Extracellular calcium is required for copper-amplified prostaglandin E2 stimulation of the release of gonadotropin-releasing hormone from median eminence explants.

Prostaglandin E2 (PGE2) is known to stimulate the release of LHRH from hypothalamic tissue incubated under in vitro conditions. We have previously shown that a short preincubation of explants of the median eminence area with copper(II) [Cu(II)] complexed to histidine (CuHis) markedly amplifies PGE2 stimulation of LHRH release. In this study, we wished to ascertain if Cu-amplified PGE2 stimulation of LHRH release is dependent on influx of extracellular calcium (Ca) and, if so, whether it is the copper and/or PGE2 action that is Ca dependent. Median eminence area explants were incubated for 5 min with 200 microM CuHis, then for 15 min with 10 microM PGE2, and finally for 45 min in buffer (Cu/PGE2). Controls were incubated with CuHis or PGE2. In the presence of Ca (1.8 mM), Cu/PGE2 stimulation of LHRH release reached a peak value within 15 min of exposure to PGE2 (accelerated phase), after which the rate of release declined, with a half-life of about 20 min (decelerated phase). In the absence of Ca, Cu/PGE2 stimulation of LHRH release was inhibited by 70% during the accelerated phase, and it was completely inhibited during the decelerated phase. When incubation was carried out in the presence of Ca and 100 microM verapamil, Cu/PGE2 stimulation of LHRH release was similar to that seen in the absence of extracellular Ca. When Ca was omitted from the incubation medium during the exposure to CuHis but was included during and after the exposure to PGE2, the response to PGE2 was fully restored. In addition, we evaluated the extracellular Ca requirement for stimulation of LHRH release by PGE2 alone (without pretreatment with CuHis) and found that release was inhibited by 65% in the absence of Ca. These results indicate that the process of PGE2 stimulation of LHRH release is partially dependent on extracellular Ca, that the process of Cu-amplified PGE2 stimulation of release is highly dependent on influx of extracellular Ca, and that PGE2 action, but not Cu action, is dependent on Ca influx. Since cAMP has been implicated in Ca2+-dependent secretion in other cells, we propose that Cu amplifies the functional state of a postreceptor component involved in the Ca-cAMP secretory pathway stimulated by PGE2.