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Biomedical subjects

A Slomiany

Publications and source records attributed to A Slomiany.

At least 253 records · Page 14Linked to original sources
PubMed1987

Intestinal release of mucin in response to HCl and taurocholate: effect of indomethacin.

1. Alkaline secretion and mucin output were analyzed along the gastrointestinal tract of a dog in response to luminal application of HCl and taurocholate with and without pretreatment with indomethacin. 2. Mucins derived from the different areas displayed similar contents of protein and carbohydrate but differed with respect to associated and covalently bound lipids. 3. Application of HCl or taurocholate in all the regions caused an increase in the output of mucins and HCO3-. However, mucins elaborated in response to HCl exhibited higher total lipid content and were richer in phospholipids. 4. Pretreatment with indomethacin prior to HCl application led to a reduction in HCO3- and caused a decrease in mucin phospholipid content, but had no effect on HCO3- secretion and the lipid content of mucins elaborated in response to taurocholate. 5. The results indicate that mucins elaborated along the gastrointestinal tract differ with respect to lipids, and that their output in response to HCl is mediated by prostaglandins.

Animals↗
PubMed1987

Expression of prostaglandin protective functions in gastric mucosa cells cultured in the presence of ethanol: effects on the synthesis, retention, secretion, and structure of mucus glycoprotein.

The magnitude of prostaglandin [16,16-dimethylprostaglandin E2 (DMPGE2)] protection against ethanol action has been evaluated by studying the intracellular events leading to synthesis, modification, intracellular retention, and secretion of mucus glycoprotein in the rat gastric mucosal cell culture. When metabolic activity of the cultured cells was expressed as the amount of radioactive tracer in purified mucus glycoprotein, it was found that ethanol at low concentration (0.1 M) caused an 8- to 9-fold increase in proline and a 5- to 6-fold increase in palmitic acid incorporation into mucus glycoprotein; however, at 1.5 M ethanol, the synthetic processes ceased to function. In the presence of DMPGE2 (10 ng/ml), a 2-fold increase in proline and a 3-fold increase in palmitic acid incorporation into mucus glycoprotein were observed. A simultaneous addition of DMPGE2 (10 ng/ml) and ethanol (0.1-1.5 M), or pretreatment with DMPGE2 (10 ng/ml) for 20 min followed by the addition of ethanol (0.1-1.5 M), resulted in the stabilization of glycoprotein synthesis and secretion, and in restoration of the function at the level observed with DMPGE2 alone. The addition of 10 ng/ml of DMPGE2 caused a 32% increase in mucus glycoprotein secretion and an 11% increase in the intracellular content of the glycoprotein. The amount of mucus apoprotein precursor rose by 18%, and the fatty acylation of the synthesized peptides was up by 38%. Addition of DMPGE2, together with ethanol, prevented depletion of the intracellular glycoprotein stores. As observed with ethanol alone, the secretion was elevated by 16-27%, whereas the intracellular glycoprotein stores remained similar to those of controls. The synthesis of the mucus apoprotein precursor was highly sensitive to ethanol, and addition of DMPGE2 only partially prevented its inhibitory action. Pretreatment with DMPGE2, however, eliminated ethanol toxicity, and the precursor pool level remained elevated (28-30%) at all concentrations of ethanol tested. The fatty acylation, although positively affected by DMPGE2, decreased steadily with increments of ethanol concentration. The results show that DMPGE2 stabilizes the cellular membrane processes and thus imposes control over mucus glycoprotein synthesis, secretion, and its intracellular retention.

16,16-Dimethylprostaglandin E2↗
PubMed1987

Prostaglandin protection against ethanol-induced gastric injury: regulatory effect on the mucus glycoprotein metabolism.

Effects of ethanol and prostaglandin on the metabolic processes of gastric mucosal cells have been evaluated by studying the biosynthesis and intra- and extracellular distribution of mucus glycoprotein. The rat gastric mucosal cell suspensions were subjected to a short-term tissue culture in the presence of 0-1.5 M ethanol and 0-100 ng/ml 16,16-dimethyl prostaglandin E2 (DMPGE2), using [3H]proline and [3H]palmitic acid as markers of mucin apoprotein synthesis and modification. Ethanol at concentrations of 0.02-0.1 M stimulated the glycoprotein synthesis, but the product was 2-3 times more extensively and rapidly degraded by pepsin than the glycoprotein synthesized in the absence of ethanol. Higher concentrations of ethanol (0.1-1.5 M) caused a marked reduction in the glycoprotein synthesis and a depletion of the intracellular mucus glycoprotein stores, and at 1.5 M ethanol the synthetic processes ceased to function. When the incubated tissue cultures were challenged with DMPGE2, the highest synthetic and secretory stimulation was achieved at 10 ng/ml. The peptic susceptibility of the glycoprotein synthesized in the prostaglandin-enriched culture was somewhat lower than that of controls, and the proportion of the undegraded glycoprotein remaining after 22 h of digestion was significantly higher. Furthermore, the intracellular compartments were not depleted of mucus glycoprotein and the amount of the mucin apoprotein precursor increased to about 30%. Addition of DMPGE2 prior to ethanol treatment resulted in the stabilization of cellular processes and the cells responded as if ethanol was not present in the medium. Moreover, the intracellular stores of mucus glycoprotein were not depleted and the secretory rate was moderately elevated. The regulatory effect of DMPGE2 on the glycoprotein synthesis and distribution was significant, but diminished with increasing amounts of ethanol in the medium. The results suggest that DMPGE2 imposes a stabilizing effect on the secretory processes and controls the mucus glycoprotein synthesis, but the extent of this protective action against ethanol is limited and depends upon the concentration of ethanol penetrating the mucosal cells.

16,16-Dimethylprostaglandin E2↗
PubMed1987

Sulfation of glycolipids by human gastric mucosa in disease.

The activity levels of sulfotransferase enzymes involved in the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate to mucosal membrane and mucus gel glycolipids were studied in fundic and antral mucosal biopsies of patients with severe and chronic gastritis, gastric atrophy, gastric ulcer, and gastric cancer. With sulfotransferase which catalyzes the sulfation of mucus triglucosyl glyceroglucolipid increase in enzyme activity over the control was observed in patients with chronic and severe gastritis, and gastric atrophy, while a decrease in activity was noted in patients with gastric ulcer and gastric cancer. The differences were significant at p less than 0.001 for severe gastritis, gastric ulcer and gastric cancer. The increase in activity of sulfotransferase enzyme involved in the sulfation of membrane galactosylceramide over the control was observed in antral and fundic mucosa of all patients. Significant (p less than 0.001) differences were found in patients with severe gastritis, gastric atrophy and gastric ulcer. The results indicate that considerable changes in the activities of the mucosal sulfotransferase enzymes involved in the synthesis of membrane and secretory sulfolipids occur in gastric disease.

Adult↗
PubMed1987

Effect of solon on gastric mucus viscosity, permeability to hydrogen ion, and susceptibility to pepsin.

The effect of a new antiulcer drug, solon (sofalcone), on gastric mucus viscosity, permeability to hydrogen ion and degradation by pepsin was investigated using an in vitro system. Preincubation of the isolated gastric mucus with solon produced a marked enhancement in mucus viscosity. This enhancement was concentration dependent and at 2.2 X 10(-1) M solon reached a value of 230%. Permeability measurements showed that 2.2 X 10(-2) M solon increased the retardation ability of mucus to hydrogen ion by 32%, while 43% increase was obtained with 2.2 X 10(-1) M solon. The drug had no effect on the viscosity and hydrogen ion retardation capacity of albumin. The results of peptic activity assay indicated that solon had an inhibitory effect on the rate of mucus and albumin proteolysis. The rate of inhibition of peptic activity was proportional to the solon concentration up to 1.0 X 10(-5) M, at which concentration the proteolysis of mucus was inhibited by 60% and that of albumin by 45%. The results obtained here under in vitro conditions suggest that solon, by inhibiting peptic erosion of the mucus layer, increasing its viscosity and enhancing the ability to impede the hydrogen ion penetration, strengthens the gastric mucosal integrity and thus could aid in ulcer healing.

Animals↗
PubMed1987

Enzymatic sulfation of mucin in gastric mucosa: effect of sofalcone, sucralfate and aspirin.

A sulfotransferase activity which catalyzes the transfer of a sulfate group from 3'-phosphoadenosine-5'-phosphosulfate to gastric mucus glycoprotein has been demonstrated in the rat gastric mucosa. Subcellular fractionation studies revealed that the enzyme activity was present in a Golgi-rich membrane fraction. Optimum enzymatic activity for sulfation of mucus glycoprotein was obtained with 0.5% Triton X-100 and 30 mM NaF at a pH of 6.8. The apparent Km of the enzyme for gastric mucus glycoprotein was 10.5 microM, and the sulfate ester was found incorporated into the carbohydrate chains of mucin. The sulfo-transferase activity of the Golgi enzyme was stimulated by sofalcone, while reduction in the rate of sulfation occurred in the presence of sucralfate and aspirin. The rate of enhancement of mucin sulfation by sofalcone was proportional to the drug concentration up to 5 X 10(-7) M, at which concentration a 17% increase in the glycoprotein sulfation was attained. The rate of inhibition of mucin sulfation was proportional to concentrations of aspirin up to 3 X 10(-4) M and of sucralfate up to 1 X 10(-4) M, at which concentrations about 50% reduction in sulfotransferase activity was obtained. The apparent KI values calculated from the double-reciprocal plots were 15.1 microM for aspirin and 19.6 microM for sucralfate. The results suggest that although both sucralfate and sofalcone are potent gastric mucosal strengthening agents, only sofalcone is capable of enhancement of the sulfotransferase enzyme involved in gastric mucin sulfation.

Animals↗
PubMed1987

Carbohydrate heterogeneity of fibronectins. Synovial fluid fibronectin resembles the form secreted by cultured synoviocytes but differs from the plasma form.

Large quantities of fibronectin (Fn) are present in inflammatory synovial fluid. Inflammatory synovial fluid Fn, while indistinguishable from plasma Fn on the basis of reactivity to polyclonal antibodies, displays alterations in molecular size and charge. Since biochemical differences between plasma and synovial fluid fibronectins might be in part due to differences in glycosylation we have compared the carbohydrate composition of plasma Fn, synovial fluid Fn, and Fn from synoviocyte conditioned medium by biochemical assay, glycopeptide analysis, and binding to a series of lectins. Synovial fluid Fn has a greater carbohydrate content but contains less sialic acid when compared with plasma Fn. Glycopeptides formed from synovial fluid Fn are smaller than plasma Fn glycopeptides. These data suggest the presence of an additional N-linked oligosaccharide chain on synovial fluid Fn. In addition, synovial fluid Fn contains N-acetyl galactosamine indicating the presence of O-linked oligosaccharides. Synovial fluid Fn and Fn isolated from rheumatoid synoviocyte-conditioned medium display strong reactivity with the lectins wheat germ agglutinin (WGA) and peanut agglutinin (PNA), whereas normal and rheumatoid plasma Fn react weakly. The PNA reactivity of synovial fluid Fn is mediated by terminal beta-galactose residues on the gelatin-binding domain, whereas the enhanced WGA reactivity of synovial Fn is mediated by a sialic acid containing oligosaccharide located on a 27-kD C-terminal fragment. These data demonstrate domain-specific biochemical differences between plasma and synovial fluid fibronectins. These differences suggest a local origin for synovial fluid Fn and may contribute to functional differences between these forms of the protein.

Acetylgalactosamine↗
PubMed1986

Mucus glycoprotein secretion by duodenal mucosa in response to luminal arachidonic acid.

The effect of luminal application of arachidonic acid on the alkaline secretion, prostaglandin generation, and mucus glycoprotein output and composition was studied in proximal and distal duodenum of conscious dogs. Surgically prepared duodenal loops were instilled in vivo for up to 2 h with saline (control) followed by various concentrations (12.5-100 micrograms/ml) of arachidonic acid. The experiments were conducted with and without intravenous pretreatment with indomethacin. The recovered instillates were assayed for the content of prostaglandin and HCO3-, and used for the isolation of mucus glycoprotein. Exposure of duodenal mucosa to arachidonic acid led to concentration-dependent increase in the output of HCO3- and prostaglandin generation. In both cases this response was greater in the proximal duodenum. Pretreatment with indomethacin caused reduction in the basal HCO3- and prostaglandin output, and prevented the increments evoked by arachidonic acid. The proximal and distal duodenum displayed similar basal output and composition of mucus glycoprotein. Comparable increases in these glycoproteins were also obtained with arachidonic acid, the effect of which was abolished by indomethacin. Compared to basal conditions, mucus glycoproteins elaborated in response to arachidonic acid exhibited higher contents of associated lipids and covalently bound fatty acids, and contained less protein. The associated lipids of mucus glycoproteins elaborated in the presence of arachidonic acid showed enrichment in phospholipids and decrease in neutral lipids. The carbohydrate components in these glycoproteins also exhibited higher proportions of sialic acid and sulfate. The changes brought about by arachidonic acid were prevented by indomethacin pretreatment, and in both cases the glycoprotein composition returned to that obtained under basal conditions. The enrichment of mucus glycoprotein in lipids, sialic acid and sulfate in response to endogenous prostaglandin may be of significance to the function of this glycoprotein in the hostile environment of the duodenum.

Animals↗
PubMed1986

Effect of acetylsalicylic acid on gastric mucin viscosity, permeability to hydrogen ion, and susceptibility to pepsin.

The effect of acetylsalicylic acid (aspirin) on peptic degradation of gastric mucin, its viscosity and the ability to retard the diffusion of hydrogen ion was investigated. The results of peptic degradation indicated that, in the absence of the drug, the rate of proteolysis was proportional to mucin concentration up to 400 micrograms and remained constant with time for up to 1 hr. Introduction of aspirin led to an enhancement in the rate of proteolysis. The apparent Km value of pepsin toward mucus glycoprotein was 8.7 X 10(-7) M in the absence of the drug and 6.9 X 10(-7) M in its presence. Viscosity measurements showed a drop in mucin viscosity following preincubation with aspirin. This decrease was concentration dependent and at a 4.0 X 10(-5) M concentration of the drug reached a value of 75%. Permeability studies revealed that preincubation with 2.0 X 10(-5) M aspirin increased the permeability of mucin to hydrogen ion by 10%, while an 18% increase was obtained with 4.0 X 10(-5) M aspirin. The results suggest that aspirin weakens the integrity of the gastric mucus layer by promoting its peptic degradation, decreasing viscosity, and reducing the ability to resist hydrogen ion penetration.

Animals↗
PubMed1986

Cotranslational attachment of fatty acids to nascent peptides in gastric mucus glycoprotein.

Using gastric mucous cells which are involved exclusively in the synthesis of secretory O-glycosidic glycoprotein (mucin), the relationship between protein core synthesis and its acylation with fatty acids was investigated. Labeling of the cells with [3H]palmitic acid and [35S]methionine followed by isolation of peptidyl-tRNA and release of nascent peptides, indicated that these peptides contain covalently bound fatty acids. The high performance thin layer chromatography, SDS-gel electrophoresis, and radioactivity scanning revealed that the preparation contained three fractions labeled with palmitate (Mr 15,000-3,600) and two (Mr 1,500 and less) without this label. Based on these data and the nascent peptides amino acid analysis, we conclude that the protein core of the O-glycosidic glycoprotein is acylated with fatty acids during translation, when the peptide chain is longer than 21 amino acid residues.

Animals↗
PubMed1986

Changes in mucus glycoprotein synthesized in rat gastric mucosa exposed to ethanol.

The resistance to proteolysis by pepsin of gastric mucus glycoprotein synthesized by tissue culture in the presence and absence of 0.1 M ethanol was investigated. The glycoprotein product of ethanol-supplemented culture was found to contain 68% less associated lipids and 81% less covalently bound fatty acids, but exhibited unaltered content of carbohydrate and protein. The lipid and fatty acyl deficient glycoprotein was 5-times more rapidly and 2-3-times more extensively degraded by pepsin than the glycoprotein synthesized in the absence of ethanol. Following delipidation with organic solvents and deacylation with hydroxylamine both glycoproteins were digested at the same rate and degraded to the same extent. The lower content of fatty acyl residues markedly affected the overall pattern of the proteolytic fragments identified by SDS gel electrophoresis. The peptides corresponding to the acylated fragments of control were degraded and an increase in the amount of smaller peptides was observed. The in vitro assays of the fatty acyltransferase activity towards the substrates obtained from control and alcohol-containing cultures revealed that the enzyme activity was similar and increased proportionally with increased concentration of both glycoprotein substrates and enzyme. However, addition of 0.1 M ethanol to the assay tubes containing complete incubation mixture decreased the acylation of either glycoprotein by 40%. Based on the results presented here, and on previous studies of mucus glycoprotein synthesis in the presence of ethanol, we conclude that ethanol interferes with the process of acylation of mucus glycoprotein with fatty acids.

Acylation↗
PubMed1986

Mucus glycoprotein of human saliva: differences in the associated and covalently bound lipids with caries.

A high molecular weight mucus glycoprotein has been isolated from submandibular saliva of caries-resistant and caries-susceptible individuals by a procedure involving fractionation on Bio-Gel P-100 and A-50 columns followed by equilibrium density-gradient centrifugation in CsCl. The purified caries-resistant mucus glycoprotein displayed a buoyant density of 1.50 and accounted for 9.5% of the dry weight of caries-resistant saliva. The caries-susceptible mucus glycoprotein represented 14.1% of the dry weight of caries-susceptible saliva and gave a buoyant density of 1.43. Both glycoproteins exhibited similar protein and carbohydrate content, but the caries-resistant mucus glycoprotein contained 28.7% less associated lipids and 3-times less covalently bound fatty acids than the caries-susceptible mucus glycoprotein. The associated lipids were represented by neutral lipids, glycolipids and phospholipids, whereas the covalently bound fatty acids consisted mainly of hexadecanoate, octadecanoate and docosanoate. Extraction of associated lipids caused the caries-resistant glycoprotein to band in CsCl gradient at the density of 1.54 and caused the caries-susceptible glycoprotein to band at the density of 1.52. A further shift in the buoyant densities occurred following removal of the covalently bound fatty acids, and both glycoproteins banded at the density of 1.57. While the intact caries-resistant and caries-susceptible glycoproteins were susceptible to proteolysis by pronase, the lipid-rich caries-susceptible glycoprotein was degraded to a lesser extent. Extraction of associated lipids increased the degradation of both glycoproteins, but the caries-susceptible glycoprotein still remained 25% less susceptible. However, the susceptibility to pronase of the delipidated and deacylated caries-resistant and caries-susceptible glycoproteins was essentially identical. The caries-resistant and caries-susceptible mucus glycoproteins also differed in susceptibility to peptic degradation. The apparent Km values for intact caries-resistant and caries-susceptible glycoproteins were 10.5 X 10(-7) M and 8.1 X 10(-7) M, while the values for the delipidated and deacylated caries-resistant and caries-susceptible glycoproteins were 13.0 X 10(-7) M and 12.4 X 10(-7) M. The results suggest that the differences in the content of associated lipids and covalently bound fatty acids are responsible for the different physiochemical characteristics of caries-resistant and caries-susceptible salivary mucus glycoproteins, which may be determining factors in the resistance to caries.

Chromatography, Gel↗
PubMed1986

In vitro fatty acid acylation of mucus glycoprotein from sublingual salivary glands.

The enzyme activity which catalyzes the transfer of palmitic acid from palmitoyl-coenzyme A to sublingual gland mucus glycoprotein has been demonstrated in the detergent extracts of the microsomal fraction of rat sublingual and parotid salivary glands. The acyltransferase activity of this fraction was similar in both types of glands. Further subcellular fractionation performed on sublingual glands revealed that the enzyme is associated with the Golgi-rich membrane fraction. Optimum enzymatic activity for fatty acylation of mucus glycoprotein was obtained using 0.5% Triton X-100, 2 mM dithiothreitol, 25 mM NaF, and 10 mM MgCl2 at a pH of 7.4. Higher concentrations of NaF, MgCl2 and dithiothreitol, however, were inhibitory. The apparent Km of the sublingual glands microsomal enzyme for mucus glycoprotein was 0.55 mg/ml and for palmitoyl-CoA, 3.5 X 10(-5) M. A 15% decrease in the acyltransferase activity was obtained with the reduced and alkylated mucus glycoprotein and it showed no activity towards the proteolytically degraded glycoprotein. The 14C-labeled product of the enzyme reaction gave in CsCl density gradient a band at the density of 1.49 in which the 14C label coincided with the glycoprotein. The 14C label in this glycoprotein was susceptible to deacylation with hydroxylamine, and the released labeled material was identified as palmitate.

Acylation↗
PubMed1986

Enzymic acylation of mucus glycoprotein with palmitic acid in rat submandibular salivary gland.

The enzymic activity which catalyses transfer of palmitic acid from palmitoyl coenzyme A to mucus glycoprotein was found in Triton X-100 extracts of the microsomal fraction of rat submandibular and sublingual salivary glands. The acyltransferase activity of this fraction was 1.3-1.4 times greater in submandibular gland than in sublingual gland. Further subcellular fractionation of submandibular gland showed that the enzyme activity was associated with a Golgi-rich membrane fraction. Optimum enzyme activity for fatty acylation of mucus glycoprotein was at pH 7.4 using 0.5 per cent Triton X-100, 2 mM dithiothreitol 25 mM NaF and 10 mM MgCl2; higher concentrations were inhibitory. The apparent Km of the submandibular microsomal enzyme for mucus glycoprotein was 5.9 X 10(-7) M, and for palmitoyl-CoA, 3.3 X 10(-5) M. The 14C-labelled glycoprotein product of the reaction co-migrated on CsCl equilibrium, density-gradient centrifugation with submandibular mucus glycoprotein, and contained ester-bound palmitic acid. The fatty acyltransferase showed no activity with proteolytically-degraded glycoprotein; the acceptor capacity of reduced and S-carboxymethylated glycoprotein was only about 10 per cent lower than that of the intact mucus glycoprotein. This suggests that the acylation of salivary mucus glycoprotein with fatty acids occurs at its non-glycosylated, proteolysis-susceptible regions, and that the majority of these fatty acids are linked to the glycoprotein through hydroxyl esters.

Acylation↗
PubMed1986

Lipid composition and viscosity of parotid saliva in Sjögren syndrome in man.

Extraction of the dialysed and lyophilized saliva of patients with this syndrome by chloroform-methanol yielded 15.9 +/- 2.4 mg of lipid/100 ml of secretion, a level 2-times higher than in normal individuals. The saliva of such patients also had 3-times more glycolipid and 20-times more phospholipid than normal, but differences in the content of neutral lipids were less apparent. The neutral lipids, however, had higher proportions of glycerides, and lower proportions of cholesterol and cholesteryl esters than normal. Viscosity measurements, made with a cone/plate viscometer at shear rates between 1.15 and 230 s-1, revealed similarities between the saliva of normal individuals and Sjögren's syndrome.

Cholesterol↗
PubMed1986

Tooth surface-pellicle lipids and their role in the protection of dental enamel against lactic-acid diffusion in man.

The lipid content and composition of the enamel pellicle from caries-resistant (CR) and caries-susceptible (CS) subjects and their effect on its ability to retard the diffusion of lactic acid were investigated. Lipids accounted for 22.2 per cent of the dry weight of CR pellicle and 23.7 per cent of CS pellicle. The content of glycolipids in both groups was similar but CR pellicle contained 42 per cent less neutral lipids and 31 per cent less phospholipids. CR lipids had a higher content of cholesterol, cholesterol esters and sphingomyelin, whereas CS pellicle was richer in free fatty acids and phosphatidylethanolamine. Retardation of lactic-acid diffusion by CR pellicle was 45 per cent higher than by CS. Removal of lipids caused 50 per cent reduction in retardation by CR pellicle and 35 per cent by CS pellicle.

Adult↗
PubMed1986

Prostaglandin effect on the physical properties of gastric mucus glycoprotein and its susceptibility to pepsin.

The effect of 16,16-dimethyl prostaglandin E2 (DMPGE2) on gastric mucus glycoprotein viscosity, permeability to hydrogen ion and degradation by pepsin was investigated. Preincubation with DMPGE2 produced a marked enhancement in the glycoprotein viscosity. The increase was concentration dependent and at 2.6 X 10(-5)M DMPGE2 reached a value of 178%. Permeability measurements revealed that 2.6 X 10(-7)M DMPGE2 increased the retardation ability of the glycoprotein to hydrogen ion by 10%, while 22% increase was obtained with 2.6 X 10(-4)M DMPGE2. The results of peptic activity assay showed that DMPGE2 had no inhibitory effect on the rate of glycoprotein proteolysis, and actually a small stimulatory influence was consistently observed. The results suggest that prostaglandins beneficially affect the physical properties of mucus glycoprotein which are considered to be essential for the protective function of gastric mucus.

16,16-Dimethylprostaglandin E2↗