Respiratory decline

Respiratory decline consists of an inability of liver tissue from rats in the latent phase of dietary necrotii liver degeneration to maintain normal respiratory activity in vitro (Fig. 2). Whereas a vitamin E-supplemented liver will continue at approximately the initial rate of oxygen consumption for a period of 4-6 hours, the deficient liver tissue declines in oxidation after the first half-hour, so that during the 60-90 minute interval only approximately 20 % of the initial oxygen consumption is observed. 

Interpretation of much of the earlier work on respiratory decline of liver slices (Rodnan d al., 1956 Schwarz, 1958b Mertz and Schwarz, 1958, 

Vitamin E-free animal fat, stripped by molecular distillation (Distillation Products Division, Rochester New York). 

Of the two primary protective agents against liver necrosis, tocopherol appears more immediately related to respiratory decline and its prevention than Factor 3/selenium. Whereas in vivo application of vitamin E fully pievents respiratory failure in all systems used for its study, Factor 3-active selenium compounds afford only marginal protection in some of 

Factor 3/selenium are without any influence whatsoever on the breakdown of oxygen consumption. These differences between the effects of vitamin E and those of Factor 3/selenium show once more that these two agents do not substitute for each other, as pointed out previously (Schwarz, 1961b, 1962). It is also evident from this discrepancy that the principal mode of action of tocopherol cannot be dismissed in terms of antioxidant activity. More intricate metabolic relationships must play a part. 

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Experiments performed by Corwin and Schwarz (1960) gave evidence that the a-tocopherol metabolite (X) (Fig. 7) exerts tocopherol-like activity in the respiratory decline test. In order to mal e some material available for further biological testing, the tritium-labeled y-lactone (X) was synthesized following the lines given by Weichet et al. (1959) ... 

Vitamin E, Trace Elements and Sulfliydryl Groups in Respiratory Decline... 

Fig. 2. Respiratory decline of liver slices during the latent phase of necrotic liver degeneration (Chemick et al., 1955).

Effect op Dietary Selenium on Respiratory Decline op Liver Slices and Homogenates... 

After the basic aspects of respiratory decline had been clarified in liver slices, attempts were made to study the phenomenon with liver mitochondria since they are the main site of respiratoiy activity in the cell. It was surprising to see that isolated mitochondria of prenecrotic livers, in contrast to intact liver slices, demonstrated a behavior which was in most respects indistinguishable from that of normal mitochondria which were obtained from vitamin E-supplemented animals (Corwin and Schwarz, 1959). The only consistent difference existed in the utilization of oxal-acetate. All other areas of substrate utilization in the citric acid cycle appeared normal. The impairment of oxalaeetate metabolism became evident when malate or succinate was used as substrate in the presence of DPN. In the sequence from succinate through malate to oxalaeetate, accumulation of oxalaeetate leads to an inhibition of oxygen consumption. 

Lack or Correlation between TBA-Reactive Material and Respiratory Decline (Addition op Fresh Homogenate to Declining System)... 

The potencies of various tocopherols, K vitamins, ubiquinones, and similar substances in the prevention of respiratory decline have been assayed by supplementation of graded dose levels to the whole homogenate system. For each dose level, averages of at least four experiments were established. From the dose-response curves, the 50 % effective dose (EDbo) was derived. The EDso for df-a-tocopherol was found to be 1.1 ng per 3 ml of medium containing 50 mg of homogenized liver (Table VII). A comparison of the potencies of a-, /3-, 7-, and 5-tocopherols gave the same relative order of activity as the resorption sterility assay for vitamin E. df-a-To-copheryl acetate demonstrated only 3 % of the activity of the free vitamin. a-Tocopherylquinone was about 10% as active as tocopherol itself. The Simon metabolite (Simon et al., 1956) (Fig. 4) showed 40% of the activity of di-a-tocopherol, in spite of the fact that it was supplied in the quinone form. 

Not only substances of the tocopherol series, but also dimethyl- and trimethylbenzoquinones with isoprenoid side chains, ubiquinones, and members of the vitamin K family were effective in preventing respiratory decline. The activity of these substances, all of them supplemented in the... 

Prevention op Respiratory Decline (Vitamin E-Deficient Liver Homogenates)... 

From inhibitor studies at various intermediate steps of electron transfer and from other considerations, such as the substrate specificity of tocopherol-responsive respiratory decline, it seemed likely that the site of the main metabolic block leading to respiratory decline was not in the electron transfer chain proper, or in oxidative phosphorylation, as suspected earlier, but in certain dehydrogenase systems which connect the carboxylic acid cycle wdth the cytochrome chain. Using a-ketoglutarate as the substrate. 

Fig. 5. Lipoyl dehydrogenase and respiratory decline in rat liver homogenates...

Respiratory decline, characteristic of vitamin E-deficient liver tissue during the prenecrotic phase of dietary necrotic liver degeneration, consists of the breakdown of respiration in vitro, after brief, initial periods of normal oxygen consumption. The phenomenon is observed with liver slices and also homogenates, but not with isolated mitochondria from the livers of animals during the latent phase of the disease. Respiratory decline is not related to the rate of peroxide formation in the homogenate. Combination experiments disclosed that miorosomes exert a deleterious effect on the... 

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