Heat loss responses and blockade of prostaglandin E2-induced thermogenesis elicited by α1-adrenergic activation in the rostromedial preoptic area

The unilateral microinjection of noradrenaline (NA), but not vehicle solution, into the rostromedial preoptic area (POA) elicited simultaneous increases in cutaneous temperatures of the tail and sole of the foot and decreases in the whole-body O₂ consumption rate, heart rate, and colonic temperature in urethane–chloralose-anesthetized rats, suggesting a coordinate increase in heat loss and decrease in heat production. The magnitude of these responses increased dose-dependently over the range of 1–100 pmol, except for the metabolic and bradycardic responses. Similar hypothermic responses were elicited by the microinjection of 40 pmol methoxamine (an α₁-adrenergic agonist), but not by that of clonidine (an α₂-agonist) or isoproterenol (a β-agonist). Sites at which microinjection of NA elicited hypothermic responses were in the vicinity of the organum vasculosum of the lamina terminalis including the median preoptic nucleus, whereas no thermal or metabolic response was elicited when NA was microinjected into the lateral POA or caudal part of the medial POA. The microinjection of 130 fmol prostaglandin (PG) E₂ into the NA-sensitive site always elicited thermogenic, tachycardic, and hyperthermic responses. Furthermore, the PGE₂-induced febrile responses were greatly attenuated by prior administration of NA at the same site. These results demonstrate that NA in the rostromedial POA exerts α₁-adrenoceptor-mediated hypothermic effects and opposes PGE₂-induced fever.     

Comparison of the Effects of Prostaglandins E1, E2 and F2α on the Sympathetically Stimulated Rabbit Heart

PGE₁, PGE₂ and PGF_2α in concentrations ranging from 3×10^-9M to 1.5 × 10^-6 M were infused into the isolated perfused, sympathetically innervated rabbit heart in order to assess their capacity to inhibit the chronotropic, inotropic and noradrenaline overflow responses to sympathetic nerve stimulation, as well as the chronotropic and inotropic responses to infusion of noradrenaline. The coronary flow was increased by PGE₁ but not by PGE₂ of PGF_2α. The three compounds did not change the heart rate or the contractile force, indicating that the reported increase in heart rate after i.v. infusion of PGE₁ or PGE₂ is reflex in origin. PGE₁ and PGE₂ inhibited the outflow of noradrenaline as well as the chronotropic and inotropic responses to nerve stimulation in a dose-dependent way, while PGF_2α was ineffective. None of the compounds altered the chronotropic or inotropic response to exogenous noradrenaline. It is concluded that PGE₁ and PGE₂ but not PGF_2α, inhibit the sympathetic neurotransmission in the rabbit heart, and that they do this mainly by reducing the release of the transmitter from the adrenergic nerve terminals.     

Comparison of the action of prostaglandin with endotoxin on thermoregulatory response thresholds

Prostaglandin E₂ (PGE₂) and lipopolysaccharide (LPS) derived fromE. coli were injected into the lateral cerebral ventricle of rabbits at 30° C ambient temperature. The threshold core temperatures for ear cutaneous vasoconstriction. (Th _v) and shivering (Th _sh) were determined by whole-body cooling with an intestinal thermode. Each threshold, as determined at the plateau phase of LPS fever and PGE₂ hyperthermia respectively, were compared with the control values before LPS and PGE₂ injection.Th_sh was not changed by the injection of LPS, whileTh _v was increased. After PGE₂ injection bothTh _sh andTh _v were increased in comparison to their control levels. These changes paralleled the elevation of core temperature.The present study does not exclude prostaglandins as humoral mediators involved in some of the central processes generating fever, but suggest at the same time that there are additional properties of LPS fever for which prostaglandins do not account.     

Effects of Prostaglandins on the Isolated Human Bladder and Urethra

The effects of prostaglandins F_2α (PGF_2α), E₂ (PGE₁) and E₂ (PGE₂) on the human lower urinary tract were studied in vitro in preparations obtained from patients undergoing total cystourethrectomy because of bladder malignancy. Tissue specimens were taken from different parts of the urethra, the urethrovesical junction, and the bladder. From these specimens, smooth muscle preparations were dissected and mounted in organ baths, that were filled with Krebs solution (37°C) and bubbled with carbogen. Isometric tension was recorded. Preparations from the bladder and all parts of the urethra were contracted by PGF_2α. This effect was not affected by tetrodotoxin, phenoxybenzamine, or atropine; isoprenaline relaxed the PGF_2α induced contractions. PGE₁ and PGE₂ both contracted strips from the bladder. However, urethral preparations contracted by PGF_2α or noradrenaline were relaxed by these agents. This relaxing effect was at least as pronounced as that produced by isoprenaline; it was not affected by propranolol.     

Bradykinin-stimulated prostaglandin E2 production by endothelial cells and its modulation by antiinflammatory compounds

Prostaglandin production was studied in cultures of pig aorta endothelial cells using radioimmunoassay, radiochromatography, and smooth muscle bioassay. PGE₂ was produced in higher concentrations than other prostaglandins. Bradykinin produced a rapid dose-related stimulation of PGE₂ production. These results provided the basis for establishment of a simplified test system for investigating new compounds which alter prostaglandin synthesis and might therefore affect inflammatory responses. It was also observed that these endothelial cells do not metabolize prostaglandins via 15-hydroxyprostaglandin dehydrogenase.     

Prostaglandin E2 in basal gastric secretion and during stimulation of muscarinic receptors in man

The physiological importance of prostaglandin E₂ (PGE₂) biosynthesis in the gastric mucosa is unknown. A role of endogenous prostaglandins in protecting the gastrointestinal epithelia has been suggested, but the evidence is unsufficient and rarely supported by concomitant measurement of PG production. Amounts of PGE₂ in luminal gastric contents which can be sampled atraumatically may reflect PGE₂ synthesis in the gastric mucosa in vivo. To confirm earlier reported measurements made with radioimmunoassay we have measured by gas chromatography - mass spectrometry (GC-MS) PGE₂ in gastric juice of five healthy men under basal conditions and during stimulation of muscarinic receptors with iv. bethanechol which in dog is reported to enhance PGE₂ output. PGE₂ was detected in all basal samples. The output was in median 32.1 pmol/15 min (range 17.0–105.4, 1 pmol=0.352 ng), which is similar to results from earlier studies. Bethanechol infusion (60 μg x kg^-1 x h^-1) did not affect PGE₂ outputs systematically in spite of a significant increase in outputs of acid and chlorides. Stimulation of muscarinic receptors does not seem to influence PGE₂ synthesis in gastric mucosa in vivo. Alternatively changes in PGE₂ synthesis may be masked by rapid chemical or enzymatical degradation or reabsorption of PGE₂.Studies are under way to explore those phenomena.     

Relaxant effect of prostaglandin E1 on the isolated intestine of the toad (bufo melanostictus)

The pharmacological actions of prostaglandins E₁, F₁, E₂ and A₁ were studied on the longitudinal and circular muscles of the isolated small intestine of the toad. Prostaglandin E₁ caused relaxation, whereas prostaglandin A₁ was inactive and prostaglandins F₁ and E₂ caused contractions. Other substances which relaxed the toad intestine were adrenaline, noradrenaline and isoprenaline. On a molar basis, prostaglandin E₁ was seven times less potent than isoprenaline, but it was three times more potent than adrenaline and seventeen times more potent than noradrenaline. Phentolamine and propranolol blocked the relaxant effects of catecholamines in concentrations which did not alter the relaxant effect of prostaglandin E₁. The results suggested that prostaglandin E₁ acted directly on the intestinal smooth muscle of the toad rather than by the local release of catecholamines.     

The modulatory effects of prostaglandins on both excitatory and inhibitory non-adrenergic non-choIinergic neurotransrnission in guinea-pig airways

Johansson -Rydberg , I. G. M., Andersson , R. G. G. & Grundström , N. 1 992 , The modulatory effects of prostaglandins on both excitatory and inhibitory non-adrenergic non-cholinergic neurotransmission in guinea-pig airways. Acta Physiol Scand 144 , 439444. Received 28 August 1 991 , accepted 20 November 1991. ISSN 0001–6772. Department of Pharmacology, University Hospital of Linkoping, Sweden. Guinea-pig trachea and bronchi were used to investigate the effects of indomethacin and prostaglandin E₂ (PGE₂) on non-adrenergic non-cholinergic excitatory (e-NANC) and inhibitory (i-NANC) neurotransmission evoked by electrical field stimulation. Indomethacin potentiated e-NANC responses in bronchi with intact epithelium but had no effect on epithelium-denuded preparations. Inhibitory NANC responses were increased by indomethacin independent of the epithelium. Both i-NANC and e-NANC neurotransmission were suppressed by PGE₂ in a dose-dependent manner. These results indicate that endogenous prostaglandins (e.g. PGE₂) generated from the epithelium have an inhibitory effect on i-NANC and e-NANC nerve responses in airways. The epithelium is presumably not the only source for generation of prostaglandins that are involved in i-NANC neurotransmission.     

Effects of prostaglandin E1, E2 and 16,16-dimethyl-E2 on gastric mucosal microcirculation and basal acid output in the rat*

The effects of prostaglandins E, (PGE₁), E₂ (PGE₂) and 16, 16-dimethyl-E₂ (16, 16-dm-PGE₂) on the gastric mucosal microcirculation and (spontaneous) acid output were studied in anaesthetized rats. The superficial mucosal vessels were monitored on a TV screen using a microscope, TV camera and videorecorder for off-line analysis of red cell velocities (V_RBC) and vessel diameters, from which the blood flow (Q_RBC) was calculated. The prostaglandins were either applied topically to the solution bathing the exposed mucosa or administered intravenously as a continuous infusion. Topical application of PGE₁ (0.5 or 5 μgml^-1), PGE₂ (5 or 50 μg ml^-1) or 16, 16-dm-PGE₂ (0.005, 0.05 or 0.5 μg ml^-1) increased V_RBC dose-dependently without altering acid output, except for the highest dose of PGE₂ (50 μg ml^-1) which inhibited acid output. The latter occurred in spite of a seven-to eight-fold increase in V_RBC. Mucus secretion (evidenced by an impaired resolution of the TV image) also increased during topical application of the prostaglandins especially at higher doses. Intravenous PGE₁, PGE₂ (2.0 μg kg^-1 min^_1) or 16, 16-dm-PGE₂ (0.02 μg kg^-1 min^_1) caused an initial and transient (5–10 min) fall in systemic arterial blood pressure and a decrease in V_RBC and acid output. Intravenous 16, 16-dm-PGE₂ in a dose which did not affect secretion or systemic arterial blood pressure (0.002 μg kg^-1 min^-1) still significantly reduced V_RBC. Thus, topically applied PGE₁, PGE₂ or 16, 16-dm-PGE₂ dose-dependently increase V_RBC while intravenous administration of the same prostaglandins reduce V_RBC.     

Antidiuretic responses to thermal stimulation of hypothalamus and spinal cord in the conscious goat

Summary At various ambient temperatures the effects of hypothalamus temperature and spinal cord temperature on urine formation and heat production were studied in conscious goats with chronically implanted thermodes. At neutral air temperature cooling hypothalamus or spinal cord induced a fall in urine volume and a rise in urine osmolality. This antidiuretic response was concurrent with a rise in heat production. Simultaneous occurrence of antidiuresis and increased heat production was also found after cessation of hypothalamic warming. At hot ambient temperature cooling hypothalamus affected neither urine formation nor heat production. Since hypothalamic cooling and spinal cord cooling produce identical effects on kidney function it is concluded that this response is linked to the complex cold defence activity as a whole. The predominent change of free water clearance is tentatively interpreted as caused by an increased ADH concentration in the blood during the cold defence activity.     

Effects of prostaglandin E1, E2, and F2α on isolated pial arteries of cat

Responses to prostaglandin (PG), E₁, E₂, and F_2α were studied on isolated feline middle cerebral arteries. At resting state PGF_2α produced strong dose-dependent contractions. PGE₂ elicited weak relaxations at low concentrations, followed by powerful contractions at higher doses. PGE₁ had little effect on resting pial vessels. The relative constrictory potency was PGF_2α > PGE₂ > PGE₁. During active tone, induced by administration of either potassium, norepinephrine, or 5-hydroxytryptamine, relaxations induced by PGE₁ were enhanced, whereas PGE₂-induced relaxations were unaffected. PGE₁ induced relaxations were more pronounced when the active tension had been produced by administration of PGF_2α than with either of the vasoactive amines or potassium. This study demonstrates the importance of smooth muscle tone, and by what means this is achieved, when examining the responses of PG's on cerebral blood vessels.     

Protection of the rat gastric mucosa by prostaglandin E2: Possible relation to stimulation of the alkaline secretion

Exogenous prostaglandins have specific protective effects on the gastric mucosa called cytoprotection which is proposed to be connected to the stimulatory effects of prostaglandins on the gastric nonparietal secretions. The protection by oral prostaglandin E₂ (PGE₂) against indomethacin-induced gastric erosions was studied in the rat, as was the effect on the protection of blocking the gastric alkaline secretion by acetazolamide. PGE₂ reduced dose-dependently the indomethacin gastric erosion formation, confirming previous results from others. Acetazolamide caused very little damage when given alone but potentiated the indomethacin erosion formation in a dose-related way. PGE₂ was less protective or without effect against lesions caused by indomethacin when given together with acetazolamide, but protection could be obtained by increasing the doses of PGE₂. Indomethacin and acetazolamide are both blockers of the gastric bicarbonate secretion, which is stimulated by PGE₂. The potentiation of indomethacin induced lesions by acetazolamide and the antagonistic actions between acetazolamide and PGE₂ on mucosal protection are compatible with the hypothesis that stimulation of the alkaline secretion is one mechanism of cytoprotection of the gastric mucosa by PGE₂.     

Differential modulation of T helper type 1 (Th1) and T helper type 2 (Th2) cytokine secretion by prostaglandin E2 critically depends on interleukin-2

Prostaglandin E₂ (PGE₂) favors T helper type 2 (Th2)-like cytokine secretion profiles in murine and human CD4⁺ T cells by inhibiting the production of the Th1-associated cytokines interleukin-2 (IL-2) and interferon-γ (IFN-γ) and up-regulating the production of the Th2-associated cytokines IL-4 and IL-5 in a dose-dependent way. However, the potent inhibition of IL-2 production by PGE₂ seems to be in contrast with the simultaneous up-regulation of IL-4 and IL-5 production, because the induction of these cytokines requires IL-2. We, therefore, investigated to which extent the net modulatory effect of PGE₂ is determined by the availability of IL-2. To this aim, we examined the effects of PGE₂ on the cytokine secretion profiles of a panel of human Th0 clones upon stimulation via different activation pathways, resulting either in high or low IL-2 production. The differential modulation of Th1 and Th2 cytokines by PGE₂ was observed only upon modes of stimulation resulting in high IL-2 production. When IL-2 production was low, PGE₂ inhibited the secretion of all four cytokines. These different modulation patterns were directly related to the IL-2 availability, because (i) neutralizing antibody to IL-2 abrogated the up-regulatory effect of PGE₂ on IL-4 and IL-5 secretion in experiments with high endogenous IL-2 levels, (ii) lack of differential cytokine modulation by PGE₂ in conditions with low levels of endogenous IL-2 could be restored with exogenous IL-2, and (iii) cell viability was comparable in all conditions. These results demonstrate that the net modulatory effect of PGE₂ on the cytokine secretion profile of T cells critically depends on the availability of IL-2. Since this parameter varies with the experimental conditions and the T cell population studied, this finding may explain why certain immune responses may be either up- or down-regulated by PGE₂ under different conditions.     

Observations on the thermoregulatory effects of preoptic warming in rats

Experimental warming of the preoptic-anterior hypothalamic area was used to evaluate behavioral and autonomic thermoregulatory heat-loss responses. Hypothalamic warming was associated with reduced behavioral heat intake and decreased core and peripheral temperatures in rats working for radiant heat reward in a cold environment. Baseline rates of responding for external heat were determined by ambient temperature, but the magnitude of changes in core or peripheral temperatures during preoptic warming were not. Behavioral responses compensated for variations in ambient temperature so that the threshold hypothalamic temperature above which heat loss was activated by preoptic warming was not altered by changing ambient temperatures. Heat loss during hypothalamic warming was a function of both autonomic and behavioral thermoregulatory responses because the decrease in body heat content during preoptic warming could not be accounted for by the decreased behavioral heat intake alone. The threshold hypothalamic temperature for elicitation of tail vasodilation decreased systematically as ambient temperature increased when no behavioral option was available. In the rat, both behavioral and autonomic thermoregulatory responses cooperate to determine the magnitude of heat loss which is proportional to the magnitude of preoptic warming.     

Renal degradation and distribution between urinary and venous output of prostaglandins E2 and I2

Renal degradation and distribution between urinary and venous output of prostaglandins E₂ and I₂ Acta Physiol Scand 130 , 467–474. Received 25 November 1986, accepted 11 February 1987. ISSN 0001–6772. University of Oslo, Institute for Experimental Medical Research, Ullevaal Hospital, Oslo, Norway. To examine renal degradation and distribution between urine and renal venous blood, prostaglandins E₂ and I₂ (PGE₂ and PGI₂), and a metabolite of PGI₂, bketo-PGF_1α, were infused into the suprarenal aorta of anaesthetized dogs after blocking prostaglandin synthesis by indomethacin, 10 mg kg^-1 body wt iv. During one passage through the kidney 80% of PGE, and only 25% of PGI₂ and 6-keto-PGF_1α, were metabolized. Prostaglandin degradation and arterial input were proportional (r > 0.90). To stimulate the intrarenal prostaglandin synthesis in unblocked kidneys, arachidonic acid was infused at rates ranging from 24 to 160 μg min^-1 kg^-1 body wt. During arachidonic acid and PGE₂ infusion the urinary excretion of PGE₂ was about 20% of the renal venous output over a wide range of infusion rates. During arachidonic acid and PGI₂ infusion urinary excretion of bketo-PGF_1α was about 10% of total renal output, but failed to increase further when total renal output exceeded 70 pmol min^-1. Further increase in output occurred only in the renal vein. In contrast, during 6-keto-PGF_1α infusion the urinary excretion and the renal venous output of this metabolite were related as 1:2 over a wide range of infusion rates. Thus, PGI₂ is much less degraded by renal tissue than PGE₂, and the distribution patterns differ. Similar distributions between urine and renal venous blood during aortic infusion and stimulated intrarenal synthesis suggest a pre-glomerular vascular origin of both prostaglandins.     

Effects of altering rostral brain stem temperature on temperature regulation in the Adelie penguin,Pygoscelis adeliae

Summary In 4 Adelie penguins, thermodes were implanted in the rostral brain stem. Two animals were additionally equipped with spinal canal thermodes. At thermoneutral (+ 8 to + 16°C) and cold (–18 to –22° C) ambient conditions, the effects of hypothalamic heating and cooling on the surface temperature of one flipper (skin blood flow), oxygen consumption (metabolic heat production) and esophageal (core) temperature were observed in the conscious animals.—Heating the rostral brain stem induced heat defence responses: Heat production was reduced in the cold and skin vasodilatation was evoked at thermoneutral ambient conditions. As a rule, core temperature fell during rostral brain stem heating.—Cooling the rostral brain stem did not induce clear-cut cold defence responses. On the contrary, strong cooling at thermoneutral ambient conditions induced vasodilatation in the skin. In the cold, even slight degrees of rostral brain stem cooling decreased metabolic heat production. As a rule, core temperature fell when the rostral brain stem was cooled.—It is concluded from the results that thermosensitive structures in the stimulated section of the rostral brain stem of the Adelie penguin contribute to the central temperature signal input in the range of normal to elevated core temperatures. These hypothalamic warm signals appear to be at least as effective as spinal warm signals in controlling skin blood flow and metabolic heat production. The inhibition of ongoing thermoregulatory effector activity by rostral brain stem cooling suggests positive temperature coefficients of the integrative and/or efferent neurons in the hypothalamic temperature regulation center of the Adelie penguin.A preliminary report was given at the 45th meeting (autumn meeting) of the Deutsche Physiologische Gesellschaft, Wien, Sept. 23–26, 1975. Pflügers Arch.359, R57 (1975).     

Safe cooling limits from exercise-induced hyperthermia

We evaluated the cooling rate of hyperthermic subjects, as measured by three estimates of deep core temperatures (esophageal, rectal and aural canal temperatures), during immersion in a range of water temperatures. The objective of the study was to compare the three indices of core temperature and define safe cooling limits when using rectal temperature to avoid the development of hypothermia. On 4 separate days, seven subjects (four males, three females) exercised for 45.4±4.1 min at 65% at an ambient temperature of 39°C, RH: 36.5%, until rectal temperature (T _re) increased to 40.0°C (39.5°C for two subjects). Following exercise, the subjects were immersed in a circulated water bath controlled at 2, 8, 14 and 20°C until T _re returned to 37.5°C. When T _re reached normothermia during the cooling period (37.5±0.05°C), both esophageal (T _es) (35.6±1.3°C) and aural canal (T _ac) (35.9±0.9°C) temperatures were approaching or reaching hypothermia, particularly during immersion in 2°C water (T _es=34.5±1.2°C). On the basis of the heat loss data, the heat gained during the exercise was fully eliminated after 5.4±1.5, 7.9±2.9, 10.4±3.8 and 13.1±2.8 min of immersion in 2, 8, 14 and 20°C water, respectively, with the coldest water showing a significantly faster cooling rate. During the immersion in 2°C water, a decrease of only 1.5°C in T _re resulted in the elimination of 100% of the heat gained during exercise without causing hypothermia. This study would therefore support cooling the core temperature of hyperthermic subjects to a rectal temperature between 37.8°C (during immersion in water >10°C) and 38.6°C (during immersion in water <10°C) to eliminate the heat gained during exercise without causing hypothermia.     

Central cardiovascular and thermal effects of prostaglandin E2 in rats1

Prostaglandin E₂ (PGE₂) increased the blood pressure, heart rate and body temperature, when administered at the doses of 0.001–10 μg into the lateral cerebral ventricle (i. c. v.) of the urethane-anesthetised rat. The highest dose of 10 μg/rat induced a strong initial hypotensive effect. Intravenously (i. v.), PGE₂ at the doses of 0.01–10 μg/rat caused a biphasic blood pressure response with dose-related initial decreases followed by slight increases in blood pressure. The heart rate and body temperature were slightly increased by i. v. administrations of PGE₂. The highest i. v. dose of 10 μg/rat initially decreased also the heart rate. Central pretreatment with indomethacin (1 mg/rat i. c. v.) partly antagonised all of the recorded central effects of PGE₂, while sodium meclofenamate (1 mg/rat i. c. v.) abolished the hypertensive response to i. c. v. administered PGE₂ but failed to significantly affect the PGE₂-induced rises of heart rate and body temperature. The results support the previous suggestions that PGE₂ may participate in the central cardiovascular and thermoregulatory control. The results also suggest that indomethacin and sodium meclofenamate antagonize the effects of exogenous prostaglandins. Since sodium meclofenamate, unlike indomethacin, affected preferentially the hypertensive response to centrally administered PGE₂, there may be differences in the sites and/or modes of action between these drugs.     

Weakening of the hyperthermic effect of prostaglandin E2 by cholinomimetics,monoamines, and calcium ions

Experiments on unanesthetized rats showed that the hyperthermic effect of prostaglandin E₂ (PG-E₂) is not prevented by aspirin, but can be considerably weakened by injection of arecoline, noradrenalin, serotonin, histamine, and CaCl₂ into the lateral ventricles of the brain or by intraperitoneal injection of eserine. Experiments on unanesthetized rabbits showed that arecoline and nicotine have a similar action on PG-E₂-induced hyperthermia if injected into the 3rd ventricle. Effects of serotonin and arecoline also were found when reinjected into the cerebral ventricles. In the center for heat loss there are evidently mechanisms which incorporate cholinergic neurons whose activity is not totally inhibited by prostaglandins.Department of Normal Physiology, Minsk Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov). Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 87, No. 2, pp. 168–171, February, 1979.     

Lansoprazole inhibits nitric oxide and prostaglandin E(2) production in murine macrophage RAW 264.7 cells

Aberrantly activated macrophages, which overproduce inflammatory mediators, are involved in the pathogenesis of many inflammatory diseases. We analyzed the anti-inflammatory activity of lansoprazole (LPZ), a typical proton pump (P-ATPase) inhibitor, on RAW264.7 murine macrophages. Treatment of lipopolysaccharide (LPS)-stimulated RAW264.7 cells with LPZ inhibited the production of nitric oxide (NO) and prostaglandin E₂ (PGE₂). Since P-ATPase expression was not observed in RAW264.7 cells, the anti-inflammatory effect of LPZ was independent of ATPase. In contrast, diphenylene iodonium (DPI), an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, decreased NO but not PGE₂ levels. LPZ suppressed the LPS-stimulated production by RAW264.7 cells of reactive oxygen species (ROS), which plays an important role in inflammatory responses. ROS elevation in these cells was associated with NO but not PGE₂ production, suggesting that LPZ inhibits NO production by suppressing NADPH oxidase activity. These findings suggest that LPZ may be useful in the treatment of many inflammatory diseases associated with activated macrophages.