Evidence for synergism between copper and prostaglandin E2 in stimulating the release of gonadotropin-releasing hormone from median eminence explants: Na+/Cl- requirements.
Copper (Cu) and PGE2 are known to stimulate LHRH release from explants of the median eminence area (MEA) by two mechanisms distinguishable by their Ca2+ dependence. Moreover, exposure to Cu and PGE2 results in an amplified release of LHRH which is partially Ca2+ dependent, thus, resembling the release process stimulated by PGE2 alone. We have shown that LHRH release stimulated by Cu alone is Na+/Cl- dependent. By defining the Na+/Cl- dependence of PGE2- and Cu/PGE2-stimulated release of LHRH, we wished to ascertain if there is synergism between Cu and PGE2 actions. MEA of adult male rats were incubated for 5 min with 150 microM Cu and then for 15 min with 10 microM PGE2 (Cu/PGE2). Controls were incubated with Cu or PGE2. LHRH release into the medium was evaluated by RIA. Substituting Cl- in the incubation buffer with the non-permeant anion, isethionate, did not alter PGE2 stimulation of LHRH release, but it drastically inhibited Cu/PGE2 stimulation of LHRH release, indicating that this process requires a permeant monovalent anion. PGE2 and Cu/PGE2 stimulation of LHRH release were both inhibited when Na+ was substituted with Li+, or when 0.5 mM ouabain was included in the Na+-containing buffer; neither 10 microM tetrodotoxin (TTX) nor 100 microM amiloride were inhibitory. To ascertain if Na+ is required for Cu uptake, we evaluated the uptake of 67Cu by MEA explants and found that neither ouabain nor Li+ inhibited uptake, indicating that the extracellular Na+ and the activity of Na+/K+ ATPase are required for the process of LHRH release.(ABSTRACT TRUNCATED AT 250 WORDS)
Barnea
A
A
Cecil H. and Ida Green Center for Reproductive Biology Sciences, University of Texas Health Science Center, Dallas 75235.
Colombani-Vidal
M
M
Cho
G
G
Hartter
D E
DE
D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D003300:Copper / Q000494:pharmacology*; D003301:Copper Radioisotopes; D046508:Culture Techniques; D015232:Dinoprostone; D004357:Drug Synergism; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D008297:Male; D008473:Median Eminence / Q000378:metabolism*; D011458:Prostaglandins E / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
D002712:Chlorides; D003301:Copper Radioisotopes; D011458:Prostaglandins E; D007987:Gonadotropin-Releasing Hormone; D003300:Copper; D012964:Sodium; D015232:Dinoprostone