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THEODORE O. SIPPEL; Energy Metabolism in the Lens During Aging. Invest. Ophthalmol. Vis. Sci. 1965;4(4):502-513.
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From a survey of studies pertaining to the effect of age on energy metabolism in the lens, it appears that during aging there is a decrease in the metabolic activity of the lens cytoplasm probably accompanied by an increase in the degree of utilization of aerobic reactions. Evaluation of metabolic activity from measurements of aerobic glycolysis and respiration requires defining a suitable basis of reference for which the water content of the lens seems appropriate. The reduction with age in activity defined on this basis may be controlled in part by the decrease in the surface/volume ratio during growth of the lens. No correlation of over-all energy production and growth rate was found, but there is a suggestion that respiratory activity specifically might be coupled with growth. Indirect evidence of a decrease in glycolytic activity with age is provided by observed decreases in lactic acid concentration, turnover of phosphate in glycolytic intermediates, and possibly cation transport. Any change in ATP conitent is not conclusive evidence of a change in metabolic activity; the constancy of ATP turnover with age, however, suggests unchanging metabolic activity in at least the outer layers of the lens. The total picture of phosphate turnover in the lens at different ages points to relative changes in the types of reactions utilized for energy production. Evidence of an increase in the use of aerobic pathways relative to anaerobic in older bovine lenses is provided both by direct studies with 14C-glucose and indirectly by the increase in the ratio of pyruvate to lactate. The situation in the rat lens is not clear, but in general a decrease in aerobic metabolism appears to be indicated.
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