The proteinuria and urinary levels of six glycosidases (β-N-acetylhexosaminidase (NAG), β-galactosidase, β-glucosidase, β-glucuronidase, α-mannosidase and α-L-fucosidase) were studied as a function of ageing in rats ranging in age from newborns to 25 months old. All the enzyme activities were raised with statistical significance in the newborns as compared with the older rats. A similar pattern of enzymuria was found for NAG, β-galactosidase, β-glucuronidase and α-L-fucosidase activities. The levels of all these enzymes increased in rats from 1 to 3 months old, later decreasing with ageing. The daily excretion of proteins was markedly increased in rats of 3 months old with respect to that of 1 month-old animals, but it did not vary later with ageing. The highest protein concentration in kidney homogenates was found in adults (1-3 months old). These concentrations increased from the embryonic age and decreased in the old rats. The isoenzyme profile of kidney NAG as a function of ageing revealed that NAG B increases significantly from embryos to adults, slowly decreasing in older rats. The above results indicate that there are age-dependent differences in urinary glycosidase levels as well as in protein excretion among rats of different ages. The results concerning urinary glycosidase levels in relation to ageing indicate that the levels of three of them - NAG, β-galactosidase and α-L-fucosidase - can be used to monitor the kidney damage resulting from aminoglycoside antibiotic therapy. The effect caused by antibiotics is dose-dependent. The best information was obtained when enzyme activity levels were measured before, during and several days after the end of the treatments. Moreover, the study of the isoenzyme profiles of NAG and the separation of urinary proteins by SDS-polyacrylamide gel electrophores is provides valuable information as to the nature and severity of antibiotic nephrotoxicity. On the basis of our results, sisomicin proves to be more nephrotoxic than tobramycin or amikacin in rats.
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