Val A L
Instituto Nacional de Pesquisas da Amazônia, Manaus, AM, Brasil.
Braz J Med Biol Res. 1995 Nov-Dec;28(11-12):1119-27.
A wide range of organismic, physiological and biochemical adjustments to improve oxygen transfer is observed in fish exposed to environmental hypoxia and during anemia. Many fish species of the Amazon obtain oxygen directly from air when water oxygen is low. The accessory air-breathing organs include modifications of the gills, mouth, stomach and intestine, and swimbladder vascularization. Other species extend the lower lip and skim to improve oxygen uptake from the oxygen-rich surface layer of the water. The amount of oxygen uptake from air was estimated for Hoplosternum littorale and Lipossarcus pardalis. In addition, the oxygen uptake from the water surface was estimated for Colossoma macropomum. Blood oxygen content was reduced by 30% in Hoplosternum littorale and Colossoma macropomum and 70% in Lipossarcus pardalis if they were denied access to air. Adjustments of intraerythrocytic levels of ATP and GTP significantly improve oxygen transfer in fish during environmental hypoxia and anemia. In contrast to environmental hypoxia, intraerythrocytic levels of ATP and GTP increase during anemia in fish facilitating oxygen unloading to the tissues. It is suggested that the increase in ATP and GTP levels during anemia occurs because the conditions required to increase the activity of adenylate and guanylate phosphate synthetic pathways are similar.
在暴露于环境低氧和贫血状态的鱼类中，可观察到一系列广泛的机体、生理和生化调节以改善氧气传递。当水中氧气含量低时，亚马逊地区的许多鱼类会直接从空气中获取氧气。辅助呼吸器官包括鳃、口、胃和肠道的形态改变以及鳔的血管化。其他物种会伸展下唇并掠过水面以提高从富含氧气的水表层摄取氧气的能力。已对饰纹兵鲶和豹纹脂鲤从空气中摄取的氧气量进行了估算。此外，还对巨脂鲤从水面摄取的氧气量进行了估算。如果不让饰纹兵鲶和巨脂鲤接触空气，它们的血氧含量会降低30%，而豹纹脂鲤的血氧含量会降低70%。在环境低氧和贫血状态下，红细胞内ATP和GTP水平的调节可显著改善鱼类的氧气传递。与环境低氧不同，鱼类在贫血期间红细胞内ATP和GTP水平会升高，这有利于向组织卸载氧气。有人认为，贫血期间ATP和GTP水平升高是因为增加腺苷酸和鸟苷酸合成途径活性所需的条件相似。
