Resistance to anoxia

We have been studying the anaerobic response in cotton, a crop which experiences a reduction in growth rate during irrigation or waterlogging. Cotton shows a level of anaerobically inducible ADH activity comparable with that of maize, a plant which is relatively resistant to anoxia (A. Millar, unpublished data T.L. Setter, unpublished data). However, in cotton the level of the enzyme catalysing the preceding step in the fermentation pathway, PDC, is relatively low and this may lead to low rates of ethanol synthesis and hence low tolerance to anoxia. 

CNS damage in foetuses after CO exposure of the mother [50]. It is well known that the foetal brain is rather resistant to anoxia, and thus the severe alterations occurring in the foetus point to a specific damage incurred by the CO exposure of the mother. 

Autoregulatory action helps to reduce nerve cell destruction resulting from brain tissue anoxia. Two possible mechanisms include flow controller dynamics in the form of pure delays and time constant lags and oxygen consumption control with Michaelis-Menten behavior. Response curves also suggest the possibility of facilitated or active transport of oxygen in tissue and resistance to the diffusion of oxygen from the tissue into the blood stream. 

The greater resistance to oxygen deficiency of the just born brain is accompanied by slower metabolic rates (Thurston McDougal, 1969) and by lower energy requirements (Duffy et al., 1975) in comparison with the mature brain. Our studies on lipids in relation to anoxia in newborn brain included two aspects. Firstly we observed the fatty acid composition of brain lipid classes and secondly the labeling of brain lipids by C-glycerol or C-arachidonic acid. 

The sluggish production of free fatty acids in the newborn brain in response to anoxia and ischemia (Bazan, 1976) may be related to the greater resistance of the newborn CNS to sustaining longer periods under such conditions. Conversely, in the mature brain the rapid production of free fatty acids due to blood shortage may be involved in the irreversible impairment of brain function (Bazan, 1976). It is interesting that not only phospholipase A2 activity but also a rapid reduction of the incorporation of the fatty acid into the lipids contributes to the accumulation of free arachidonic acid. 

The rate of uptake is temperature-dependent, with a Qio of about 2-0. Uptake is relatively resistant to metabolic inhibitors, such as cyanide, iodoacetate, and dinitrophenol, or to anoxia or lack of glucose. However, if both aerobic and anaerobic energy metabolism is inhibited, the uptake of exogenous catecholamines is blocked. This indicates that the energy needed to transport the very small amounts of catecholamine can be provided by either aerobic or anaerobic metabolism. 

To be suitable for long-term wear, a contact lens material has to satisfy several criteria. It must be hydrophilic enough to maintain a stable, continuous tear film on its surface, resist fouling by tear components, not irritate the eye, and be comfortable to wear. It should also be realized that the metabolism of the cornea is highly dependent on dissolution and adsorption of atmospheric oxygen and therefore any lens material must have sufficient oxygen permeability to maintain this, else corneal anoxia will set in. 

Modification of radiation injury produced by these chemical agents must be mediated by neutralization of either the direct or the indirect effects of radiation or by altering the physiologic state of the cells to a more or less resistant state. These general problems have been considered in detail by Patt (9, 44). It would appear superficially that sulfhydryl compounds and anoxia exert their protective effect through partial neutralization of the indirect effects of radiation and not through neutralization of the effects of direct ionization and excitation of solute molecules. 

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