諸臓器TCA回路系酵素活性に及ぼす低酸素呼吸の影響
スポンサーリンク
概要
- 論文の詳細を見る
Haldane and Barcroft's postulate in 1920 (Lancet) that "anoxemia not only stops the machine, but wrecks the machinery", leads to the concept that the enzyme activities of tissues should be damaged in anoxemia. There are reports that activities of enzymes which metabolize substrates located near the entrance to the TCA cycle, namely pyruvate and citrate, are depressed due to hypoxia, especially with studies on myocardial tissues (Kimura, S., from our department; Jap. Circulation J. 21 : 376,1957). However, information on tissues of other organs is relatively lacking. Also, comparative studies concerning the influence of hypoxemia, caused by low percentage oxygen respiration under normal atmospheric pressure, on the above mentioned enzyme activities of the heart and other organs are lacking. Furthermore, there is a question unclarified, whether acute hypoxia can sometimes increase respiratory enzyme activity, and also the relation between the changes in the enzyme activity and the degree of hypoxia is left unclarified.The present study was undertaken to elucidate the above points, with experiments on tissues of the heart, brain, liver and kidney.Materials and Methods Male albino rats, weighing about 150 grams, were placed in gas mixtures containing 10,5 or 3±0.2% O_2 with adequate ventilation at normal atmospheric pressure for several minutes to 5 hours and decapitated.Estimations of dehydrogenase activities were made on tissues homogenates of myocardium, cerebral cortex, liver and kidney, by the Thunberg technique. Sodium salts of lactic, pyruvic, citric and succinic acids were used as substrates. The decolorizing time of methylene blue was used for statistical analyses, but the ratio-methylene blue reduced (γ)/decolorizing time (minutes)- was considered an indicator of methylene blue reducing, i.e. substrate oxidizing, capacity of tissue homogenates, and used for the calculation of percentage changes.The endogenous respirations of homogenates of myocardium and cerebral cortex, were determined by the Lemley and Meneely's method. Also, the Qo_2 of homogenates with pyruvate, citrate or succinate as substrate were obtained.Results Obtained 1. Normal controls The oxidizing capacities of tissue homogenates when pyruvate, citrate or succinate is used as substrate are-myocardium>kidney>liver>brain-the brain being especially weak. Also, with these substrates, the Qo_2 of myocardial homogenates are larger than that of the brain. The addition of citrate had little or no effect on the oxidizing capacity and Qo_2 of brain homogenates. It was felt, as reported by others, that the TCA cycle activity was weak in the brain tissue.2. Effects of various degrees of hypoxia a) Relatively mild hypoxia (10 % O_2) for 2 hours : The homogenates of myocardium and brain showed no significant change in their oxidizing capacity, but significant increases were observed with liver and kidney homogenates. Especially with the liver, compared to control values, the endogenous oxidizing capacity was increased by +47 % (P<0.01), and with lactate, pyruvate or citrate as substrate, respective increases of +39 % (P<0.01), +23 % (P<0.05) and +34 % (P<0.02) were noted.It was concluded that relatively mild hypoxia of this degree and duration, could cause increases in the oxidizing capacities of liver and kidney tissues, while those of the myocardium and brain were maintained.b) Moderate hypoxia (5 % O_2) for 10 minutes to 5 hours : The oxidizing capacity of tissue homogenates showed no significant change after 10 minutes of 5 % O_2 respiration. One hour of hypoxia caused decreases in the oxidizing capacities of myocardial homogenates, only when pyruvate (-22%, P<0.01) or citrate (-33%, P<0.01) were used as substrates.After 2 hours of hypoxia, significant decreases were found in all tissues studied. The decreases with pyruvate or citrate as substrate were as follows : Myocardium; pyruvate -31% (P<0.01), citrate -43% (P<0.01). Brain; p
- 社団法人日本循環器学会の論文
- 1960-09-20