Preventive effect of pretreatment with zinc on cadmium nephrotoxicity in rats--evaluation by changes of urinary enzyme activities.

Abstract

The preventive effect of pretreatment with zinc (Zn) on cadmium (Cd) nephrotoxicity in rats was evaluated by the measurement of enzyme activity in urine. The enzymes examined were γ-glutamyltranspeptidase (γ-GTP, EC 2.3.2.2), glycylproline-diaminopeptidase (GP-DAP, EC 3.4.14.4), alkaline phosphatase (Al-P, EC 3.1.3.1) and leucine aminopeptidase (LAP, EC 3.4.11.1).Three groups of male Sprague-Dawley rats were used. The first group received a single subcutaneous injection of 5.0 mg/kg body weight (5 rats, Cd Group), the second received a dosage of 250 μmol Zn/kg 24 hours prior to the same dosage of Cd (5 rats, Zn-Cd Group) and the third received the same dosage of Zn (5 rats, Zn Group).On the 1st day after Cd injection, significant elevation of both γ-GTP and GP-DAP activities in urine were observed in Cd Group, while in Zn-Cd Group the two enzyme activities were not elevated significantly compared to the reference values. On the 2nd day, γ-GTP and GP-DAP activities of Cd Group were reduced comparing with the first increase and those of Zn-Cd Group showed first a significant increase. On the 3rd day and after, both enzyme activities were almost the same as the reference value. The increase of enzyme activities in urine was explained to be caused by the leakage from renal cells. In Zn Group, both enzyme activities were observed little change in the course of the experiment.The excretion pattern of Al-P and LAP into urine differed from those of γ-GTP and GP-DAP in all groups.No histopathological changes under optical microscopy were observed in the livers and the kidneys of all groups.From these results, it appears that Zn Pretreatment showed a preventive effect on Cd nephrotoxicity in terms of enzyme activities in urine before any histophthological changes were seen.