Prostaglandin stimulation of gastrointestinal transit in post-operative ileus rats

The prostaglandins PGF_2α, PGE₂ and 16,16-dimethyl PGE₂, when administered intravenously, orally, subcutaneously or intraduodenally to laparotomized rats, decreased gastric emptying, small intestinal transit and colonic transit as compared to unoperated controls. All three prostaglandins increased colonic transit above that found with unoperated controls. This activity was independent of small intestinal fluid accumulation (i.e., enteropooling) since ligating the ileal-cecal junction had no effect on colonic transit. Small intestinal transit was increased, but not normalized, by PGE₂ and 16,16-dimethyl PGE₂. 16,16-Dimethyl PGE₂ completely restored gastric emptying when given intravenously to laparotomized rats at doses greater than 5.0 μg/kg. This effect on gastric emptying lasted approximately 4 hrs. Thus, 16,16-dimethyl PGE₂, when given intravenously, normalized gastric emptying, significantly increased small intestinal transit, and made the colon hypermotile. Prostaglandins may be beneficial in the treatment of post-operative ileus and other conditions of sluggish gastrointestinal propulsion.     

Partial characterization of the gastrointestinal weight changes produced in the female rat by 16,16-dimethylprostaglandin E2

Oral and subcutaneous administration of 16,16-dimethylprostaglandin E₂ (16,16-dimethyl PGE₂) resulted in an increase in the dry weight of the stomach and small intestine of the female rat. This weight response was rapid, controlled rather than continuously progressing, dose dependent and reversible. The dry weight of the colon also increased but this was not studied in detail.Two-day treatment with 16,16-dimethyl PGE₂ caused an increase in the incorporation of ³H-thymidine into the duodenum, jejunum and colon suggesting an increase in cell number. Incorporation into the stomach and ileum was not changed.The number of goblet cells per crypt was increased by prostaglandin treatment in all parts of the small intestine. Since these are mucus producing cells, the small intestine may have increased in cell number and mucus production.Both anti-secretory and cytoprotective doses of 16,16-dimethyl PGE₂ caused weight increases in the stomach and small intestine. However, the weight gain by itself was not sufficient to protect the stomach or small intestine from necrotic agents after the prostaglandin was discontinued.     

Effects of prostaglandin E2, 16,16-dimethyl prostaglandin E2 and a prostaglandin endoperoxide analogue (U-46619) on gastric secretory volume, [H] and mucus synthesis and secretion in the rat

The effects of orally administered prostaglandin E₂, 16,16-dimethyl prostaglandin E₂ and U-46619, an analogue of the prostaglandin endoperoxide PGH₂, on gastric secretory volume, acid and mucus were studied in the rat. All of the compounds significantly increased the volume of gastric secretion, mucus secretion, measured as N-acetylneuraminic acid and mucus synthesis measured as the incorporation of [³H]-glucosamine into mucosal glycoprotein; however, only PGE₂ and 16,16-dimethyl PGE₂ inhibited acid secretion. U-46619, 1.5 mg/kg provided significant protection against ethanol-induced gastric ulcers, an effect that has been previously shown for the other two compounds. These studies provide additional evidence that prostaglandin induced mucosal protection may by related to an effect on mucus and on stimulation of nonparietal cell gastric secretion. Further study of these parameters may be important in the development of antiulcer drugs for long term clinical use.     

Changes in thymidine uptake in the gastrointestinal tract of the rat following treatment with 16,16-dimethyl prostaglandin E2

Thymidine uptake in the organs of the gastrointestinal tract of the rat was studied to determine if cell synthesis was involved in the increases in weight of the stomach, small intestine and colon which result from treatment with 16,16-dimethyl prostaglandin E₂ (16,16-dimethyl PGE₂). Animals were treated for 2 days with 16,16-dimethyl PGE₂. They were injected with the ³H-thymidine, sacrificed and the organs of interest were removed. The total amount of tritium in the stomach, duodenum, jejunum, ileum, and colon was determined.Thymidine uptake was significantly increased in the duodenum (1.50 times), jejunum (1.53 times), and colon (1.40 times) but not in the stomach and ileum. The increases were dose related in the duodenum and jejunum. The colon showed a similar dose response pattern but the changes with dose did not reach significance.These results confirm and extend a previous report that 16,16-dimethyl PGE₂ increased thymidine uptake in the duodenum but not the stomach (1). This is different from gastrin which has been shown by others to increase thymidine uptake in the stomach, duodenum, ileum and colon (2,3).     

Sex differences in gastric mucosal protection after 16, 16-dimethyl PGE2 and lithium chloride

While the incidence of duodenal ulcer disease has been documented to be greater in men than in women, this observation has not been previously noted in animal studies of the upper gastrointestinal tract. In this study, we questioned whether the cytoprotective properties of 16, 16-dimethyl PGE₂ were sex-related by comparing the degree of ethanol-induced hemorrhagic gastritis in male and female rats pretreated with 16,16-dimethyl PGE₂ or lithium chloride. Animals receiving 16,16-dimethyl PGE₂ or lithium chloride had significantly less ethanol-induced hemorrhagic gastritis (1.17±0.15 and 1.24±0.13, respectively, p<0.001) when compared with controls (2.69±0.10). Female rats treated with 16,16-dimethyl PGE₂ had 59% less hemorrhagic gastritis than male rats treated similarly (0.76±0.14 vs 1.86±0.19 respectively, p<0.001). This sex-related difference in hemorrhagic gastritis was not noted in male and female rats receiving lithium chloride (1.24±0.15 vs 1.23±0.27, respectively). However, female rats treated with 16, 16-dimethyl PGE₂ had significantly less hemorrhagic gastritis when compared with female rats receiving lithium chloride (0.76±0.14 vs 1.24±0.15 respectively, p<0.05).These findings suggest that the protective properties of 16, 16-dimethyl PGE₂ are sex-related while those of lithium chloride are not.     

Prostaglandin analogues and uterotonic potency: A comparative study of seven compounds

The uterotonic potency of seven prostaglandin analogues has been investigated using the single intravenous injection technique and comparison of threshold uterine contractility achieved during continuous intravenous infusion. The degree and duration of uterine stimulation in response to graded doses of some of the analogues was also evaluated following intra-amniotic, oral and vaginal administration. 17-Phenyl substituted PGE₂ and PGF_2α are reported upon for the first time. Among the prostaglandin compounds tested, the free acid of 16,16-dimethyl PGE₂ not only is the most potent compound but it may also have great potential for clinical application as an easily administered vaginal abortifacient.     

PGE2 involvement in experimental infection with Trypanosoma cruzi subpopulations

PGE₂ involvement in experimental Trypanosoma cruzi infection depends on the lethal capacity of the parasite subpopulation used. Mice acutely infected with non-lethal K98 displayed an enhancement in PGE₂ serum levels during the acute period, while those infected with lethal T. cruzi subpopulations (RA or K98-2) showed levels not different from normal mice. The enhancement detected in K98 group could be related both to an increased number of CD8+ T cell number and to enhanced PGE₂ release per cell by CD8+; values of PGE₂ release by adherent cells were not altered in this group. Treatment with cyclooxygenase inhibitors enhanced mortality rates of mice infected with K98, and administration of 16,16-dimethyl PGE₂ (dPGE) reversed this effect. However, mice infected with RA did not reduce their mortality rates by administration of diverse doses of dPGE. These findings suggest that PGE₂ could play a role in resistance in mice infected with K98.     

The effects of PGF1α, PGE2 and 16,16 dimethyl PGE2 on gastric emptying and small intestinal transit in rat

Prostaglandins are well known for their ability to stimulate contraction in gastrointestinal smooth muscle, yet very little information is available on how their activity affects propulsion . Thus, studies were undertaken to determine the effect of various prostaglandins on qastric emptying (GE) and small intestinal transit (SIT) in unanesthetized fasted rats. Rats were treated with intravenous, subcutaneous, or oral PGF_2α, PGE₂, or 16,16 dimethyl PGE₂ at various doses, followed 1 (intravenous), 20 (subcutaneous) or 10 (oral) mins later by intragastric ⁵¹Cr oxide in black ink. Forty-five mins later, rats were sacrificed by CO₂ asphyxiation, the pylorus clamped, and the gut excised. SIT was expressed as the percent of intestinal length traveled by the most distal portion of ink. GE was expressed as the percent of the ⁵¹Cr emptied into the intestines. If GE was affected by prostaglandin treatment, the experiments were repeated with rats pre-implanted with duodenal cannula. This preparation allowed the visual transit marker to be deposited directly into the dueodenum, thus avoiding acceleration or delay of SIT caused by fluctuations in GE. The results of these studies show that: (1) intravenous 16,16 dimethyl PGE₂ (5–50 μg/kg), but not PGF_2α or PGE₂, accelerates GE and delays SIT; (2) oral prostaglandin administration increases SIT; (3) oral 16,16 dimethyl PGE₂ delays GE; (4) subcutaneous 16,16 dimethyl PGE₂ accelerates, has no effect upon, or delays GE depending upon dose, but accelerates SIT at all doses tested; and (5) subcutaneous PGE₂ accelerates SIT while PGF_2α does not. Thus, the effect of prostaglandins on GE and SIT depends upon the dosage and route of administration as well as type of prostaglandin used.     

In vitro modulation of human and murine melanoma growth by prostanoid analogues

The inhibitory effect of various prostaglandin analogues on the anchorage independent growth of murine and human melanoma cells was measured. PGA analogues (which were modified at C-16 and C-18) did not demonstrate any major improvement in activity over PGA alone. These included 16, 16-dimethyl PGA₁, 16,16-dimethyl-PGA₂, 16,16-dimethyl-18-oxa-PGA₂ and trans-δ-2-15-α acetoxy-16,16-dimethyl-18-oxa-11-deoxy-PGE₁-methylester. The thromboxane synthetase inhibitor, U51605, demonstrated weak anti-proliferative activity. PGD₂ (with a ketone at C-11 versus C-9 for PGA and PGE) was the most potent prostaglandin tested. Cells from melanoma lines displayed species differences in their sensitivities. PGA₁ and PGE₁ were the most potent inhibitors of the anchorage independent growth of murine melanoma cells. On human melanoma cells PGD₂ was the most active prostaglandin, 2–3 times more potent than PGA₁; PGE₁ was a very weak inhibitor.     

16,16-Dimethyl PGE2 and fatty acids protect hepatocytes against CCl4-induced damage

Summary 16,16-Dimethyl PGE₂ (dmPGE₂) has previously been shown to protect the in vivo rat liver against CCl₄-induced damage. These studies were undertaken to determine if this protection could be demonstrated in vitro where factors of absorption, secretion, and blood flow are not present. Primary hepatocyte cultures were established by perfusing rat liver with collagenase. Hepatocytes were plated at a density of 2×10⁴ cells/cm, allowed 90 min to attach, then stabilized in L15 medium for 18 h. Hepatocytes were then challenged with CCl₄ with concomitant exposure to 10⁻⁹ to 10⁻⁵ M dmPGE₂, stearic acid, oleic acid, or ethanol vehicle (0.00001 to 0.1%). After 1 h, challenge was aspirated and cells were stained with 0.04% trypan blue to determine viability. Hepatocytes in the vehicle groups took up more trypan when exposed to CCl₄ than those treated with dmPGE₂, stearic acid, or oleic acid at concentrations of 10⁻⁹ to 10⁻⁷ M. At 0.1% ethanol vehicle protected as well as all other treatments. Protection against CCl₄ by dmPGE₂, stearic, and oleic acids as well as high concentrations of ethanol may occur by altering the metabolism of CCl₄.     

Alpha-fetoprotein and serum hormone levels following liver intoxication with carbon tetrachloride

Rats were submitted to carbon tetrachloride intoxication at two different doses. Serum level of estradiol, progesterone, cortisol and thyroxin were measured by radioimmunoassays and correlated with the histological evidences of liver regeneration and serum alpha-fetoprotein levels. A two fold increase of progesterone was observed 48hrs after CCl₄ administration. Cortisol levels were moderately increased at both doses of CCl₄. Despite the five fold increase of alpha-fetoprotein (which is the major estradiol binding protein in these sera) no changes in estradiol levels were observed. Thyroxin levels showed a two fold increase after 72hrs. This result contrasts with the drop of this hormone after partial hepatectomy which has been previously published. These experiments show that a new hormonal imbalance (directly or indirectly due to the toxic) is involved both in liver regeneration and alpha-feto-protein synthesis.     

Marked inhibition of gastric secretion by two prostaglandin analogs given orally to man

Two prostaglandin analogs, 15(S)-15-methyl PGE₂, methyl ester, and 16, 16-dimethyl PGE₂ were administered to human volunteers for their possible effect in inhibiting gastric secretion. Both analogs, given orally, inhibited gastric secretion stimulated by pentagastrin, and the effect was dose dependent. The inhibition lasted for more than 4 hours, and no side-effects were noted at the doses used. When given intraduodenally, through a thin tube swallowed the night before, 15($\text{S}$)-15-methyl PGE₂, methyl ester was more active than 16, 16-dimethyl PGE₂. In view of their oral and prolonged activity, these analogs may have clinical potential in the treatment of peptic ulcer.     

Role of intracellular prostaglandin E2 in cancer-related phenotypes in PC3 cells

Prostaglandin E₂ (PGE₂) and hypoxia-inducible factor-1α (HIF-1α) affect many mechanisms that have been shown to play a role in prostate cancer. In PGE₂-treated LNCaP cells, up-regulation of HIF-1α requires the internalization of PGE₂, which is in sharp contrast with the generally accepted view that PGE₂ acts through EP receptors located at the cell membrane. Here we aimed to study in androgen-independent PC3 cells the role of intracellular PGE₂ in several events linked to prostate cancer progression. To this end, we used bromocresol green, an inhibitor of prostaglandin uptake that blocked the immediate rise in intracellular immunoreactive PGE₂ following treatment with 16,16-dimethyl-PGE₂. Bromocresol green prevented the stimulatory effect of 16,16-dimethyl-PGE on cell proliferation, adhesion, migration and invasion and on HIF-1α expression and activity, the latter assessed as the HIF-dependent activation of (i) a hypoxia response element-luciferase plasmid construct, (ii) production of angiogenic factor vascular endothelial growth factor-A and (iii) in vitro angiogenesis. The basal phenotype of PC3 cells was also affected by bromocresol green, that substantially lowered expression of HIF-1α, production of vascular endothelial growth factor-A and cell proliferation. These results, and the fact that we found functional intracellular EP receptors in PC3 cells, suggest that PGE₂-dependent intracrine mechanisms play a role in prostate cancer Therefore, inhibition of the prostaglandin uptake transporter might be a novel therapeutic approach for the treatment of prostate cancer.     

The potential effects of pomegranate (Punica granatum) juice on carbon tetrachloride-induced nephrotoxicity in rats

The purpose of this study was to evaluate the effect of pomegranate (Punica granatum) in inhibiting and reversing the nephrotoxicity of carbon tetrachloride, a potent oxidative stress inducer which induces cellular kidney damage. Rats were intraperitoneally injected with carbon tetrachloride (2 mL/kg body weight) which produced severe renal tissue damage, as demonstrated by decreased uric acid and dramatic elevation of urea and creatinine. In addition, carbon tetrachloride injection caused oxidative stress in rats, as evidenced by increased lipid peroxidation and nitrite/nitrate (NO _x ) concentrations in the renal tissue, along with a remarkable reduction in superoxide dismutase, catalase, glutathione transferase, glutathione reductase, glutathione peroxidase activities and glutathione content. We suggested that pomegranate juice was able to elevate the antioxidant defense system, clean up free radicals, lessen oxidative damages and protect the kidney against carbon tetrachloride-induced toxicity, thus having a potential protective effect.     

Synthesis and biological properties of 9-deoxo-16,16-dimethyl-9-methylene-PGE2

The in vivo monkey uterine stimulating potency of 9-deoxo-16,16-dimethyl-9-methylene-PGE₂ is similar to that of 16,16-dimethyl-PGE₂ and approximately 15 times that of PGE₂. Low doses of this compound stimulated uterine contractions when administered vaginally. Pregnancy was terminated prematurely following subcutaneous, intramuscular or vaginal suppository treatment. Estimates of potential for gastrointestinal side effects using the rat enteropooling assay and in vivo monkey effects indicate that diarrhea will be substantially reduced with retention of uterine stimulating potency.     

Hepatic protection by 16,16-dimethyl prostaglandin E2 (DMPG) against acute aflatoxin B1-induced injury in the rat

Studies were conducted to assess the possible protective action of 16,16-dimethyl prostaglandin E₂ (DMPG) against acute aflatoxin B₁ (AFB₁) induced hepatic injury in the rat. Evaluation of liver damage of histopathologic techniques and clinical chemistry indicated that hepatic necrosis was ameliorated by treatment with DMPG even though binding of radiolabeled (3H)-AFB₁ to hepatic DNA was unaffected by this prostaglandin. However, DMPG did not protect rats against AFB₁-induced mortality. These data suggest that hepatic protection by DMPG was due to mechanisms other than an interference with the activation or hepatic binding of AFB₁.     

Methylated analogues of prostaglandin E2 and the gastric mucosal barrier

15(R)-methyl PGE₂ methyl ester (15MPG) and 16,16-dimethyl PGE₂ methyl ester (16DMPG) were assessed for their effect on gastric mucosal permeability to Na⁺ and H⁺ in dogs prepared by antrectomy and vagally-denervated fundic pouches. 15MPG did not increase mucosal permeability to either ion when given topically (18.75 – 300 μg) or parenterally (30 μg), and did not affect permeability increases induced by topical 5mM sodium taurocholate in acid solution. 16DMPG caused significant increases in net Na⁺ gain when given topically (18.75 – 75 μg) but did not affect net H⁺ loss from the pouch lumen. Attempts to use higher doses of 16DMPG were abandoned because of bleeding from the pouch, and perforation in one animal. It is conceivable that 16DMPG could cause adverse effects on the gastric mucosal barrier if used to suppress gastric secretion therapeutically. 15MPG does not share this potentially harmful property and remains worthy of further study as an inhibitor of gastric secretion with therapeutic promise.     

Effect of indomethacin, tiaprofenic acid and dicrofenac on rat gastric mucosal damage and content of prostacyclin and prostaglandin E2

Gastric ulcerogenicity and depletion of endogenous prostaglandins (PGs) content induced by tiaprofenic acid, dicrofenac and indomethacin were examined using the same antiinflammatory effective doses. Male Wistar rats were given each of these drugs intragasrically 24, 18, and 3 hrs before sacrifice in the following doses (mg/kg): indomethacin (0.8, 4 and 20); tiaprofenic acid (1.2, 6 and 30); dicrofenac (0.8, 4 and 20). Endogenous prostacyclin (PGI₂) and PGE₂ in fundic mucosa were determined by radioimmunoassay. The three compounds produced fundic mucosal lesions in a dose-dependent manner. However, tiaprofenic acid and dicrofenac were both less potent than indomethacin in producing gastric mucosal lesions at similar antiinflammatory doses. Mucosal PGE₂ content was abolished by the three compounds in the following doses (mg/kg): indomethacin (4 and 20); tiaprofenic acid (6 and 30); dicrofenac (20). Mucosal PGI₂ was maintained around 50% of the control value in rats given tiaprofenic acid in a dose of 6 mg/kg or dicrofenac in a dose of 4 mg/kg, while indomethacin in a dose of 4 mg/kg markedly reduced mucosal PGI₂ to 17% of the control value. In larger doses, tiaprofenic acid and dicrofenac were also significantly less potent in reducing mucosal PGI₂ than idomethacin. These results suggest that the difference in ulcerogenicity between idomethacin and the other two compounds was closely related to their potency in decreasing PGI₂ in the gastric (fundic) mucosa.     

Autocrine prostaglandin E2 signaling promotes tumor cell survival and proliferation in childhood neuroblastoma

Background

Prostaglandin E₂ (PGE₂) is an important mediator in tumor-promoting inflammation. High expression of cyclooxygenase-2 (COX-2) has been detected in the embryonic childhood tumor neuroblastoma, and treatment with COX inhibitors significantly reduces tumor growth. Here, we have investigated the significance of a high COX-2 expression in neuroblastoma by analysis of PGE₂ production, the expression pattern and localization of PGE₂ receptors and intracellular signal transduction pathways activated by PGE₂.

Principal Findings

A high expression of the PGE₂ receptors, EP1, EP2, EP3 and EP4 in primary neuroblastomas, independent of biological and clinical characteristics, was detected using immunohistochemistry. In addition, mRNA and protein corresponding to each of the receptors were detected in neuroblastoma cell lines. Immunofluorescent staining revealed localization of the receptors to the cellular membrane, in the cytoplasm, and in the nuclear compartment. Neuroblastoma cells produced PGE₂ and stimulation of serum-starved neuroblastoma cells with PGE₂ increased the intracellular concentration of calcium and cyclic AMP with subsequent phosphorylation of Akt. Addition of 16,16-dimethyl PGE₂ (dmPGE₂) increased cell viability in a time, dose- and cell line-dependent manner. Treatment of neuroblastoma cells with a COX-2 inhibitor resulted in a diminished cell growth and viability that was reversed by the addition of dmPGE₂. Similarly, PGE₂ receptor antagonists caused a decrease in neuroblastoma cell viability in a dose-dependent manner.

Conclusions

These findings demonstrate that PGE₂ acts as an autocrine and/or paracrine survival factor for neuroblastoma cells. Hence, specific targeting of PGE₂ signaling provides a novel strategy for the treatment of childhood neuroblastoma through the inhibition of important mediators of tumor-promoting inflammation.