Copper stimulation of LHRH release from median eminence explants. I. A divalent metal specific process that does not require extracellular calcium.

We have previously shown that chelated copper stimulates the release of LHRH from explants of the median eminence area (MEA) incubated under in vitro conditions, and that this stimulation involves a ligand specific interaction. To further elucidate the mechanism of action of copper, we addressed two questions: (a) What is the divalent metal [metal(II)] specificity for this release process? (b) Is the stimulation of LHRH release by CuHis dependent on influx of extracellular calcium? MEA obtained from adult male rats were incubated for 15 min with one of the following divalent metals Cu, Ni, Fe, Zn, Cd or Mn (each complexed to histidine at an equimolar ratio; 100 microM) and then in the absence of metal for an additional period of 30 min. We found that CuHis and to a lesser extent NiHis stimulated LHRH release, and that FeHis, ZnHis, CdHis or MnHis did not do so. In addition, MEA were incubated for 15 min with CuHis in the presence or absence of CaCl2. Under these two conditions, the temporal pattern and magnitude of CuHis-stimulated LHRH release were identical, indicating that extracellular calcium is not required for copper action. Since, in this series of metals, Cu2+ and Ni2+ are the most potent oxidizing agents, our finding strongly supports our previous proposition that an oxidation reaction is involved in the process of copper stimulation of LHRH release. It has yet to be elucidated whether copper action is totally independent of an increase in intracellular calcium or whether copper leads to LHRH release via mobilization of calcium from intracellular stores.