Induction of metallothionein-like cadmium-binding protein in the testis by oral cadmium administration in rats.

The possible induction of a metallothionein (MT)-like Cadmium (Cd) binding protein (MT-like Cd-BP) was investigated in rat testis after oral Cd administration. Male Wistar rats were given Cd by oral administration (20 mgCd/kg, for 10 weeks), while the experimental controls were given Cd by intraperitoneal (i.p.) injection (2 mgCd/kg). Cd concentration increased in the testes after both administrations. However, much more Cd (about 4 times) accumulated in the tests of rats receiving oral Cd administration than in rats receiving Cd ip injection (experimental control). Meanwhile, MT-like Cd-BP decreased dramatically in the testes after Cd i.p. injection compared to that in the testes of untreated control rats. However, this testicular MT-like Cd-BP after oral Cd administration increased significantly up to about 1.4 times of the amount found in the testes of untreated control rats. Inhibition of glutathione S-transferase (GST) activity and decreased glutathione (GSH) in the testes was not observed in rats after oral Cd administration. However, enzyme activity and GSH concentration were inhibited and decreased significantly in the testis by Cd toxicity after Cd i.p. injection. These results indicate that testicular MT-like Cd-BP, assumed to be MT and to be hardly inducible by Cd, is an inducible protein corresponding to increased Cd accumulation in the testis without damage by Cd toxicity after oral Cd administration.