A correlation between the ligand specificity for 67copper uptake and for copper-prostaglandin E2 stimulation of the release of gonadotropin-releasing hormone from median eminence explants

We have previously shown that copper (Cu) leads to a 3- to 4-fold amplification of prostaglandin E2 (PGE2) stimulation of LHRH release from explants of the median eminence area (MEA), that this amplification is a saturable function of Cu], and that complexed Cu but not ionic Cu is the active form of the metal. This implicates a ligand-specific site in Cu action. In this study we address the following questions. Is there a ligand specificity for Cu amplification of PGE2 stimulation of LHRH release, and if so, does it correlate with the ligand specificity for Cu uptake? MEAs of 1-month-old female rats were incubated for 5 min with 150 microM Cu solution and then for 15 min with 10 microM PGE2 (Cu/PGE2); LHRH released into the medium was evaluated by RIA. To assess Cu uptake, MEAs were incubated with 100 microM67 Cu solution for 15 min, and 67Cu accumulation by the MEA was evaluated. The Cu was complexed to one of the following ligands: histamine, His, Cys, Thr, Gly, glutathione, Gly-His-Lys, or albumin. There was a high degree of correlation (r = 0.943) between the ligand specificity for Cu/PGE2 stimulation of LHRH release (Cu action) and 67Cu uptake. Complexation of ionic Cu with His facilitated Cu action and 67Cu uptake 3-fold each, and this was completely prevented by the inclusion of His in a 100-fold excess over the concentration of the Cu/His complex. Histamine, the amino acids, and the peptides facilitated Cu action and 67Cu uptake, whereas albumin did not do so. Of these facilitatory ligands, histamine and His were the most effective and Gly-His-Lys was the least effective. In summary, both 67Cu uptake and Cu action are ligand-dependent and ligand-specific; the Cu interactive sites have a common recognition for the Cu-ligand complex and for the ligand itself; and the ligand specificity for 67Cu uptake and for Cu action are highly correlated. These results are consistent with the ligand specificity for Cu uptake being the primary determinant of the ligand specificity for Cu/PGE2 stimulation of LHRH release.