Transport of prostaglandins and other eicosanoids by the choroid plexus: its characterization and physiological significance

Obesity Impacts Fever and Sickness Behavior During Acute Systemic Inflammation

Obesity is reaching dramatic proportions in humans and is associated with a higher risk for cardiovascular disease, diabetes, and cognitive alterations, and a higher mortality during infection and inflammation. The focus of the present review is on the influence of obesity on the presentation of fever, sickness behavior, and inflammatory responses during acute systemic inflammation.

Pharmacological significance of prostaglandin E2 and D2 transport at the brain barriers

Prostaglandin (PG) E2 and PGD2, which are biosynthesized from arachidonic acid generated by enzymatic cleavage of membrane phospholipid in response to various stimuli, play key roles in multiple brain pathophysiological processes, including modulation of synaptic plasticity, neuroinflammation, and sleep promotion. Concentrations of PGE2 and PGD2 in brain interstitial fluid (ISF) and cerebrospinal fluid (CSF) are maintained at appropriate levels for normal brain function by regulatory systems. The blood-brain barrier (BBB) and the blood-CSF barrier (BCSFB) possess ISF/CSF-to-blood efflux transport systems that are the primary cerebral clearance pathways for PGE2 and PGD2. However, regulatory dysfunction at the brain barriers may seriously affect brain function. In a mouse inflammation model, significant reduction of PGE2 efflux transport at the BBB has been observed. Several kinds of cephalosporin antibiotics and nonsteroidal anti-inflammatory drugs inhibit the BBB- and BCSFB-mediated efflux transport of PGE2 and PGD2. Especially, drugs that inhibit multidrug resistance-associated protein 4 (MRP4)-mediated PGE2 transport are capable of reducing PGE2 efflux at the BBB. Thus, it might be important in the treatment of inflammatory and infectious diseases to use drugs that do not inhibit clearance of PGE2 at the brain barriers, in order to avoid unexpected adverse CNS effects. Further, considering that PGD2 in CSF is a natural sleep-promoting factor, changes in the activity of the PGD2 efflux transport system at the BCSFB may modify the PGD2 level in CSF, thus affecting physiological sleep. These findings indicate that the efflux transport systems at the brain barriers play key roles in the pathophysiology and pharmacology of PGE2 and PGD2.

A clearance system for prostaglandin D2, a sleep-promoting factor, in cerebrospinal fluid: role of the blood-cerebrospinal barrier transporters

Although the level of prostaglandin (PG) D(2) in cerebrospinal fluid (CSF) affects the action of D-type prostanoid receptors that promote physiological sleep, the regulatory system of PGD(2) clearance from the CSF is not fully understood. The purpose of this study was to investigate PGD(2) elimination from the CSF via the blood-CSF barrier (BCSFB). The in vivo PGD(2) elimination clearance from the CSF was 16-fold greater than that of inulin, which is considered to reflect CSF bulk flow. This process was inhibited by the simultaneous injection of unlabeled PGD(2). The characteristics of PGD(2) uptake by isolated choroid plexus were, at least partially, consistent with those of PG transporter (PGT) and organic anion transporter 3 (OAT3). Studies using an oocyte expression system showed that PGT and OAT3 were able to mediate PGD(2) transport with a Michaelis-Menten constant of 1.07 and 7.32 μM, respectively. Reverse transcription-polymerase chain reaction and immunohistochemical analyses revealed that PGT was localized on the brush-border membrane of the choroid plexus epithelial cells. These findings indicate that the system regulating the PGD(2) level in the CSF involves PGT- and OAT3-mediated PGD(2) uptake by the choroid plexus epithelial cells, acting as a pathway for PGD(2) clearance from the CSF via the BCSFB.

Prostaglandin E2 metabolism in rat brain: Role of the blood-brain interfaces

BACKGROUND

Prostaglandin E2 (PGE2) is involved in the regulation of synaptic activity and plasticity, and in brain maturation. It is also an important mediator of the central response to inflammatory challenges. The aim of this study was to evaluate the ability of the tissues forming the blood-brain interfaces to act as signal termination sites for PGE2 by metabolic inactivation.

METHODS

The specific activity of 15-hydroxyprostaglandin dehydrogenase was measured in homogenates of microvessels, choroid plexuses and cerebral cortex isolated from postnatal and adult rat brain, and compared to the activity measured in peripheral organs which are established signal termination sites for prostaglandins. PGE2 metabolites produced ex vivo by choroid plexuses were identified and quantified by HPLC coupled to radiochemical detection.

RESULTS

The data confirmed the absence of metabolic activity in brain parenchyma, and showed that no detectable activity was associated with brain microvessels forming the blood-brain barrier. By contrast, 15-hydroxyprostaglandin dehydrogenase activity was measured in both fourth and lateral ventricle choroid plexuses from 2-day-old rats, albeit at a lower level than in lung or kidney. The activity was barely detectable in adult choroidal tissue. Metabolic profiles indicated that isolated choroid plexus has the ability to metabolize PGE2, mainly into 13,14-dihydro-15-keto-PGE2. In short-term incubations, this metabolite distributed in the tissue rather than in the external medium, suggesting its release in the choroidal stroma.

CONCLUSION

The rat choroidal tissue has a significant ability to metabolize PGE2 during early postnatal life. This metabolic activity may participate in signal termination of centrally released PGE2 in the brain, or function as an enzymatic barrier acting to maintain PGE2 homeostasis in CSF during the critical early postnatal period of brain development.

Effects of LPS stimulation on the expression of prostaglandin carriers in the cells of the blood-brain and blood-cerebrospinal fluid barriers

Prostaglandins produced in cerebral endothelial cells (CECs) are the final signal transduction mediators from the periphery to the brain during fever response. However, prostaglandins are organic anions at physiological pH, and they enter cells poorly using simple diffusion. Several transporters have been described that specifically transport prostaglandins across cell membranes. We examined the expression of the two principal prostaglandin carriers, prostaglandin transporter (PGT), and multidrug resistance-associated protein 4 (MRP4) in cells of the blood-brain barrier and in choroid epithelial cells in vitro as well as in vivo in rat brain in control conditions and after lipopolysaccharide (LPS) challenge. We detected PGT in primary cultures of rat CECs, astrocytes, pericytes, and choroid epithelial cells. LPS stimulation had no effect on the expression level of PGT in these cells; however, after LPS stimulation the polarized, dominantly luminal, expression pattern of PGT significantly changed. MRP4 is also expressed in CECs, and its level was not influenced by LPS treatment. In rat brain, PGT was highly expressed in the supraoptic and paraventricular nuclei of the hypothalamus, in the ependymal cell layer of the third ventricle, and in the choroid plexus. LPS treatment increased the expression of PGT in the supraoptic and paraventricular nuclei. Our results suggest that PGT and MRP4 likely play a role in transporting prostaglandins through the blood-brain and blood-cerebrospinal fluid barriers and may be involved in the maintenance of prostaglandin homeostasis in the brain and in the initiation of fever response.

Impairment of blood-cerebrospinal fluid barrier properties by retrovirus-activated T lymphocytes: reduction in cerebrospinal fluid-to-blood efflux of prostaglandin E2

The choroid plexus epithelium forms the interface between the blood and the CSF. In conjunction with the tight junctions restricting the paracellular pathway, polarized specific transport systems in the choroidal epithelium allow a fine regulation of CSF-borne biologically active mediators. The highly vascularized stroma delimited by the choroidal epithelium can be a reservoir for retrovirus-infected or activated immune cells. In this work, new insight in the implication of the blood-CSF barrier in neuroinfectious and inflammatory diseases is provided by using a differentiated cellular model of the choroidal epithelium, exposed to infected T lymphocytes. We demonstrate that T cells activated by a retroviral infection, but not non-infected cells, reduce the transporter-mediated CSF-to-blood efflux of organic anions, in particular that of the potent pro-inflammatory prostaglandin PGE2, via the release of soluble factors. A moderate alteration of the paracellular permeability also occurs. We identified the viral protein Tax, oxygenated free radicals, matrix-metalloproteinases and pro-inflammatory cytokines as active molecules released during the exposure of the epithelium to infected T cells. Among them, tumour necrosis factor and interleukin 1 are directly involved in the mechanism underlying the decrease in some choroidal organic anion efflux. Given the strong involvement of CSF-borne PGE2 in sickness behaviour syndrome, these data suggest that the blood-CSF barrier plays an important role in the pathophysiology of neuroinflammation and neuroinfection, via changes in the transport processes controlling the CSF biodisposition of PGE2.

Expression of genes controlling transport and catabolism of prostaglandin E2 in lipopolysaccharide fever

Prostaglandin (PG) E(2) is a principal downstream mediator of fever and other symptoms of systemic inflammation. Its inactivation occurs in peripheral tissues, primarily the lungs and liver, via carrier-mediated cellular uptake and enzymatic oxidation. We hypothesized that inactivation of PGE(2) is suppressed during LPS fever and that transcriptional downregulation of PGE(2) carriers and catabolizing enzymes contributes to this suppression. Fever was induced in inbred Wistar-Kyoto rats by intravenous LPS (50 microg/kg); the controls received saline. Samples of the liver, lungs, and hypothalamus were harvested 0, 0.5, 1.5, and 5 h postinjection. The expression of the two principal transmembrane PGE(2) carriers (PG transporter and multispecific organic anion transporter) and the two key PGE(2)-inactivating enzymes [15-hydroxy-PG dehydrogenase (15-PGDH) and carbonyl reductase] was quantified by RT-PCR. All four genes of interest were downregulated in peripheral tissues (but not the brain) during fever. Most remarkably, the expression of hepatic 15-PGDH was decreased 26-fold 5 h post-LPS, whereas expression of pulmonary 15-PGDH was downregulated (as much as 18-fold) throughout the entire febrile course. The transcriptional downregulation of several proteins involved in PGE(2) inactivation, first reported here, is an unrecognized mechanism of systemic inflammation. By increasing the blood-brain gradient of PGE(2), this mechanism likely facilitates penetration of PGE(2) into the brain and prevents its elimination from the brain.

Prostaglandin transport

Newly synthesized prostaglandins (PGs) efflux from cells by simple diffusion, driven by pH and the membrane potential. Metabolic clearance requires energy-dependent uptake across the plasma membrane, followed by cytoplasmic oxidation. Several PG carriers have been cloned and characterized. PGT is broadly expressed in cyclooxygenase (COX)-positive cells, appears to be a lactate/PG exchanger, and is coordinately regulated with COX. By analogy with neurotransmitter release and re-uptake, PGT may regulate pericellular PG levels via re-uptake. PGT may also direct PGs towards and/or away from specific sets of PG receptors. Other members of the OATP transporter family also catalyze PG uptake; these are variably expressed and have variable affinities for PGs. The OATs are alpha-ketoglutarate/organic anion exchangers that accept PGs; these probably represent the uptake step in renal and hepatic PG degradation and excretion. Finally, certain glutathione-conjugated leukotrienes and PGs are actively extruded from cells by the MRPs; these may also play a role in metabolic clearance of PGs.

Perinatal changes in choroidal 15-hydroxyprostaglandin dehydrogenase: implications for prostaglandin removal from brain

We have previously shown in the sheep fetus at 0.7 and 0.9 gestation that the choroid plexus, unlike brain parenchyma, catabolizes prostaglandins (PGs). Peculiarly, in the choroid plexus, PGE(2) catabolism persists throughout the neonatal period to abate in the adult, while PGF(2alpha) catabolism abates shortly after birth. To explain this differential behavior and elucidate the function of catabolic enzymes, we examined the cellular location and activity of the rate-limiting enzyme for PGE(2) and PGF(2alpha) catabolism, 15-hydroxyprostaglandin dehydrogenase (15-PGDH). Immunofluorescence histochemistry and immunogold electronmicroscopy revealed abundant 15-PGDH expression in the epithelial cytosol close to the brush-border membrane at 0.7 and 0.9 gestation. In contrast, at 5 and 15 days postnatal, 15-PGDH was found throughout the cytosol of stromal fibroblasts. No staining was observed at either location in pregnant adults. PGF(2alpha) catabolism was minimal in the total homogenate and 100000xg supernatant of the fetal choroid plexus at 0.7 and 0.9 gestation, while PGE(2) catabolism was evident at 0.7 gestation only. In contrast, both PGs were catabolized in minced specimens at either age. In conclusion, our study shows immunoreactive 15-PGDH in the choroid plexus from fetal and neonatal, but not pregnant adult, sheep. Results suggest that PGE(2) catabolism is not as critically dependent as that of PGF(2alpha) on tissue integrity and 15-PGDH location. Given the key role being assigned to the choroid plexus in PG removal from brain, we speculate that persistence of PGE(2) catabolism into the early postnatal period protects against central respiratory depression caused by the compound during this susceptible stage of development.

Multidrug resistance protein 1 protects the choroid plexus epithelium and contributes to the blood-cerebrospinal fluid barrier

Multidrug resistance protein 1 (MRP1) is a transporter protein that helps to protect normal cells and tumor cells against the influx of certain xenobiotics. We previously showed that Mrp1 protects against cytotoxic drugs at the testis-blood barrier, the oral epithelium, and the kidney urinary collecting duct tubules. Here, we generated Mrp1/Mdr1a/Mdr1b triple-knockout (TKO) mice, and used them together with Mdr1a/Mdr1b double-knockout (DKO) mice to study the contribution of Mrp1 to the tissue distribution and pharmacokinetics of etoposide. We observed increased toxicity in the TKO mice, which accumulated etoposide in brown adipose tissue, colon, salivary gland, heart, and the female urogenital system. Immunohistochemical staining revealed the presence of Mrp1 in the oviduct, uterus, salivary gland, and choroid plexus (CP) epithelium. To explore the transport function of Mrp1 in the CP epithelium, we used TKO and DKO mice cannulated for cerebrospinal fluid (CSF). We show here that the lack of Mrp1 protein causes etoposide levels to increase about 10-fold in the CSF after intravenous administration of the drug. Our results indicate that Mrp1 helps to limit tissue distribution of certain drugs and contributes to the blood-CSF drug-permeability barrier.

Differential uptake and catabolism of prostaglandin (PG)E(2) versus PGF(2alpha) in the sheep choroid plexus during development

The early postnatal decrease in prostaglandin (PG)E(2) levels in cerebrospinal fluid (CSF) likely contributes to the establishment of continuous breathing. To elucidate mechanisms underlying this event, choroid plexuses from lateral (L-CP) and third/fourth (III/IV-CP) ventricles were incubated with [3H]-PGE(2) and label uptake (tissue-to-medium ratio for radioactivity, T/M) and catabolism (%radioactivity associated with metabolites, PGM) were measured. [3H]-PGF(2alpha) was a reference. Uptake of [3H]-PGE(2) was lower than [3H]-PGF(2alpha) in the term fetus (L-CP: 5.9+/-0.5 vs. 9.6+/-0. 9, n=11; III/IV-CP: 2.7+/-0.4 vs. 7.7+/-1.0, n=5) and 17 d lamb (L-CP: 5.3+/-0.8 vs. 11.0+/-1.2, n=7; III/IV-CP: 3.1+/-0.2 vs. 11. 6+/-2.8, n=3 and 4, respectively). This difference was not significant in the pregnant adult. Release of the two compounds was similar and did not change with age. [3H]-PGE(2) uptake was reduced by probenecid (1 mM) and excess PG (60 microM PGE(2) or PGF(2alpha)). Excess PG also reduced catabolism in the fetus, which was extensive for [3H]-PGE(2) and [3H]-PGF(2alpha)60%). In the lamb, catabolism remained high for [3H]-PGE(2) (L-CP: 64+/-4%, n=7; III/IV-CP: 41+/-4%, n=3), but not [3H]-PGF(2alpha) (L-CP: 26+/-4%, n=7; III/IV-CP: 4+/-1%, n=4). In the pregnant adult, catabolism was above background only for [3H]-PGE(2) in the L-CP (26+/-5%, n=11). Unlike the perinatal animal, this catabolism was reduced by probenecid. In conclusion, PGE(2) uptake and catabolism operate independently in the choroid plexus from perinatal sheep. Differences between PGE(2) and PGF(2alpha) are developmentally-regulated for both mechanisms. While neither process explains the postnatal decrease in CSF PGE(2), both may help keep CSF levels low during early postnatal development.

Effects of ischemia on prostaglandin H synthase-2 expression in piglet choroid plexus

We examined effects of ischemia on expression of prostaglandin H synthase-1 (PGHS-1) and prostaglandin H synthase-2 (PGHS-2) in piglet choroid plexus. Ten minutes of ischemia was induced by increasing intracranial pressure. Whole choroid plexus was removed and fixed and/or frozen after 1, 2, 4, and 8 h of recovery from anoxic stress. In addition, tissues were obtained from untreated animals or from time control animals. Tissues were analyzed for mRNA, using RNase protection assays, and for proteins, using immunohistochemical approaches. Limited, but detectable PGHS-2 immunoreactivity was present in choroid plexus under normal conditions, and there was no difference between time-control and non-treated animals. Further, PGHS-2 mRNA increased by 2-4 h after ischemia, and enhanced immunoreactivity for PGHS-2 was present at 8 h after ischemia. Enhanced immunoreactivity for PGHS-2 was present in vascular endothelial cells as well as cuboidal epithelial cells and macrophages. In contrast, PGHS-1 mRNA did not increase following ischemia. We conclude that PGHS-2 is present in piglet choroid plexus under normal conditions and that ischemia increases levels of PGHS-2 in choroid plexus.

Molecular mechanisms of prostaglandin transport

Despite the fact that prostaglandins (PGs) have low intrinsic permeabilities across the plasma membrane, they must cross it twice: first upon release from the cytosol into the blood, and again upon cellular uptake prior to oxidation. Until recently, there were no cloned carriers that transported PGs. PGT is a broadly-expressed, 12-membrane-spanning domain integral membrane protein. When heterologously expressed in HeLa cells or Xenopus oocytes, it catalyzes the rapid, specific, and high-affinity uptake of PGE2, PGF2 alpha, PGD2, 8-iso-PGF2 alpha, and thromboxane B2. Functional studies indicate that PGT transports its substrate as the charged anion. The PGT substrate specificity and inhibitor profile match remarkably well with earlier in situ studies on the metabolic clearance of PGs by rat lung. Because PGT expression is especially high in this tissue, it is likely that PGT mediates the membrane step in PG clearance by the pulmonary circulation. Evidence is presented that PGT may play additional roles in other tissues and that there may be additional PG transporters yet to be identified molecularly.

Internalization and down-regulation of the prostacyclin receptor in human platelets

The internalization of [3H]iloprost, a prostacyclin analogue, was studied in human platelets by binding studies. After incubation with [3H]iloprost at 37 degrees C, addition of unlabelled ligand at either 37 degrees C or 4 degrees C caused dissociation of 74% and 52% of the bound ligand respectively, suggesting that a portion had been internalized. The percentage of [3H]iloprost bound at equilibrium to the surface (evaluated by acid treatment) at either 37 degrees C or 4 degrees C was markedly different (80% versus 25%). Internalization was dependent on time and on the ligand nature and concentration. Energy-depleting agents (dinitrophenol and 2-deoxyglucose) completely inhibited internalization, whereas probenecid (inhibitor of organic anion transporters) did not affect it significantly. Subcellular fractionation indicated that, at 4 degrees C or in the absence of ligand, most of the receptor was present in membrane fractions (pellet at 27000 or 105000 g), whereas, when platelets were preincubated at 37 degrees C with iloprost, the receptor was found mainly in the cytosolic fraction. In platelets preincubated with iloprost at 4 degrees C, two classes of binding sites were present, whereas after preincubation at 37 degrees C only the lower-affinity sites were detected. After exposure to the agonist, iloprost-induced inhibition of platelet aggregation and activation of adenylate cyclase and cAMP production were significantly lower. Taken together, these data demonstrate that human platelets can internalize a high-affinity binding site for iloprost, presumably the prostacyclin receptor.

Prostaglandin uptake and catabolism by the choroid plexus during development in sheep

We have previously reported that prostaglandin(PG) E2 levels in sheep cerebrospinal fluid (CSF) are high prenatally and abate rapidly after birth. This event may contribute to the establishment of continuous breathing. To explain this change, we have examined PG disposal mechanisms in the perinatal and adult (pregnant and non-pregnant animal) sheep brain by measuring the capacity of the isolated choroid plexus to concentrate [3H]PGF2alpha and [3H]PGE2. At 0.9 gestation, [3H]PGF2alpha uptake (expressed as the tissue-to-medium ratio, T/M) attained a steady-state by 15 min and was maintained thereafter (T/M at 60 min, 5.6 +/- 0.6; n = 16). Likewise, [3H]PGE2 was taken up by the tissue, but the actual accumulation was smaller (T/M at 60 min, 2.6 +/- 0.2; n = 8). Thin-layer radiochromatographic analysis of the tissue following incubation with [3H]PGF2alpha showed that 55 +/- 4% (n = 10) of radioactivity migrated as the 15-keto-13,14-dihydro metabolite. [3H]PGF2alpha uptake decreased upon treatment with probenecid (1 mM) (T/M, 2.5 +/- 0.2; n = 10) or after adding unlabelled PGF2alpha to the medium (1-60 microM) (T/M at 60 microM, 1.8 +/- 0.1; n = 13). The yield of labelled metabolite was also lower when using excess PGF2alpha (14% of control at 60 microM; n = 13), while it was not affected by probenecid. Uptake of both PGs did not change through development, from 0.7 gestation to day 18 postnatal, and attained higher values in the pregnant adult. Conversely, PGF2alpha catabolism decreased postnatally and became negligible by adult age. We conclude that during the perinatal period PGs can be removed from CSF by two distinct processes in the choroid plexus, active transport and catabolism. Neither process, however, can account for the birth-related change in CSF PGE2.

The prostaglandin transporter is widely expressed in ocular tissues

Prostaglandins (PGs) play important physiological and therapeutic roles in the eye. Our laboratory recently identified a novel PG transporter in the rat that we call "PGT" (Science 268:866, 1995). We have also recently cloned the human PGT cDNA (J Clin Invest 98:1142, 1996). To determine whether PGT might play a role in human ocular tissues, we performed Northern blot analysis of RNA obtained from human ocular tissues and from the nonpigmented ciliary epithelium cell line "ODM-2." PGT transcripts were clearly evident in all ocular tissues. Given that the functional profile of PGT expressed in vitro strongly suggests a role in PG uptake and degradation, the present results suggest that PGT may function in various regions of the human eye for purposes of terminating the signal(s) produced by locally-synthesized PGs.

Cloning, in vitro expression, and tissue distribution of a human prostaglandin transporter cDNA(hPGT)

We recently identified a cDNA in the rat that encodes a broadly expressed PG transporter (PGT). Because PGs play diverse and important roles in human health and disease, we cloned human PGT (hPGT) from an adult human kidney cDNA library. A consensus sequence (4.0 kb) derived from several clones, plus 3' polymerase chain reaction amplification, exhibited 74% nucleic acid identity and 82% amino acid identity compared to rat PGT. When transiently expressed in HeLa cells, a full-length clone catalyzed the transport of PGE1, PGE2, PGD2, PGF2alpha, and, to a lesser degree, TXB2. Northern blotting revealed mRNA transcripts of many different sizes in adult human heart, placenta, brain, lung, liver, skeletal muscle, pancreas, kidney, spleen, prostate, ovary, small intestine, and colon. hPGT mRNAs are also strongly expressed in human fetal brain, lung, liver, and kidney. The broad tissue distribution and substrate profile of hPGT suggest a role in the transport and/or metabolic clearance of PGs in diverse human tissues.

Active transport system of prostaglandins: clinical implications and considerations

We hypothesize that two factors are essential in the development of epinephrine-induced cystoid macular edema (CME): (1) the stimulation of prostaglandin synthesis by some tissues, presumably the anterior uvea by epinephrine; (2) the dysfunction of the active transport (Bito's pump) which is responsible for the removal of prostaglandins from intraocular fluids. We conducted several experimental studies to confirm these hypotheses. The results strongly suggest that epinephrine maculopathy is induced by a mechanism involving prostaglandins or, possibly, other related eicosanoids and not simply by epinephrine itself, as has been postulated. This suggests the existence of some common factors in the pathogenesis of epinephrine maculopathy and aphakic or pseudophakic CME.

Two possibly distinct prostaglandin E1 receptors in N1E-115 clone: one mediating inositol trisphosphate formation, cyclic GMP formation, and intracellular calcium mobilization and the other mediating cyclic AMP formation

Prostaglandin E1 (PGE1)-mediated transmembrane signal control systems were investigated in intact murine neuroblastoma cells (clone N1E-115). PGE1 increased intracellular levels of total inositol phosphates (IP), cyclic GMP, cyclic AMP, and calcium ([Ca2+]i). PGE1 transiently increased inositol 1,4,5-trisphosphate formation, peaking at 20 s. There was more than a 10-fold difference between the ED50 for PGE1 at cyclic AMP formation (70 nM) and its ED50 values at IP accumulation (1 microM), cyclic GMP formation (2 microM), and [Ca2+]i increase (5 microM). PGE1-mediated IP accumulation, cyclic GMP formation, and [Ca2+]i increase depended on both the concentration of PGE1 and extracellular calcium ions. PGE1 had more potent intrinsic activity in cyclic AMP formation, IP accumulation, and cyclic GMP formation than did PGE2, PGF2 alpha, or PGD2. A protein kinase C activator, 4 beta-phorbol 12 beta-myristate 13 alpha-acetate, had opposite effects on PGE1-mediated IP release and cyclic GMP formation (inhibitory) and cyclic AMP formation (stimulatory). These data suggest that there may be subtypes of the PGE1 receptor in this clone: a high-affinity receptor mediating cyclic AMP formation, and a low-affinity receptor mediating IP accumulation, cyclic GMP formation, and intracellular calcium mobilization.

Lumbar CSF eicosanoids in neonates

Lumbar CSF eicosanoids were measured in 11 neonates with perinatal asphyxia and 12 neonates with suspected sepsis. In the asphyxia group low levels of thromboxane B2 and prostaglandin F2a were detected in five neonates, all of which had had a lumbar puncture prior to 4 hours of age. In the group with suspected sepsis two infants had positive blood cultures and one had strep meningitis. CSF eicosanoids were nondetectable in all patients in this second group with the exception of the infant with meningitis. With meningitis CSF eicosanoids were markedly elevated. These findings suggest that lumbar CSF eicosanoids do not appear to be a clinically useful tool. The data further suggest that eicosanoids are involved in the inflammatory response to meningitis.