Coordinate regulation of zinc metabolism and metallothionein gene expression in rats.

Regulation of zinc metabolism by dibutyryl cAMP, glucagon, and epinephrine was examined in rats fed adequate amounts of zinc. Dibutyryl cAMP, epinephrine, and glucagon each produced an increase in liver metallothionein levels by 10 h after they were first administered. The increase in liver metallothionein was inversely related to the serum zinc concentration. Treatment with dexamethasone, a glucocorticoid, accentuated these effects to some extent. Both metallothionein I and II were induced by dibutyryl cAMP and glucagon. Levels of metallothionein mRNA in total liver RNA extracts were measured by dot blot hybridization using a synthetic 21-base oligonucleotide complimentary to the 5' region of both the metallothionein I and II genes. Individual administration of dibutyryl cAMP, glucagon, and epinephrine increased the number of metallothionein mRNA molecules per cell by up to fourfold. The data suggest that glucagon and epinephrine are primary regulators of metallothionein gene expression acting at least in part via cAMP. In adrenalectomized rats, glucagon, dibutyryl cAMP, and epinephrine had a less potent effect in terms of metallothionein induction and depression of serum zinc concentrations. These effects were largely restored when dexamethasone was also given. Collectively these data suggest that changes in zinc metabolism associated with acute stress involve coordinate regulation mediated by many factors, including glucocorticoids and cAMP.