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The Effects of Zinc Deficiency on Turnover of Cadmium-Metallothionein in Rat Liver¹

Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, WI 53706

The object of this experiment was to determine the effects of Zn deficiency on the turnover of Cd-induced metallothionein (MT) in rat liver. Male rats were fed a purified Zn-deficient or Zn-adequate diet. After 13 days, the rats were given three daily injections of Cd²⁺ totaling 1.5 or 3.0 (Zn-deficient) and 3.0 or 6.0 (Zn-adequate) mg Cd/kg body weight. The MT was labeled by injecting the rats with [³⁵S]cystine 2 hours after the final Cd injection. One, 3 or 5 days after labeling, the rats were killed, and their livers were assayed for MT ³⁵S and metal content. The metal composition of MT (mole %) was 41–42% Cd, 51–54% Zn and 4–7% Cu in the Zn-adequate groups and 64% Cd, 27–31% Zn and 6–9% Cu in the Zn-deficient groups. The half-lives of Cd-induced MT in the Zn-deficient rats were 2.6 days (1.5 mg Cd/kg) and 2.8 days (3.0 mg Cd/kg). In the Zn-adequate rats, the half-lives were 3.6 days (3.0 mg Cd/kg) and 3.1 days (6.0 mg Cd/kg). The half-lives of general, soluble hepatic proteins were 4.1 to 4.3 days in all groups. Despite the stabilizing effect of the higher Cd content, the half-life of hepatic MT in the Zn-deficient rats was significantly shorter than in the Zn-adequate rats. These results indicate that hepatic MT degradation is faster in Zn-deficient animals.

KEY WORDS: • zinc • deficiency • cadmium • metallothionein • turnover

¹ Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI.

² Present address: Department of Microbiology, Sigma Chemical Co., St. Louis, MO 63178.

Manuscript received 16 January 1984.