Endogenous PGs Research Articles

Discovery, characterization and clinical utility of prostaglandin agonists for the treatment of glaucoma.

Topical ophthalmic formulations of analogues of the endogenous arachidonic acid cyclooxygenase metabolite, PGF2α , are the standard of care treatment for the blinding disease glaucoma. These are the most potent and efficacious medical therapies for lowering intraocular pressure (IOP), the most important risk factor identified for disease progression. They have few side effects and offer the convenience of once-a-day dosing. It was initially believed that endogenous PGs raised IOP and caused substantial ocular surface adverse effects. However, carefully designed experiments demonstrated that esterification of the carboxylic acid afforded potent and efficacious topical ocular hypotensive activity. The final hurdle to be overcome was improvement of the side effect profile. A hypothesis was advanced that the IOP-lowering effect of PGF2α isopropyl ester was due to activation of its cognate PG-FP receptor, while side effects were largely due to promiscuous interaction with other PG receptors. This hypothesis was validated by modification of the ω chain (carbons 13-20) to a phenyl group. This provided the first marketed FP-class PG agonist analogue (FP-PGA) ocular hypotensive agent, latanoprost. Since the introduction of latanoprost into clinical medicine to lower and control IOP, a number of additional FP-PGAs have been discovered, characterized and marketed, including travoprost, tafluprost, unoprostone isopropyl ester and bimatoprost (an amide). LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

Roles of prostaglandin E2-EP1 receptor signaling in regulation of gastric motor activity and emptying

It is widely accepted that the inhibition of gastric motor activity as well as the maintenance of gastric mucosal blood flow and mucous secretion are important for the homeostasis of the gastric mucosa. The present study was performed to ascertain whether or not endogenous PGs, which can protect the stomach from noxious stimuli, affect gastric motor activity and emptying. The myoelectrical activity of rat gastric smooth muscle was increased at intragastric pressures of over 2 cmH(2)O. Replacement of intragastric physiological saline with 1 M NaCl solution significantly increased PGI(2) and PGE(2) in stomach and suppressed the myoelectrical activity under a pressure of 2 cmH(2)O by 70%. Indomethacin inhibited the suppression of myoelectrical activity by 1 M NaCl. The myoelectrical activity under a pressure of 2 cmH(2)O was suppressed by continuous infusion of a selective EP1 agonist (ONO-DI-004, 3-100 nmol·kg(-1)·min(-1)) into the gastric artery in a dose-dependent manner, but not by that of the PGI receptor agonist beraprost sodium (100 nmol·kg(-1)·min(-1)). Suppression of myoelectrical activity with 1 M NaCl was inhibited by continuous infusion of a selective EP1 antagonist (ONO-8711, 100 nmol·kg(-1)·min(-1)) into the gastric artery. Furthermore, gastric emptying was tested in EP1 knockout mice and their wild-type counterparts. Gastric emptying was strongly suppressed with intragastric 1 M NaCl in wild-type mice, but this 1 M NaCl-induced suppression was not seen in EP1 knockout mice. These results suggest that PGE(2)-EP1 signaling has crucial roles in suppression of myoelectrical activity of gastric smooth muscles and inhibition of gastric emptying and that EP1 is an obvious target for drugs that control gastric emptying.

W1715 Effect of Carbon Monoxide/Heme Oxygenase On Duodenal HCO3- Secretion in Rats

Background/Aims: Carbon monoxide (CO) with free iron and biliverdin are generated from degradation of heme catalyzed by constitutive heme oxygenase (HO-2) and inducible HO1. Particularly, HO-1 is recognized as the stress protein, which is up-regulated by various stresses and exerts a protective action against tissue injury. By the way, HCO3secretion is one of protective mechanisms in the duodenum against acid stress. However, no information is available concerning the relation of HO-1/CO with HCO3secretion. In the present study, we examined the effect of a CO donor on HCO3secretion in the rat duodenum and investigated whether HO-1 is involved in the physiological regulation of this secretion. Methods: Male SD rats were used after 18 h fasting. Under urethane anesthesia, a proximal duodenal loop was perfused with saline, and HCO3secretion was measured at pH 7.0 using a pH-stat method. CORM-2 (a CO donor; 0.5-2 mM), biliverdin (10 mg/ml) or ruthenium (III) chloride (Ru; a negative control; 5 mM) was applied to the loop for 5 min. Mucosal acidification was performed by exposing the loop to 10 mM HCl for 10 min. Acetazolamide (an inhibitor of CA), indomethacin or L-NAME (a NOS inhibitor) was given SC 1 h or 3 h before the administration of agonists, while SnPP (an inhibitor of HO), CuPP (a negative inhibitor) or hemin was given IP 1 h before. Expression of HO protein was examined by western blot. Results: Topical application of CORM-2 significantly increased duodenal HCO3secretion in a concentration dependent manner, while neither Ru nor biliverdin have any effect. The stimulatory effect of CORM-2 was significantly attenuated by indoemthacin and acetazolamide but not L-NAME. The secretion of HCO3was increased by acidification of the mucosa, in an indomethacin-inhibitable manner. The acid-induced HCO3response was also markedly inhibited by SnPP but not CuPP. Furthermore, the inhibitory effect of SnPP was significantly reversed by the pretreatment with hemin. On the other hand, perfusion of the duodenal loop with 100 mM HCl for 2 h caused hemorrhagic lesions, and this response was significantly worsened by the prior administration of SnPP as well as indomethacin. In addition, the expression of HO-1 but not HO-2 protein was markedly up-regulated in the duodenum following acid perfusion for 4 h. Conclusions: These results suggest that CO stimulates HCO3secretion in the duodenum, and this effect is mediated by endogenous PGs and partly dependent on CO2 generated from the reaction of CO with O2. It is assumed that HO-1 plays an important role in maintaining the integrity of the duodenal mucosa when the tissue is exposed to acid stress.

Stimulatory effect of Coca-ColaTM on gastroduodenal HCO3− secretion in rats

We examined the effect of various carbonated beverages, especially Coca-ColaTM, on the HCO3− secretion in the rat stomach and duodenum. Under urethane anaesthesia, a chambered stomach or a proximal duodenal loop was perfused with saline, and HCO3− secretion was measured at pH 7.0 using a pH-stat method and by adding 2 mM HCl. The amount of CO2 contained in these beverages was about 4–7 g/mL. Coca-ColaTM topically applied to the mucosa for 10 min significantly increased the HCO3− secretion in both the stomach and the duodenum. The HCO3− response in the duodenum was totally abolished by indomethacin and also partially inhibited by acetazolamide, an inhibitor of carbonic anhydrase. Likewise, the response in the stomach was also markedly inhibited by either acetazolamide or indomethacin. The mucosal application of Coca-ColaTM increased the PGE2 contents in both the stomach and the duodenum. Other carbonated beverages, such as sparkling water, Fanta GrapeTM or cider, also increased the HCO3− secretion in these tissues. These results suggest that Coca-ColaTM induces HCO3− secretion in both the stomach and the duodenum, and these responses may be attributable to both the intracellular supply of HCO3− generated via carbonic anhydrase, and endogenous PGs, probably related to the acidic pH of the solution.

Uterine region-dependent differences in responsiveness to prostaglandins in the non-pregnant porcine myometrium

To clarify the uterine region-dependent distribution of prostanoid receptors, we compared the mechanical responses to selective prostanoid receptor agonists (FP, EP 3, DP, EP 2) and naturally occurring prostaglandins (PGF 2α, PGE 2, PGD 2) in longitudinal and circular muscles isolated from three different regions (cornu, corpus and cervix) of the non-pregnant porcine uterus. Expression levels of FP receptor and cyclooxygenase (COX-1 and COX-2) in the respective regions were also examined using RT-PCR and Western blotting. The contractile responses to fluprostenol (an FP agonist) and PGF 2α in both longitudinal and circular muscles were strongest in the cornu but weak in the corpus and cervix. Expression levels of mRNA and protein of FP receptor were highest in the cornu, consistent with the contractile responses. ONO-AE-248 (an EP 3 agonist) caused contraction of both muscle layers, but region-related difference in responsiveness was observed only in the longitudinal muscle. ONO-AE1-259 (an EP 2 agonist) inhibited spontaneous contraction of the myometrium, and inhibition was conspicuously stronger in the cervix. PGE 2 caused contraction (<100 nM, cornu > corpus = cervix) and inhibition (>300 nM, cornu = corpus ≦ cervix) of contractility depending on the concentration in both muscle layers. BW245C (a DP agonist) inhibited the spontaneous contraction, and region-dependent different responsiveness was marked in the longitudinal muscle (cervix = corpus > cornu). COX-1 but not COX-2 was detected in the non-pregnant porcine uterus. Expression level of COX-1 was different in the longitudinal muscle (cornu > corpus = cervix) but the same in the circular muscle. SC-560 inhibited the spontaneous contraction of longitudinal muscles in all regions. The results of the present study indicate that there are region-related heterogeneous distributions of contractile (FP and EP 3, cornu > cervix) and relaxant (EP 2 and DP, cervix > cornu) prostanoid receptors and COX-1 in the porcine uterus. The results also suggest involvement of endogenous PGs in the regulation of spontaneous uterine contractility. Region-related differences in COX-1 and prostanoid receptors might be necessary to produce a gradient of uterine motility decreasing from the cornu to the cervix that manages movement of luminal contents.

Environmental and endogenous peroxisome proliferator-activated receptor gamma agonists induce bone marrow B cell growth arrest and apoptosis: interactions between mono(2-ethylhexyl)phthalate, 9-cis-retinoic acid, and 15-deoxy-Delta12,14-prostaglandin J2.

The common commercial use of phthalate esters has resulted in significant human exposure to these bioactive compounds. The facts that phthalate ester metabolites, like endogenous PGs, are peroxisome proliferator-activated receptor (PPAR) agonists, and that PPARgamma agonists induce lymphocyte apoptosis suggest that phthalate esters are immunosuppressants that could act together with PGs to modulate early B cell development. In this study we examined the effects of a metabolite of one environmental phthalate, mono(2-ethylhexyl)phthalate (MEHP), and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), on developing B cells. MEHP inhibited [(3)H]thymidine incorporation by primary murine bone marrow B cells and a nontransformed murine pro/pre-B cell line (BU-11). Cotreatment with a retinoid X receptor alpha ligand, 9-cis-retinoic acid, decreased [(3)H]thymidine incorporation synergistically, thereby implicating activation of a PPARgamma-retinoid X receptor alpha complex. These results were similar to those obtained with the natural PPARgamma ligand 15d-PGJ(2). At moderate MEHP concentrations (25 or 100 microM for primary pro-B cells and a pro/pre-B cell line, respectively), inhibition of [(3)H]thymidine incorporation resulted primarily from apoptosis induction, whereas at lower concentrations, the inhibition probably reflected growth arrest without apoptosis. Cotreatment of bone marrow B cells with 15d-PGJ(2) and MEHP significantly enhanced the inhibition of [(3)H]thymidine incorporation seen with MEHP alone, potentially mimicking exposure in the bone marrow microenvironment where PG concentrations are high. Finally, MEHP- and 15d-PGJ(2)-induced death does not result from a decrease in NF-kappaB activation. These data demonstrate that environmental phthalates can cooperate with an endogenous ligand, 15d-PGJ(2), to inhibit proliferation of and induce apoptosis in developing bone marrow B cells, potentially via PPARgamma activation.

Mild irritant prevents ethanol-induced gastric mucosal microcirculatory disturbances through actions of calcitonin gene-related peptide and PGI2in rats

Pretreatment with a mild irritant such as 1 M NaCl prevented ethanol-induced mucosal injury, which was abolished by indomethacin, suggesting involvement of endogenous PGs. With the use of intravital microscopy, we investigated the mechanism in microcirculation whereby a mild irritant prevents ethanol-induced mucosal injury. Microcirculation of the basal part of gastric mucosa in anesthetized rats was observed through a window with transillumination. Diameters of arterioles, collecting venules, and venules were measured with an electric microscaler. One molar NaCl alone caused dilation of arterioles and constrictions of collecting venules and venules, which were inhibited by indomethacin. Ethanol (50%) applied to mucosa constricted collecting venules and venules but dilated arterioles. Constriction of collecting venules resulted in mucosal congestion. Pretreatment with 1 M NaCl inhibited ethanol-induced constrictions of collecting venules and venules, and administration of indomethacin or a calcitonin gene-related peptide (CGRP) antagonist, CGRP-(8-37), abolished elimination of constrictions. Topical application (1 nM-10 microM) of PGE2 or beraprost sodium (a PGI2 analog) to microvasculature markedly and dose-dependently dilated arterioles, whereas that of PGE2, but not beraprost, slightly constricted collecting venules. Pretreatment of microvasculature with a nonvasoactive concentration of PGE2 (100 nM) or beraprost (1 nM) completely inhibited ethanol-induced constriction of collecting venules. The inhibitory effect of beraprost but not of PGE2 was abolished by CGRP-(8-37). Present results suggest that the mechanism whereby 1 M NaCl prevents ethanol-induced injury is elimination of constrictions of collecting venules and venules by CGRP whose release may be enhanced by PGI2 but not by PGE2.

PG-mediated closure of paracellular pathway and not restitution is the primary determinant of barrier recovery in acutely injured porcine ileum.

Small bowel epithelium is at the frontline of intestinal barrier function. Restitution is considered to be the major determinant of epithelial repair, because function recovers in parallel with restitution after acute injury. As such, studies of intact mucosa have largely been replaced by migration assays of cultured epithelia. These latter studies fail to account for the simultaneous roles played by villous contraction and paracellular permeability in recovery of barrier function. NSAIDs result in increased intestinal permeability and disease exacerbation in patients with inflammatory bowel disease (IBD). Thus we examined the reparative attributes of endogenous PGs after injury of ileal mucosa by deoxycholate (6 mM) in Ussing chambers. Recovery of transepithelial electrical resistance (TER) from 20-40 Omega.cm2 was abolished by indomethacin (Indo), whereas restitution of 40-100% of the villous surface was unaffected despite concurrent arrest of villous contraction. In the presence of PG, resident crypt and migrating epithelial cells were tightly apposed. In tissues treated with Indo, crypt epithelial cells had dilated intercellular spaces that were accentuated in the migrating epithelium. TER was fully rescued from the effects of Indo by osmotic-driven collapse of the paracellular space, and PG-mediated recovery was significantly impaired by blockade of Cl- secretion. These studies are the first to clearly distinguish the relative contribution of paracellular resistance vs. restitution to acute recovery of epithelial barrier function. Restitution was ineffective in the absence of PG-mediated paracellular space closure. Failure of PG-mediated repair mechanisms may underlie barrier failure resulting from NSAID use in patients with underlying enteropathy.

Targeted disruption of cftr increases the resistance of duodenal epithelial cells to luminal acid challenge in mice

indomethacin-sensitive manner. In lP (-/-) mice, however, the HCOf secretion was similarly increased in response to acid but not capsaicin. By contrast, the acid-induced duodenal HCO3 secretion was profoundly mitigated in EP3 (4-) mice while capsaicin increased the HCO3 secretion in these knockout mice. In addition, cicaprost, the PG12 agonlst, increased HCO3 secretion in both WT ( + / + ) and EP3 (4-) mice, but this response disappeared in IP (4-) animals. Conclusion: The presence of EP3 but not IP receptors is essential for acidinduced duodenal HCOf secretion in mice, although activation of 1P receptors results in stimulation of the HCOf secretion. In contrast, the capsaicin-induced HCO3 secretion is dependent on endogenous PGs and requires the presence of IP but not EP3 receptors. It is assumed that both acidand capsaicin-induced HCOf secretion depend on the afferent neurons, yet the mode of their interaction with the afferem neurons may be different regarding the PGI2/IP receptor dependency.

Prostaglandin EP receptor subtypes and gastric cytoprotection

This article reviews recent studies dealing with the relationship between the cytoprotective action of PGE2 and the EP receptor subtypes in the gastric mucosa. Gastric cytoprotection afforded by PGE2 was mimicked by EP1 agonists and attenuated by the EP1 antagonist. Likewise, the adaptive cytoprotection induced by a mild irritant was attenuated by the EP1 antagonist and indomethacin. By contrast, capsaicin-induced protection was mitigated by indomethacin as well as sensory deafferentation but not by the EP1 antagonist. PGE2 failed to provide both direct and adaptive cytoprotection in EP1-receptor knockout mice, while capsaicin-induced protection was observed in the animals lacking either EP1 or EP3 receptors but disappeared in IP receptor knockout mice. We conclude that PGs, either generated endogenously or administered exogenously, exhibit gastric cytoprotection directly through activation of EP1 receptors, and endogenous PGs also contribute to the mucosal protection induced by capsaicin by sensitizing sensory neurons, probably through IP receptors.

Indomethacin impairs LPS-induced behavioral fever in toads.

We tested the hypothesis that PGs mediate lipopolysaccharide (LPS)-induced behavioral fever in the toad Bufo paracnemis. Measurements of preferred body temperature (T(b)) were performed with a thermal gradient. Toads were injected intraperitoneally with the cyclooxygenase inhibitor indomethacin (5 mg/kg), which inhibits PG biosynthesis, or its vehicle (Tris) followed 30 min later by LPS (0.2 and 2 mg/kg) into the lymph sac. LPS at the dose of 0.2 mg/kg caused a significant increase in T(b) from 7 to 10 h after injection, and then T(b) returned toward baseline values. LPS at the dose of 2 mg/kg produced a different pattern of response, with a longer latency to the onset of fever (10th h) and a longer duration (until the end of the experiment at the 15th h). Tris significantly attenuated the fever induced by LPS at 0.2 mg/kg, but not at 2 mg/kg. Moreover, indomethacin completely blocked the fever evoked by LPS (2 mg/kg). These results indicate that the behavioral fever induced by LPS in toads requires the activation of the COX pathway, suggesting that the involvement of PG in fever has an ancient phylogenetic history and that endogenous PGs raise the thermoregulatory set point to produce fever, because behavioral thermoregulation seems to be related to changes in the thermoregulatory set point.

Lipids and nitric oxide in porcine retinal and choroidal blood vessels.

Lipid profiles of porcine retina, and retinal and choroidal vessels were analyzed using the gas chromatography/mass spectrometry (GC/MS) technique. The retina and both isolated retinal and choroidal vessels contained saturated fatty acid stearic acid and polyunsaturated fatty acids, including arachidonic (C20:4, AA), a precursor for vasoactive prostaglandin (PG-2) series, and W-6 docosahexaenoic acids (C22:6, DHA). However, eicosapentaenoic acid (C20:5, EPA), a precursor for PG-3 series, was not detected in these vessels. When stearic acid was used for normalization of tissue sample, the retina contained relatively higher amounts of DHA than AA, retinal vessels had equal amounts of AA and DHA, while choroidal vessels contained higher amounts of AA than DHA. We also examined the endogenous synthesis of vasoactive endothelial-derived factors like PGs and nitric oxide (NO). Since vasoactive angiotensin II (Ang II) releases these products from blood vessels, this polypeptide was used in a porcine retinal circulation model. The porcine retinal central artery was perfused with oxygenated/heparinized physiological salt solution at 37 degrees C. Changes in A1 and A2 arteriolar diameters induced by Ang II were determined in the absence and presence of the nitric oxide synthase inhibitor, l-NO Arginine (LNOA), and cyclooxygenase inhibitor, flurbiprofen (FB). The central retinal artery designated as the first order arteriole A1 and subsequent branch was defined as A2. Luminal diameters of Al and A2 arterioles were 35 +/- 2 am and 10 +/- 1 microm, respectively. Topical Ang II (10(-10) M-10(-6) M) caused small vasoconstrictions in a dose-dependent manner. This response was enhanced after inhibition of PG synthesis by (10-6 M) FB. Ang II induced-constrictions were further enhanced in the presence of NO synthase inhibitor, LNOA (10(-7) M). There was slightly more increase in Ang II-induced vasoconstrictions in the presence of both NO and PG inhibitors, suggesting that NO may cause release of PGs from these vessels. This study demonstrates that the porcine retinal arterioles have the ability to regulate vasoconstriction responses induced by Ang II by synthesis and release of endogenous vasodilating PGs and NO (especially NO); and these substances may play a vital role in porcine retinal circulation.

Tissue hypoxia inhibits prostaglandin and nitric oxide production and prevents ductus arteriosus reopening.

Regulation of ductus arteriosus (DA) tension depends on a balance between oxygen-induced constriction and PG and nitric oxide (NO)-mediated relaxation. After birth, increasing Pa(O(2)) produces DA constriction. However, as the full-term ductus constricts, it develops severe tissue hypoxia in its inner vessel wall (oxygen concentration <0.2%). We used isolated rings of fetal lamb DA to determine why the constricted ductus does not relax and reopen as it becomes hypoxic. We used a modification of the 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide (EF5) technique (Clyman RI, Chan CY, Mauray F, Chen YQ, Cox W, Seidner SR, Lord EM, Weiss H, Wale N, Evan SM, and Koch CJ. Pediatr Res 45: 19-29, 1999) to determine mean tissue oxygen concentration. A decrease in the ductus' mean tissue oxygen concentration from 1.4 to 0.1% lowers the isometric tone of the ductus by 15 +/- 10% of its maximal active tension (the maximal tension that can be produced by the ductus). Although decreases in oxygen concentration diminish ductus tension, most of the vasoconstrictor tone in the ductus is independent of ambient oxygen concentration. This oxygen-independent tone is equivalent to 64 +/- 10% of the maximal active tension. At mean tissue oxygen concentrations >0.2%, endogenous PGs and NO inhibit more than 40% of the active tension developed by the ductus. However, when tissue oxygen concentrations drop below 0.2%, the constitutive relaxation of the ductus by endogenous PGs and NO is lost. In the absence of PG and NO production, tension increases to a level normally observed only after treatment of the ductus with indomethacin and nitro-L-arginine methyl ester (inhibitors of PG and NO production). Therefore, under conditions of severe hypoxia (tissue oxygen concentration <0.2% oxygen), the loss of PG- and NO-mediated relaxation more than compensates for the loss of oxygen-induced tension. We hypothesize that this increased ductus tone enables the vessel to remain closed as it undergoes tissue remodeling.

Cyclooxygenase-2 selective inhibitors aggravate kainic acid induced seizure and neuronal cell death in the hippocampus

Cyclooxygenase-2 (COX-2) in the brain is expressed constitutively and also increased in pathological conditions such as seizure, cerebral ischemia, and inflammation. This study examined the role of COX-2 in kainic acid-induced seizure and in the following neuronal death by using selective inhibitors. Systemic kainate injection (50 mg/kg; i.p.) in mice evoked seizure within 15 min and led to 29% mortality within 2 h. TUNEL-positive neuronal death peaked at 3 days after injection and was prominent in CA 3a regions of the hippocampus. NS-398 or celecoxib (10 mg/kg, COX-2 selective inhibitor) and indomethacin (5 mg/kg, nonselective inhibitor) exaggerated kainic acid-induced seizure activity and mortality. COX-2 selective inhibitors induced the seizure at earlier onset and more severe mortality within the first hour than indomethacin and aspirin. NS-398 also aggravated kainic acid-induced TUNEL positive neuronal death and decreased Cresyl violet stained viable neurons, and extended lesions to CA 1 and CA 3b. Kainic acid increased the levels of PGD 2, PGF 2a and PG E 2 in the hippocampus immediately after injection. Indomethacin attenuated the production of basal and kainic acid-induced prostaglandins. In contrast, NS-398 failed to reduce until the first 30 min after kainic acid injection, during which the animals were severely seizured. It has been challenged the endogenous PGs might have anticonvulsant properties. Thus, COX-2 selective inhibitor, including nonselective inhibitor such as indomethacin, aggravated kainic acid-induced seizure activity and the following hippocampal neuronal death even with variable prostaglandin levels.

Effects of selective cyclooxygenase-2 inhibitors on alkaline secretory and mucosal ulcerogenic responses in rat duodenum

Effects of the selective cyclooxygenase-2 (COX-2) inhibitors such as NS-398 and nimesulide on duodenal HCO 3 − secretory and ulcerogenic responses to mucosal acidification were examined in rats, in comparison with indomethacin, a nonselective COX inhibitor. Duodenal HCO 3 − secretion in anesthetized rats was increased in response to mucosal acidification. The increased HCO 3 − response to acid was significantly suppressed by pretreatment with indomethacin (10 mg kg −1, s.c.), while both NS-398 and nimesulide (10 mg kg −1, s.c.) had no effect on this response. The luminal release of prostaglandin E2 (PGE2) was increased during and after mucosal acidification, and this response was significantly inhibited by indomethacin but not NS-398 or nimesulide. Indomethacin provoked hemorrhagic lesions in the duodenum when acid hypersecretion was concomitantly induced by histamine (8 mg kg −1 hr −1, i.V.), while either NS-398 or nimesulide did not cause damage in the duodenum. Either of these drugs had no effect on histamine-induced acid secretion. On the other hand, both NS-398 and nimesulide showed a significant suppression against carrageenan-induced rat paw edema, similar to indomethacin. The present study supports a mediator role for endogenous PGs in duodenal HCO 3 −1 secretion in response to mucosal acidification and suggests that COX-1 but not COX-2 is a key enzyme in regulating this process and maintaining the mucosal integrity against acid in the duodenum.

Prostaglandin F 2αand its Analogs Induce Release of Endogenous Prostaglandins in Iris and Ciliary Muscles Isolated from Cat and Other Mammalian Species

Prostaglandin F 2α(PGF 2α) and its analog latanoprost are effective in lowering intraocular pressure (IOP) in both animal and human subjects. There is mounting experimental evidence now which indicates that the IOP-lowering effect of these PGs occurs through an increased uveoscleral outflow of aqueous humor. The ciliary muscle constitutes the main resistance in this pathway. Work from several laboratories, including our own, has shown that in this smooth muscle PGF 2αhas little effect on cAMP accumulation or on Ca 2+mobilization. In the present study, we hypothesized that some of the effects of PGF 2αand its analogs may be mediated through the release of endogenous PGs. The purpose of this work was to determine whether or not PGF 2αand its analogs can enhance the release of endogenous PGs in iris and ciliary muscles isolated from different species. This report documents for the first time that exogenous PGF 2αand its analogs, PhXA85 and latanoprost, stimulate the formation of PGE 2, PGD 2and PGF 2αin iris and ciliary muscles isolated from cat, bovine, rabbit, dog, rhesus monkey and human. PG-induced PG release was demonstrated by means of both radioimmunoassay and radiochromatography. Kinetic studies on cat iris revealed that PGF 2α-induced PGE 2release is time ( t 1 2=1.7 min) and dose-dependent (EC 50=45 n M). The increase in PGE 2release was blocked by indomethacin (Indo) and by dexamethasone in a dose-dependent manner with IC 50s of 9.2 n Mand 2.6 μ m, respectively. Furthermore, dexamethasone inhibited arachidonic acid (AA) release, suggesting the involvement of phospholipase A 2in PGF 2α-induced PG release. The data presented demonstrate that PGF 2αand its analogs interact with the PG receptor to stimulate phospholipase A 2and release AA for PG synthesis. Relaxation of ciliary muscle by PGF 2αand its analogs, via release of endogenous PGE 2, a potent activator of the adenylate cyclase system, could in part explain how these PGs may increase uveoscleral outflow and consequently lower IOP.

Inhibitory action of 5-hydroxytryptamine on propulsive activity of the guinea-pig isolated colon

The effects of 5-hydroxytryptamine (5-HT) and its receptor subtype agonists on spontaneous propulsive activities of the segment, and on changes in tension of the muscle strips were examined in the guinea-pig isolated distal colon. 5-HT, 5-carboxamidotryptamine (5-CT), α-methyl-5-HT and t-methoxytryptamine (5-MeOH), applied to the serosal side of the segment, inhibited spontaneous propulsive activities, but 2-methyl-5-HT did not. On the indomethacin-treated segment, 5-HT and its receptor subtype agonists all stimulated propulsive activity. 5-HT, 5-CT, α-methyl-5-HT and 5-MeOH relaxed circular muscle strips, which were inhibited in the presence of tetrodotoxin. However, these agonists showed contractile effects on the indomethacin-treated circular muscle strips. These results suggest that 5-HT may inhibit spontaneous propulsive activities of the colonic segment via release of endogenous PGs (e.g., E and I types) in the circular muscle cells mediated by an inhibitory neurotransmitter, which release was stimulated by 5-HT 1-like 5-HT 2; and 5-HT 4 receptors on the myenteric neurones in the circular muscle layer.

Prostaglandin-induced changes and the influence of cyclo-and lipoxygenase inhibitors on the uterine collagen concentration in late pregnancy in rats.

During late pregnancy, the influence of PGF2 alpha and PGE2 on the collagen concentration in a rat's uterus was analysed. In order to evaluate the influence of endogenous prostaglandins and leukotrienes on connective tissue metabolism, a cyclooxygenase inhibitor (Diclofenac) and a dual cyclo-and 5-lipoxygenase inhibitor (BW755C) were administered prior to the collection of samples. Total collagen and its soluble fraction as well as water content were determined in the uteri in a population of 58 pregnant rats treated with PGF2 alpha (n = 16), PGE2 (n = 11), Diclofenac (n = 11), BW755C (n = 7) and controls (n = 13). The most evident changes in tissue hydration and collagen concentration were observed in the PGF2 alpha and Diclofenac treated groups. The results clearly show the affinity of PGF2 alpha to the uterus and the role of endogenous PGs in the maintenance of pregnancy by influencing connective tissue metabolism.

Eicosanoids and radiation.

radiotherapy depends on the tolerance of the critical normal tissue within the radiation field. Consequently, any attempt to improve the efficacy of radiotherapy must be aimed at increasing tumour radioresponse and/or reducing normal tissue complications. To achieve this objective, many diverse approaches have been investigated, including modulation of levels of eicosanoids, especially prostaglandins (PCs), in both normal tissues and tumours. Eicosanoids are produced in response to a variety of cellular injuries, and exogenous eicosanoids have been shown to modulate injury induced by a wide array of agents. Therefore, it was logical to infer their involvement in tissue injury by ionising radiation. During the past 20 years, there has been significant research into the role of eicosanoids, primarily PGs, in radiation damage. Attempts have been made to modulate normal tissue damage by administering exogenous PGs or inhibiting endogenous PGs. Other studies have been conducted to increase tumour response to radiation by modulating PG levels in tumours. This overview considers major fmdings on the role of eicosanoids in the expression and modification of radiation damage, with special emphasis on its therapeutic potential. EICOSANOIDS Eicosanoids is a collective term for PGs, thromboxanes (TXs), leucotrienes (LTs), and various hydroxy and hydroperoxy fatty acids. They are metabolites of polyunsaturated fatty acids, such as arachidonic acid, and are produced by virtually all tissues via the cycle-oxygenase (for PGs and TXs) and lipoxygenase (for LTs) pathways. These end products of the arachidonic acid cascade are bioactive substances; for example, there is an array of PGs: PGEi, PGE2, PGF,,, PGD*, PGIz (prostacyclin), etc., each exhibiting different biological actions. It is no wonder then that eicosanoids display an astonishingly wide range of pharmacological, physiological, and pathological effects. They play a regulatory role in many physiological homeostatic processes including immunomodulation, vasomotility (constriction and dilatation) and platelet aggregation, along with regulating

Effects of H-89, an inhibitor of protein kinase A, on the acetylcholine release from myenteric plexus of guinea pig ileum.

In order to clarify the involvement of cyclic AMP-dependent protein kinase (protein kinase A) in acetylcholine (ACh) release from myenteric plexus of guinea pig ileum, the effect of H-89, a specific inhibitor of protein kinase A, on the ACh release was investigated. H-89 (0.1-10 microM) inhibited the spontaneous and nicotine-induced release of ACh in a concentration dependent manner. It at 1 microM decreased both kinds of release of ACh to almost half of the control, but it did not affect the ACh release evoked by electrical field stimulation and by 5-hydroxytryptamine. H-89 had no significant effect on the indomethacin (IND), an inhibitor of PG synthesis, -insensitive component of the spontaneous and nicotine-induced release of, ACh. OP-41483, an analog of PGI2 and forskolin, an activator nicotine-induced release of, ACh. OP-41483, an analog of PGI2 and forskolin, an activator of adenylate cyclase, reversed the inhibitory effect of IND on the ACh release. H-89 at 1 microM completely inhibited the reverse effects of OP-41483 and forskolin. These results suggest that activation of protein kinase A is essential for modulation of the nicotine-induced and spontaneous ACh release from myenteric plexus of guinea pig ileum and the activity of protein kinase A is regulated by endogenous PGs via intracellular cyclic AMP level.