ABSTRACT

It is well known in biology that certain vertebrate species have evolved unusual capabilities for surviving prolonged periods without oxygen or with greatly reduced supplies of oxygen. Studies of such species [some being so anoxia tolerant they are referred to as ‘‘facultative’’ anaerobes (1)] have revealed several seemingly universal strategies of hypoxia adaptation. Two of the most significant of these include severe downregulation of energy turnover (2-6) and upregulation of energetic efficiency of ATP-producing pathways (7). The latter involve stoichiometric efficiencies. In hypoxia adaptation, pathways that maximize the yield of ATP per mole oxygen are favored, while in anoxia adaptation, anaerobic pathways that maximize the yield of ATP per mole of H formed in the fermentation are favored (8,9). In hypoxia or anoxia adaptation, the ratio of anaerobic/aerobic metabolic potential may well be upregulated, coincident with upregulation of glycogen (fermentable substrate) and of buffering capacities. Even if all these mechanisms are useful in surviv-

* Only literature up to 1996 was surveyed for this chapter.