Differential response of testicular and ovarian heme oxygenase activity to metal ions

Abstract

The response of the microsomal heme oxygenase in the testis to metal ions distinctly differed from that of the ovarian source. The activity of the ovarian enzyme in rats treated with Co 2+ (250 μmol/kg, 24 h) responded in consonance with that of the liver and the kidney, i.e., heme oxygenase activity was elevated. In contrast, similar treatments did not increase the activity of testicular heme oxygenase. In addition, other metal ions, such as Cu 2+, Sn 2+, Pb 2+, and Hg 2+, known for their potency to increase heme oxygenase activity, were ineffective in increasing the enzyme activity in the testis. The unprecedented response of heme oxygenase in the testis to metal ions did not reflect an unusual nature of the enzyme protein insofar as it displayed a similar cofactor requirement and inhibition by known inhibitors of the enzyme activity, such as KCN and NaN 3. Moreover, the apparent K m 's for oxidation of hematoheme by the testicular and ovarian microsomal fractions were comparable and measured 2.3 and 1.4 μ m, respectively. In the testis of Co 2+-treated rats, the concentration of cytochrome P-450 in the rough and smooth endoplasmic reticular fractions was significantly decreased. The decrease in the hemoprotein level, however, did not reciprocate the activity of heme oxygenase in the fractions. The inability of metal ions to induce heme oxygenase activity in the testis did not represent the general refractory nature of the enzymes of heme metabolism to metal ions in this organ, since in rats treated with Co 2+ the activity of δ-aminolevulinate synthetase was significantly decreased 24 h after treatment. However, the activities of uroporphyrinogen-I synthetase, δ-aminolevulinate dehydratase, and ferrochelatase and the content of porphyrins were not altered in the testis of rats treated with Co 2+. The response of δ-aminolevulinate synthetase in the ovarian tissue to Co 2+ treatment contrasted that of the testis. In the ovary, the enzyme activity significantly decreased 6 h after treatment. This decrease was followed by a rebound increase at 24 h after administration of Co 2+. The presently described inability of metal ions to induce testicular heme oxygenase activity suggests that the activity of the enzyme in the testis is controlled by factor(s) which differ from those regulating the enzyme activity in other organs, including another steroidogenic organ, the ovary.