Hidehiro Hayashi

Increased metallothionein content in rat liver and kidney following X-irradiation

Hepatic and renal metallothionein (MT) contents were measured in rats following whole-body X-irradiation. When compared with control rats, the hepatic MT-Zn content increased fivefold and MT protein content increased 15-fold by 18 hr following irradiation (2000 rad). Administration of actinomycin-D inhibited both the mobilization of zinc to the liver and the irradiation-induced increase in metallothionein synthesis. Serum zinc levels did not change after irradiation alone, although serum zinc following actinomycin-D treatment and irradiation was significantly elevated. An increase in renal MT-Zn was also observed. In comparison with control, the increase in renal MT-Zn content after irradiation (2000 rad) did not occur earlier than 12 hr but was increased twofold by 24 hr. In comparison with kidney, the hepatic MT-Zn content following irradiation was already elevated threefold by 6 hr. Dose-response studies (250-3000 rad, 72 hr) indicated that similar dose-response relationships for the appearance of MT in the liver and kidney were observed. Total zinc was decreased in the spleen and thymus, and increased in the liver or kidney 18 hr after irradiation (2000 rad). These data indicate that X-ray treatment produces an in vivo induction of hepatic and renal MT synthesis.

Elevation in metallothionein messenger RNA in rat tissues after exposure to X-irradiation

Metallothionein (MT) mRNA levels in tissues were measured in rats following whole-body X-irradiation (2 and 20 Gy). When compared with control rats, the elevation in MT mRNA levels of liver, kidney, and thymus was observed in irradiated rats at 9 or 72 hr after irradiation. However, the elevation in MT mRNA levels was not observed in brain, spleen, lung, heart, and testis. When compared with other tissues, testicular MT mRNA levels in control rats were extremely high, and treatment with X-irradiation produced a slight decrease of testicular MT mRNA levels. Time-course experiments indicated that hepatic and renal MT mRNA reached a maximum at 6 hr after irradiation. In low-dose (2 Gy) irradiated rat, these values were returned to control values by 4 days after irradiation. However, in high-dose (20 Gy) irradiated rat, the values were not decreased to control values. These data indicate that treatment with X-irradiation produces an elevation in MT mRNA in rat tissues.