Amplification of prostaglandin E 2 stimulation of luteinizing hormone-releasing hormone release from median eminence explants: a metal(II)-specific effect of chelated copper

Abstract

We have previously demonstrated that extracellular copper amplifies prostaglandin (PG) E 2 stimulation of the release of luteinizing hormone-releasing hormone (LH-RH) from explants of the median eminence area(MEA) 1. Two questions were addressed: what is the active form of copper and the metal(II) specificity for copper action? MEA explants were incubated for 5 min in the presence of CuCl 2 (ionic) or copper complexed to histidine (CuHis) at a concentration of 200 μM each and then for 15 min in the presence of 10 μM PGE 2. It was found that chelated copper but not ionic amplified PGE 2 action, and that the magnitude of PGE 2 stimulation of LH-RH release was 3–4 fold in copper-treated than untreated tissue. Moreover, PGE 2-stimulated release was directly related to the dose of CuHis. To test the metal specificity, MEA explants were incubated for 5 min with one of the following metal(II) complexes: CuHis, NiHis, FeHis, ZnHis, CdHis, MnHis, or BaHis (200 μM each) and then for 15 min with 10 μM PGE 2. Controls were incubated with metal(II) complex or PGE 2. Of these complexes, only CuHis and to a lesser extent NiHis stimulated LH-RH release. However, CuHis was the only complex that amplified PGE 2 stimulation of LH-RH release. Thus, amplification is specific for copper. The finding that chelated copper but not ionic copper amplifies PGE 2 is suggestive that the copper-interactive sites on the LH-RH neurons are not exposed to the extracellular space but that they are either embedded in the plasma membrane, facing the intracellular space, or in the cytoplasm. Such an orientation is consistent with copper modulation of the functional state of a postreceptor component involved in the cascade of events initiated by PGE 2 and leading to LH-RH release.