species usually seen in northwest China and part of north China, and it is responsible for most snakebite accidents in these area. However, it is useful for human being due to the important roles that this population play in the ecosystem and the potential use at medical field. The morphology, herpetofauna, feeding and ecology, biochemistry and the toxicology of the venom have been studied and reported previously. But there is no data about the venom secretion, storage and the mechanism of venom delivery.The venom delivery system (VDS) is the most effective defense weapon, which was formed during the long river of evolution. The VDS was composed of the main venom gland, the primary duct, the accessory gland, the secondary duct and the fangs. The VDS is of high evolutionary value. Researches have demonstrated that VDS was rare in vertebrates and was found only in three families of snakes: the Viperidae, the Elapidae and several species of the Colubridae. It presents for the favorable aspects for venomous snakes in the behavioral, ecological, physiological and phylogenetic diversity. The phylogenesis of these apparatus is still controversial.VDS, especially the microstructure and ultrastructure of the venom glands, have been the subject of numerous studies due to the highly toxic nature and the potential medical values of their secretions and the important evolutionary significance for several decades. But most of these studies were involved with Crotalus, Vipera and Deinagkistrodon. Little was known about Gloydius. To approach these issues and enrich the knowledge of venom secretion, storage and expulsion, in the present study, we have explored the microstructure and ultrastructure of the venom gland of G. intermedius, which was collected from the suburb of Yan'an city of north Shaanxi province during the summer of 2006, by light microscopy, scanning electron microscopy and transmission electron microscopy.The results was as following: 1. For the first time in China, microvesicles with electron-dense content and secretory lysosomes were observed on the secretory cells of venom glands of viperid snakes. They exerted different physiological functions. 2. There were obvious structural differences in venom glands between G. intermedius and Deinagkistrodon acutus. There was not a large, basally located central main gland lumen in G intermedius, which existed in D. acutus. 3. The modes of venom secretion in the venom gland of G. intermedius included partial secretion, apocrine secretion and holocrine secretion at cellular level. 4. A detailed study of the microstructure and ultrastructure of the accessory gland revealed that in the accessory gland, there were at least six distinct cell types: serous secretory cells, mucus-secreting cells, mitochondria-rich cells with apical vesicles, mitochondria-rich cells with electron-dense secretory granules, horizontal cells, and "dark" cells. The proximal part of the accessory gland contained a large number of serous secretory cells. At its distal end, the accessory gland primarily contained large mucus-secreting cells. The arrangement of the cell types in G. intermedius accessory gland suggested that venom components from the main gland could be activated by proximally located cell secretions of the accessory gland, requiring mucus secretion to protect the distal parts of the venom gland apparatus from the hydrolytic effects of venom. 5. The results further demonstrated the mechanism of venom expulsion. The venom pressure generated by the contraction of the compressor muscle, the change of the volume about venom chamber, the displacement of the fang sheath and the displacement of the inner fang membrane were the premise of venom expulsion.In conclusion, the systematic microstructural and ultrastructural observation of the venom gland of G. intermedius in the present study primarily delineated the mechanism of venom secretion, storage and expulsion. These data may undoubtedly be helpful to the understanding of venom apparatus evolution and the improvement of envenomation administration.