Regulation of prostaglandin production by osteoblast-rich calvarial cells

The effect of various factors upon prostaglandin (PG) production by the osteoblast was examined using osteoblast-rich populations of cells prepared from newborn rat calvaria. Bradykinin and serum, and to a lesser extent, thrombin, were also shown to stimulate PGE₂ and 6-keto-PGF_1α (the hydration product of PGI₂) secretion by the osteoblastic cells. Several inhibitors of prostanoid synthesis, dexamethasone, indomethacin, dazoxiben and nafazatrom, were tested for their effects on the calvarial cells. All inhibited PGE₂ and PGI₂ (the major arachidonic acid metabolites of these cells) production with half-maximal inhibition by all four substances occuring at approximately 10⁻⁷ M. For dazoxiben and nafazatrom, this was in contrast to published results from experiments which have indicated that the compounds stimulated PGI₂ production. Finally, since the osteoblasts is responsive to bone-resorbing hormones, these were tested. Only epidermal growth factor (EGF) was shown to modify PG production. At early time EGF stimulated PGE₂ release, however, the predominant effect of the growth factor was an inhibition of both PGE₂ and PGI₂ production by the osteoblastic cells. The present results suggest that the bone-resorbing hormones do not act to cause an increase in PG by the esteoblast and that any increase in PG production by these cells may be in response to vascular agents     

Prostaglandin E2-stimulated glandular ion and water secretion in isolated frog skin (Rana esculenta)

Summary Prostaglandins are known to stimulate the active sodium absorption in frog skin. In this paper it is shown that prostaglandin E₂ (PGE₂) stimulates an active secretion of Cl^–, Na⁺, and K⁺ from the skin glands inRana esculenta. The active Cl secretion is enhanced more than the Na and K secretion. Therefore, in skins where the Na absorption is inhibited by amiloride, the addition of PGE₂ results in an increase in the short-circuit current (SCC). The PGE₂-stimulated Cl secretion could be inhibited by the presence of ouabain or furosemide in the basolateral solution or diphenylamine-2-carboxylate in the apical solution. The PGE₂-stimulated Cl secretion was enhanced by the phosphodiesterase inhibitor, theophylline, indicating that the effect of PGE₂ was caused by an increase in the intracellular cAMP level in the gland cells. The calcium ionophore A23187, which increases the PGE₂ synthesis in frog skin, stimulated the glandular Cl secretion. This secretion could be blocked by the prostaglandin synthesis inhibitor indomethacin, indicating that A23187 acts by increasing the prostaglandin synthesis and not by a direct action of Ca²⁺ ionsper se. The net water flow (J _w) and the Cl secretion were measured simultaneously under the conditions outlined above. The stimulation, inhibition, and the time-course of the outward-directedJ _w were similar to the change observed for the Cl secretion. These results show that PGE₂ stimulates a glandular secretion of Cl and water in frog skin, probably by increasing the cAMP level in the gland cells.     

Prostaglandin E2 modulates components of the Wnt signaling system in bone and prostate cancer cells

Both Wnt signaling and prostaglandin E₂ (PGE₂) play pivotal roles in bone development, remodeling, osteoporosis and prostate cancer (PCa) bone metastases. We investigated the effects of PGE₂ on Wnt signaling in osteoblast-lineage cells and Wnt-inhibitor expression in PCa cells. We demonstrate that low dose PGE₂ (0.1 μM) promotes Wnt signaling while higher doses of PGE₂ (1.0-10 μM) inhibit these same parameters in osteoblast-lineage cells. The differential effects of low vs high-dose PGE₂ on pre-osteoblasts may be attributed to dose-dependent modulation of prostaglandin receptor (EP) subtype expression; with lower doses increasing the expression the cAMP-stimulatory EP4 receptor subtype and higher doses increasing the expression of the cAMP-inhibitory EP3 receptor subtype. Moreover, we demonstrate that high expression levels of COX-2 and PGE₂ promote the secretion of Wnt inhibitors from prostate cancer cells. These data demonstrate that there are dose-dependent effects of PGE₂ on Wnt activation in osteoblast-lineage cells and Wnt-inhibitor expression in PCa cells which may have clinical implications in the management.     

PGE2 secretion from organ cultured gastric mucosa: Correlation with cyclooxygenase activity and endogenous substrate release

In gastrointestinal research the in vitro release of prostaglandins from incubated or cultured biopsies is a widely used method to estimate prostaglandin synthesis. We therefore investigated the rate limiting mechanisms of PGE₂ release in organ cultured gastric mucosa of the rabbit, determining PGE₂ secretion from organ cultured mucosal biopsies by radioimmunoassay and prostaglandin synthesizing capacity by in vitro incubation of mucosal homogenate or microsomes with [¹⁴C]-arachidonic acid.Freshly taken biopsies secreted PGE₂ at an initial high rate, that decreased during the following 4 hrs of culture. This PGE₂ release was dose dependently reduced by inhibitors of the prostaglandin cyclooxygenase. 5mM acetylsalicylic acid (ASA) maximally suppressed PGE₂ secretion to 7% of controls, and the inhibition by ASA was quantitatively similar at every given culture period. PGE₂ release was markedly increased by carbenoxolone but was only slightly activated by extracellular calcium and the Ca⁺⁺-ionophore A23187. However, Ca⁺⁺/A23187 were unable to maintain PGE₂ secretion at the initial rate.PGE₂ secretion was undisturbed in calcium-free medium but was reduced to 50–60% of controls by excess EDTA. The intracellular calcium chelator 1,2-bis-(2-aminophenoxy)-ethane-N,N,N′,N′,-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) similarly inhibited PGE₂ release to 72% of controls. In contrast, PGE₂ release was unaffected by the intracellular calcium antagonist 3,4,5-trimethylene-bis(4-formylpyridinium bromide) dioxime (TMB-8), the calmodulin antagonists N-(6-aminohexyl)-1-5-chloro-1-naphthalenesulfonamide (W-7) and calmidazolium (compound R24571) or various direct inhibitors of endogenous arachidonic acid release like tetracaine, bromophenacyl bromid, neomycine or low dose quinacrine, indicating that the reduction of PGE₂ release by EDTA or BAPTA may be mediated by mechanisms different from substrate release. In contrast, an inhibition of PGE₂ secretion by quinacrine at high concentrations (≥ 0.8mM) was attributed to a direct inhibition of the prostaglandin cyclooxygenase, similar to ASA. Finally, the reduction of the prostaglandin synthesizing capacity by ASA was strongly correlated with the inhibition of PGE₂ secretion, also at low concentrations and minor degrees of inhibition.From these data we conclude, that the activity of the prostaglandin cyclooxygenase is rate limiting for PGE₂ secretion from organ cultured mucosal biopsies rather than arachidonic acid release by a phospholipase A₂. This should be considered for interpretation of studies based on prostaglandin release from cultured mucosa.     

Role of prostaglandis in the control of renin secretion in the dog (II)

Infusion of prostaglandin E₁ (PGE₁) into the renal artery of anesthetized dogs (1.03 μg/min) caused increases in urine flow rate (V), renal plasma flow (RPF) and renin secretion rate without any change in mean arterial blood pressure (MABP), whereas infusion of prostaglandin F₂α (PGF_2α), (1.03 μg/min) caused no consistent change in V, RPF, or renin secretion rate. Infusion of prostaglandin E₂ (PGE₂) (1.03 μg/min) into the renal artery of “non-filtering” kidneys caused renin secretion rate to rise from 567.7 ± 152.0 U/min(M ± SEM) during control periods to 1373.6 ± 358.5 U/min after 60 minutes of infusion of PGE₂ (P < 0.01), without significant change in MABP (P > 0.1). The data suggest that PGE₁ and PGE₂ play a role in the control of renin secretion. The data further suggest that PGE may control renin secretion through a direct effect on renin-secreting granular cells.     

Promotion of the prehierarchical follicle growth by postovulatory follicles involving PGE2–EP2 signaling in chickens

The postovulatory follicle (POF) in birds is an enigmatic structure, the function of which remains largely unknown. Previous studies on chickens have shown that removal of POFs leads to the postponement of oviposition and the disturbance of broody behavior. One suggestion is that POFs may secrete some crucial hormones or cytokines to act on reproductive organs. However, such secretions and their specific target organs remain to be identified. Here, we investigate the putative functions of POFs in promoting the development of prehierarchical follicles in chickens and explore the possible signaling mechanisms controlling these processes. Results show that POFs express steroidogenic acute regulatory protein (STAR), cholesterol side‐chain cleavage enzyme (CYP11A1), cyclooxygenase 1 (COX1), and COX2 in granulosa cells (GCs), and, most notably, that POF1 produces more prostaglandin E2 (PGE₂) or prostaglandin F2α than do the F1 follicle or the other POFs. Using coculture systems, we also found that POF1 or GCs from POF1 (POF1‐GCs) significantly promote the proliferation of theca externa cells of small white follicles (SWFs, one phase of the prehierarchical follicle). Treatment with PGE₂ significantly facilitates theca externa cell proliferation in SWFs. This POF‐stimulating effect on SWF growth was prevented by treatment with indomethacin (COX inhibitor) or TG6‐10‐1 (PGE₂ type 2 receptor [EP2] antagonist). Therefore, POF1 may secrete PGE₂ to stimulate the progression of SWF by PGE₂–EP2 signaling. These results indicate that POF1 may serve as a transient supplementary endocrine gland in the chicken ovary that stimulates the development of the prehierarchical follicles through PGE₂–EP2 signaling.     

Effects of prostaglandin E2, 16,16-dimethyl prostaglandin E2 and a prostaglandin endoperoxide analogue (U-46619) on gastric secretory volume, [H] and mucus synthesis and secretion in the rat

The effects of orally administered prostaglandin E₂, 16,16-dimethyl prostaglandin E₂ and U-46619, an analogue of the prostaglandin endoperoxide PGH₂, on gastric secretory volume, acid and mucus were studied in the rat. All of the compounds significantly increased the volume of gastric secretion, mucus secretion, measured as N-acetylneuraminic acid and mucus synthesis measured as the incorporation of [³H]-glucosamine into mucosal glycoprotein; however, only PGE₂ and 16,16-dimethyl PGE₂ inhibited acid secretion. U-46619, 1.5 mg/kg provided significant protection against ethanol-induced gastric ulcers, an effect that has been previously shown for the other two compounds. These studies provide additional evidence that prostaglandin induced mucosal protection may by related to an effect on mucus and on stimulation of nonparietal cell gastric secretion. Further study of these parameters may be important in the development of antiulcer drugs for long term clinical use.     

Evidence for a possible prostaglandin link in ACTH-induced steroidogenesis

The steroidogenic response to ACTH and prostaglandin E₂ (PGE₂) was studied in cat adrenocortical cells dispersed with trypsin. The dose-response curves of both agents were qualitatively and quantitatively similar. Exposure to PGE₂ or ACTH in the presence of labeled steroid precursor (acetate) resulted in the accumulation of comparable levels of steroid intermediates and end-product. Submaximal or maximal concentrations of ACTH and PGE₂ given simultaneously elicited a response which was no greater than that obtained with either stimulant alone. Although calcium was required for optimal PGE₂ stimulation of steroid production, this requirement for calcium was less than the requirement with ACTH as the stimulant, but greater than with butyryl cyclic AMP. PGE₂-induced increase in the adrenal cyclic AMP was not statistically significant and was small in relation to that found with equipotent steroidogenic ACTH concentrations. The possible relationship between prostaglandins, cyclic AMP, and calcium in the action of ACTH is discussed.     

Urinary prostaglandin E2 excretion in renal allotransplantation in man

The urinary prostaglandin E₂ excretion was measured daily for 28 days in 15 patients (10 men and 5 women) after renal allotransplantation. Patients with acute oliguric renal failure immediately after the transplantation showed high urinary PGE₂ concentrations, but no or minimal increase in the total excretion rates. The median PGE₂ excretion was 211 μg/24 h after establishment of stable renal function, but with great individual variations. Rejection crises were characterized by a two-fold increase in PGE₂ excretion, with a subsequent fall induced by the steroid treatment. The PGE₂ excretion correlated better with urinary sodium excretion than diuresis.The pathophysiological role of the renal prostaglandin ssynthesis remains incompletely defined. The prostaglandin E₂ (PGE₂) appears to act as a modulator of the renal salt and water excretion (1,2) and prostaglandins are important mediators of the immunresponses (3,4). The eraly renal allograft rejection is an event characterized by salt and water retention together with decreasing renal function (5). Antibodies against renal tissue as well as cytotoxic leukocytes (“killer cells”) are active in the process (6,7) and many hormonal systems are involved, among them renin and vasopressin (8). Both hormones are known to stimulate the synthesis of prostaglandin in the kidneys and interact with its effect (9,10,11). The present material was therefore designed to study the urinary excretion of PGE₂ in the kidney allografts before and during rejection crises.     

Role of intracellular prostaglandin E2 in cancer-related phenotypes in PC3 cells

Prostaglandin E₂ (PGE₂) and hypoxia-inducible factor-1α (HIF-1α) affect many mechanisms that have been shown to play a role in prostate cancer. In PGE₂-treated LNCaP cells, up-regulation of HIF-1α requires the internalization of PGE₂, which is in sharp contrast with the generally accepted view that PGE₂ acts through EP receptors located at the cell membrane. Here we aimed to study in androgen-independent PC3 cells the role of intracellular PGE₂ in several events linked to prostate cancer progression. To this end, we used bromocresol green, an inhibitor of prostaglandin uptake that blocked the immediate rise in intracellular immunoreactive PGE₂ following treatment with 16,16-dimethyl-PGE₂. Bromocresol green prevented the stimulatory effect of 16,16-dimethyl-PGE on cell proliferation, adhesion, migration and invasion and on HIF-1α expression and activity, the latter assessed as the HIF-dependent activation of (i) a hypoxia response element-luciferase plasmid construct, (ii) production of angiogenic factor vascular endothelial growth factor-A and (iii) in vitro angiogenesis. The basal phenotype of PC3 cells was also affected by bromocresol green, that substantially lowered expression of HIF-1α, production of vascular endothelial growth factor-A and cell proliferation. These results, and the fact that we found functional intracellular EP receptors in PC3 cells, suggest that PGE₂-dependent intracrine mechanisms play a role in prostate cancer Therefore, inhibition of the prostaglandin uptake transporter might be a novel therapeutic approach for the treatment of prostate cancer.     

Relationships among mammalian gonadotropin-releasing hormone, prostaglandins, and sex steroids in the brain of the crested newt, Triturus carnifex

The present study was carried out to evaluate the in vitro brain release of prostaglandin F_2α (PGF_2α), prostaglandin E₂ (PGE₂), androgens, and 17β-estradiol in male and female crested newt, Triturus carnifex, during three different periods of the annual sexual cycle; in addition, the effects of mammalian gonadotropin-releasing hormone (mGnRH), PGF_2α, and PGE₂ on prostaglandins and steroids release by the brain were evaluated during the same periods. In brain incubations of both sexes, PGF_2α and estradiol were higher during postreproduction, while PGE₂ and androgens were higher during reproduction. In both sexes, mGnRH increased PGF_2α and estradiol during postreproduction, and PGE₂ during reproduction; PGF_2α increased estradiol secretion during postreproduction. Only in the male, did both mGnRH and PGE₂ increase androgens during reproduction. It could be suggested that in Triturus carnifex, the regulation of the reproductive activity in the central nervous system (CNS) depends on the relationships among mGnRH, prostaglandins and steroids. In particular, PGF_2α and PGE₂ seem to play different roles in the CNS of the newt: PGF_2α is involved in the postreproductive processes, through estradiol secretion, while PGE₂ in the reproductive ones (through androgens secretion?).     

Transport-active renal tubular epithelial cells (MDCK and LLC-PK1) in culutre. Prostaglandin biosynthesis and its regulation by peptide hormones and ionophore

Renal tubular epithelial cells isolated from dog and pig kidney (MDCK and LLC-PK₁, respectively) transport water and electrolytes in culture. MDCK cells resemble collecting tubule cells by additional, but not all, morphologic and biochemical criteria. It has previously been reported that PGE₂ appears to regulate transport activity by MDCK cells as well as their proliferation. We investigated prostaglandin biosynthesis by MDCK and LLC-PK₁ cells and assessed the effects of peptide hormones, bradykinin and vasopressin, on the cells' prostaglandin biosynthesis. Thin-layer chromatography of radioactive products released by MDCK cells labelled with octatritiated of [¹⁴C] arachidonic acid indicated the presence of materials comigrating with PGE₂, PGI₂ (detected as 60oxo0PGF₁α) and PGF₂α, in decreasing order of abundance. Maclofenamate inhibited the biosynthesis of all radioactive peaks comigrating with PGs, thus confirming their identities as product of fatty acid cyclo-oxygenase activity. The chemical identities of [³H] PGE₂ and [³H] 6-oxo-PGF₁α made by the cells were further confirmed by treatment with KOH. Radioimmunoassay of culture fluids incubated with MDCK cells verified that PGE₂ was the most abundant prostaglandin. Tranylcypromine, thought to be a specific inhibitor of prostacyclic synthetase, inhibited PGE₂ as well as PGI₂ biosynthesis indicating a lack of specificity of the inhibitor. The observation of PGE₂ and PGF₂α as respectively the most and least abundant prostaglandinds made by MDCK was in disagreement with results from another laboratory in which the reverse order of abundance was found. This suggests the presence of more than one cell line identified as MDCK but having different biochemical properties.Bradykinin stimulated acylhydrolase activity as well as PGE₂ and PGI₂ biosynthesis in MDCK cells while vasopressin had little or no effect. These results support the hypothesis that bradykinin's natriuretic effects may be mediated by prostaglandinds and that vasopressin is unlikely to acutely stimulate prostaglandin biosynthesis in collecting tubule cells $\text{in}$$\text{vivo}$. Endogenous PGE₂ may also regulate the proliferation of MDCK cells in culture.In contrast to MDCK cells, LLC-PK₁ cells lacked significant prostaglandin biosynthetic capability as documented by radiometric thin-layer chromatography and radioimmunoassay. This suggests that prostaglandins may have a modulatory rather than an obligatory role in regulating transport activity by tubular epithelial cells.     

Stimulation of prostaglandin E2 (PGE2) production by arachidonic acid, oestrogen and parathyroid hormone in MG-63 and MC3T3-E1 osteoblast-like cells

Polyunsaturated fatty acids (PUFAs) as well as oestrogen (E2) and parathyroid hormone (PTH) affect bone cells. The aim of the study was to determine whether arachidonic acid (AA), E2, and PTH increase prostaglandin E₂ (PGE₂) synthesis in MG-63 and MC3T3-E1 osteoblastic cells and the level of mediation by COX-1 and COX-2. PGE₂ levels were determined in the conditioned culture media of MG-63 and MC3T3-E1 osteoblasts after exposure to AA, PTH and E2. Cells were pre-incubated in some experiments with the unselective COX inhibitor indomethacin or the COX-2 specific blocker NS-398. Indirect immunofluorescence was performed on MG-63 cells to detect the presence and location of the two enzymes involved. AA increased PGE₂ secretion in both cell lines; production by MC3T3-E1 cells, however, was significantly higher than that of MG-63 cells. This could be due to autoamplification via the EP₁ subtype of PGE receptors in mouse MC3T3-E1 osteoblasts. Both COX-1 and COX-2 affected the regulation of PGE₂ synthesis in MG-63 cells. E2 had no effect on PGE₂ secretion in both cell lines, while PTH caused a slight increase in PGE₂ synthesis in the MG-63 cell line.     

Plasma concentrations of 13,14-dihydro-15-keto-prostaglandin E2 in rabbits bearing the VX2 carcinoma: Effects of hydrocortisone and indomethacin

In rabbits bearing the prostaglandin-producing VX₂ carcinoma, the plasma concentration of 13,14-dihydro-15-keto-PGE₂ (PGE₂-M) was elevated within one week after tumor implantation and preceded the development of hypercalcemia. Both the rate of rise and magnitude of the increase were greater for the metabolite than for PGE₂; at the time of peak hypercalcemia (about 4 to 5 weeks after tumor implantation), the increase over basal in plasma PGE₂-M was about 75 fold whereas it was previously shown that the increase in PGE₂ was less than 2 fold. Indomethacin, which inhibits PGE₂ synthesis in VX₂ cells in culture, lowered in parallel plasma calcium and PGE₂-M in tumor-bearing rabbits. Administration of hydrocortisone to rabbits bearing the VX₂ tumor prevented the development of hypercalcemia when given at the time of tumor implantation and reversed the elevated plasma calcium in previously untreated animals; the steroid hormone also lowered plasma concentrations of PGE₂-M. These findings are consistent with our hypothesis that the hypercalcemic syndrome in VX₂ tumor-bearing rabbits is due to the secretion of PGE₂ by the tumor.     

Uncoordinate regulation of collagenase,stromelysin, and tissue inhibitor of metalloproteinases genes by prostaglandin E2: Selective enhancement of collagenase gene expression in human dermal fibroblasts in culture

The degradative effects of interleukin-1 (IL-1) on the extracellular matrix of connective tissue are mediated primarily by metalloproteinases and prostaglandins. Clinical observations suggest that these effects can be prevented, to some extent, by the use of non-steroidal anti-inflammatory drugs. We have examined the role of prostaglandin E₂ (PGE₂) in IL-1-induced gene expression by human skin fibroblasts in culture. Incubation of confluent fibroblast cultures with varying concentrations (0.01–1.0 μg/ml) of PGE₂ led to a dose-dependent elevation of collagenase mRNA steady-state levels, the promoter activity, and the secretion of the protein, whereas relatively little effect was observed on stromelysin and TIMP gene expression. Exogenous PGE₂ had no additive or synergistic effect with IL-1 on collagenase gene expression. Furthermore, commonly used non-steroidal anti-inflammatory drugs (indomethacin, acetyl salicylic acid and ibuprofen), at doses which block prostaglandin synthesis in cultured fibroblasts, failed to counteract IL-1-induced collagenase and stromelysin gene expression, nor did they affect TIMP expression. Although the effects of PGE₂ did not potentiate those of IL-1 on collagenase gene expression in vitro, one could speculate that massive production of PGE₂ by connective tissue cells in vivo in response to inflammatory mediators such as IL-1 or tumor necrosis factor-α, could lead to sustained expression of collagenase in connective tissue cells after clearance of the growth factors.     

E-type Prostaglandins and Gastric Acid Secretion in the Rat

IT is known that prostaglandins of the ? series (PGEs) inhibit gastric acid secretion^1–4, but the relative potencies of prostaglandin E₁ and prostaglandin E₂ have not been evaluated. We report observations which indicate that orally administered PGE₂ has a considerably longer duration of action than an equipotent oral dose of PGE₁ in inhibiting pentagastrin-induced gastric acid secretion in the rat and that this inhibitory action appears to be due to a local action on the gastro-intestinal wall rather than to absorption of prostaglandins into the systemic circulation.     

Suppression of prostaglandin synthesis by analogues of cyclic AMP and forskolin in chondrocyte monolayer cultures

Recent experimental studies indicated that prostaglandin E₂ (PGE₂) is the most abundant prostanoid synthesized by rabbit articular chondrocytes. Exogenous PGE₂ stimulates cyclic AMP (cAMP) synthesis in these cells. Analogues of cAMP and forskolin have now been shown to suppress the biosynthesis of PGE₂ in the presence of serum in a time-dependent manner. The most abundant prostanoid, PGE₂ was most markedly affected. PGF_2α was unaffected. These results indicated that intracellular accumulation of cAMP in chondrocytes and relative resistance of cAMP to phosphodiesterases control prostanoid synthesis in a negative feedback loop.     

Characterisation of the prostaglandin E2-ethanolamide suppression of tumour necrosis factor-α production in human monocytic cells

Background and purpose

Prostaglandin ethanolamides or prostamides are naturally occurring neutral lipid derivatives of prostaglandins that have been shown to be synthesised in vivo following COX-facilitated oxygenation of arachidonoyl ethanolamine (anandamide). Although the actions of prostaglandins have been extensively studied, little is known about the physiological or pathophysiological effects of prostamides. Since prostaglandin E₂ has potent immunosuppressive/immunomodulating actions, the aim of the present study was to determine whether the derivative, prostaglandin E₂ ethanolamide (PGE₂-EA), could modulate the production of the pro-inflammatory cytokine tumour necrosis factor-α in human blood and human monocytic cells and indicate whether this action involved the same receptor systems/signals as PGE₂.

Experimental approach

Whole human blood, monocytes isolated from the blood or the human monocytic cell line THP-1 was incubated with LPS and the level of TNF-α produced was measured by ELISA assay. The actions of PGE₂-EA were assessed on the LPS-induced TNF-α release. In addition, in order to ascertain the receptors involved, the levels of cyclic AMP in cells were measured in monocytes and THP-1 cells in response to PGE₂-EA and directly compared to those of PGE₂. The effect of PGE₂-EA on the binding of radiolabelled PGE₂ to cells was also measured. Cells were incubated with radiolabelled arachidonic acid and ethanolamine to estimate the production of PGE₂-EA.

Key results

PGE₂-EA potently suppressed TNF-α production in blood, monocytes and the cell line THP-1 in a concentration-dependent manner. This occurred via cyclic AMP pathways as indicated by agents which interfere with these pathways and also direct ligand binding experiments. It was also shown that the cells were able to endogenously produce PGE₂-EA.

Conclusions and implications

This study reports that PGE₂-EA can downregulate the production of TNF-α by human mononuclear cells in response to an immune stimulus, i.e. LPS-activated TLR4, and that this appears to occur via a cAMP-dependent mechanism that most likely involves binding to the EP₂ receptor.     

Differential of sex steroids of prostaglandin secretion by male and female cultured piglet endothelial cells

The effect of sex steroids, 17β-estradiol and testosterone, on the production of 6-keto-prostaglandin F_1α, prostaglandin F_2α and prostaglandin E₂ was studied in cultures of piglet aorta endothelial cells. In cells isolated from female animals both steroids stimulated the secretion of prostaglandins. In contrast, sex steroids did not affect prostaglandin synthesis by endothelial cells taken from male animals. In addition, female endothelial cells convert testosterone into Estriol, estrone and estradiol. estradiol-induced stimulation of prostacyclin production may explain in part the beneficial role generally attributed to naturally occuring estrogens in cardiovascular diseases.