Tissue respiratory activity

The brain has a number of characteristics that make it especially susceptible to free- radical-mediated injury. Brain lipids are highly enriched in polyunsaturated fatty acids and many regions of the brain, for example, the substantia nigra and the striatum, have high concentrations of iron. Both these factors increase the susceptibility of brain cell membranes to lipid peroxidation. Because the brain is critically dependent on aerobic metabolism, mitochondrial respiratory activity is higher than in many other tissues, increasing the risk of free radical Teak from mitochondria conversely, free radical damage to mitochondria in brain may be tolerated relatively poorly because of this dependence on aerobic metabolism. 

The respiratory activity of the brain tissue was determined by measuring the rate of oxygen uptake with a Clark oxygen electrode (7). The sample of tissue (a brain half) was treated exactly as if used in a calcium efflux experiment except no radioactivity or RF power was used. Following this procedure which required about 55 minutes, the tissue was placed in the oxygen electrode cell containing 1.6 ml of the standard medium (pH 7.8) at 37°C and the rate of oxygen uptake was recorded. 

Figure 5. Respiratory activity of chick brain tissue.

Respiratory Activity of Brain. Questions concerning the metabolic state of the isolated brain tissue are frequently posed. Figure 5 shows the respiratory activity of a brain half which had undergone the same treatment as a sample used in calcium efflux experiments. The initial linear portion of the curve represents a respiratory rate of about 100 ng atoms oxygen/min. The rate decreased with time and more than 90% of the oxygen in the medium was depleted in less than 10 min. 

When the oxygen-depleted solution was repeatedly replaced with fresh medium, very similar curves were obtained. For example, the initial respiratory rates in the second and third replacement volumes were 6% and 15% less than the first trial, respectively. The tissue was therefore capable of respiratory activity throughout the 55 to 60 minute experimental period. Freshly excised brain samples exhibited similar responses at slightly higher respiratory rates. One should recall that Bawin et al. 

The mitochondrial Mg2+ ATPase activity from liver and brain was inhibited by about 50-60% after an administration of 100 mg Al kg 1 body weight in the diet for a period of 90-120 days. By contrast, in the heart mitochondria, the ATPase activity increased from 73 to 212% after this treatment [38]. In this work, it was also found that ADP phosphorylation rates were decreased by 46% and that the changes in the ATPase activity, in general, were paralleled to those of the respiratory rates. The author suggested that these results imply that the effects of Al3+ treatment on respiratory activity and the ATPase activity go hand in hand. Curiously, liver and brain mitochondria presented doubled aluminum concentration and impaired respiration rate, whereas the heart mitochondria, that accumulated 11 times higher amount of aluminum, presented stimulation of respiration. Thus, an indirect action of aluminum in this tissue could be suggested. 

Copper and Zinc in Aerobic Metabolism. Cytochrome oxidase, the terminal oxidase in the electron transport chain contains an atom of copper. On this enzyme the protons and electrons generated during oxidative metabolism combine with elemental oxygen to form water. During copper deficiency the tissue concentration of cytochrome oxidase is reduced. While the effects of lower cytochrome oxidase activity on exercise has not been described, it is likely that aerobic energy metabolism will be diminished. This effect of copper deficiency was first described in animals with myelin aplasls — the degeneration myelin (86). The oxidative process of phospholipid synthesis, a primary component of myelin, was depressed. Liver mitochondria had impaired respiratory activity (87). Cytochrome oxidase activity was also depressed in brain, heart and liver. 

The maturation of fat body mitochondria is affected by the neuroendocrine balance in adult male B. discoidalis. Removal of the CC arrests the maturation of the respiratory enzymes at their partly developed, 5-day level (58, Figure 1). Injections of CC extracts on days 0 to 5 result in precocious, 10-day levels of respiratory activity by 5 days of age. Administration of the uncoupling agent 2,4-dinitrophenol indicates that electron transport, rather than phosphorylation, is the rate-limiting step for respiration in fat bcxiy mitochondria (59). A situation that differs from vertebrate mitochondria where phosphorylation is limiting. This indicates that the levels of cytochrome enzymes available for electron transport in fat body mitochondria determine the respiratory and ATP synthesis capacities of the tissue and influence its biosynthetic potential. 

MAbs monoclonal antibodies NCE New Chemical Entity RIP ribosome-inactivating protein RSV respiratory syncytial virus t-PA tissue plasminogen activator VEGE vascular endothelial growth factor... 

We have as yet no information as to the importance of such a system in the general respiratory activity of plant tissues. Its importance as a means of maintaining GSH, and hence of activating and conserving the activity of the so-called SH enzymes (enzymes which are dependent on the maintenance of certain SH groups in their molecules), is self-evident but does not concern us here. The participation of ascorbic acid in a respiratory chain of reactions will be prevented in the presence of cyanide, for the last stage, the enzymatic oxidation of ascorbic acid, will be inhibited. The extent to which hydrogen is transferred in the system will depend inter alia on the concentration of GSH and dehydroascorbic acid and on the... 

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. 

Gershbein, L. L., B. K. Krotoszynsky, M. J. Brunner, and A. J. Domnas Respiratory activity and nucleic acid content of some tissues from guinea pigs sensitized to 2,4-dinitrochlorobenzene. J. invest. Derm. 27, 73—76 (1956). 

The cytochrome c concentration within tissue varies according to the respiratory activities in the tissue. 

However, among this variety of biochemical changes, citrate seems to be the only parameter whose qualitative (but not quantitative) trends are not controversial. In rat hearts imder acute intoxication with FA, the concentration of citrate can exceed control values 8-15 times (Bosakowski and Levin, 1986). Elevation of citrate concentration is in direct proportion to the respiratory activity of a tissue metabolically active tissues, such as the heart, kidneys, and spleen, maximally accumulate citrate. Though in the liver, which is also characterized by high respiratory levels and metabolic activity, a small... 

---