Role Of Endogenous Prostaglandins Research Articles

Exogenous and Endogenous Hydrogen Sulfide Protects Gastric Mucosa against the Formation and Time-Dependent Development of Ischemia/Reperfusion-Induced Acute Lesions Progressing into Deeper Ulcerations.

Hydrogen sulfide (H2S) is an endogenous mediator, synthesized from l-cysteine by cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) or 3-mercaptopyruvate sulfurtransferase (3-MST). The mechanism(s) involved in H2S-gastroprotection against ischemia/reperfusion (I/R) lesions and their time-dependent progression into deeper gastric ulcerations have been little studied. We determined the effect of l-cysteine, H2S-releasing NaHS or slow H2S releasing compound GYY4137 on gastric blood flow (GBF) and gastric lesions induced by 30 min of I followed by 3, 6, 24 and 48 h of R. Role of endogenous prostaglandins (PGs), afferent sensory nerves releasing calcitonin gene-related peptide (CGRP), the gastric expression of hypoxia inducible factor (HIF)-1α and anti-oxidative enzymes were examined. Rats with or without capsaicin deactivation of sensory nerves were pretreated i.g. with vehicle, NaHS (18–180 μmol/kg) GYY4137 (90 μmol/kg) or l-cysteine (0.8–80 μmol/kg) alone or in combination with (1) indomethacin (14 μmol/kg i.p.), SC-560 (14 μmol/kg), celecoxib (26 μmol/kg); (2) capsazepine (13 μmol/kg i.p.); and (3) CGRP (2.5 nmol/kg i.p.). The area of I/R-induced gastric lesions and GBF were measured by planimetry and H2-gas clearance, respectively. Expression of mRNA for CSE, CBS, 3-MST, HIF-1α, glutathione peroxidase (GPx)-1, superoxide dismutase (SOD)-2 and sulfide production in gastric mucosa compromised by I/R were determined by real-time PCR and methylene blue method, respectively. NaHS and l-cysteine dose-dependently attenuated I/R-induced lesions while increasing the GBF, similarly to GYY4137 (90 μmol/kg). Capsaicin denervation and capsazepine but not COX-1 and COX-2 inhibitors reduced NaHS- and l-cysteine-induced protection and hyperemia. NaHS increased mRNA expression for SOD-2 and GPx-1 but not that for HIF-1α. NaHS which increased gastric mucosal sulfide release, prevented further progression of acute I/R injury into deeper gastric ulcers at 6, 24 and 48 h of R. We conclude that H2S-induced gastroprotection against I/R-injury is due to increase in gastric microcirculation, anti-oxidative properties and afferent sensory nerves activity but independent on endogenous prostaglandins.

Gastroprotective activity of synthetic coumarins: Role of endogenous prostaglandins, nitric oxide, non-protein sulfhydryls and vanilloid receptors

Natural or synthetic coumarins showed gastroprotective and antiulcer activity in animal models. In this study, we have synthetized twenty coumarins using classic methods to evaluate their gastroprotective effects on the ethanol/HCl-induced gastric lesion model in mice at 20mg/kg. Among the coumarins synthetized, compounds 6 and 10 showed the greatest gastroprotective activity being as active as lansoprazole at 20mg/kg and reducing gastric lesions by 75 and 76%, respectively. Then, in a second experiment, compounds 6 and 10 were re-evaluated in order to understand the possible mode of gastroprotective activity. Regarding coumarin 6, the protective effect was reduced by pre-treatment of the mice with N-ethylmaleimide and l-NAME suggesting that sulfhydryl compounds and endogenous nitric oxide are involved in its gastroprotective activity. While for coumarin 10 the effect was reduced by pre-treatment with indomethacin suggesting that prostaglandins are positively involved in its gastroprotective activity.

Endogenous prostaglandins and afferent sensory nerves in gastroprotective effect of hydrogen sulfide against stress-induced gastric lesions.

Hydrogen sulfide (H2S) plays an important role in human physiology, exerting vasodilatory, neuromodulatory and anti-inflammatory effects. H2S has been implicated in the mechanism of gastrointestinal integrity but whether this gaseous mediator can affect hemorrhagic lesions induced by stress has been little elucidated. We studied the effect of the H2S precursor L-cysteine, H2S-donor NaHS, the H2S synthesizing enzyme (CSE) activity inhibitor- D,L-propargylglycine (PAG) and the gastric H2S production by CSE/CBS/3-MST activity in water immersion and restraint stress (WRS) ulcerogenesis and the accompanying changes in gastric blood flow (GBF). The role of endogenous prostaglandins (PGs) and sensory afferent nerves releasing calcitonin gene-related peptide (CGRP) in the mechanism of gastroprotection induced by H2S was examined in capsaicin-denervated rats and those pretreated with capsazepine to inhibit activity of vanilloid receptors (VR-1). Rats were pretreated with vehicle, NaHS, the donor of H2S and or L-cysteine, the H2S precursor, with or without the concurrent treatment with 1) nonselective (indomethacin) and selective cyclooxygenase (COX)-1 (SC-560) or COX-2 (rofecoxib) inhibitors. The expression of mRNA and protein for COX-1 and COX-2 were analyzed in gastric mucosa pretreated with NaHS with or without PAG. Both NaHS and L-cysteine dose-dependently attenuated severity of WRS-induced gastric lesions and significantly increased GBF. These effects were significantly reduced by pretreatment with PAG and capsaicin denervation. NaHS increased gastric H2S production via CSE/CBS but not 3-MST activity. Inhibition of COX-1 and COX-2 activity significantly diminished NaHS- and L-cysteine-induced protection and hyperemia. NaHS increased expression of COX-1, COX-2 mRNAs and proteins and raised CGRP mRNA expression. These effects of NaHS on COX-1 and COX-2 protein contents were reversed by PAG and capsaicin denervation. We conclude that H2S exerts gastroprotection against WRS-induced gastric lesions by the mechanism involving enhancement in gastric microcirculation mediated by endogenous PGs, sensory afferent nerves releasing CGRP and the activation of VR-1 receptors.

P47 Exogenous and endogenous hydrogen sulfide (H2S) in gastroprotection against ischemia/reperfusion lesions progressing into chronic ulcers. Role of endogenous prostaglandins, sensory neuropeptides and vanilloid receptors

H 2 S is an endogenous gasotransmitter which exerts vasodilatatory, neuromodulatory and anti-inflammatory activities but little is known whether this gaseous mediator affects ischemia–reperfusion (I/R)-induced gastric erosions. We studied the effect of H 2 S precursor, l -cysteine and H 2 S-donor, NaHS on I/R lesions induced by 30 min of I followed by 3 h of R and their progression into chronic gastric ulcers at 12–72 h after the end of I. Rats exposed to I/R received once daily (1) l -cysteine (2–40 mg/kg) and (2) NaHS (0.1–10 mg/kg i.g.) combined or not with the inhibitor of CSE, d , l -propargylglycine (PAG 30 mg/kg i.g.); (3) the non-selective (indomethacin; 5 mg/kg i.p.) or selective COX-1 (SC-560, 5 mg/kg i.p.) and COX-2 inhibitors (celecoxib 30 mg/kg i.g.); (4) blockade of sensory nerves by capsaicin (125 mg/kg s.c.) and the inhibition of vanilloid receptor (VR-1) by capsazepine (10 mg/kg i.g.). The number of gastric lesions was measured by planimetry, the gastric blood flow (GBF) determined by H 2 -gas clearance technique, the mucosal concentration of H 2 S was determined spectrophotometrically, the plasma IL-1beta and TNF-alpha were determined by ELISA and mRNA expressions for CSE, COX-1-, COX-2-, CGRP, IL-1beta-, and TNF-alpha were assessed by RT-PCR. I/R-induced gastric mucosal lesions progressed into gastric ulcers at 72 h following the end of I. The significant fall in the H 2 S concentration and GBF were observed in gastric mucosa of I/R and these effects persisted up to 72 h upon standard I/R. NaHS (5 mg/kg i.g.) and l -cysteine (20 mg/kg i.g.) which significantly increased H 2 S content in the gastric mucosa and GBF, significantly reduced I/R-induced gastric lesions area at 24 h and 72 h following end of I. Capsaicin denervation, capsazepine and treatment with COXs inhibitors exacerbated I/R injury and significantly reduced the GBF and these effects were reversed by co-treatment with CGRP (10 μg/kg s.c.) or dimethyl PGE 2 (5 μg/kg i.g.) in the presence of NaHS and cysteine in capsaicin-denervated or COX-1- and COX-2-inhibited animals. The mRNA expression for CSE and CBS was increased in I/R gastric mucosa and this was inhibited by NaHS and cysteine. We conclude that (1) pathogenesis of I/R injury involves the fall in the generation of H 2 S and (2) NaHS and cysteine protect the gastric mucosa against I/R lesions and accelerate the healing of these lesions progressing into gastric ulcers via an increase in GBF mediated by endogenous H 2 S, PG pathway and CGRP.

Gene expression of isoformic enzymes in arachidonate cyclooxygenase pathway and the regulation by tumor necrosis factor α during life cycle of adipocytes

Adipocytes serve not only as a storage depot of fats but also as endocrine cells secreting adipocytokines including tumor necrosis factor α (TNFα). Using preadipogenic 3T3-L1 cells, we attempt to determine the response of adipocytes at different stages of the life cycle to TNFα with respect to the gene expression of the arachidonate cyclooxygenase (COX) pathway and the role of endogenous prostaglandins (PGs). The gene expression analysis of the COX pathway revealed the marked increase in mRNA and protein levels of COX-2 in response to TNFα in preadipocytes, whereas COX-1 was expressed constitutively. Moreover, the cells at different cycle stages exhibited the specific gene expression of isoformic enzymes of prostaglandin (PG) synthases for PGs of the D 2, E 2, and F 2α series upon exposure to TNFα. The treatment of preadipocytes with TNFα along with calcium ionophore A23187 resulted in the stimulated formation of PGE 2 and PGF 2α, attenuating the apoptotic cell death induced by TNFα alone. The response of adipocytes to synthesize these PGs declined during the differentiation and maturation phases. The cells during the differentiation phase were the most sensitive to TNFα in terms of the decrease in adipogenesis without the mediation of endogenous PGs. TNFα was also effective in suppressing adipogenesis during the maturation process. Taken together, TNFα can control cell number of preadipocytes as well as the size of fat storage in mature adipocytes. The action of TNFα on preadipocytes can be modulated by the production of endogenous PGs through the induction of COX-2.

Roles of Endogenous Prostaglandins and Cyclooxygenase Isozymes in Healing of Indomethacin-Induced Small Intestinal Lesions in Rats

Roles of Endogenous Prostaglandins and Cyclooxygenase Isozymes in Healing of Indomethacin-Induced Small Intestinal Lesions in Rats

Roles of Endogenous Prostaglandins and Cyclooxygenase Isozymes in Healing of Indomethacin-Induced Small Intestinal Lesions in Rats

The role of prostaglandins (PGs)/cyclooxygenase (COX) in the healing of indomethacin-induced small intestinal ulcers was examined in rats. Animals were given indomethacin (10 mg/kg s.c.) and killed 1, 2, 3, 5, and 7 days later. Indomethacin (2 mg/kg), 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC560; COX-1 inhibitor; 3 mg/kg), and rofecoxib (COX-2 inhibitor; 3 mg/kg) were given p.o. once daily for 6 days, during the first 3 days or last 3 days of the experimental period. All COX inhibitors given for 6 days significantly impaired the healing of these ulcers. Healing was also impaired by rofecoxib given for the first 3 days or by SC560 given for the last 3 days. The expression of COX-2 mRNA in the intestine was up-regulated after ulceration, persisting for 3 days and dissipating thereafter. Mucosal PGE2 contents decreased within 3 h after ulceration, recovered 24 h later, and increased above normal 1 approximately 3 days later. The PGE2 content at 4 days after ulceration was decreased by rofecoxib but not SC560, whereas that at 7 days was suppressed by SC560 but not rofecoxib. Vascular content in the ulcerated mucosa decreased when the healing was impaired by COX inhibitors. The deleterious effect of indomethacin on healing was mimicked by a prostacyclin E receptor (EP) 4 antagonist and reversed by coadministration of PGE2 as well as an EP4 agonist. In conclusion, endogenous PGs play a role in the healing of intestinal ulcers through EP4 receptors, yet the COX isozyme involved differs depending on the stage of healing; COX-2 in the early stage and COX-1 in the late stage.

Effects of prostaglandins on form deprivation myopia in the chick.

To investigate the possible role of endogenous prostaglandins in the development of form deprivation myopia, as well as the effects of exogenous prostaglandins using atropine as a positive control. Monocular form deprivation was accomplished by mounting a translucent occluder on one eye of 2-3 day old chicks for 1-4 weeks. Ocular occlusion for 1-2 weeks was used for pharmacological blocking experiments. The axial length of the eye was measured by ultrasonography. Indomethacin, administered intramuscularly, subconjunctivally or intravitreally had no significant effect on myopia development. Exogenous PGE2, PGF2alpha and latanoprost acid administered subconjunctivally, or topically as isopropyl ester eyedrops had no statistically significant effect on the myopia development. However, PGF2alpha significantly (p<0.01) attenuated the development of myopia after intravitreal injection. The other two prostaglandins had no statistically significant effect. Endogenous prostaglandins are unlikely to play a significant role in the development of form deprivation myopia in the chick. However, PGF2alpha suprisingly seems to retard the development of form deprivation myopia, but only when administered intravitreally. Whether the mechanism of the myopia retardation is direct or indirect remains unknown.

Role of endogenous prostaglandins and nitric oxide in gastroduodenal ulcerogenic responses induced by hypothermic stress in rats

Role of endogenous prostaglandins and nitric oxide in gastroduodenal ulcerogenic responses induced by hypothermic stress in rats

P-538 - Roles of endogenous prostaglandins (PGs) and nitric oxide (NO) in gastroduodenal ulcerogenic responses induced in rats by hypothermic stress

P-538 - Roles of endogenous prostaglandins (PGs) and nitric oxide (NO) in gastroduodenal ulcerogenic responses induced in rats by hypothermic stress

Roles of endogenous prostaglandins and nitric oxide in inhibitions of gastric emptying and accelerations of gastrointestinal transit by escins Ia, Ib, IIa, and IIb in mice

We reported previously that escins Ia, Ib, IIa, and IIb, isolated from horse chestnuts, inhibited the 30-min gastric emptying (GE) in mice. In this study, the effects of escins Ia–IIb on gastrointestinal transit (GIT), and the roles of endogenous prostaglandins (PGs) and nitric oxide (NO) in the effects of escins Ia–IIb on GE and GIT were investigated in fasted mice. Escins Ia–IIb (12.5–50 mg kg , p.o.) dose-dependently accelerated GIT. Both GE inhibitions and GIT accelerations by escins Ia–IIb (25 mg kg ) were markedly attenuated by pretreatment with indomethacin (10 mg kg , s.c., an inhibitor of PGs synthesis). Pretreatment with N G-nitro-I.-arginine methyl ester ( lNAME, 10 mg kg , i.p., an inhibitor of constitutive and inducible NO synthase) attenuated the effects of escins Ia2ĪIb on GIT, but not on GE. The effect of l-NAME was reversed by l-arginine (600 mg kg , i.p., a substrate of NO synthase). but not by d-arginine (900 mg kg , i.p., the enantiomer of l-arginine). The GIT accelerations of escins Ia–IIb were not attenuated by pretreatment with d-NAME (10 mg kg , i.p., the enantiomer of l-NAME) or dexamethasone (5 mg kg , i.p., an inhibitor of inducible form of NO synthase). The results suggest that endogenous PGs play an important role in both GE inhibitions and GIT accelerations, and constitutive NO is involved in the GIT accelerations, by escins Ia–IIb in mice.

Activation of Vagal Afferents after Intravenous Injection of Interleukin-1β: Role of Endogenous Prostaglandins

Intravenous administration of interleukin-1 (IL-1) activates central autonomic neuronal circuitries originating in the nucleus of the solitary tract (NTS). The mechanism(s) by which blood-borne IL-1 regulates brain functions, whether by operating across the blood-brain barrier and/or by activating peripheral sensory afferents, remains to be characterized. It has been proposed that vagal afferents originating in the periphery may monitor circulating IL-1 levels, because neurons within the NTS are primary recipients of sensory information from the vagus nerve and also exhibit exquisite sensitivity to blood-borne IL-1. In this study, we present evidence that viscerosensory afferents of the vagus nerve respond to intravenously administered IL-1beta. Specific labeling for mRNAs encoding the type 1 IL-1 receptor and the EP3 subtype of the prostaglandin E2 receptor was detected in situ over neuronal cell bodies in the rat nodose ganglion. Moreover, intravenously applied IL-1 increased the number of sensory neurons in the nodose ganglion that express the cellular activation marker c-Fos, which was matched by an increase in discharge activity of vagal afferents arising from gastric compartments. This response to IL-1 administration was attenuated in animals pretreated with the cyclooxygenase inhibitor indomethacin, suggesting partial mediation by prostaglandins. In conclusion, these results demonstrate that somata and/or fibers of sensory neurons of the vagus nerve express receptors to IL-1 and prostaglandin E2 and that circulating IL-1 stimulates vagal sensory activity via both prostaglandin-dependent and -independent mechanisms.

Store-operated calcium influx in human gastric cells: Role of endogenous prostaglandins

Background: Store-operated calcium influx (SOCI) appears to be a key component in regulating processes such as gene expression and cellular metabolism in nonexcitable cells. Our objective was to determine what effect, if any, prostaglandin inhibition had on SOCI in human gastric cells. Methods: SOCI was induced in human gastric cells (AGS) with thapsigargin, a microsomal Ca ++ adenosine triphosphatase inhibitor. Quantitation of SOCI was achieved by two different methods: sustained intracellular calcium elevation and manganese (Mn ++) uptake. Endogenous prostaglandin E 2 (PGE 2) synthesis was measured by enzyme immunoassay. Three different nonsteroidal anti-inflammatory drugs (NSAIDs; indomethacin, ibuprofen, and aspirin) were used to minimize the nonspecific actions of any individual agent. Results: SOCI in AGS cells was inhibited by the store-operated Ca ++ channel blocker lanthanum (La +++) but not the voltage-operated Ca ++ channel antagonists verapamil or nifedipine. Each of the three NSAIDs equally inhibited SOCI. The inhibition of SOCI induced by indomethacin was partially reversed by the addition of exogenous PGE 2. Finally, AGS cells exposed to thapsigargin demonstrated significantly increased endogenous PGE 2 release. Conclusions: These data suggest that NSAIDs inhibit (or endogenous prostaglandins modulate) SOCI in human gastric cells, at least in part. Because SOCI appears to be a critical mechanism involved in cell proliferation, this may provide one explanation of how NSAIDs inhibit (and endogenous prostaglandins enhance) gastric epithelial renewal and repair. (Surgery 1998;124:429-37.)

Store-operated calcium influx in human gastric cells: Role of endogenous prostaglandins

Background: Store-operated calcium influx (SOCI) appears to be a key component in regulating processes such as gene expression and cellular metabolism in nonexcitable cells. Our objective was to determine what effect, if any, prostaglandin inhibition had on SOCI in human gastric cells. Methods: SOCI was induced in human gastric cells (AGS) with thapsigargin, a microsomal Ca++ adenosine triphosphatase inhibitor. Quantitation of SOCI was achieved by two different methods: sustained intracellular calcium elevation and manganese (Mn++) uptake. Endogenous prostaglandin E2 (PGE2) synthesis was measured by enzyme immunoassay. Three different nonsteroidal anti-inflammatory drugs (NSAIDs; indomethacin, ibuprofen, and aspirin) were used to minimize the nonspecific actions of any individual agent. Results: SOCI in AGS cells was inhibited by the store-operated Ca++ channel blocker lanthanum (La+++) but not the voltage-operated Ca++ channel antagonists verapamil or nifedipine. Each of the three NSAIDs equally inhibited SOCI. The inhibition of SOCI induced by indomethacin was partially reversed by the addition of exogenous PGE2. Finally, AGS cells exposed to thapsigargin demonstrated significantly increased endogenous PGE2 release. Conclusions: These data suggest that NSAIDs inhibit (or endogenous prostaglandins modulate) SOCI in human gastric cells, at least in part. Because SOCI appears to be a critical mechanism involved in cell proliferation, this may provide one explanation of how NSAIDs inhibit (and endogenous prostaglandins enhance) gastric epithelial renewal and repair. (Surgery 1998;124:429-37.)

Aspirin negates lipopolysaccharide (LPS) induced gastroprotection from ethanol

LPS stimulates gastric bicarbonate secretion and prevents gastric injury from acidified ethanol, possibly due to dilution and/or neutralization of this irritant. This study was conducted to determine the time course of LPS-induced alkaline secretion and its relationship with gastroprotection. The role of endogenous prostaglandins in gastroprotection was also examined. When compared to control conscious rats receiving saline, LPS (20 mg/kg IP) for 1, 2, or 3 hours, time dependently increased gastric luminal fluid accumulation (0A ± 0.08 vs. 0.55 ± 0.13, 2.1 ± 0,21, 2.6 ± 0.32 ml) and augmented gastric bicarbonate secretion (0.2 -+ 0.1 vs. 0.4 -+ 0.2, 1.6 ± 0.5, 2.3 ± 0.4 ~tEq). These LPS-induced effects were significantly (p -5/group) different from controls at 2 and 3 hours, but not at 1 hour. Thus, conscious rats received either saline or LPS for 1 hour and then were challenged with 1 ml of the luminal irritant acidified ethanol (150 mM HCI/50% ethanol) for 5 minutes. LPS reduced the magnitude of gastric mncosa involved with macroscopic damage (4.7 ± 1 vs. 15.3 ± 2%, p = 0.01) when analyzed by computerized planimetry. The gastroprotective effect of LPS was in turn negated by administration of the cyclooxygenase inhibitor aspirin (100 mg/kg IP) given 1 hour prior to LPS (14.4±2.6 vs. 4.5±0.1%, p=0.01). In the absence of acidified ethanol and using an enzyme linked immunoassay to measure endogenous prostaglandins, a 1-hour pretreatment with LPS also increased gastric mucosal levels of the prostacyclin metabolite, 6-keto-PGFla (1280±219 vs. 610~-186 pg/mg protein, p = 0.03) but did not enhance prostaglandin E 2 levels (2823 ± 437 vs. 2328 ± 230 pg/mg protein, p = NS) when compared to controls. Aspirin resulted in a 98% reduction in gastric mucosai prostaglandin levels. Consequently, these data suggest that LPSinduced gastroprotection cannot be fully explained by dilution as the protective response is present prior to any significant effect on bicarbonate secretion. Moreover, the mechanism responsible for this action is mediated in part by release of endogenous prostaglandins. This research was funded by NIGMS Grant GM 38529.

Interactive roles of endogenous prostaglandins and nitric oxide in gastric acid secretory response following damage

Interactive roles of endogenous prostaglandins and nitric oxide in gastric acid secretory response following damage

Adaptive cytoprotection against deoxycholate-induced injury in human gastric cells in vitro: is there a role for endogenous prostaglandins?

The majority of previous work investigating adaptive cytoprotection has involved in vivo studies, which have suggested that this protective response is in large part mediated by endogenous prostaglandins (PGs). The aim of this study was to investigate adaptive cytoprotection under in vitro conditions in human gastric cells and to better delineate the role of endogenous PGs in this protective response. AGS cells (a human gastric carcinoma cell line) were characterized morphologically and subsequently used for all experiments. Sodium deoxycholate was used as both the mild irritant and the damaging agent, and cell injury was quantified using both a commercial viability/cytotoxicity kit as well as transepithelial permeability studies. Finally, endogenous PG synthesis in response to varying concentrations of deoxycholate was determined. AGS cells were determined to be morphologically similar to gastric mucous cells. Pretreatment of cells with low-dose deoxycholate significantly attenuated injury upon subsequent exposure to damaging concentrations of deoxycholate, and this protection was determined to be dependent upon both concentration and duration of mild irritant exposure. Preincubation of AGS cells with indomethacin reversed protection induced by mild irritant pretreatment and also significantly increased cellular susceptibility to injury. Results of the permeability studies closely paralleled those assessing cell mortality. While deoxycholate exposure increased PG synthesis, the concentrations required were much higher than those needed to initiate protection. Adaptive cytoprotection exists in AGS cells under in vitro conditions independent of intact blood flow, neural innervation, or circulating humoral mediators. While this protection is reversed by indomethacin, it appears that this reversal results from increased cellular injury secondary to diminished basal PGs, rather than inhibition of endogenous PG synthesis.

Cyclooxygenase inhibition attenuates cholecystokinin-induced gastroprotection.

Cholecystokinin prevents gastric injury by an unknown mechanism. This study was conducted in conscious, fasted female rats in order to assess the role of endogenous prostaglandins as a potential protective mechanism for cholecystokinin-induced gastroprotection. Intravenous administration of cholecystokinin (0.05-5 nmol/kg) dose-dependently reduced macroscopic injury to the glandular portion of the stomach caused by 1 ml of orally administered acidified ethanol (150 mM hydrochloric acid-50% ethanol), an effect corroborated by histologic analysis. In time course studies, this protective action occurred as early as 10 min following cholecystokinin injection (5 nmol/kg intravenously), but was absent at 1 hr. Cyclooxygenase inhibition with either indomethacin (5 mg/kg intraperitoneally) or aspirin (100 mg/kg intraperitoneally) resulted in a partial reversal in cholecystokinin-induced gastroprotection, effects that were similar in magnitude. However, while indomethacin reduced gastric mucosal prostaglandin synthesis (enzyme-linked immunoassay) by 60%, aspirin almost totally abolished prostaglandin synthesis (95% reduction). Cholecystokinin (5 nmol/kg intravenously) did not significantly enhance gastric mucosal prostaglandin synthesis in the absence of cyclooxygenase inhibition. These data indicate that cholecystokinin requires the presence of endogenous prostaglandins in order to fully exert its gastroprotective actions. However, release of endogenous prostaglandins does not entirely explain the protective response, and additional factors likely participate in this action.

Effect of 50% Small Bowel Resection on Gastric Prostaglandin E 2 Levels in Rats

The mechanism for the production of increased gastric secretion following massive intestinal resection is not clearly defined. The loss of an intestinal inhibitor has been most frequently suggested to explain this hypersecretion. The role of endogenous prostaglandins which can inhibit gastric secretion is not established. The present study was undertaken to determine the effect of 50% proximal small bowel resection on Prostaglandin E 2 (PGE 2) levels in rat gastric mucosa. This study was performed in 30 rats divided into three groups. The first group of rats served as unoperated controls, the second group was sham operated and the third group underwent 50% resection of proximal small intestine. The PGE 2 levels in rat gastric mucosa was decreased significantly (p < 0.001) in the resection group (422.85 ± 7.66 pg/gm) as compared with the sham group (478.77 ± 7.25 pg/gm) and the control group (493.38 ± 4.61 pg/gm). Total gastric acidity was increased significantly (p llt 0.001) in the resection group (63.05 ± 2.64 mEq/L) as compared with the sham group (15.21 ± 0.99 mEq/L) and the control group (17.19 ± 0.80 mEq/L). The PGE 2 levels and total gastric acidity were not significantly changed in either the control or sham operation groups (p > 0.05). The results suggest that endogenous prostaglandin synthesis has a regulatory role in gastric hyperacidity after 50% proximal small bowel resection in rats.

Signal transduction pathways in modulation of ciliary beat frequency by methacholine.

The release of endogenous neurotransmitters plays an important role in the airway mucosal defense system. We studied the in vitro effect of methacholine, a beta-methyl ester of acetylcholine, on the ciliary beat frequency (CBF) of human adenoid explants and its mechanism of action. Tissue explants were cultured at 35 degrees C and covered with 1.0 mL of culture medium: minimum essential Eagle's medium (MEM) containing L-arginine (1.2 x 10(-3) mol/L). Methacholine was added to the cultured tissue at concentrations of 10(-10), 10(-8), and 10(-6) mol/L. The CBF was determined by phase contrast microscopy and microphotometry. Methacholine increased CBF in a dose-dependent manner with a maximum increase of 23.0% +/- 1.8% (p < .001). Atropine (10(-6) mol/L) significantly inhibited the ciliostimulatory effects of methacholine (p < .0007). The role of endogenous prostaglandins in methacholine-induced ciliostimulation was determined by treating specimens with a cyclooxygenase inhibitor (diclofenac sodium). Diclofenac (10(-6) mol/L) significantly inhibited the ciliostimulatory effects of methacholine (p < .0007). To determine if nitric oxide (NO) acts as an intermediary in ciliostimulation by methacholine, endogenous NO production was inhibited by treating specimens with an L-arginine analog, NG-nitro-L-arginine methyl ester (L-NAME), prior to addition of methacholine. L-NAME (10(-6) mol/L) inhibited the effects of methacholine in L-arginine-free MEM (p < .008), and this inhibition was reversed by L-arginine (10(-3) mol/L). To further examine the actions of NO in methacholine-induced ciliostimulation, a cyclic guanosine 3'5'-monophosphate (cGMP) kinase inhibitor (KT-5823) was used, prior to the addition of methacholine. KT-5823 (10(-6) mol/L) significantly inhibited the effects of methacholine (p < .0001). Ciliostimulation by methacholine in human upper airway mucosa involves both prostaglandin and NO second messengers and activation of a cGMP-dependent kinase.