Copper amplification of prostaglandin E2 stimulation of the release of luteinizing hormone-releasing hormone is a postreceptor event

Arachidonic acid, an omega-6 fatty acid, induces cytoplasmic phospholipase A2 in prostate carcinoma cells

For the past 60 years, dietary intake of essential fatty acids has increased. Moreover, the omega-6 fatty acids have recently been found to play an important role in regulation of gene expression. Proliferation of human prostate cells was significantly increased 48 h after arachidonic acid (AA) addition. We have analyzed initial uptake using nile red fluorescence and we found that the albumin conjugated AA is endocytosed into the cells followed by the induction of RNA within minutes, protein and PGE2 synthesis within hours. Here we describe that AA induces expression of cytosolic phospholipase A2 (cPLA2) in a dose-dependent manner and that this upregulation is dependent upon downstream synthesis of PGE2. The upregulation of cox-2 and cPLA2 was inhibited by flurbiprofen, a cyclooxygenase (COX) inhibitor, making this a second feed-forward enzyme in the eicosanoid pathway. Cox-2 specific inhibitors are known to inhibit colon and prostate cancer growth in humans; however, recent findings show that some of these have cardiovascular complications. Since cPLA2 is upstream in the eicosanoid pathway, it may be a good alternative for a pharmaceutical target for the treatment of cancer.

Studies on the feeding of cupric sulfate pentahydrate and cupric citrate to broiler chickens

Male commercial broiler strain chickens were fed either a control diet (based on corn and soybean meal) or the control diet supplemented with cupric sulfate pentahydrate or cupric citrate in seven experiments (six in floor pens, one in wire-floored batteries). In Experiment 1, feeding 125 or 250 mg/kg copper increased growth (4.9%) and decreased feed conversion ratios (3.4%), total plasma cholesterol (40.2%), and breast muscle cholesterol (37.0%). Feeding 375 mg/kg copper was without further beneficial effect. In Experiment 2, withdrawing growth promoting supplements of copper from the feed for the last 7 d caused a significant (P < 0.05) increase in breast muscle cholesterol at 42 d of age: 57.2, 48.0, and 43.2 mg/100 g meat for birds supplemented for 0, 35, or 42 d, respectively. Feeding 10 vs 260 mg/kg copper caused only small increases in tissue copper levels: 0.36 vs 0.41 mg/kg for breast meat, and 0.48 vs 0.60 mg/kg for thigh meat, respectively. Litter copper accumulations in these experiments were similar to those of earlier reports. Breast muscle cholesterol was reduced by feeding 125 mg/kg supplemental copper from cupric citrate (27.84 mg/100 g) or 125 mg supplemental copper from cupric sulfate pentahydrate (25.32 mg/100 g) compared to broilers fed the control diet (43.92 mg/100 g). Cupric citrate was efficacious for growth promotion at lower copper levels than cupric sulfate pentahydrate, resulting in reduced litter copper.

A potential mechanism for copper amplification of prostaglandin E2 action: attenuation of prostaglandin E2-induced efflux of cyclic AMP from median eminence explants

It is known that prostaglandin E2 (PGE2) stimulation of LHRH release from the median eminence-arcuate nucleus (MEA) is mediated by the cAMP pathway, and a short pretreatment with copper markedly amplifies this release process. Because stimulation of cAMP accumulation is accompanied by cAMP efflux in many tissues, we considered the possibility that attenuation of cAMP efflux is one mechanism by which copper can enhance PGE2 action. When rat MEA explants were incubated in vitro, PGE2 induced a rapid (less than 2.5 min) and sustained (15 min) increase in cAMP efflux, the degree of which was a function of [PGE2]: by 5 min exposure to 10 microM PGEs2, efflux was 8-fold greater than the control (no PGE2) and it accounted for 12.4% of the total (tissue + medium) cAMP. Unlike the dramatic increase in cAMP efflux, PGE2 induced a moderate increase in cAMP content (49%) and in the incorporation of [3H] adenine into [3H] cAMP (78%); this increase was transient: it was evident after a 2.5 but not after a 5 min period of PGE2 exposure. Copper pretreatment did not alter this PGE2-induced increase in tissue cAMP content. In contrast, copper markedly inhibited (by 49%-66%) PGE2-induced cAMP efflux and this inhibition was noted regardless of the length of PGE2 exposure and PGE2 concentration. There was no evidence for hydrolysis of [3H]3',5'-cAMP included in the medium during the incubation with PGE2 with and without copper pretreatment. In summary, copper attenuated PGE2-induced cAMP efflux from MEA explants and this attenuation is not a consequence of a reduction in the availability of intracellular cAMP nor of hydrolysis of cAMP extracellularly.

Ovulation-inducing activity of luliberin (LHRH) complexed by copper(II), nickel(II), and zinc(II) ions

We have shown that the complexation of luteinizing hormone releasing hormone, luliberin (LHRH), a hypothalamic neurohormone, by Cu(II), Ni(II), and Zn(II) may affect its basic, ovulation-inducing potency in the dose responsive manner. Some explanation of the obtained results are offered here.

High-affinity uptake of 67Cu into a veratridine-releasable pool in brain tissue

We have previously characterized two saturable, ligand-dependent processes for 67Cu uptake by hypothalamic slices: a high- and low-affinity process (22). In this study, we wished to ascertain if veratridine, a secretagogue that mimics a physiological release process, stimulates the release of newly taken up 67Cu and whether uptake of 67Cu into the releasable pool of copper is dependent on the process of 67Cu uptake. Hypothalamic or caudate slices from male rats were loaded for 30 min with 67Cu complexed to histidine (His) under conditions favoring high- or low-affinity uptake. First, we assessed the stability of the newly taken up 67Cu and found that, regardless of the mode of 67Cu entry into the tissue, greater than or equal to 85% of the 67Cu is retained in tissues incubated for 3 h in 67Cu-free buffer. Moreover, the 67Cu taken up by the high-affinity process was not displaced by 15-fold molar excess of nonradiolabeled Cu2+, histidine, albumin, or Zn2+, and only 20-30% of the 67Cu taken up by the low-affinity process was displaced by 10-fold excess Cu2+ or albumin. Next, we assessed veratridine stimulation of 67Cu release and found that 67Cu release occurred only from tissues loaded with the high- but not with the low-affinity process. This effect of veratridine was calcium dependent and was blocked by Tetrodotoxin, a specific blocker of the voltage-sensitive Na+ channel. In addition, we confirmed our earlier observation that a depolarizing concentration of K+ stimulates 67Cu release.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for release of copper in the brain: depolarization-induced release of newly taken-up 67copper

The potential importance of copper (Cu) in neurosecretion can be inferred from the demonstration that extracellular Cu modulates the secretory function of peptidergic neurons (in vitro studies) and from the presence of high Cu concentrations in nerve terminals and secretory vesicles, primarily within the soluble matrix of the latter. We have previously hypothesized that vesicular Cu is released from neurons undergoing exocytosis and that such extracellular Cu plays an important modulatory role in the central nervous system. To test this Cu release hypothesis, rat hypothalami were incubated under in vitro conditions for 1 or 2 hr with 20 nM radiolabeled Cu (67Cu), and then 67Cu release was stimulated by a depolarizing concentration (60 mM) of K+. K+ markedly (P less than 0.001) stimulated 67Cu release in a Ca2+-dependent manner (stimulated release was 95 fmol/10 min/mg protein after 1 hr 67Cu loading and 160 after 2 hr). These amounts of released 67Cu account for about 10% of the total 67Cu taken up by the tissue. These results indicate that part of the 67Cu taken up by hypothalamic explants is directed into an intracellular compartment from where it can be released by a Ca2+-dependent mechanism, thus providing strong support to our hypothesis that release of copper is operative in situ in the brain.