The interaction of cadmium‐binding proteins (Cd‐bp) and progesterone in cadmium‐induced tissue and embryo toxicity

Abstract

Previous work indicates that a dimer of Cd-thionein (Cd-bp-D, 19,000 MW) is involved in the hereditary resistance to Cd-embryotoxicity seen in the inbred NAW/Pr (NAW) mouse strain. Cd-bp-D is not detected in virgin females after Cd exposure and is detected only after the first 24 hours of exposure to Cd in an inbred strain (C57BL/10ChPr) susceptible to Cd-induced embryotoxicity (Wolkowski, '74; Wolkowski-Tyl, '78). Since progesterone (P) is critical for maintenance of pregnancy in mice, we have studied the possible relationship between this hormone and Cd-bp-D production. As a model system, was examined effects of Cd treatment on Cd-bp synthesis in NAW males. It was anticipated that this model could provide information bearing not only on the relationship between P and Cd-bp-D production, but also on that between Cd-bp-D and Cd toxicity, since a single sc injection of CdCl2 causes typical testicular hemorrhagic necrosis in NAW males, and these animals make only metallothionein and not Cd-bp-D. NAW males were, therefore, given P (0.1 g/Kg bw) and then exposed to Cd. Sephadex gel chromatography (G-200) of liver cytosol from animals killed 24 hours later detected only Cd-bp-D. Testes of these males did not show hemorrhagic necrosis. Since the adrenals of male mammals release P in response to stress, NAW males were stressed by repeated sesame oil or propylene glycol injections (5 ml/Kg bw), or the adrenal was stimulated directly with injections of ACTH (100 IU/Kg bw) for seven days prior to Cd exposure. All methods tested which significantly elevated serum P levels (as confirmed by radioimmunoassay), also resulted in production of Cd-bp-D and absence of testicular hemorrhage in Cd-treated NAW males. Suppression of P release by injection of dexamethazone or corticosterone or by adrenalectomy resulted in testicular hemorrhage and production of only metalicthionein after Cd exposure. The relevance of the interaction between P, Cd-bp-D and protection against Cd-induced toxicity seen in the model system was supported by analysis of serum P levels in pregnant females; elevated levels were seen in resistant (NAW dams on day 10 of gestation and significantly lower levels seen in dams from a Cd-sensitive strain.