Different responses of metallothionein and leptin induced in the mouse by fasting stress

Changes in metallothionein (MT) and leptin under fasting stress were studied. MT content in the liver of mice increased markedly during continuous fasting periods up to 66 h. Hepatic content of MT increased significantly in mice during the first three cycles of alternate daily fasting-feeding, and then the rate of increase gradually decreased with repetition of this cycle. At the end of 10 cycles, the hepatic MT content was still greater in stressed mice than in the control, although the rate of increase decreased. On the other hand, the plasma concentration of leptin decreased dramatically during continuous fasting. The plasma leptin level recovered to the basal level at the end of 10 cycles of fasting-feeding. These data indicate that MT induction was strongly increased, but leptin was scarcely induced under the continuous fasting stress, and that rates of the changes in MT and leptin levels were gradually reduced under the repeated fasting stress, which may result from an inborn tolerance. Fasting presumably causes translocation of zinc from intracellular to extracellular space, from which it is taken into target organs. The increased zinc-bound MT under the continuous fasting may partly result from the need to maintain zinc and protect tissues against oxidative damage.