Modulation of autonomic neurotransmission by PGD2: comparison with effects of other prostaglandins in anesthetized cats

Characterization of melittin effects in synaptosomes

The effects of melittin at increasing concentrations on: [3H]GABA release from mouse brain synaptosomes; on the radioactivity released from [3H]arachidonic acid labeled synaptosomal membranes; on synaptosomes ultrastructure and on the leakage of the cytoplasmic marker, lactate-dehydrogenase (LDH) was investigated. Melittin 0.3, 1, 3, 7, and 10 microM progressively increases [3H]GABA release, but the efficacy of melittin is decreased when the amount of tissue exposed to a constant concentration of the toxin increases. The release of [3H]GABA induced by melittin below 3 microM is Ca2+ dependent, but not that induced by the higher concentrations. The Ca2+ dependent fraction of the [3H]GABA released by 0.3 microM melittin is selectively inhibited by 10 microM quinacrine and 1 microM nordihydroguaiaretic acid (NDGA) and facilitated by 3 microM indomethacin, whereas the Ca2+ independent fraction of the [3H]GABA released by melittin is not. In the presence of Ca2+, melittin 0.3, 1 and 10 microM progressively increases [3H]arachidonic acid release over control release, but the effectiveness of melittin is also decreased as the amount of tissue increases. No apparent changes in synaptosomes ultrastructure are observed in 0.3 microM treated synaptosomes, but a noticeable disorganization is produced in 10 microM melittin-treated synaptosomes, independently on the presence of external Ca2+. LDH activity only increases over control activity in the supernatant solutions of 10 microM melittin treated synaptosomes, also in a Ca2+ independent manner. Our interpretation of these results is that the Ca2+-dependent, pharmacologic sensitive component of melittin-induced release of [3H]GABA, unmasked when 0.3 microM melittin was used, involves the activation of a Ca2+-dependent type of membrane PLA2. The Ca2+-independent release of [3H]GABA is in contrast, highly probable to be due to the membrane perturbation produced by complex melittin/lipid interactions.

Prostaglandin D2 modulates sleep-related and noradrenaline-induced activity of preoptic and basal forebrain neurons in the rat

Prostaglandin D2 (PGD2) was applied by pressure through a multibarrel micropipette to sleep-related neurons in the preoptic and neighboring basal forebrain area in head-restrained unanesthetized rats. During wakefulness, PGD2 excited six of 13 sleep-active neurons, inhibited seven of 13 waking-active neurons, and did not affect the remaining neurons. During slow-wave sleep (SWS), however, PGD2 excited only three of 17 sleep-active neurons and inhibited two of 13 waking-active neurons. State-indifferent neurons, which lacked activity related to the sleep-waking state, were insensitive to PGD2 irrespective of wakefulness (n = 24) and SWS (n = 40). These results suggest that PGD2 promotes sleep by exciting sleep-active neurons and by inhibiting waking-active neurons. Furthermore, continuous administration of PGD2 attenuated activity changes associated with wakefulness of five sleep-active and three waking-active neurons tested. Because we had suggested the involvement of preoptic noradrenaline (NA) in arousal, we examined possible modulatory effects of PGD2 on NA-induced neuron responses. PGD2 attenuated NA-induced inhibitory responses in four of six sleep-active neurons and in one of 10 state-indifferent neurons. PGD2 also attenuated NA-induced excitation in four waking-active neurons tested. Accordingly, the modulatory action of PGD2 on sleep-related neurons is important in the mechanism of sleep.

Oral administration of carvedilol and prazosin inhibits the prostaglandin F2 alpha- and noradrenaline-induced contraction of human hand veins in vivo

Carvedilol is a beta-blocker with additional vasodilating activity. This study was performed in order to determine whether the vasodilator action of orally administered carvedilol in man is based upon an alpha-adrenoceptor antagonism exclusively or if evidence for an additional mechanism could be confirmed. The influence of carvedilol (50 mg p.o.) and prazosin (2 mg p.o.) upon the vasoconstrictor effect of noradrenaline and prostaglandin F2 alpha, infused into superficial hand veins, was established in 8 healthy male volunteers. Increasing dosages of the vasoconstrictors below their threshold of systemic activity were employed in order to obtain dose-response curves of the hand veins congested at a venous occlusion pressure of 40 mmHg. These dose-response curves were repeated 1 and 3.5 h after oral administration of either carvedilol, prazosin, or placebo. The ex vivo, in vitro alpha 1-receptor occupancy in plasma was measured before and after each vasoconstrictor dose-response curve, using an alpha 1-radioreceptor binding assay. Washout periods of 48 h were kept between study days, investigating the influence of one orally administered drug upon one of the local vasoconstrictor dose-response curves at a time. In the alpha 1-radioreceptor assay, plasma concentrations from 0.9- to 1.7-fold the equilibrium dissociation constant (Ki) of carvedilol could be evaluated 1 as well as 3.5 h after medication, corresponding with a receptor occupancy of 44%-63%. After prazosin, 9-13 times the Ki values were determined, which amounts to an alpha 1-adrenoceptor occupation of about 90%-93%.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotologic findings in basilar migraine

Treatment of a patient with otologic symptoms and associated migraine-like headache presents the otolaryngologist with formidable problems. Although clinical practice and scientific publications recognize their frequent association, relationships have yet to be well defined. This study seeks to add order to disarray by delineating symptoms and signs of a clearly identified group of migraine patients. Fifty patients with well-defined basilar migraine underwent a thorough neurotologic examination, as well as comprehensive auditory and vestibular testing. Patients were selected from 5880 patients seen over a 2-year period and were prospectively entered into the study after detailed questionnaires and testing were completed for each patient. The most common symptoms found were dysequilibrium, phonophobia, and head pressure. The most common signs were positional nystagmus, low-frequency hearing loss, abnormal loudness discomfort level, and an abnormality on caloric examination. Advanced vestibular testing showed abnormal amplitude scaling, abnormal toes-down pertubation, and an abnormal sway (condition 6) on dynamic posturography. There was frequently an asymmetry on computerized rotation. The author concludes that the majority of patients have subtle findings on testing, but a few have severe peripheral injury due to the basilar migraine. Findings are consistent with the theory that basilar migraine is a central nervous system maladaptation syndrome which creates otoneurologic symptoms and, in a small percentage of cases, may injure the peripheral end-organ.

Prostaglandin E2 Receptors in the Chicken Spinal Cord: 1. Biochemical Characterization

Prostaglandins (PGs) are neuroactive substances which act in the vicinity of their site of synthesis through receptors coupled to G-proteins. Since large amounts of PGE2 can be synthesized by chicken spinal cord, binding sites for PGE2 were looked for in various cell fractions of spinal cord. In the 17 000 g pellet incubated with 0.3 nM [3H]PGE2, 70% of ligand was specifically bound. Two types of PGE2 binding site were characterized (i) high affinity, low capacity binding sites (KD1 1.34 nM, Bmax1 34.5 fmol/mg prot); (ii) low affinity, high capacity binding sites (KD2 2.23 microM, Bmax2 13.2 pmol/mg prot). The high affinity binding sites fulfil several requirements for being receptors to PGE2: (i) since the KD1 is increased in the presence of the GTP analogue, Gpp(NH)p, these binding sites would be regulated by a G-protein; (ii) a desensitization was obtained by an excess of unlabelled PGE2 and reversed by Gpp(NH)p; (iii) the competition experiments between PGE2 and various prostanoids pointed to PGE2 receptors such as EP2 or EP3. The receptor characteristics of the low-affinity binding sites were not investigated. Hence, our results support the presence of two types of PGE2 binding site in the chicken spinal cord; a high affinity site, which corresponds to a PGE2 receptor responding to nanomolar concentrations and a low affinity site sensitive to micromolar concentrations of PGE2.

Arachidonic acid cascade and signal transduction

Since a review on this topic in this Journal appeared (Wolfe, 1982), the CNS has proved to be a major focus in eicosanoid research. Although our knowledge is limited at the moment, the research in this field is rapidly growing. In this short review, we summarize recent progress of research (1982-1989) in this field with special attention directed to eicosanoid metabolism, functions of eicosanoids in the neuroendocrine system and synaptic transmission, current information on eicosanoid receptors, and the link between eicosanoids and cerebral circulation. Knowledge of the eicosanoids has paved the way to a better understanding of intercellular signal transduction systems, including neuronal functions.

Evidence for involvement of prostaglandins in central alpha adrenergic activity and LH release in sheep

Circhoral pulsatile release of immunoreactive luteinising hormone (LH) and prostaglandin F2 alpha (PGF2 alpha) occur synchronously into the jugular vein in ovariectomised sheep. Following a 4-hour control period, intra-carotid injections of phentolamine or intramuscular injections of phenoxybenzamine were given to ovariectomised sheep and the pulsatile release of LH and PGF2 alpha was monitored for a further 6 to 8 hours. Phenoxybenzamine caused a fall in LH and PGF2 alpha in jugular venous plasma. Phentolamine also reduced LH significantly but in this case a marked rise in PGF2 alpha as measured by radioimmunoassay (RIA) occurred after very high doses of phentolamine. Interpretation of the latter results was complicated by the fact that phentolamine at high dose levels interfered with the RIA of PGF2 alpha in plasma. Experiments were repeated in ovariectomised sheep with cannulae placed in the lateral ventricles of the brain for sampling cerebrospinal fluid (CSF). In contrast to the previously observed rise in jugular venous PGF2 alpha following high doses of phentolamine, a fall in CSF levels of immunoreactive PGF2 alpha occurred following intracarotid phentolamine or phenoxybenzamine in 3 out of 7 experiments, while no change was observed in the remaining 4 animals. Phentolamine did not reduce LH significantly in animals with intraventricular cannulae. The work provides support for the view that circhoral pulses of immunoreactive PGF2 alpha in sheep are neural in origin and may be related to sympathetic neurotransmission.

Isolation and identification of lipoxygenase products from the rat central nervous system

Leukotrienes B4, C4, D4 and E4, together with five monohydroxyeicosatetraenoic acids, were isolated after incubation of chopped rat brain tissue with ionophore A23187. The monohydroxyeicosatetraenoic acids were 5-hydroxy-6,8,11,14-eicosatetraenoic acid, 9-hydroxy-5,7,11,14-eicosatetraenoic acid, 11-hydroxy-5,8,12,14-eicosatetraenoic acid, 12-hydroxy-5,8,10,14-eicosatetraenoic acid and 15-hydroxy-5,8,11,13-eicosatetraenoic acid. Identification of the compounds was performed using reversed-phase high-performance liquid chromatography, ultraviolet spectroscopy and gas chromatography-mass spectrometry. Formation of the compounds was inhibited by micromolar concentrations of nordihydroguaiaretic acid. Indomethacin specifically inhibited the formation of 11-hydroxy-5,8,12,14-eicosatetraenoic acid, suggesting that this compound was produced as a by-product during cyclooxygenase-catalyzed prostaglandin synthesis.

Modulating effects of prostaglandins on parasympathetic-mediated secretory activities of rat salivary glands

Exogenously administered PGE1 or PGE2, like atropine, markedly decreased both the flow and calcium concentration of parasympathetically evoked rat parotid saliva; PGF2 alpha was less effective. Despite the fact that prostaglandins greatly reduced the Ca concentration of nerve-evoked saliva, they did not change the glandular Ca concentration of either control or parasympathetically stimulated parotid glands. Prostaglandins (20 micrograms/kg, i.a.) decreased the Na or K concentration of nerve-evoked parotid saliva, but at lower doses had no significant effect. PGE1, PGE2, PGF2 alpha or atropine markedly decreased flow rates of similarly evoked rat submandibular saliva. Prostaglandins and atropine, however, decreased the Na concentration and increased the K concentration of parasympathetically evoked submandibular saliva. PGF2 alpha, like atropine, increased the Ca concentration of such saliva. Drug vehicle, ethanol, slightly decreased the flow of both parotid and submandibular saliva but not the ion secretion, Endogenous prostaglandins themselves may not play a role in secretory activities during parasympathetic nerve stimulation of rat salivary glands, since administration of indomethacin, and inhibitor of prostaglandin biosynthesis, prior to or during nerve stimulation did not significantly alter nerve-evoked salivary secretion, The mechanisms by which prostaglandins modulate secretory responses of salivary glands during parasympathetic stimulation are not understood.

Specificity of prostaglandin D2 binding to synaptic membrane fraction of rat brain

The structural requirement of the prostaglandin D2 molecule for binding to the synaptic membrane fraction of rat brain was extensively studied by using various prostaglandin D derivatives. Most strict specificity was found in the structures of the cyclo-pentane ring and the double bond in 13,14-position. The addition and deprivation of the double bond in alpha- and omega-chain, except on 13,14-position, moderately affected the binding. The modification in the carboxyl terminus and omega-chain terminus did not seriously influence the binding. BW 245C and 9-beta-prostaglandin D2, potent agonists for the prostaglandin D2 receptor in the platelet membrane, were almost ineffective. [3H]prostaglandin D2 binding was not affected by the addition of various neuroactive substances to the binding assay mixture. Further, prostaglandin D2 did not affect the known neurotransmitter receptor bindings in the rat brain.

Production of prostaglandin D2 by murine macrophage cell lines

Several tumor-derived murine macrophage cell lines were evaluated in vitro as cloned prototypes of tissue macrophages for their ability to metabolize arachidonic acid. Unexpectedly, two cell lines, J774A.1 and WR19M.1, rapidly converted exogenous 14C-arachidonic acid (AA) to a single major prostaglandin metabolite. The compound, PGD2, was positively identified by TLC, HPLC, and GC-MS. The enzymatic formation of the PGD2 was shown by inhibition of its formation by indomethacin and reduced formation of 14C-PGD2 from 14C-PGH2 in boiled cells. When J774A.1 cells were prelabeled with 3H-AA, cultured for 24 hours, and stimulated with lipopolysaccharide (LPS), PGD2 was again the predominant product. No other tumor derived cell lines, including several other murine macrophage lines, produced significant amounts of PGD2. Elicited and activated murine peritoneal macrophages produced only small amounts of PGD2, but resident peritoneal macrophages produced modest amounts of PGD2. Exaggerated formation of PGD2 by J774A.1 and WR19M.1 cells may be a consequence of neoplastic transformation or the clonal expansion of a minor subpopulation of normal tissue macrophages.

Effects of thromboxane synthase inhibition on vascular responsiveness in the in vivo rat mesentery

The purpose of this investigation was to determine the effects of thromboxane synthase inhibition on vascular responsiveness. To achieve this goal, the effects of thromboxane synthase inhibitors on mesenteric vascular responses to sympathetic nerve stimulation, norepinephrine, and angiotensin II were determined in vivo. In normotensive rats, chronic treatment with the thromboxane synthase inhibitor, UK38,485 (100 mg/kg X d X 7 d), attenuated vascular responses to nerve stimulation and angiotensin II, but not to norepinephrine. Indomethacin treatment (5 mg/kg X three doses) did not attenuate vascular responses, but did prevent chronic UK38,485 administration from attenuating vascular reactivity. A single dose of UK38,485 (100 mg/kg) did not modify vascular responses to nerve stimulation or angiotensin II, even though platelet thromboxane synthase was inhibited completely. In spontaneously hypertensive rats, chronic administration (100 mg/kg X d X 7 d) of either UK38,485, OKY1581, or U-63557A (three structurally distinct thromboxane synthase inhibitors) attenuated vascular responses to nerve stimulation and angiotensin II. Only U-63557A suppressed responses to norepinephrine. Chronic treatment with UK38,485 or U-63557A did not influence vascular reactivity in hypertensive rats treated with indomethacin. Also, chronic administration of lower doses of UK38,485 or U-63557A (30 mg/kg X d X 7 d) did not affect vascular responsiveness in hypertensive rats, despite complete blockade of platelet thromboxane synthase. These data indicate that chronic administration of high doses of thromboxane synthase inhibitors attenuates vascular responses to sympathetic nerve stimulation and angiotensin II, but not usually to norepinephrine. This action may be mediated by endoperoxide shunting within the blood vessel wall.

Metabolic fate of endogenously synthesized prostaglandin D2 in a human female with mastocytosis

Increased production of prostaglandin D2 was recently demonstrated in patients with systemic mastocytosis. One female patient investigated with mastocytosis was found to have overproduction of prostaglandin D2 of such magnitude (150-fold above normal) that it provided the unique opportunity to delineate the metabolic fate of endogenously synthesized prostaglandin D2. A five percent aliquot of a twenty-four hour urine collection from this patient was extracted, purified by silicic acid chromatography, methylated, and finally subjected to high pressure liquid chromatography. Column fractions collected were derivatized and analyzed by gas chromatography-mass spectrometry. Increased quantities of sixteen urinary metabolites were identified and included a series of metabolites retaining the PGD-ring as well as a series of metabolites with a PGF-ring. PGF-ring metabolites were excreted in approximately 4-fold greater relative abundance than PGD-ring metabolites. More than one apparent isomeric form of some PGF-ring metabolites were found. The predominant urinary metabolite was 2,3-dinor-prostaglandin F2. This study provides evidence that endogenously synthesized prostaglandin D2 is converted in substantial part to prostaglandin F2 metabolites in vivo in humans.

Modulatory effects of prostaglandin D2, E2 and F2 alpha on the postsynaptic actions of inhibitory and excitatory amino acids in cerebellar Purkinje cell dendrites in vitro

For the purpose of revealing the physiological functions or roles of prostaglandins (PGs), PGD2 in particular, in the central nervous system, the effects of PGD2, E2 and F2 alpha on the postsynaptic actions of GABA, taurine, L-glutamate and L-aspartate on Purkinje cell dendrites in guinea pig, cerebellar slices were electrophysiologically investigated using intradendritic recording. Iontophoretic application of PGD2 alone either depolarized or hyperpolarized some Purkinje cell dendrites, while PGE2 and F2 alpha induced only depolarizations. All PGs tested showed fairly strong potentiation of the inhibitory action of GABA or taurine and of the excitatory action of L-glutamate or L-aspartate on Purkinje cell dendrites. As a possible mechanism of action, the change of the cyclic nucleotide level induced by PGs was tentatively suggested as being involved in the potentiating action of PGs on excitatory amino acids.

The effects produced by prostaglandin D2 on serotonin turnover and release and tryptophan uptake

In earlier studies, it was proposed that there was a serotonergic involvement in the ability of prostaglandin D2 (PGD2) to potentiate pentobarbital sleeping time. The actions of PGD2 on neuronal turnover and release of serotonin and uptake of tryptophan were examined in mice. The effect of PGD2 administration on serum tryptophan levels was also investigated. PGD2 (1 and 4 mg/kg) increased the concentrations in whole brain of endogenous tryptophan (TRYP) and of 3H-tryptophan (3H-TRYP) following an intravenous (IV) injection of 3H-tryptophan. Formation of 3H-5-hydroxyindoleacetic acid (3H-5HIAA) was doubled after PGD2 administration (1 and 4 mg/kg). Whole brain concentrations of endogenous serotonin (5HT) and 3H-serotonin (3H-5HT) were unchanged after the administration of the prostaglandin. PGD2 (10(-4) to 10(-10)M) in vitro had no effect on spontaneous or K+-evoked release of 3H-5HT from whole brain synaptosomes. Uptake of 3H-tryptophan in synaptosomes was neither stimulated nor depressed by (10(-4) to 10(-12)M) PGD2. There was also no change in serum tryptophan levels after administration of this prostaglandin. Thus, PGD2 administration does affect the serotonergic system but no direct neurochemical correlate of sedation can be shown.

Participation of prostanoids in chemical activation of the pericardial pressor reflex in dogs

Experiments were performed on anaesthetized, open-chest dogs to determine the reflex effects on systemic blood pressure and heart rate produced by stimulation of the parietal pericardium with bradykinin, prostacyclin, prostaglandin E2 (PGE2), prostaglandin D2 (PGD2) and arachidonic acid. Pericardial application of bradykinin (1 microgram) consistently elicited reflex increases in blood pressure and heart rate, whereas application of prostanoids or arachidonic acid in doses up to 10 micrograms failed to produce any cardiovascular responses. Indomethacin, applied either directly to the parietal pericardium (1 microgram/ml) or given intravenously (5 mg/kg) caused a long lasting reduction of the reflex responses to bradykinin. The reflex effects of bradykinin could be temporarily restored by treatment of the pericardium with either prostacyclin (0.1 microgram/min) or PGE2 (0.1 microgram/min). PGD2 (0.1-1 microgram/min) did not influence the bradykinin induced pericardial reflex. Superfusion of arachidonic acid (3 micrograms/min) over the pericardium amplified the reflex effects of bradykinin when given before, but not when given after indomethacin treatment. The results indicate that locally formed prostanoids, specifically prostacyclin and PGE2, can facilitate activation of the pericardial pressor reflex by bradykinin. The findings may be relevant to the changes in cardiovascular activity occurring during pericardial inflammation.

Brain arachidonic acid metabolites. Functions and interactions with ethanol

The formation and potential function of arachidonic acid metabolites in brain are reviewed briefly. Cyclooxygenase metabolites of arachidonic acid are formed in brain, but the lipoxygenase derivatives have not been demonstrated. Evidence clearly indicates that the cyclooxygenase products act as neuromodulators. Possible effects of leukotrienes on brain function remain in doubt, although several studies have suggested a role for the leukotrienes and it appears that these agents have a long-lasting effect. Potential interactions between ethanol and brain arachidonic acid metabolites have received minimal attention. Several studies indicate that pretreatment with prostaglandin synthetase inhibitors produces antagonism of ethanol's behavioral effects. These observations may be related to preliminary findings that ethanol increases brain prostaglandin content.

Attenuation of noradrenergic neurotransmission by the thromboxane synthetase inhibitor, UK 38,485

The purpose of this study was to determine the effects of chronic administration of the thromboxane synthetase inhibitor, UK 38,485, on noradrenergic neurotransmission. Male Sprague Dawley rats (n = 14) were treated once daily with either UK 38,485 (100 mg/kg; n = 7) or the vehicle of UK 38,485 (olive oil; n = 7) by gavage. The dose of UK 38,485 chosen was sufficient to inhibit ex vivo platelet TXB2 production by greater than 90% for 24 hours. One week into the treatment animals were prepared for in situ perfusion of their mesenteric vascular beds. Vasoconstrictor responses to both exogenous norepinephrine and periarterial nerve stimulation were determined both before and during an infusion of angiotensin II (9 ng/min) into the superior mesenteric artery. UK 38,485 significantly (P less than 0.02) attenuated the vascular response to periarterial nerve stimulation without altering the vascular response to either norepinephrine or angiotensin II. UK 38,485 did not influence the baseline perfusion pressure, the mean arterial blood pressure or the potentiation of neurotransmission by angiotensin II. These data indicate that in the in situ rat mesentery UK 38,485 attenuates the release of neurotransmitter from sympathetic nerve terminals.

Facilitation of synaptic transmission by prostaglandin D2 at synapses between NG108-15 hybrid and muscle cells

The effect of prostaglandin (PG) D2 on neuronal functions was investigated in neuroblastoma X glioma NG108-15 hybrid cells. PGD2 caused a sustained increase in miniature end-plate potentials (MEPPs) recorded from cultured striated muscle cells which had formed junctions with NG108-15 cells. PGD2 initially hyperpolarized and then depolarized NG108-15 cells. The time course of depolarization fitted well to the facilitative phase of MEPPs. The same action on synaptic transmission and membrane potentials was detected with PGF2 alpha but not with PGE1. PGD2 (10(-4)M) produced a 3-fold increase of adenylate cyclase activity in NG108-15 cell homogenates through its receptors that are distinct from those of PGE1 and PGI2. These results show that PGD2 facilitates MEPP frequency from NG108-15 cells due to depolarization, and suggest that PGD2 may act as a physiological neuromodulator for synaptic transmission in vivo.

Neuroeffector actions of prostaglandin D2 on isolated dog mesenteric arteries

Treatment with prostaglandin (PG) D2 in concentrations (10(-8) to 10(-7) M) insufficient to alter the basal tone potentiated the contractile response of helical strips of dog mesenteric arteries to transmural electrical stimulation but did not influence the response to norepinephrine. The potentiating effect of PGD2 was not prevented by treatment with diphloretin phosphate, a PG antagonist, whereas contractions of dog cerebral arteries induced by PGD2 were suppressed. The 3H-overflow evoked by transmural stimulation in superfused mesenteric arterial strips previously soaked in 3H-norepinephrine containing media was significantly increased in PGD2. It is concluded that PGD2 increases the stimulation-evoked release of norepinephrine from adrenergic nerves innervating the arterial wall. PGD2 appears to act differently on receptive sites responsible for increasing the release of norepinephrine and for producing arterial contraction.

Autoradiographic localization of a binding protein(s) specific for prostaglandin D2 in rat brain

The specific [3H]prostaglandin (PG) D2 binding was detected by using the slide-mounted sections of rat brain fixed by perfusion with 2% paraformaldehyde. The binding was reversible, saturable, high affinity, Na+ dependent, and highly specific for PGD2. These binding characteristics are essentially similar to those observed with the synaptic membrane of rat brain as previously reported. Using autoradiographic image analyses by computerized densitometry and color coding, we visualized the localization of [3H]PGD2 binding in rat brain. A high density of the binding sites was observed in the cerebral cortex, preoptic area, amygdala, hypothalamic nuclei (arcuate nucleus, ventromedial nucleus, and posterior hypothalamic nucleus), thalamic nuclei (reuniens nucleus and rhomboid nucleus), hippocampus, pineal body, and cerebellar cortex. The binding was not significantly observed in the striatum and also was negative in the white matter, arachnoid membranes, and vasculatures.

Prostanoids and cardiac reflexes of sympathetic and vagal origin

Prostaglandins in concentrations too low to stimulate afferent nerve endings in the heart may sensitize them to chemical or mechanical stimuli that activate cardiac reflexes during myocardial ischemia. Bradykinin, which is released from the heart during ischemia, elicits sympathetically mediated reflex pressor effects and tachycardia when applied in low doses (0.1 to 1 microgram) to the epicardium of the left ventricle in open-chest, anesthetized dogs. The reflex pressor effects evoked by bradykinin are reduced after inhibition of prostaglandins biosynthesis with indomethacin and potentiated by concomitant topical application of low doses (0.1 to 0.3 microgram/min) of PGE1 or PGE2 and prostacyclin (PGI2). The pressor and tachycardic responses to bradykinin are also enhanced after temporary (10-minute) coronary occlusion; this potentiation is abolished by indomethacin treatment and can be restored by superfusing the ventricle with prostaglandins. Nicotine is known to excite mechanosensitive vagal receptors with afferent C fibers, which supply the left ventricle, and to elicit reflex hypotension and bradycardia. This depressor vagal reflex evoked by epicardial or intracoronary administration of nicotine (10 to 50 micrograms) was not affected by either indomethacin or by topical application of PGE1, PGE2, or PGI2. Also, intracoronary infusion of PGE2 (0.1 to 0.3 microgram/min), which enhanced the pressor reflex effects of bradykinin, was without effect on nicotine-induced depressor reflex. However, intracoronary infusion of PGI2 (0.1 to 0.3 microgram/min) significantly enhanced the hypotensive and bradycardic responses to nicotine and, at the same time, reduced sympathetically mediated reflex effects of bradykinin. The hypotensive effects induced by epicardial or intracoronary administration of nicotine were also significantly enhanced during intravenous infusion of subdepressor doses of PGI2 (5 to 20 ng/kg/min). Treatment with captopril, which enhances the endogenous production of prostaglandins, greatly enhanced the reflex depressor effects of nicotine; this potentiating effect of captopril was completely abolished by indomethacin treatment. An increase in the magnitude of nicotine-induced reflex depressor effects was also observed after intravenous injection (1 microgram/kg) or infusion (25 to 50 ng/kg/min) of prostaglandin D2. A working hypothesis is proposed to account for the role of prostanoids in activation of cardiac reflexes during myocardial ischemia.

Potential anticonvulsive properties of endogenous prostaglandins formed in mouse brain

The levels of 5 different prostanoids (PGD2, PGF2 alpha, PGE2, TXB2 and 6-keto-PGF1 alpha) formed in whole mouse brain in vivo were measured by specific radioimmunoassays. Basal concentrations were found to be very low (few ng/g wet weight). A marKed increase occurred during convulsions induced by either pentylenetetrazole or by electroconvulsive shock. Under both conditions the major cyclooxygenase product detected was PGD2, followed by PGF2 alpha and lower concentrations of the other prostanoids. The non-steroidal anti-inflammatory drugs flurbiprofen, indomethacin, and diclofenac dose-dependently inhibited the pentylenetetrazole-induced formation of prostaglandins. Concomitantly these 3 compounds dose-dependently increased the acute toxicity of pentylenetetrazole (decrease in LD50). Conversely, if levels of cerebral prostaglandins were enhanced by a preceding electroshock, the toxicity of pentylenetetrazole was significantly reduced (increase in LD50), and the time of onset of clonic seizures was markedly prolonged. Both the effect on the latency time and the LD50 could be reversed if the cerebral prostaglandin synthesis was prevented by indomethacin, or if the time interval between the electroshock and pentylenetetrazole administration was extended, so that the electroshock-stimulated prostaglandin concentrations had declined to basal levels again. These findings indicate that endogenous prostanoids formed in mouse brain during convulsions might possess anticonvulsive properties.

Eicosanoids: prostaglandins, thromboxanes, leukotrienes, and other derivatives of carbon-20 unsaturated fatty acids

In recent years, knowledge of the biochemistry of oxygenated metabolites of arachidonic acid has greatly increased. Their biological functions in acceleration and prevention of platelet aggregation and in inflammatory and immune reactions are becoming much clearer. The therapeutic value, particularly of PGI2 as well as selective inhibitors of synthesis, is also rapidly advancing. Despite much effort, the functional importance of prostaglandins and thromboxanes in the cNS in normal ongoing physiological processes is still quite uncertain. However, when parenchymal or vascular elements are damaged or invaded by extraneural cells, the synthesis of one or the other member of the eicosanoids is greatly increased and contributes significantly to pathophysiological reactions. Thus, prevention of synthesis is likely to have increasing importance in clinical neurology, particularly in cerebrovascular diseases.

Different responsiveness of a variety of isolated dog arteries to prostaglandin D2

The addition of prostaglandin (PG) D2 contracted helical strips of dog cerebral, coronary, renal and femoral arteries; the contraction was greatest in cerebral arteries. The contractile response of cerebral arteries was potentiated by aspirin and attenuated by polyphloretin phosphate. In the arterial strips contracted with PGF2 alpha, PGD2 elicited a concentration-related relaxation; the relaxation was greatest in mesenteric arteries. In mesenteric arterial strips contracted with norepinephrine, a lesser degree of relaxation was induced, and in the K+-contracted arteries, only a contraction was induced. Treatment with PGD2 attenuated the contractile response of cerebral and mesenteric arteries to PGF2 alpha or PGE2; this inhibitory effect was approximately 10 times greater in mesenteric arteries. However, the response to serotonin (for cerebral arteries) or norepinephrine (for mesenteric) was unaffected. It may be concluded that the heterogeneity of responses to PGD2 of a variety of dog arteries is due to different contributions of vasoconstrictor and vasodilator mechanisms. PGD2 appears to share the mechanism underlying arterial contraction with PGF2 alpha and PGE2, and interferes with the effect of these PG's possibly on receptor sites.

Prostaglandin D synthase in microvessels from the rat cerebral cortex

Microvessels, a mixture composed predominantly of small arterioles and capillaries (7-80 micro diameter), were isolated from the rat cerebral cortex by selective nylon sieving and glass bead elutriation. The morphology and purity of the microvessel and cerebral cortex filtrate (virtually free of vascular contamination) were monitored by light microscopy and by the activity of several enzymes: gamma -glutamyl transpeptidase, GSH-S-transferase, prostacyclin synthase and PGD synthase. Prostacyclin and PGD synthesizing activities as well as gamma-glutamyl transpeptidase activity were localized to the microvessels of the rat cerebral cortex whereas GSH-S-Transferase was restricted to the non-vascular filtrate fraction. The characteristics of the PGD synthase were similar to those of the purified enzyme previously described for the rat brain. The microvessel (MV) PGD synthase was localized to the cytosol fraction of the microvessels and did not require reduced glutathione for activity. The enzyme was inhibited by pre-incubation with p-hydroxymercuribenzoate (ImM) or N-ethylmaleimide (ImM). The MV RGD synthase saturated at 15-20 microM PGH2, exhibited an apparent Km of 9.6 microM, and a pH optimum of 8.0-8.1. These findings suggest roles for both prostacyclin and PGD synthesis by the rat cerebral vasculature in the autoregulation of cerebral blood flow and/or neural function. These studies also indicate that the major source of PGI2 and PGD2 synthesis by rat brain homogenates is the microvasculature.

Actions of indomethacin and prostaglandins E2 and D2 on nerve transmission in the nictitating membrane of the cat

The effects of PGE2, PGD2 and cyclooxygenase inhibitors on sympathetic nerve transmission in the nictitating membrane of anesthetized cats were studied to further characterize the actions of these prostaglandins and to define their possible role as neuromodulators. PGD2 depressed neurotransmission throughout a broad range of stimulus free quencies, apparently by presynaptic inhibition of norepinephrine release. PGE2 enhanced the effects of both nerve stimulation and exogenous norepinephrine in intact preparations but only depressed the effects of exogenous norepinephrine in the chronically denervated nictitating membrane, suggesting that part of the effect of PGE2 on neurotransmission was presynaptic. When norepinephrine reuptake was blocked by desipramine, PGE2 still enhanced neurotransmission. Indomethacin, but not other cyclooxygenase inhibitors (aspirin, ibuprofen, flurbiprofen, meclofenamic acid), inhibited the response of the nictitating membrane to nerve stimulation without depressing the effects of exogenous norepinephine. Curiously, indomethacin, but again not other cyclooxygenase inhibitors, specifically antagonized the ability of PGE2 to enhance nerve transmission. These results further characterize the pharmacological effects of PGE2 and PGD2 at the nictitating membrane. The lack of effect of cyclooxygenase inhibitors suggests that neither endogenous PGE2 or PGD2 play a functional role at this synapse. The effects of indomethacin appear to be unrelated to inhibition of prostaglandin synthesis.

Regional distribution of arachidonic acid metabolites in rat brain following convulsive stimuli

Seizures were induced in female Wistar rats by electroconvulsive shock (ECS) or administration of pentetrazole (PTZ). Brain content of various prostanoids measured by radioimmunoassay showed time-dependent changes after the induction of convulsions; highest levels were found for PGD2 followed by PGF2 alpha, PGE2, TXB2 and 6-keto-PGF1 alpha. Analysis of the various arachidonic acid metabolites in seven parts of the rat brain dissected according to the method of Glowinski and Iversen revealed the largest increases in hippocampus and cerebral cortex and smaller ones also in hypothalamus and corpus striatum both after ECS and PTZ. The ratios of the different cyclo-oxygenase products remained virtually the same in whole brain as well as in those regions where the formation of prostaglandins was markedly elevated. 15-keto-13,14-dihydro-PGF2 alpha also increased simultaneously in parallel to its parent compound, PGF2 alpha and was detected in significant amounts only in hippocampus and cerebral cortex. However, concentrations of 15-keto-13,14-dihydro-PGF2 alpha in these brain regions as well as in whole brain represented only 3-10% of the amounts found for PGF2 alpha. Thus, the metabolizing enzymes 15-hydroxy-PG-dehydrogenase and delta 13-PG-reductase seem to be of minor importance for the inactivation of prostanoids in brain tissue.

Influence of prostaglandins on vasoconstrictor responses in the hindquarters vascular bed of the cat

The effects of prostaglandins (PG), A1, A2, B2, E1, 6-keto-E1, F2 alpha and indomethacin on vascular resistance and vasoconstrictor responses were investigated in the feline hindquarters vascular bed under conditions of controlled flow so that changes in perfusion pressure directly reflect changes in vascular resistance. Infusion of PGE1, PGE2 and 6-keto-PGE1 (3 microgram/min) into the abdominal aorta significantly dilated the hindquarters vascular bed and inhibited vasoconstrictor responses to sympathetic nerve stimulation and intra-arterial injections of angiotensin, whereas hindquarters vasoconstrictor responses to tyramine and exogenous norepinephrine were unaffected. Infusion of PGA1, A2, B2 and F2 alpha at a similar rate produced transient changes in hindquarters vascular resistance and did not consistently alter vasoconstrictor responses to sympathetic nerve stimulation, angiotensin, norepinephrine and tyramine. Indomethacin in a dose which greatly attenuates the response to intravenous administration of arachidonic acid enhanced responses to nerve stimulation and norepinephrine. In addition, indomethacin had little or no effect on hindquarters perfusion pressure and systemic arterial pressure. These data suggest that E series prostaglandins possess the ability to modulate the actions of the sympathetic nervous system and angiotensin in the feline hindquarters vascular bed. In addition, these data suggest that PGEs, upon enzymatic conversion and dehydration to A and B series prostaglandins, lose their ability to consistently affect vasoconstrictor responses. Experiments with indomethacin further suggest that locally formed prostaglandins do modulate the effects of the sympathetic nervous system of the feline hindquarters.