Leukotriene C4 transport by the choroid plexus in vitro

Differential expression of the multidrug resistance-related proteins ABCb1 and ABCc1 between blood-brain interfaces

Cerebral homeostasis results from the presence of the protective blood-brain and blood-cerebrospinal fluid barriers located respectively at the brain capillary endothelium and the choroid plexus epithelium. ABCb1 (Pgp) and ABCc1 (Mrp1) transporters are two major proteins of neuroprotection whose localization and functional significance at both barriers remain partly unsettled. We conducted a comparative analysis of their relative protein content between the two blood-brain interfaces. Microvessels and choroid plexuses located in the fourth and lateral ventricles were isolated from developing and adult rat brains, and whole homogenates were submitted to quantitative Western blot analysis by using standard curves generated from one of the samples. In adult, choroid plexus-associated Pgp content was less than 0.5% of the level in microvessels, whereas Mrp1 content in microvessels was 4% of that in the fourth ventricle choroid plexus. Pgp but not Mrp1 was enriched in microvessels over parenchyma. In choroid plexuses, Mrp1 displayed a basolateral epithelial localization, and reached its high adult protein level, early during postnatal development. In postnatal as in adult microvessels, Pgp localization appeared luminal. However, by contrast to Mrp1, the level of this transporter increased 4.6-fold between 9-day-old and adult animals. Western blot analysis of human samples confirmed the mirror image of Pgp and Mrp1 expression between the two barriers. We conclude that there are major differences in the mechanisms by which blood-brain interfaces fulfill their neuroprotective functions. The data also highlight the significance of the neuroprotective function of the choroid plexus during brain maturation, when the microvasculature is still developing.

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.

Pro-Inflammatory Cytokines Modulate Matrix Metalloproteinase Secretion and Organic Anion Transport at the Blood-Cerebrospinal Fluid Barrier

Neuroinflammation and neuroinfection trigger cytokine-mediated responses that include an increase in the cerebrospinal fluid (CSF) levels of pro-inflammatory matrix metalloproteinases (MMPs) and organic anions such as leukotrienes and prostaglandins. The choroid plexus (CP) epithelium forming the interface between the blood and the CSF regulates the CSF concentration of bioactive organic anions and is involved in neuro-immune regulation. We demonstrated that both fourth and lateral ventricle CPs are a source of pro- and active MMP-2 and MMP-9 in the brain. Using a cellular model of the blood-CSF barrier, we showed that a pro-inflammatory cytokine treatment leads to an increase in the choroidal MMP secretion at either the apical or the basolateral membrane, depending on the ventricular origin of the choroidal cells. This effect was not concomitant with an alteration in the structural blood-CSF barrier. Neither was the pool of antioxidant sulfhydryls in the choroidal cells challenged. In contrast, the efficiency of the choroidal epithelium to clear the CSF from organic anions was highly reduced. Thus, during inflammation, the CPs could be one source of MMPs found in the CSF facilitate leucocyte migration by secreting MMPs into the choroidal stroma, and promote the inflammatory process by failing in its ability to clear deleterious compounds from the brain.

Expression of leukotriene C4 synthase mRNA by the choroid plexus in mouse brain suggests novel neurohormone functions of cysteinyl leukotrienes

Leukotriene C(4) is a potent mediator of allergic and inflammatory reactions, and is formed from arachidonic acid and glutathione through the sequential action of 5-lipoxygenase and leukotriene C(4) synthase (LTCS). These enzymes are predominantly expressed in cells of myeloid lineage. In this report, we have investigated LTCS mRNA expression in mouse brain. Expression was demonstrated using RT-PCR and RNase protection assays. In situ hybridization experiments showed exclusive staining of the choroid plexus of all brain ventricles. This expression pattern may provide a mechanism for the generation of LTC(4) on the cerebral side of the blood-brain barrier and suggests a possible novel regulator function of LTC(4) in the formation of cerebrospinal fluid.

Drug efflux transporters in the CNS

The central nervous system (CNS) contains important cellular barriers that maintain homeostasis by protecting the brain from circulating toxins and through the elimination of toxic metabolites generated in the brain. The barriers that limit the concentration of toxins and xenobiotics in the interstitial fluids of the CNS are the capillary endothelial cells of the blood-brain barrier (BBB) and the epithelial cells of the blood-cerebrospinal fluid barrier (BCSFB). Both of these barriers have cellular tight junctions and express transport systems which serve to actively transport nutrients into the brain, and actively efflux toxic metabolites and xenobiotics out of the brain. This review will focus on the expression and function of selected drug efflux transporters in these two barriers, specifically the multidrug resistance transporter, p-glycoprotein, and various organic anion transporters, such as multidrug resistance-associated proteins, organic anion transporter polypeptides, and organic anion transporters. These transport systems are increasingly recognized as important determinants of drug distribution to, and elimination from, different compartments of the CNS. Consequences of drug efflux transporters in barriers of the CNS include limiting the distribution of substrates that are beneficial to treat CNS diseases, and increasing the possibility of drug-drug interactions that may lead to untoward toxicities. Therefore, the study of these transporters is important in examining the various determinants of drug delivery to the CNS.

Organic anion transport across the choroid plexus

Several organic anion transport systems have recently been identified and localized at the apical and basolateral plasma membrane domains of choroid plexus epithelial cells. These organic anion transporters include (1) indirectly coupled Na(+)/dicarboxylate cotransport and dicarboxylate/organic anion exchange, which is represented on the molecular level by a member of the "kidney"-type organic anion transporter (OAT) family at the apical plasma membrane domain; (2) the organic anion transporting polypeptide 1 (Oatp1) and Oatp2, which both mediate typical "liver"-like organic anion transport activities at the apical and basolateral plasma membrane domains, respectively; and (3) the multidrug resistance protein Mrp1/MRP1 at the basolateral plasma membrane domain, and the P-glycoprotein Mdr1/MDR1 at an apical and subapical membrane vesicle compartment. This cellular transport polarity can account, at least in part, for the previously suggested physiologic transport properties of the choroid plexus epithelium and provides a framework for the identification and localization of additional organic anion transporters involved in the absorption and/or excretion of drugs and drug metabolites at the choroid plexus.

Demonstration of a coupled metabolism-efflux process at the choroid plexus as a mechanism of brain protection toward xenobiotics

Brain homeostasis depends on the composition of both brain interstitial fluid and CSF. Whereas the former is largely controlled by the blood-brain barrier, the latter is regulated by a highly specialized blood-CSF interface, the choroid plexus epithelium, which acts either by controlling the influx of blood-borne compounds, or by clearing deleterious molecules and metabolites from CSF. To investigate mechanisms of brain protection at the choroid plexus, the blood-CSF barrier was reconstituted in vitro by culturing epithelial cells isolated from newborn rat choroid plexuses of either the fourth or the lateral ventricle. The cells grown in primary culture on semipermeable membranes established a pure polarized monolayer displaying structural and functional barrier features, (tight junctions, high electric resistance, low permeability to paracellular markers) and maintaining tissue-specific markers (transthyretin) and specific transporters for micronutriments (amino acids, nucleosides). In particular, the high enzymatic drug metabolism capacity of choroid plexus was preserved in the in vitro blood-CSF interface. Using this model, we demonstrated that choroid plexuses can act as an absolute blood-CSF barrier toward 1-naphthol, a cytotoxic, lipophilic model compound, by a coupled metabolism-efflux mechanism. This compound was metabolized in situ via uridine diphosphate glururonosyltransferase-catalyzed conjugation, and the cellular efflux of the glucurono-conjugate was mediated by a transporter predominantly located at the basolateral, i.e., blood-facing membrane. The transport process was temperature-dependent, probenecid-sensitive, and recognized other glucuronides. Efflux of 1-naphthol metabolite was inhibited by intracellular glutathione S-conjugates. This metabolism-polarized efflux process adds a new facet to the understanding of the protective functions of choroid plexuses.

Immunohistochemical study of localization of gamma-glutamyl transpeptidase in the rat brain

Gamma-glutamyl transpeptidase (gamma-GTP) is a membrane-bound enzyme which is known to play a crucial role in active transport of amino acids across membrane barriers. We prepared a monoclonal antibody recognizing specifically rat gamma-GTP and investigated localization of the enzyme in the rat brain by immunohistochemistry with this antibody. The antigen was localized on the ependyma, epithelia of the choroid plexus and microvessels. More precise localization of gamma-GTP was examined with immuno-electron microscopy. The antigen was recognized on the microvilli and cilia of the ependymal cells, microvilli of the choroid epithelial cells and luminal membranes of the vascular endothelial cells.

Leukotriene C4 uses a probenecid-sensitive export carrier that does not recognize leukotriene B4

The export of leukotriene (LT) C4 from human eosinophils, a carrier-mediated process that is temperature-dependent and saturable, was characterized further in eosinophils and in two human leukemia cell lines that do not present an intact 5-lipoxygenase pathway. In eosinophils, KG-1 cells, and dimethyl sulfoxide (DMSO)-differentiated HL-60 cells, the respective Q10 values for temperature-dependent LTC4 export were 3.7, 3.3, and 3.4 and for energy of activation were 28.2 kcal/mol, 23.0 kcal/mol, and 27.8 kcal/mol (1 kcal = 4.18 kJ). When human eosinophils, KG-1 cells, and DMSO-differentiated HL-60 cells were preloaded with defined amounts of intracellular LTC4 by incubation with LTA4 and with incremental amounts of a glutathione conjugate, S-dinitrophenyl glutathione (GS-DNP) by sequential incubation with 1-chloro-2,4-dinitrobenzene, GS-DNP inhibited the export of LTC4 in a dose-dependent manner. By plotting the ratio of total GS-DNP (cell retained plus released) to the sum of total GS-DNP plus total LTC4 against the percentage inhibition of LTC4 release, IC40 values of 0.839, 0.803, and 0.841 were obtained for eosinophils, KG-1 cells, and DMSO-differentiated HL-60 cells, respectively. When cells preloaded with LTC4 were resuspended in incremental concentrations of the organic acid transport inhibitor, probenecid, there was a dose-dependent decrease in LTC4 release; GS-DNP and probenecid inhibited LTC4 release in a cumulative fashion, whereas neither inhibited the release of LTB4 from preloaded nondifferentiated HL-60 cells. Therefore, LTC4 export from cells of bone marrow origin occurs through a probenecid-sensitive membrane carrier shared by other glutathione conjugates and distinct from the LTB4 carrier export system.

Flow cytometric analysis of transport activity in lymphocytes electroporated with a fluorescent organic anion dye

Organic anion transport in polarized epithelia and macrophages has previously been studied by monitoring the efflux of fluorescent organic anion dyes from cells. We adapted this strategy to the study organic anion transport in lymphocytes. Cloned lymphoma cells and normal and activated human T cells were loaded with a membrane-impermeant, organic anion dye (Lucifer Yellow) by electroporation. Dye efflux in lymphocytes was rapid, energy-dependent, and inhibitable by organic anion transporter inhibitors. Dye efflux could not be attributed to the effects of electroporation. In addition, electroporated, dye-loaded T helper cells retained the ability to properly respond to specific antigen. Thus, dye loss occurred in viable, functionally competent cells. These experiments demonstrate that electroporation is an effective means of loading cells with Lucifer Yellow, and that lymphocytes possess organic anion transporters that are functionally similar to those previously described for secretory epithelia and macrophages.

Inhibition of organic anion transport in endothelial cells by hydrogen peroxide

ATP loss is a prominent feature of cellular injury induced by oxidants or ischemia. How reduction of cellular ATP levels contributes to lethal injury is still poorly understood. In this study we examined the ability of H2O2 to inhibit in a dose-dependent manner the extrusion of fluorescent organic anions from bovine pulmonary artery endothelial cells. Extrusion of fluorescent organic anions was inhibited by probenecid, suggesting an organic anion transporter was involved. In experiments in which ATP levels in endothelial cells were varied by treatment with different degrees of metabolic inhibition, it was determined that organic anion transport was ATP-dependent. H2O2-induced inhibition of organic anion transport correlated well with the oxidant's effect on cellular ATP levels. Thus H2O2-mediated inhibition of organic anion transport appears to be via depletion of ATP, a required substrate for the transport reaction. Inhibition of organic anion transport directly by probenecid or indirectly by metabolic inhibition with reduction of cellular ATP levels was correlated with similar reductions of short term viability. This supports the hypothesis that inhibition of organic anion transport after oxidant exposure or during ischemia results from depletion of ATP and may significantly contribute to cytotoxicity.

Distribution and metabolism of leukotriene C4 after cisternal injection in guinea pigs

Following cisternal injection of [3H8]LTC4 into guinea pigs, leukotriene metabolites were identified in the brain, cerebellum, perilymph, blood, liver and kidneys. LTC4 was metabolized into LTD4 and LTE4 in the cerebrospinal fluid and LTE4 was transported into the blood for general circulation and uptake into the liver and kidneys. The excretion of LTE4 from CNS to blood seemed to be the rate-limiting step in the elimination of leukotrienes from the body. Leukotrienes were also transported into the perilymph. The conversion of LTC4 into LTD4 and LTE4 was lower in perilymph as compared to the cerebrospinal fluid, suggesting a rate limiting function of the cochlear aqueduct that can be defined as a cerebrospinal fluid-labyrinth barrier.

Biosynthesis of leukotrienes in canine cerebral vasospasm

We produced cerebral vasospasm in 29 dogs by the "two-hemorrhage" method of intracisternal injections, 2 days apart, of autogenous arterial blood. Leukotriene (LT) C4, LTD4, and LTE4 were purified from incubated basilar artery, medulla oblongata, hypothalamus, median eminence, and blood clot from around the basilar artery using reverse-phase high-performance liquid chromatography, and the amount of each LT was quantified separately by bioassay with guinea pig ileum. The biosynthetic capacity for total LTs was approximately three times higher in the hypothalamus and median eminence than in the basilar artery and medulla oblongata in the eight normal dogs. In the dogs with subarachnoid hemorrhage, the biosynthetic capacity was increased significantly both before and 2 hours after the second injection of blood on Day 2 and was normal on Day 7 in the basilar artery and medulla oblongata, whereas the biosynthetic capacity was decreased significantly 2 hours after the first and second injections of blood and was increased significantly on Day 7 in the hypothalamus and median eminence. In blood clot the biosynthetic capacity was increased continuously after the first injection of blood. Thus, the biosynthetic capacity for total LTs showed a time- and tissue-specific change after subarachnoid hemorrhage.

Formation of cysteinyl-leukotrienes by human brain tissue

Using sensitive radioimmunoassay techniques, the formation of cysteinyl-leukotrienes (LT) and prostaglandin (PG) F2 alpha was investigated in human brain tissue slices in vitro. Under basal conditions spontaneous release of considerable amounts of LTC4-like material and PGF2 alpha could be detected from slices of both human grey and white matter. Ionophore A23187 stimulated the release of large amounts of LTC4-like material while leaving unaffected the formation of the cyclo-oxygenase product PGF2 alpha. Incubation of grey or white matter in the presence of the cyclo-oxygenase inhibitor indomethacin inhibited the release of PGF2 alpha but did not affect that of LTC4-like material. Preincubation of brain tissue in the presence of the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) abolished the ionophore A23187-induced release of LTC4-like material from both grey and white matter and also significantly reduced the spontaneous release of LTC4-like material from white matter slices. Formation of PGF2 alpha was not affected by NDGA. Using the isolated guinea pig ileum the LTC4-like material was shown to possess biological activity which could be antagonized with the slow-reacting substance of anaphylaxis (SRS-A) antagonist FPL 55712. By reversed phase HPLC the immunoreactive LTC4-like material from human grey matter was shown to coelute with authentic LTC4, LTD4 and LTE4, while material from human white matter coeluted with authentic LTD4 and LTE4. The capacity of human brain tissue to synthesize cysteinyl-LT may be important for cellular functions in the central nervous system.

Characterization of seizure-induced cysteinyl-leukotriene formation in brain tissue of convulsion-prone gerbils

Tonic-clonic seizures elicited in convulsion-prone gerbils resulted in a large increase in immunoreactive prostaglandin (PG) F2 alpha and in a smaller increase in immunoreactive leukotriene (LT) C4-like material in brain tissue. Brain tissue contents of both eicosanoids were found to reach a maximum at 6 min after the onset of seizures and were still elevated at 54 min after the beginning of convulsions. By reversed phase HPLC the immunoreactive LTC4-like material was identified as LTC4 and LTD4 at 6 min after the onset of convulsions, whereas at 54 min after the onset, transformation of LTD4 to LTE4 could be detected as well. In gerbils showing only weak seizure activity a small increase in PGF2 alpha but no increase in immunoreactive LTC4-like material could be detected at 6 min after the onset of convulsions. Pretreatment with indomethacin abolished the formation of PGF2 alpha but significantly enhanced the biosynthesis of immunoreactive LTC4-like material at 18 min after the beginning of seizures. The results demonstrate formation of cysteinyl-LT following tonic-clonic convulsions in spontaneously convulsing gerbils which could be enhanced by inhibition of the cyclooxygenase pathway of arachidonic acid metabolism. Since cysteinyl-LT have potent biological actions in various organs this finding warrants further investigations on the potential role of cysteinyl-LT in the CNS.

Brain eicosanoid levels in spontaneously hypertensive rats after ischemia with reperfusion: leukotriene C4 as a possible cause of cerebral edema

The relation of brain eicosanoids to progression of cerebral edema was studied in stroke-resistant spontaneously hypertensive rats subjected to incomplete global brain ischemia induced by bilateral occlusion of the common carotid arteries. Thromboxane B2 and 6-keto prostaglandin F1 alpha levels were significantly elevated 5 minutes after reperfusion but returned to control levels by 30 minutes. In contrast, leukotriene C4 levels increased 2 hours after bilateral common carotid artery occlusion and peaked 30 minutes after reperfusion, with higher levels persisting until 60 minutes after reperfusion. Cerebral ischemia was accompanied by cerebral edema early after reperfusion. The edema correlated with increased leukotriene C4 levels. That the increased brain water content was causally related to an increase in leukotriene C4 was supported by results obtained following administration of the 5-lipoxygenase inhibitors ONO-LP-016 and AA-861. Both inhibitors suppressed the increased leukotriene C4 and brain water contents after reperfusion. Our results indicate that leukotriene C4 is closely associated with an induction of ischemic cerebral edema.

Macrophages possess probenecid-inhibitable organic anion transporters that remove fluorescent dyes from the cytoplasmic matrix

We introduced several membrane-impermeant fluorescent dyes, including Lucifer Yellow, carboxyfluorescein, and fura-2, into the cytoplasmic matrix of J774 cells and thioglycollate-elicited mouse peritoneal macrophages by ATP permeabilization of the plasma membrane and observed the subsequent fate of these dyes. The dyes did not remain within the cytoplasmic matrix; instead they were sequestered within phase-lucent cytoplasmic vacuoles and released into the extracellular medium. We used Lucifer Yellow to study these processes further. In cells incubated at 37 degrees C, 87% of Lucifer Yellow was released from the cells within 30 min after dye loading. The dye that remained within the cells at this time was predominantly within cytoplasmic vacuoles. Lucifer yellow transport was temperature dependent and occurred against a concentration gradient; therefore it appeared to be an energy-requiring process. The fluorescent dyes used in these studies are all organic anions. We therefore examined the ability of probenecid (p-[dipropylsulfamoyl]benzoic acid), which blocks organic anion transport across many epithelia, to inhibit efflux of Lucifer Yellow, and found that this drug inhibited this process in a dose-dependent and reversible manner. Efflux of Lucifer Yellow from the cells did not require Na+ co-transport or Cl- antiport; however, it was inhibited by lowering of the extracellular pH. These experiments indicate that macrophages possess probenecid-inhibitable transporters which are similar in their functional properties to organic anion transporters of epithelial cells. Such organic anion transporters have not been described previously in macrophages; they may mediate the release of naturally occurring organic anions such as prostaglandins, leukotrienes, glutathione, bilirubin, or lactate from macrophages.

Immunohistochemical demonstration of proteinase inhibitor alpha-1-antichymotrypsin in normal human central nervous system

The presence of alpha-1-antichymotrypsin, a serine proteinase inhibitor with a high affinity for cathepsin G, is demonstrated in the normal human central nervous system (CNS) by immunohistochemical techniques. Paraffin-embedded normal human CNS tissue from five adult, two fetal, one neonatal and three newborn autopsies were stained with monospecific rabbit antibodies to human alpha-1-antichymotrypsin using biotinylated goat anti-rabbit antibodies and an avidinbiotin-peroxidase complex. Positive immunostaining was seen in neurons and glial cells in the cerebral cortex, basal ganglia, hippocampus, cerebellum, brainstem, and spinal cord of the adults. The epithelium of the adult choroid plexus had the most intense staining in apical granular organelles corresponding in position to lysosomes or secretory granules. Ependymal cells, particularly those near the choroid plexus, were immunostained. The fetal CNS had no alpha-1-antichymotrypsin staining. Limited staining of choroid plexus, ependyma, and frontal lobe was found in the newborns. Immunostaining in the neonatal temporal lobe was only found in the choroid-plexus epithelium. These observations establish a widespread distribution of this proteinase inhibitor in the normal human CNS. Developmental regulation of this inhibitor in the human CNS is also indicated.

Regional distribution of leukotriene and mono-hydroxyeicosatetraenoic acid production in the rat brain. Highest leukotriene C4 formation in the hypothalamus

The regional distribution of ionophore A23187-induced synthesis of leukotrienes and mono-hydroxyeicosatetraenoic acids in the rat brain in vitro was investigated. Pronounced differences in leukotriene C4 formation were observed, with the highest synthetic capacity in the hypothalamus. The formation of leukotriene C4 was about 12-times higher in the hypothalamus as compared to the cerebellum. This finding is in agreement with a possible neuroendocrine role for leukotriene C4. In contrast, the activity of leukotriene B4 synthesis was widely distributed without pronounced regional differences in the rat brain. Formation of 5-, 9-, 11-, 12- and 15-monohydroxyeicosatetraeonoic acid was detected in all regions. The major lipoxygenase product in the hypothalamus and thalamus was 5-hydroxyeicosatetraenoic acid, while other monohydroxyeicosatetraenoic acids predominated in the remaining regions tested.

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

Choroid plexi from the lateral ventricles of rabbits, cats, and dogfish (Mustelus canis) were used to characterize the prostaglandin (PG) uptake process and to establish its kinetic parameters and substrate specificity. The apparent Kt for PGF2 alpha transport by the rabbit choroid plexus was 20 microM; the Jmax was 27 nmol g-1 min-1. The Ki of inhibition of PGF2 alpha transport by PGE2 was 20 microM; the Jmax of PGF2 alpha transport was unaltered by PGE2. A concentration of p-aminohippuric acid of up to 1 mM did not appreciably affect the Kt or the Jmax of PGF2 alpha transport. The rate of PGF2 alpha accumulation by rabbit choroid plexus was reduced by incubation at 4 degrees C, under anaerobic conditions, in the absence of sodium or in the presence of ouabain, probenecid, or bromcresol green. The choroid plexi of all three species also accumulated thromboxane B2, PGI2, and 6-keto-PGF1 alpha, suggesting that most, if not all, eicosanoids are substrates for this transport system. It is concluded that the choroid plexus transport system satisfies all the criteria of an active, energy-dependent transport system and that this system functions effectively at concentrations of eicosanoids present in the ventricular system under normal or pathological conditions. Hence, this transport system must make an important contribution to the pharmacokinetics of eicosanoids within the brain.

Biological actions of leukotrienes. State of the art lecture

Leukotrienes are novel mediators derived from arachidonic acid through the 5-lipoxygenase enzyme system. Leukotriene B4 has potent effects on leukocyte function and in vivo induces leukocyte accumulation and changes in vascular permeability and modulates pain responses. Peptido-lipid leukotrienes are potent smooth muscle--contracting agents. They may have important cardiovascular actions through mechanisms involving either vasoconstriction or indirect vasodilatation. Evidence for leukotriene production has been found in subjects with allergic conditions and psoriasis, indicating a putative role for these substances in human disease.

Leukotriene C4 transport and metabolism in the central nervous system

The transport and metabolism of radiolabeled leukotriene (LT) C4 in the CNS were investigated after intraventricular injection. Under thiopental (Pentothal) anesthesia, New Zealand white rabbits were injected intracerebroventricularly with 0.2 ml of artificial CSF containing 2.5 microCi of [3H]LTC4 (36 Ci/mmol), 0.3 microCi of [14C]mannitol, and, in some cases, 0.9 mg of probenecid, 1.8 mg of cysteine, 1.4 micrograms of unlabeled LTC4, or 2 mg of tolazoline HCl. After 2 h, the conscious rabbits were killed, and the quantity and nature of the 3H and 14C were determined in CSF, choroid plexus, and brain. The [3H]LTC4 recovered in CSF and brain was not extensively metabolized, as greater than 70% of the 3H remained [3H]LTC4, although some spontaneous conversion to 11-trans-[3H]LTC4 occurred. Oxidized forms of [3H]LTC4, [3H]LTD4, and [3H]LTE4 did not exceed 18% in CSF and brain. After intraventricular injection of [3H]LTC4, 3H was transferred from the CSF to blood by a probenecid-sensitive, but tolazoline-insensitive, transport system in the CNS much more rapidly than mannitol. Cysteine decreased the retention of [3H]LTC4 in brain. These results are consistent with previous in vitro observations that [3H]LTC4 is transferred from CSF into blood by an efficient transport system for LTC4 in choroid plexus.