RESULTS

The dose-related effects of Cd'+ treatment on the testicular heme oxygenase activity and the content of heme are shown in Fig. 1. These studies were conducted using the RER and SER fractions. As shown, the treatment of rats with 20 pmol/kg of Cd'+ markedly decreased heme oxygenase activity and concomitantly increased the heme content in both ER fractions. The activity of heme oxygenase and the heme content in the SER were more responsive to Cd'+ treatment than those of the RER. As shown, the treatment of rats with 7 pmol/kg of Cd'+ caused a marked decrease in the activity of heme oxygenase in the SER but not in the RER fraction. Similarly, the concentration of heme was significantly increased in response to 7 pmol/kg of Cd" in the SER fraction only. The protein content of the RER and SEK fractions was not decreased in response to treatment with either dose of Cd". Rather, a slight increase in the RER protein (5-10%) in response to 20pmol/kg of Cd'+ was observed (data not shown). Moreover, the activity of biliverdin reductase was not inhibited in the testicular cytosol fraction. These findings strongly suggest that the observed inhibition of heme oxygenase was not a result of generalized inhibition of protein biosynthesis activity in the testicular tissue. Rather, it may be interpreted to indicate a selective inhibition by Cd" of the synthesis of heme oxygenase and/or its activity. However, the possibility that Cd" may have altered the sedimentation property of the ER membranes and the extent of their recovery in the course of isolation cannot be ruled out. The in~ itro effect of Cd" on the enzyme activity was investigated in order to establish whether the observed effect of Cd'+ on heme oxygenase activity is due to the direct inhibiting action of the metal ion on the pre-existing enzyme. The ER membrane preparations were treated with various- SER

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