ABSTRACT
Environmental anaerobiosis can easily be studied in frogs. Such information is likely to be relevant also to higher vertebrates and man because frogs and mammals share the basic morphological and functional organization of vertebrates. Frogs have a lower standard metabolic rate than endothermic vertebrates; hence, the effects of hypoxia/anoxia on metabolism and function of the various organs and particularly their coordination and integration can be followed on an extended time scale. Hypoxia/anoxia brings about coordinated reactions of the whole body and its organs that are aimed at reducing energy expenditure while maintaining crucial functions of the CNS and the circulation. The reactions to hypoxia include: decrease in metabolic rate, marked bradycardia, reduced ventilation, redirection of blood flow, and increased catabolism of glycogen and glucose, particularly in the CNS. The ample glycogen store of brain is almost depleted during 3 h of anoxia while lactate is accumulated. Nevertheless, the energy state of brain tissue is continuously decreased during anoxia, while it is not affected in heart and skeletal muscle, and the function of brain centers is lost at a time when a frog is still able to maintain its body posture. The brain is, therefore, the most critical organ for postanoxic revival.
Frogs are apt “models” also for the study of exercise anaerobiosis in working muscle. Anaerobic glycolysis is again the main pathway for ATP production but exercise requires rapid and maximal increase in substrate flux to power locomotion. Although environmental and exercise anaerobiosis bring about similar changes in glycolytic intermediates and products, the mechanisms for control of glycolytic rates are markedly different in the two situations.
