Brain Prostaglandin Research Articles

The effect of chronic lithium on arachidonic acid release and metabolism in rat brain does not involve secretory phospholipase A 2 or lipoxygenase/cytochrome P450 pathways

The mood-stabilizer lithium, when chronically administered to rats at therapeutic concentrations, has been shown to downregulate brain arachidonic acid (AA) turnover and total phospholipase A 2 (PLA 2) activity, as well as protein and mRNA levels of cytosolic cPLA 2. These effects are accompanied by a decrease in cyclooxygenase (COX)-2 protein level, COX activity, and brain prostaglandin E 2 (PGE 2) concentration. The involvement of Ca 2+-dependent secretory PLA 2 (sPLA 2) in the mechanism of action of lithium has not been investigated. The purpose of this study was to examine, whether the effect of lithium is selectively directed to cPLA 2 or it also affects sPLA 2 protein and enzyme activity and whether other AA metabolizing enzymes (5-lipoxygenase and cytochrome P450 epoxygenase) were also altered. Furthermore, to determine if the reduction of brain PGE 2 concentration was due only to downregulation of COX-2 protein or if it also involves the terminal PGE synthase, we determined brain microsomal PGE synthase protein level. Male Fischer-344 rats were fed lithium chloride for 6 weeks, whereas, control rats were fed lithium-free chow under parallel conditions. We found that chronic lithium did not significantly change sPLA 2 activity or protein level. 5-Lipoxygenase and cytochrome P450 epoxygenase protein levels were unchanged, as were levels of the terminal PGE synthase. These results indicate that the effect of lithium selectively involves the cPLA 2/COX-2 pathway, which might be responsible for the therapeutic effect in bipolar disorder.

Burn injury enhances brain prostaglandin E2 production through induction of cyclooxygenase-2 and microsomal prostaglandin E synthase in cerebral vascular endothelial cells in rats

To examine whether peripheral burn injury in rats elevates prostaglandin E2 in the central nervous system and to determine where in the central nervous system enzymes responsible for prostaglandin E2 synthesis are expressed. Prospective controlled animal study. University research laboratory. Sprague-Dawley rats. Rats received either approximately 25% full-thickness burn injury or sham treatment. At 36 hrs after the injury, the cerebrospinal fluid was sampled to measure prostaglandin E2, and the brain and the spinal cord were sampled for immunohistochemical detection of cyclooxygenase-2 and microsomal-type prostaglandin E2 synthase, enzymes that are responsible for prostaglandin E2 production. The prostaglandin E2 concentration in the cerebrospinal fluid was significantly elevated in the injured rats, and this elevation was suppressed by a cyclooxygenase-2-specific inhibitor, NS398. Only in the injured rats, cyclooxygenase-2 and microsomal-type prostaglandin E synthase proteins were detected in vascular endothelial cells throughout the central nervous system with no regional difference. A double-immunofluorescence study revealed that cyclooxygenase-2 and microsomal-type prostaglandin E synthase were coexpressed in the perinuclear region of the endothelial cells. These results indicate that peripheral burn injury induces cyclooxygenase-2 and microsomal-type prostaglandin E synthase in endothelial cells of the central nervous system. These enzymes likely elevate the cerebrospinal fluid concentration of prostaglandin E2, a prostanoid that, in turn, activates prostaglandin E2 receptors on the central nervous system neurons involved in the general symptoms following burn injury.

Gastric Tolerability and Prolonged Prostaglandin Inhibition in the Brain with a Nitric Oxide-Releasing Flurbiprofen Derivative, NCX-2216 [3-[4-(2-Fluoro-α-methyl-[1,1′-biphenyl]-4-acetyloxy)-3-methoxyphenyl]-2-propenoic acid 4-nitrooxy butyl ester

NCX-2216 [3-[4-(2-fluoro-alpha-methyl-[1,1'-biphenyl]-4-acetyloxy)-3-methoxyphenyl]-2-propenoic acid 4-nitrooxy butyl ester] is an NO-releasing flurbiprofen derivative that also contains a ferulic acid (antioxidant) moiety. NCX-2216 has been shown to be effective in reducing beta-amyloid deposition in a transgenic mouse model of Alzheimer's disease. The tolerability of this compound in the stomach and its ability to suppress prostaglandin synthesis in the brain are not known. The purpose of this study was to assess the contribution of nitric oxide (NO) and ferulic acid to the pharmacological properties of NCX-2216 versus flurbiprofen; thus, we compared their gastric tolerability and suppression of prostaglandin synthesis, peripherally and centrally. Oral flurbiprofen produced extensive gastric damage and suppressed gastric prostaglandin synthesis. In contrast, while suppressing prostaglandin production, equimolar doses of NCX-2216 did not cause detectable gastric injury. The NO-releasing moiety of NCX-2216 (but not the ferulic acid moiety) was crucial for the gastric safety of this compound. NCX-2216 substantially inhibited prostanoid synthesis despite not being detectable in plasma and despite producing only low amounts of flurbiprofen in plasma and in the brain. Inhibition of brain prostaglandin synthesis by NCX-2216 (22 mg/kg) persisted for a much longer period of time (up to 48 h) than was seen with flurbiprofen (<or=12 h). These results demonstrate that a single administration of NCX-2216 can produce prolonged suppression of brain prostaglandin synthesis without causing gastric injury. It is likely that an active metabolite of NCX-2216 contributes to the suppression of cyclooxygenase activity. NCX-2216 may represent an attractive alternative to conventional nonsteroidal anti-inflammatory drugs for long-term treatment of a variety of inflammatory disorders, especially those occurring in the central nervous system.

Intracerebral HIV-1 glycoprotein 120 produces sickness behavior and pituitary–adrenal activation in rats: Role of prostaglandins

HIV infection is associated with profound neurobehavioral and neuroendocrine impairments. Previous studies demonstrated that HIV causes neuropathological alterations indirectly, via shedding of glycoprotein 120 (gp120) within the brain. To extend these findings, we examined the neurobehavioral and neuroendocrine effects of central administration of gp120, as well as the role of brain prostaglandins in mediating these effects. Intracerebroventricular (icv) injection of gp120 in rats produced a marked sickness behavior syndrome, consisting of reduced exploratory behavior, suppressed consumption of food and saccharin solution, and reduced body weight. Gp120 also induced a significant febrile response and increased serum levels of ACTH and corticosterone. Following icv gp120 administration, the ex vivo production of PGE 2 by the hypothalamus, frontal cortex, and hippocampus was significantly elevated, and indomethacin, a prostaglandin synthesis inhibitor, attenuated this elevation. Pre-treatment with indomethacin reduced the fever and adrenocortical activation induced by gp120 administration, but not its behavioral effects. These findings indicate that gp120 may be responsible for some of the behavioral and endocrine abnormalities seen in HIV-infected patients. Prostaglandins are important mediators of the physiological, but not the behavioral effects of brain gp120.

Roles of brain prostaglandin E 2 and thromboxane A 2 in the activation of the central sympatho-adrenomedullary outflow in rats

We examined the effects of centrally administered active metabolites of the arachidonic acid cascade on activation of the central sympatho-adrenomedullary outflow using urethane-anaesthetized rats. Intracerebroventricularly (i.c.v.) administered prostaglandin E 2 (0.3 nmol/animal) significantly elevated plasma levels of noradrenaline while levels of adrenaline were not affected. Prostaglandin D 2, prostaglandin F 2α and prostaglandin I 2 at the same dose (0.3 nmol/animal, i.c.v.) had no effect on plasma levels of either catecholamine. Thromboxane A 2 mimetic, 7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo [2.2.1]hept-2-yl], [1 S-[1α,2α( Z),3β(1 E,3 S),4α]]-5-heptenoic acid (I-BOP) (5 and 10 pmol/animal) microinjected into the paraventricular nucleus of the hypothalamus significantly elevated plasma levels of adrenaline, but had little effect on plasma levels of noradrenaline. The I-BOP-induced (10 pmol/animal) elevation of plasma adrenaline levels was abolished by (+)-(1 R,2 R,3 S,4 S)-(5 Z)-7-(3-[4- 3H]-phenylsulphonyl-aminobicyclo[2.2.1]hept-2-yl)hept-5-enoic acid sodium salt [(+)-S-145] (a blocker of thromboxane A 2 receptors) [625 nmol (250 μg)/animal, i.c.v.]. These results suggest that brain prostaglandin E 2 and thromboxane A 2 are respectively involved in the activation of the central sympathetic and adrenomedullary outflow in rats.

Prostaglandins and other lipid mediators in Alzheimer’s disease

In the central nervous system (CNS), prostaglandin (PG) and other bioactive lipids regulate vital aspects of neural membrane biology, including protein–lipid interactions, trans-membrane and trans-synaptic signaling. However, a series of highly reactive PGs, free fatty acids, lysophospolipids, eicosanoids, platelet-activating factor, and reactive oxygen species (ROS), all generated by enhanced phospholipase A 2 (PLA 2) activity and arachidonic acid (AA) release, participate in cellular injury, particularly in neurodegeneration. PLA 2 activation and PG production are among the earliest initiating events in triggering brain-damage pathways, which can lead to long-term neurologic deficits. Altered membrane-associated PLA 2 activities have been correlated with several forms of acute and chronic brain injury, including cerebral trauma, ischemic damage, induced seizures in the brain and epilepsy, schizophrenia, and in particular, Alzheimer’s disease (AD). Biochemical mechanisms of PLA 2 overactivation and its pathophysiological consequences on CNS structure and function have been extensively studied using animal models and brain cells in culture triggered with PLA 2 inducers, PGs, cytokines, and related lipid mediators. Moreover, the expression of both COX-2 and PLA 2 appears to be strongly activated during Alzheimer’s disease (AD), indicating the importance of inflammatory gene pathways as a response to brain injury. This review addresses some current ideas concerning how brain PLA 2 and brain PGs are early and key players in acute neural trauma and in brain-cell damage associated with chronic neurodegenerative diseases such as AD.

Cyclooxygenase-2 regulates prostaglandin E2 signaling in hippocampal long-term synaptic plasticity.

The functional significance of cyclooxygenases (COX-1 and -2), the key enzymes that convert arachidonic acid (AA) to prostaglandins (PGs) in brain, is unclear, although they have been implicated in cellular functions and in some neurologic disorders, including stroke, epilepsy, and Alzheimer's disease. Recent evidence that COX-2 is expressed in postsynaptic dendritic spines (which are specialized structures involved in synaptic signaling) and is regulated by synaptic activity implies participation of COX-2 in neuronal plasticity. However, direct evidence is lacking. Here we demonstrate that selective COX-2 inhibitors significantly reduced postsynaptic membrane excitability, back-propagating dendritic action potential-associated Ca2+ influx, and long-term potentiation (LTP) induction in hippocampal dentate granule neurons, while a COX-1 inhibitor is ineffective. All of these actions were effectively reversed by exogenous application of PGE2 but not of PGD2 or PGF(2alpha). Our results indicate that COX-2-generated PGE2 regulates membrane excitability and long-term synaptic plasticity in hippocampal perforant path-dentate gyrus synapses.

Effect of Mycoplasma fermentans on Brain PGE2: Role of Glucocorticoids and Their Receptors

Objectives: Mycoplasmas are a group of eubacteria, which cause various diseases in animals and in humans, and can contribute to diseases produced by other infectious agents, particularly HIV. We have recently reported that intracerebral administration of Mycoplasma fermentans (MF) produces both neuroendocrine and behavioral alterations. Some of these responses were mediated by MF-induced production of prostaglandin E₂(PGE₂). The aim of this study was to examine the role of glucocorticoids (GC) in regulating MF-induced brain prostaglandin production. Methods: Male rats were injected intracerebroventricularly with various doses of heat-inactivated MF, LPS or IL-1β and the following parameters were measured: (1) ex vivo production of hippocampal PGE₂, (2) serum levels of ACTH and corticosterone, and (3) binding capacity of [³H]-dexamethasone (DEX) to hippocampal cytosol. Results: MF caused a small increase in hippocampal PGE₂ production, but higher doses failed to produce a further increase. In contrast, the effects of LPS or IL-1β on PGE₂ were dose-dependent. Removal of circulating GC by bilateral adrenalectomy significantly enhanced MF-induced brain PGE₂ production. The three immune stimulators increased serum levels of ACTH and corticosterone to the same extent. Finally, MF, but not IL-1β increased the specific binding of [³H]-DEX to hippocampal cytosol. Conclusions: Brain PGE₂ induced by MF is regulated by endogenous GC. These hormones have an attenuating effect on PGE₂production, probably through an MF-induced increase in GC binding by brain tissue. This mechanism may be important in the pathological effect of MF within the brain of AIDS patients.

Antinociceptive profiles of aspirin and acetaminophen in formalin, substance P and glutamate pain models

Aspirin (ASA) is widely used oral analgesics and acts as an inhibitor of cyclo-oxygenase. Also, acetaminophen (APAP) is effective analgesics and may selectively inhibit brain prostaglandin synthetase. However, their mechanisms of action in CNS are poorly defined, although several authors have shown that the antinociceptive effects of ASA and APAP have different underlying mechanisms and play some possible roles on spinal nociceptive processing, such as inhibition of prostaglandin synthesis. To define and characterize antinociceptive profiles of ASA and APAP on various pain models, we performed intraplantar formalin injection test, intrathecal (i.t.) substance P (0.7 μg)-induced nociceptive response test, and i.t. glutamate (20 μg)-induced nociceptive response test after ASA or APAP (from 10 to 300 mg/kg) administered orally to the mouse. In the formalin test, ASA produced an antinociceptive effect during only the 2nd phase (20–40 min), but not the 1st phase (0–5 min), in a dose-dependent manner. However, APAP showed a dose-dependent antinociceptive effect during both phases of the formalin test. In addition, both ASA and APAP reduced nociceptive behavior induced by glutamate administered i.t. in a dose-dependent manner. In substance P-induced nociceptive response, APAP, but not ASA, showed antinociceptive effect in a dose-dependent manner. Our results suggest that ASA and APAP administered orally may be mediated by different nociceptive processing at the spinal cord level.

Age-Dependent Cognitive Deficits and Neuronal Apoptosis in Cyclooxygenase-2 Transgenic Mice

The cyclooxygenases catalyze the rate-limiting step in the formation of prostaglandins from arachidonic acid and are the pharmacological targets of (NSAIDs). In brain, cyclooxygenase-2 (COX-2), the inducible isoform of cyclooxygenase, is selectively expressed in neurons of the cerebral cortex, hippocampus, and amygdala. As an immediate-early gene, COX-2 is dramatically and transiently induced in these neurons in response to NMDA receptor activation. In models of acute excitotoxic neuronal injury, elevated and sustained levels of COX-2 have been shown to promote neuronal apoptosis, indicating that upregulated COX-2 activity is injurious to neurons. COX-2 may also contribute to the development of Alzheimer's disease, for which early administration of NSAIDs is protective against development of the disease. To test the effect of constitutively elevated neuronal COX-2, transgenic mice were generated that overexpressed COX-2 in neurons and produced elevated levels of prostaglandins in brain. In cross-sectional behavioral studies, COX-2 transgenic mice developed an age-dependent deficit in spatial memory at 12 and 20 months but not at 7 months and a deficit in aversive behavior at 20 months of age. These behavioral changes were associated with a parallel age-dependent increase in neuronal apoptosis occurring at 14 and 22 months but not at 8 months of age and astrocytic activation at 24 months of age. These findings suggest that neuronal COX-2 may contribute to the pathophysiology of age-related diseases such as Alzheimer's disease by promoting memory dysfunction, neuronal apoptosis, and astrocytic activation in an age-dependent manner.

Intracerebroventricular interleukin-1β impairs clearance of tumor cells from the lungs: role of brain prostaglandins

We have previously demonstrated that central administration of interleukin (IL)-1β suppresses natural killer (NK) cell activity, impairs NK-mediated lung clearance of tumor cells, and enhances tumor colonization. The central pathways activated by IL-1β are as yet unknown. Using an in vivo model of tumor colonization, this study examined the role of central noradrenergic, opioid and prostaglandin mechanisms in mediating the effect of IL-1β on lung clearance of tumor cells. We demonstrate that central noradrenergic and opioid systems are not critically involved in this effect. Neither depletion of central noradrenergic pathways, or administration of the opioid antagonist, naltrexone (50 ug), blocked the impaired lung clearance of MADB106 tumor cells induced by central administration of IL-1β (20 ng). Central prostaglandins (PGs) do, however, appear to play a critical role. Central administration of the prostaglandin antagonist, diclofenac (250 ug), but not ibuprofen, completely blocked the effect of IL-1β on lung clearance of tumor cells. Antagonism of the effects of IL-1β was shown to be due to the effects of centrally and not of peripherally acting prostaglandins.

Cyclooxygenase in the vagal afferents: is it involved in the brain prostaglandin response evoked by lipopolysaccharide?

The vagal afferents are proposed to transmit abdominal immune signals to the brain. In this immune–brain communication, prostaglandins might play a mediator role. In fact, prostaglandin receptors are abundant in the vagal afferents. We examined here the presence of cyclooxygenase, an enzyme necessary for prostaglandin biosynthesis, in the vagal afferents of rats. We also tested whether the vagal afferents contribute to the elevation of prostaglandin E 2 in the brain after intraperitoneal injection of lipopolysaccharide. Under normal conditions, cyclooxygenase-1-like immunoreactivity was constitutively expressed in the vagal afferents at their central terminals and in their cell bodies. Cyclooxygenase-2-like immunoreactivity was absent in the vagal afferents under normal as well as lipopolysaccharide-challenged conditions. Instead, cyclooxygenase-2-like immunoreactivity was induced in brain endothelial cells by the lipopolysaccharide challenge. The elevation of prostaglandin E 2 in the cerebrospinal fluid after lipopolysaccharide challenge was not inhibited, but was rather enhanced, by the bilateral vagotomy. These results suggest that the vagal afferents potentially generate prostaglandins, which may locally modulate the vagal signal transmission, but that the vagal afferents are not essential to the elevation of prostaglandin E 2 in the brain after intraperitoneal challenge with LPS.

Angiotensin II does not mediate the pressor response to PGD2 (icv).

The objective of the present studies was to examine the interaction between brain-derived angiotensin II (Ang II) and prostaglandins in order to identify the mechanisms mediating the pressor response produced by these neuroregulators. Inhibiting synthesis of prostaglandins with indomethacin [indocin, 200 microg/ 5 microl artificial cerebrospinal fluid (aCSF)], administered intracerebroventricularly (icv) to conscious adult male Sprague-Dawley rats, reduced blood pressure to values below basal levels. When injected prior to Ang II (50 ng/5 microl aCSF; icv), indomethacin completely abolished the pressor response induced by the octapeptide. The increase in blood pressure produced by prostaglandin D(2) (PGD(2), 20 microg/5 microl; icv), the most prominent prostaglandin in the rat brain, however, was not prevented by losartan (25 microg/5 microl; icv), an Ang II AT(1)-receptor antagonist. Collectively, these results indicate that prostaglandins produced tonically in the brain maintain resting arterial blood pressure and that the pressor action of Ang II is dependent on de novo synthesis of a prostaglandin.

Divergence of brain prostaglandin H synthase activity and oxidative damage in mice with encephalitis.

Several lines of evidence point to inflammation and increased oxidant injury in brain regions of patients with Alzheimer disease (AD). Prostaglandin H synthase (PGHS) catalyzes the limiting step in prostaglandin synthesis and generates a potent oxidizing agent as by-product. One form of PGHS, PGHS-2, is induced by pro-inflammatory signals; thus leading to the 2-step hypothesis that pro-inflammatory signals in AD brain induce PGHS-2 that in turn contributes to brain oxidant injury. Here we have tested directly this 2-step hypothesis in a murine reovirus type 3 encephalitis model by measuring cerebral PGHS activity and quantifying oxidant injury. Our results showed a robust chronic inflammatory infiltrate and a 2-fold increase in PGHS activity in encephalitic mice compared with controls. Despite these changes, there was no significant increase in F2-isoprostanes or F4-neuroprostanes, accurate in vivo biomarkers of oxidant injury, and only minimal accumulation of protein adducts from the lipid peroxidation product 4-hydroxy-2-nonenal in the most intensely inflamed brain regions. These results challenge the proposal of others that pro-inflammatory induction of PGHS activity significantly contributes to oxidant injury in brain.

Chapter 15 Prostaglandin system in the brain: sites of biosynthesis and sites of action under normal and hyperthermic states

This chapter reviews the recent progress in research on the brain prostaglandin (PG) system, with special attention on the in vivo location of enzymes involved in their biosynthesis and of their specific receptors under physiological, as well as pathological conditions. The recent biochemical studies, especially those that employed molecular biological techniques, have provided a great deal of information on the molecular nature of individual components of the PG system. Fever and hyperthermia are essentially distinct patho-physiological states, the former representing regulated elevation of the body temperature caused by immunological challenge and the latter representing its passive elevation caused by excessive heat load. In fact, inhibitors of PG synthesis, such as indomethacin, suppress fever but are not effective against hyperthermia. The release of PGs is dramatically increased by ischemia/reperfusion of the brain or by traumatic injury of the central nervous and treatment with a cyclooxygenase inhibitor, such as indomethacin, improves the neuronal injury. The onset and progression of Alzheimer's disease may be also slowed by the treatment with cyclooxygenase inhibitors. Thus, PGs are the key molecules involved in pathological changes in the central nervous system.

Proconvulsant actions of brain prostaglandins demonstrated in cyclooxygenase-2 (COX-2) knockout mice

Proconvulsant actions of brain prostaglandins demonstrated in cyclooxygenase-2 (COX-2) knockout mice

Δ13-Reductase dependent metabolism of prostaglandins in the mammalian brain and eye

This paper describes the distribution of NAD +-dependent 15-hydroxy prostaglandin dehydrogenase ( Δ 13-reductase) in the mammalian brain and eye tissues. In addition, an NADH-dependent 15-ketoprostaglandin Δ 13-reductase (15-PGDH) activity was determined in the brain and eye tissue of some species. The rabbit brain and eye tissues were obtained after arterial perfusion with PBS buffer while the monkey, bovine and porcine tissues were obtained without any treatment. [ 3H]-PGF 2α or [ 3H]-15-keto-17-phenyl-18,19,20-trinor-PGF 2α-1-isopropyl ester was incubated with different eye tissue preparations under various conditions. No 15-PGDH activity was observed in the monkey brain while 14% of exogenous PGF 2α was metabolized to its 15-keto-13,14-dihydro-metabolite by the porcine brain. The 15-PGDH activity in the monkey eye tissue was undetectable. Both brain and different eye tissues hydrolysed 15-keto-17-phenyl-18,19,20-trinor-PGF 2α-1-isopropyl ester to its free acid and the free acid was further metabolized to 15-keto-13,14-dihydro-17-phenyl-18,19,20-trinor-PGF 2α by the reduction of 13,14-double bond indicating the presence of a Δ 13-reductase in these tissues. These data suggest that besides the presence of esterases the mammalian brain and eye tissues possess variable amounts of Δ 13-reductase in spite of their low 15-PGDH activity which may be of importance in physiology and drug metabolism of these tissues.

Inhibition of brain cyclooxygenase-2 activity and the antipyretic action of nimesulide

The antipyretic action and the mechanism of action of 4-nitro-2-phenoxymethanesulfonanilide (nimesulide), a new nonsteroidal antiinflammatory drug, were investigated in yeast-induced febrile rats. Yeast-injected rats developed marked fever and exhibited an approximately 7-fold increase in brain levels of prostaglandin E 2 and an approximately 2-fold increase in the expression of cyclooxygenase-2 mRNA despite an almost unchanged expression of cyclooxygenase-1 mRNA. Nimesulide produced a dose dependent antipyretic action, which was stronger than that of indomethacin and ibuprofen, and decreased dose dependently the increased brain prostaglandin E 2 levels, whereas it did not influence the expression of cyclooxygenase-2 mRNA. It inhibited markedly the enhanced brain cyclooxygenase activity, primarily cyclooxygenase-2, in vivo and dose dependently increased brain cyclooxygenase activity in vitro. These results suggest that the marked antipyretic action of nimesulide is primarily mediated through the selective inhibition of the activity of brain cyclooxygenase-2 induced under febrile conditions.

PGE2, mainly through EP3 receptors, regulates expression of the constitutive neuronal and endothelial nitric oxide synthases (n- and e-NOS) in brain during the perinatal period. † 244

Increased NOS activity in brain during the perinatal period may be important for preservation of cellular and circulatory functions; but the mechanisms that regulate NOS activity are not known. Prostaglandins (PGs) may affect (inducible) NOS expression in cells. We postulated that high PG levels in the perinatal period control constitutive NOS expression in neural tissue. In rat brain n-NOS and cyclooxygenase (COX)-2 mRNA were highest on postnatal day 10 and thereafter declined by ≈4-fold to adult levels. Likewise in pig brain and microvessels, n-NOS, e-NOS and COX-2 mRNA were 3-4 fold higher in newborn (NB) than adult; (COX-1 was stable). Corresponding nitrite (stable product of NO) and PG synthesis were also 5-8 fold higher in NB than adult tissues. To assess if high PG levels control NOS expression in the perinatal period, NB rats were treated 24 h i.p. with COX-2 selective (nimesulide 1 mg/kg/day) or non-selective COX inhibitors (ibuprofen 40 mg/kg/day) to reduce brain PG levels to those of adult. Consistent with predominant COX-2 role in PG formation in NB brain, both COX inhibitors reduced comparably n-NOS mRNA. The in vivo effect of COX inhibitors in rat brain n-NOS was confirmed for e-NOS on isolated NB pig cerebral microvessels incubated 18 h with COX blockers: e-NOS mRNA and nitrite production in NB brain microvasculature decreased 4-fold to adult values after COX inhibition. In addition, the PGE2 analogue, 16,16-dimethyl PGE2, but not the PGI2 analogue, carbacyclin, or PGD2 prevented this downregulation of NOS by COX inhibition. Of the 3 PGE2 receptors in brain EP3 (sulprostone) and EP1 (17-phenyl trinor PGE2) stimulation respectively increased and slightly reduced NOS expression; EP2 stimulation was ineffective. Data indicate that high perinatal PGE2 levels control constitutive NOS expression in brain mainly through EP3 activation. Because PGE2 and NO exert important cellular functions including cytoprotection, we speculate that the positive interaction described between these agents could facilitate their concerted actions in perinatal neuroprotection.

Brain prostaglandins mediate the bombesin-induced increase in plasma levels of catecholamines

Intracerebroventricular (i.c.v.) administration of bombesin (0.1, 1.0, 10.0 nmol/animal) in urethane-anesthetized rats induced long-lasting and dose dependent increases in plasma levels of adrenaline and noradrenaline. These effects of bombesin were inhibited by i.c.v. pretreatment with indomethacin (50–500 μg/animal), while the same dose of indomethacin by the intravenous route was without effect. The bombesin-induced increases in plasma levels of catecholamines were also inhibited by i.c.v. pretreatment with diclofenac (100–500 μg/animal), a cyclooxygenase inhibitor other than indomethacin. I.c.v. administration of thyrotropin releasing hormone (TRH) (10 nmol/animal) also induced increases in plasma levels of adrenaline and noradrenaline, however, these increases were not modified by i.c.v. pretreatment with indomethacin. The present results suggest that the bombesin-induced increases in plasma levels of catecholamines are probably due to prostaglandins synthetized in the brain with this neuropeptide. Furthermore, it is likely that prostaglandins are not always involved in central activation of sympatho-adrenomedullary system by other brain neuropeptides.