A ligand-specific action of chelated copper on hypothalamic neurons: stimulation of the release of luteinizing hormone-releasing hormone from median eminence explants.

Abstract

We have previously shown that chelated copper stimulates the release of luteinizing hormone-releasing hormone (LHRH) from isolated hypothalamic granules. In this study, we wished to ascertain if chelated copper acts on hypothalamic neurons to stimulate LHRH release and, if so, what is the ligand specificity of this interaction. An in vitro system of explants of the median eminence area (MEA) was established and characterized. MEA explants were exposed for 15 muin to 50 /uM copper, and then they were incubated for 75 min in copper-free medium. Copper led to a transient increase in the rate of LHRH release; the maximal rate was attained 15 min after transfer of the MEA to copper-free medium. In addition, we found that copper complexed to histidine (Cu-His), but not ionic copper, stimulated LHRH release, the magnitude of which was dependent on the dose of Cu-His. The chelator specificity for Cu complex action was such that Cu-His stimulated LHRH release 4.9-fold and Cu-Cys stimulated release 2.5-fold, whereas neither Cu-Thr, Cu-Gly-His-Lys, Cu-bovine serum albumin, nor ceruloplasmin stimulated LHRH release. Based on these results and those of others indicating that the concentration of copper in hypothalamic axonal terminals is 1-2 orders of magnitude greater than plasma, we propose that copper released in the vicinity of the LHRH neurons interacts with specific sites on the LHRH axonal terminals, which leads to release of the peptide.A small amount of cupric sulfate (50 ,g) leads to ovulation if it is administered into the posterior median eminence of the rabbit but not into other regions of the brain (1). Tsou et al.(2) observed increased levels of luteinizing hormone-releasing hormone (LHRH) in the pituitary stalk of the rabbit after the systemic administration of cupric acetate. We showed (3-5) that copper, at a concentration within the range required for the activity of several copper-dependent enzymes (6-9), markedly stimulates the release of LHRH from isolated hypothalamic granules. Based on these findings, we proposed (4) that copper plays a role in regulating LHRH release from LHRH neurons in the following manner. Newly taken up copper interacts with LHRH granules that are in close proximity to or in the process of fusing with the plasma membrane. Intraneuronal copper does not interact with LHRH granules, because it would be inactivated by reduced glutathione and copper-binding proteins (10,11).It is well established that tissues obtain their copper supply from the circulation, where copper is chelated by proteins (ceruloplasmin, albumin), peptides, and amino acids. The current view is that the readily exchangeable pool of copper is that associated with albumin, small peptides, and amino acids (12, 13). The following observations support the view that an active uptake mechanism for copper is operative in the hypothalamus. Copper is present in the hypothalamus in concentrations much greater than in blood (14, 15), and in hypothalamic homogenates, copper is highly concentrated in synaptosomes (pinche...

Effect of supplemental copper proteinate on reproductive performance of first- and second-parity sows

“…Those workers reported that dairy cows fed a mineral (Cu, Zn, and Mn) proteinate had a reduced incidence of cystic ovaries and days to first estrus. In rats, a Cu-histidine complex stimulates LHRH release from hypothalamic neurons (Barnea and Colombani-Vidal 1984;Barnea et al 1986). Swine studies have shown that LHRH raises LH secretion [see the review by Estienne et al (1997)] and that higher LH secretion before weaning is associated with an early return to estrus in postweaning sows (Shaw and Foxcroft 1985;King and Martin 1989;Tokach et al 1992).…”

“…A higher level of luteinizing hormone (LH) before weaning was associated with a shorter weaning-to-estrus interval in sows (Shaw and Foxcroft 1985;King and Martin 1989;Tokach et al 1992). Copper-histidine complex stimulates the release of luteinizing hormone-releasing hormone (LHRH) from hypothalamic neurons in rats (Barnea and Colombani-Vidal 1984;Barnea et al 1986) and maybe in pigs. The mineral proteinates used by Spears and Flowers (1995) included a CuP containing 10% copper and 1% histidine.…”

Postovariectomy Decline in the in vitro Release of LH-Releasing Hormone Is Not Manifested in Aging Female Rats

“…In vitro incubations o f the MEA explants were carried out as pre viously described in detail [7,11]. Briefly, explants (1 MEA/0.6 ml KRP) were incubated at 37 °C under air.…”

“…We have previously established that after the 30 min equilibration period, LHRH release from nonstimulated tissue pro ceeds at a constant rate for at least 2 h [ 11 ] and that when MEA are treated with Cu and PGE2, maximal rate of LHRH release is manifested within the 15-min period o f PGE2 exposure [3,6,7). This time course of Cu/P G E t stimulation of LHRH release was reconfirmed in this study using MEA of intact, ovariectomized, and ovariectomized-estrogentreated rats.…”

Effects of Castration and Maturational Age of Male Rats on the Process of Copper-Stimulated Release of Luteinizing Hormone Releasing Hormone from Median Eminence Explants: Evidence that Androgens Increase the Affinity of the Copper-Interactive Sites for Copper

“…Using explants of the median eminence area (MEA) [4] or LHRH secretory granules isolated from the MEA [2,6,26,27] incubated under in vitro conditions, we have demon strated that extracellular chelated copper can lead to LHRH release from LHRH neuronal terminals and that one site of action of chelated copper is the secretory granule itself. Our observation of a strict ligand specificity for the action of chelated copper at both the level of the axonal terminal and the secretory granule is suggestive that copper interacts with specific sites present on these cellular com partments.…”