Relation between prostaglandin E2, F2α, and cyclic nucleotides levels in rat brain and induction of convilsions

Fully convulsant doses of pentamethylenetetrazole cause marked increase in rat brain cortical PGF_2α, PGE₂, cGMP and cAMP during seizures, whereas subconvulsant doses cause an increase of rat brain cortical PGF_2α without affecting the other biochemical parameters considered. Rat cerebellar prostaglandins were not modified by the convulsant agent at either dosage.     

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.     

Effects of 9-deoxo-16, 16-dimethyl-9-methylene PGE2 on muscle contractile activity and collagen synthesis in the human cervix

The in vitro effects of a stable PGE-analogue (9-deoxo-16, 16-dimethyl-9-methylene PGE₂ (9-methylene PGE₂) on human cervical tissue was investigated. The influence of the analogue on collagen biosynthesis was studied by measuring the incorporation of ³H-proline, while smooth muscle effects were evaluated by isometric recording of contractile activity. The specimens were obtained by needle biopsy from women in early and late pregnancy and from nonpregnant women of fertile age.9-methylene PGE₂ compared with controls increased the incorporation of ³H-proline in the secretory phase and before the 9th week of pregnancy, whereas radiolabelling was decreased in the follicular phase, in the 9th–12th week and at term. With respect to incorporation of 3-H-proline, 9-methylene PGE₂ was equipotent to PGE₂. 9-methylene PGE₂ inhibited spontaneous contractile activity in early as well as in late pregnancy but increased muscular activity in nonpregnant patients. The inhibitory effects of the analogue was similar to that of PGE₂ but the natural compound was considerably more potent in this respect.     

Antiabsorptive effects of 16, 16 dimethyl prostaglandin E2 and isolated rat colon

Ulcerative colitis is distinguished by abundant prostaglandin E₂ (PGE₂) in the stools and by severe diarrhea. To determine whether luminal PGE₂ alters normal colonic absorption, Na⁺ and Cl⁻transport across isolated rat proximal colon were studied before and after 16, 16 dimethyl PGE₂ (dmPGE₂) addition to flux chambers. Luminal administration of dmPGE₂ significantly reduced the net mucosal to serosal fluxes of Na⁺ and Cl⁻. These antiabsorptive tive effects of dmPGE₂ on Na⁺ and Cl⁻ active transport were reflected by a reduced metabolic rate of colonic tissue slices incubated with dmPGE₂. Addition of dmPGE₂ significantly reduced oxidation of glucose by the colon. Structurally, dmPGE₂ reduced the length of colonic mucosal microvilli, thereby decreasing absorptive surface area. These results suggest that PGE₂ released into the colonic lumen of patients with ulcerative colitis exerts antiabsorptive effects on the colon and in this way contributes to the associated diarrhea.     

Effect of Prostaglandins on Hepatic Cyclic Nucleotide Concentration,Carbohydrate and Lipid Metabolism

The effects of exogenous prostaglandin E₁ (PGE₁) or prostaglandin E₂ (PGE₂) were studied in the isolated perfused rat liver and in the intact canine liver in order to determine the possible physiological role of prostaglandins on hepatic carbohydrate and lipid metabolism. The data indicate that PGE₁ and PGE₂ did not stimulate cyclic AMP (cAMP) and cyclic GMP (cGMP) concentrations in intact dog liver and PGE₁ failed to stimulate cAMP or cGMP in fed or fasted perfused rat liver. PGE₁ did not promote hyperglycemia, glycogenolysis, lipolysis, or prevent epinephrine-induced hyperglycemia in the isolated perfused rat liver. Other known glycogenolytic agents including glucagon and epinephrine increased cAMP and glycogenolysis in the same perfusion system. This study does not support a physiologic role for PGE₁ on hepatic glycogenolysis or lipolysis. If PGE₁ subsequently is found to influence other metabolic parameters such as lipogenesis, gluconeogenesis, ureogenesis or amino acid transport in isolated perfused liver, such alterations would probably occur independent of changes in cyclic nucleotide activity.     

16, 16 Dimethyl prostaglandin E2 reduces histamine release from the stomach and protects the gastric mucosal barrier altered by ethanol in neutral solution

Damage to the gastric mucosal barrier results in histamine release from intramucosal stores. Previous reports have shown that 16, 16 dimethyl prostaglandin E₂ (dm PGE₂) protects the stomach from injury by various damaging agents in either acidic or neutral solution. Furthermore histamine released in response to a damaging drug in an acidic medium was reduced by dm PGE₂. Using the Heidenhain pouch dog preparation, the present study examined the action of dm PGE₂ on ethanol-induced barrier breaking and histamine release in neutral solution. Topical ethanol treatment (15% w/v) damaged the gastric mucosal barrier as evidenced by increased net fluxes of Na+ and K+ and an increase in the histamine content of the fluid irrigating the Heidenhain pouch. Intravenous injection of dm PGE₂ in the doses of 0.01, 0.10 and 1.00 μg/kg one-half hour before ethanol administration significantly reduced the appearance of Na+, K+ and histamine. It is concluded that dm PGE₂ effectively protects the canine gastric mucosa from damaging agents in neutral solution as evidenced by a reduction in the luminal appearance of Na+, K+ and histamine.     

Synthesis of (±)-16-thioketal and 16-keto prostaglandins

The synthesis of ((±)-16-thioketal and 16-keto PGE₂ methyl ester ( and ) is herein described.     

Simultaneous extraction and assay of cyclic nucleotides, prostaglandins, and DNA from cat alveolar bone

A method for the simultaneous extraction of cAMP, cGMP, PGE₂, PGF_2α, and DNA from a small sample of mineralized bone and the subsequent assay of these substances is described. Various solvents were tested for efficiency of extraction for the fatty acids, and water or 40% ethanol was found to extract more than 90% of labeled prostaglandin. In order to avoid enzymatic degradation, the substances were extracted at ?5°C requiring a solvent which would not freeze during extraction. Frozen alveolar cat bone samples were homogenized in 40% ethanol in the presence of 5 mm EDTA to inhibit phosphodiesterase. Small aliquots of the homogenate were withdrawn for the spectrofluorophotometric assay of DNA. After centrifugation, the supernatant was extracted first with petroleum ether, in order to take out neutral lipids, followed by ethyl acetate partition. The ethyl acetate layer was dired with N₂ gas, reconstituted with assay buffer, and assayed for PGE₂ and PGF_2α. A portion of the aqueous fraction was used for cAMP binding assay, while the rest was column chromatographed to elute the cGMP for radioassay. On the basis of per microgram of DNA, values for each of the following in cat alveolar bone were: 0.346 ± 0.049 pmol for cAMP, 0.026 ± 0.001 pmol for cGMP, 5.52 ± 1.46 pg for PGE₂, and 1.00 ± 0.29 pg for PGF_2α. Values calculated after the dilution of the sample aliquots or addition of standards to cAMP, cGMP, or PGE₂ showed no significant difference (P < 0.05) to their respective values. Within the limits of the sensitivity for each of the assay systems, it is feasible to measure cAMP, cGMP, PGE₂, and PGF_2α in alveolar bone from the same sample.     

Abortifacient action of orally administered 16, 16 dimethyl prostaglandin E2 and its methyl ester

16, 16 dimethyl Prostaglandin E₂ (Free acid and methyl ester) administered orally have a stimulant effect on the pregnant human uterus. Pregnancy was terminated in twelve out of twenty women by two hourly oral doses of 100μg of these analogues The relatively high incidence of gastrointestinal side effects — nausea, vomitting and diarrhoea — would tend to limit the usefulness of orally administered 16, 16 dimethyl PGE₂ and its methyl ester as abortifacients.     

Effect of prostaglandins on cyclic nucleotide levels in cultured keratinocytes

Guinea pig ear epidermal cells (keratinocytes) were established in primary cultures using trypsin, and treated in their proliferative phase of growth with prostaglandins E₁, D₁, F_1α, E₂, D₂, or F_2α. This phase is induced by the addition of retinoic acid during cell plating. Intracellular content of cAMP and cGMP was measured by radioimmunoassay at various times after treatment.Maximum stimulation of cAMP levels was observed with PGD₂, smaller increases with PGE₂ and relatively transient rises with PGF_2α which were of low significance, but confirm earlier data. Similar results were observed with PGD₁, PGE₁, and PGF_1α with smaller increases. The effects of D and E PGs were biphasic. Significant increases in cGMP were immediately observed with PGD₂ and PGE₂. With PGF_2α, maximum cGMP levels were noted after some delay.All PGs tested showed some effect in elevating cyclic nucleotides in keratinocytes. The most striking result was the increase in cAMP on PGD₂ treatment.     

Inhibition by 16, 16-dimethyl PGE2 of ethanol-induced gastric mucosal damage and leukotriene B4 and C4 formation

The effects of PGE₂ and its stable analogue, 16, 16 dimethyl PGE₂ (dmPGE₂) were investigated on ethanol-induced gastric mucosal haemorrhagic lesions and leukotriene formation in the rat. Exposure of the rat gastric mucosa to ethanol , produced a concentration-related increase in the mucosal formation of leukotriene B₄ (LTB₄) which was correlated with macroscopically-apparent haemorrhagic damage to the mucosa. Challenge with absolute ethanol likewise enhanced the mucosal formation of LTC₄ whereas the mucosal formation of 6-keto-PGF_1α was unaffected. Challenge of the rat gastric mucosa with ethanol induced a concentration-dependent increase in the formation of LTB₄ and LTC₄, but not 6-keto PGF_1α. Pretreatment with PGE₂ (200–500μg/kg p.o.) prevented the haemorrhagic mucosal damage induced by oral administration of absolute ethanol but not the increased formation of leukotrienes by the mucosa. In contrast, pretreatment with a high dose of dmPGE₂ (20μg/kg p.o.) prevented both the gastric mucosal lesions and the increase mucosal leukotriene formation. The differences in the effects of these prostaglandins may be related to the nature or degree of protection of the gastric mucosa. Thus, high doses of dmPGE₂ but not PGE₂ may protect the cells close the luminal surface of the mucosa and hence reduce the stimulation of leukotriene synthesis by these cells.     

Synthesis and gastric antisecretory properties of allenic 16-phenoxy-omega-tetranor prostaglandin E analogs

In order to improve the modest oral activity of PGE₂ as an inhibitor of gastric acid secretion, analogs were prepared and tested orally in histamine-challenged rats. Insertion of a double bond at C-4, resulting in the 4,5-allene analog of PGE₁, gave a small increase in activity. Introduction of the ω-tetranor-16-phenoxy lower sidechain, a modification know to enhance activity in the PGF series, gave an eight-fold increase in activity. The analog having both modifications (enprostil, ) showed a six hundred-fold increase in oral antisecretory activity over PGE₂, which may reflect a potentiation effect. Modification of enprostil at C-1 (various esters) and at C-11 (11-methyl, 11-deoxy) generally resulted in compounds of high activity while modifications at other sites generally resulted in significant reductions in activity.     

Production of arachidonic acid metabolites by operationally defined macrophage subsets

The antitumor activity and arachidonic acid metabolism of operationally defined macrophage populations was examined. Macrophages from mice injected with (strain BCG) or with pyran-copolymer were cytotoxic for tumor cells. The major arachidonic acid metabolite of these cells was PGE₂. Neither resident nor elicited macrophages were cytotoxic. However, elicited macrophages as well as macrophages from BCG injected mice inhibited tumor cell growth. The production of arachidonic acid metabolites by elicited cells, while low initially, was followed by a rapid increase in PGE₂. The major metabolites of resident cells were PGE₂ and prostacyclin. The cAMP:cGMP ratio correlated with the metabolic activity of the cells.     

Structure activity studies leading to a tissue-selective hypotensive prostaglandin analog, 13,14-dihydro-16-phenyl-ω-tetranor PGE2

During our systematic search for prostaglandins with improved tissue selectivity and metabolic stability, we synthesized a series of PGE₂ analogs in which the n-amyl carbinol side chain was systematically substituted by a phenyl ring, based on structural considerations incorporating the 17,18-cis-double bond of PGE₃ into an aromatic ring. These compounds were evaluated for uterine stimulant, bronchodilator and hypotensive activity. Among the divergent biological profiles exhibited by these analogs, noteworthy was the tissue-selective hypotensive profile displayed by 13,14-dihydro-16-phenyl-ω-tetranor PGE₂.     

Direct Melanoma Cell Contact Induces Stromal Cell Autocrine Prostaglandin E2-EP4 Receptor Signaling That Drives Tumor Growth,Angiogenesis, and Metastasis

The stromal cells associated with tumors such as melanoma are significant determinants of tumor growth and metastasis. Using membrane-bound prostaglandin E synthase 1 (mPges1^−/−) mice, we show that prostaglandin E₂ (PGE₂) production by host tissues is critical for B16 melanoma growth, angiogenesis, and metastasis to both bone and soft tissues. Concomitant studies in vitro showed that PGE₂ production by fibroblasts is regulated by direct interaction with B16 cells. Autocrine activity of PGE₂ further regulates the production of angiogenic factors by fibroblasts, which are key to the vascularization of both primary and metastatic tumor growth. Similarly, cell-cell interactions between B16 cells and host osteoblasts modulate mPGES-1 activity and PGE₂ production by the osteoblasts. PGE₂, in turn, acts to stimulate receptor activator of NF-κB ligand expression, leading to osteoclast differentiation and bone erosion. Using eicosanoid receptor antagonists, we show that PGE₂ acts on osteoblasts and fibroblasts in the tumor microenvironment through the EP4 receptor. Metastatic tumor growth and vascularization in soft tissues was abrogated by an EP4 receptor antagonist. EP4-null Ptger4^−/− mice do not support B16 melanoma growth. In vitro, an EP4 receptor antagonist modulated PGE₂ effects on fibroblast production of angiogenic factors. Our data show that B16 melanoma cells directly influence host stromal cells to generate PGE₂ signals governing neoangiogenesis and metastatic growth in bone via osteoclast erosive activity as well as angiogenesis in soft tissue tumors.     

Inhibition of PGE1-stimulated cAMP accumulation in human platelets by thromboxane A2

The prostaglandin endoperoxide PGH₂, HHT, HETE, thromboxane A₂, and thromboxane B₂, which are all products of arachidonic acid metabolites of human platelets, were tested for their ability to modulate platelet cyclic nucleotide levels. None of the compounds tested altered the basal level of cAMP or cGMP, and only PGH₂ and thromboxane A₂ inhibited PGE₁-stimulated cAMP accumulation. Thromboxane A₂ was found to be a more potent inhibitor of PGE₁-stimulated cAMP accumulation and inducer of platelet aggregation thatn PHG₂.     

Prostaglandin E1 (PGE1), but not prostaglandin E2 (PGE2), alters luteal and endometrial luteinizing hormone (LH) occupied and unoccupied LH receptors and mRNA for LH receptors in ovine luteal tissue to prevent luteolysis

Loss of luteal progesterone secretion at the end of the ovine estrous cycle is via uterine PGF₂α secretion. However, uterine PGF₂α secretion is not decreased during early pregnancy in ewes. Instead, the embryo imparts a resistance to PGF₂α. Prostaglandins E (PGE; PGE₁ + PGE₂) are increased in endometrium and uterine venous blood during early pregnancy in ewes to prevent luteolysis. Chronic intrauterine infusion of PGE₁ or PGE₂ prevents spontaneous or IUD, estradiol-17β, or PGF₂α-induced premature luteolysis in nonbred ewes. The objective was to determine whether chronic intrauterine infusion of PGE₁ or PGE₂ affected mRNA for LH receptors, occupied and unoccupied receptors for LH in luteal and caruncular endometrium, and luteal function. Ewes received Vehicle, PGE₁, or PGE₂ every 4 h from days 10 to 16 of the estrous cycle via a cathether installed in the uterine lumen ipsilateral to the luteal-containing ovary.Jugular venous blood was collected daily for analysis of progesterone and uterine venous blood was collected on day-16 for analysis of PGF₂α and PGE. Corpora lutea and caruncular endometrium were collected from day-10 preluteolytic control ewes and day-16 ewes treated with Vehicle, PGE₁ or PGE₂ for analysis of the mRNA for LH receptors and occupied and unoccupied receptors for LH. Luteal weights on day-16 in ewes treated with PGE₁ or PGE₂ and day-10 control ewes were similar (P ≥ 0.05), but were greater (P ≤ 0.05) than in day-16 Vehicle-treated ewes. Progesterone profiles on days 10–16 differed (P ≤ 0.05) among treatment groups: PGE₁ > PGE₂ > Vehicle-treated ewes. Concentrations of PGF₂α and PGE in uterine venous plasma on day-16 were similar (P ≥ 0.05) in the three treatment groups. Luteal mRNA for LH receptors and unoccupied and occupied LH receptors were similar (P ≥ 0.05) in day-10 control ewes and day-16 ewes treated with PGE₂ and were lower (P ≤ 0.05) in day-16 Vehicle-treated ewes. PGE₂ prevented loss (P ≤ 0.05) of day-16 luteal mRNA for LH receptors and occupied and unoccupied LH receptors. Luteal and caruncular tissue mRNA for LH receptors and occupied and unoccupied LH receptors were greater (P ≤ 0.05) on day-16 of PGE₁-treated ewes than any treatment group. mRNA for LH receptors and occupied and unoccupied receptors for LH in caruncules were greater (P ≤ 0.05) in day-16 Vehicle or PGE₂-treated ewes than in day-10 control ewes. It is concluded that PGE₁ and PGE₂ share some common mechanisms to prevent luteolysis; however, only PGE₁ increased luteal and endometrial mRNA for LH receptors and occupied and unoccupied LH receptors. PGE₂ prevents a decrease in luteal mRNA for LH receptors and occupied and unoccupied receptors for LH without altering endometrial mRNA for LH receptors or occupied and unoccupied receptors for LH.     

Prostaglandins, not cyclic GMP, inhibit oxytocinase isoenzymes from human amniotic fluid in vitro

Two isoenzymes of oxytocinase (EC 3.4.11.3) activity were fractionated from human amniotic fluid samples between the 14th and 22nd weeks of gestation by Ultrogel acrylamide-agarose gel filtration and partially characterized. The isoenzymes were competitively inhibited by PGE₁, PGE₂ and PGF_2α more at pH 6.2 than at pH 6.8, whereas cyclic GMP (cGMP) and its 8-bromo derivative had no effect at either pH. The implications of these findings are discussed and it is suggested that since the activity of amniotic fluid oxytocinases is very low or minimal at or near term, inhibition of these by prostaglandins may not have physiological significance in the initiation of human parturition.     

Desensitization and Recovery of Prostaglandin-Stimulated Adenylate Cyclase Activity in a Murine Virus-Induced T Lymphoma Cell Line BL/VL3

Abstract

Prolonged (16 h) preexposure to prostaglandin E₁ (PGE₁) of cells from a murine virus-induced T lymphoma cell line BL/VL₃ provoked, in their membranes, a dose-dependent reduction of PGE₁-mediated adenylate cyclase stimulation. Smaller (but significant) decreases of helodermin- and isoproterenol-mediated stimulations were also observed. After a 16 h incubation of these cells with 1 µM PGE₁, that reduced by 85%, the PGE₁-mediated adenylate cyclase stimulation in membranes, 50% of the PGE₁ response recovered after 2 h of PGE₁ withdrawal from the incubation medium. Over the following 2 - 24 h time interval, further recovery was limited. Protein synthesis was required for this resensitization mechanism of functional PGE₁ receptors coupled to adenylate cyclase, as judged by the inhibitory effects of cycloheximide.     

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.