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Changes in Dietary Zinc Result in Specific Alterations of Metallothionein Concentrations in Newborn Rat Liver¹

Departments of Pharmacology/Toxicology and Pathology, University of Western Ontario, London, Ontario, Canada N6A 5C1

To investigate the role of metallothionein (MT) in the sequestration and storage of zinc in newborn rat livers, a cross-fostering experiment was performed in which zinc-deficient (Zn-D) pups were suckled from Zn-sufficient (Zn-S) dams and vice versa. At consecutive days during lactation, groups of pups were killed. The experiment was continued for 22 d. Zinc concentrations in various tissues and MT concentrations in livers and kidneys were analyzed. The retention of injected ⁶⁵Zn, as well as body weight, was also studied in both groups. Higher whole-body retention of ⁶⁵Zn in the zinc-depleted (Zn-Dp) rats indicates a decreased zinc turnover. These rats also showed markedly reduced growth. The observation that the zinc-repleted (Zn-Rp) pups, although showing ⁶⁵Zn retention similar to that of controls, grew less than controls suggests that Zn-Rp may not compensate for gestational zinc deficiency. Zn-Rp pups showed an increased accumulation of zinc into hepatic MT until d 10, whereas Zn-Dp pups showed a more accelerated degradation of MT than controls. These data indicate that hepatic MT levels fluctuate directly in response to dietary zinc status in newborn rats. Various tissues such as spleen, heart, lung and intestine showed no difference in zinc concentration among all groups at d 22 postpartum. Thus the rapid degradation of hepatic MT in zinc deficiency that may occur to maintain the required zinc levels in other tissues supports the role of MT as a zinc storage protein in newborn rats.

KEY WORDS: • metallothionein • Zn depletion/repletion • newborn

¹ This work was supported by the Medical Research Council of Canada.

² Supported by a studentship from the Medical Research Council of Canada.

³ To whom correspondence and reprint requests should be sent.

Manuscript received 2 June 1986. Revision accepted 10 December 1986.