Altitude, metabolic effects

Altitude. Altitude can either increase or decrease toxicity. It has been suggested that these effects are related to the metabolism of toxicants rather than to physiological mechanisms involving the receptor system, but in most examples this has not been demonstrated clearly. Examples of altitude effects include the observations that at altitudes of > 5000 ft, the lethality of digitalis or strychnine to mice is decreased, whereas that of D-amphetamine is increased. 

C. Clinical Uses The major application of carbonic anhydrase inhibitors is in the treatment of glaucoma. Acetazolamide must be administered orally, but topical analogs are now available (dorzolamide, brinzolamide) for use in the eye. Carbonic anhydrase inhibitors are also used to prevent acute mountain (high-altitude) sickness. These agents are used for their diuretic effect only if edema is accompanied by significant metabolic alkalosis. 

Hypoxia Hypoxia is a lack of metabolic oxygen reaching cells. A complete lack of oxygen at the cell level is anoxia. A reduction in oxygen transport affects cell metabolism. One can express the oxygen deficiency in altitude, saturation of red cells, or partial pressure. The effects are a result of the degree of hypoxia. 

The space age requires the consideration of still another environmental factor, namely the effect of altitude on drug metabolism, since it has been shown that mice maintained at 18,000 feet exhibited an increased metabolism of hexobarbital . Dietary proteins are also important factors in drug metabolism. It was shown that feeding rats a high protein diet led to an increase, and feeding a low or non-protein diet. 

Atmospheric constituents reported to change plant lipids or their metabolism include sulphur dioxide, oxides of nitrogen and ozone [3,6]. Atmospheric CO2 is changing, because of the "Greenhouse Effect" but, in addition, the partial pressure of CO2 varies significantly with altitude. Recent experiments (see below) show that CO2 alone has significant effects on lipid metabolism, perhaps because of its action of leaf development and morphology [15]. 

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