Prostaglandin synthesis along the gastrointestinal tract of the rabbit: differences in total synthesis and profile

In the present study we systematically investigated the synthesis of prostaglandins in the mucosa and the muscle layer along the length of the rabbit gut. Homogenates of mucosa and muscle layer were incubated with (14C)-labelled arachidonic acid, and prostaglandin formation was determined using thin-layer chromatography. With respect to total prostaglandin synthesis the highest values in the mucosa were measured in fundus, antrum and colon, whereas the prostaglandin synthesis in the muscle layer was maximal in the small bowel, particularly the ileum. In the mucosa, the prostaglandins E2 and F2a predominated, and there were minor differences along the gastrointestinal tract. In the muscle layer of the stomach, high amounts of 6-keto prostaglandin F1a, the stable degradation product of prostacyclin were produced, while small and large bowel homogenates synthesized mostly F2a. Consistently the prostaglandins A2/B2 were a major product in most locations. In addition, PG E2 catabolism to 15-keto PG E2 and 13,14-dihydro-15-keto PG E2 in the absence of NAD was slow. No significant changes in total prostaglandin synthesis and prostaglandin profile were detected between 24 hrs fasted and normally fed rabbits at any part of the gastrointestinal tract.     

Prostaglandin synthesis and catabolism in the gastric mucosa: studies in normal rabbits and rabbits immunized with prostaglandin E2

Antral and fundic mucosal homogenates obtained from prostaglandin E2-immunized rabbits converted 14C-arachidonic acid to prostaglandin E2, 6-keto prostaglandin F1 alpha, prostaglandin F2 alpha, and prostaglandin D2. Percentage conversion of 14C-arachidonic acid to these prostaglandin products was not significantly different in prostaglandin E2-immunized rabbits compared with control rabbits (thyroglobulin-immunized and unimmunized rabbits combined). Synthesis of 6-keto prostaglandin F1 alpha, prostaglandin E2 and 13,14-dihydro 15-keto prostaglandin E2 from endogenous arachidonic acid after vortex mixing fundic mucosal homogenates was similar in prostaglandin E2 immunized rabbits and control rabbits. Both in prostaglandin E2-immunized rabbits and controls, 3H-prostaglandin E2 was catabolized extensively by the fundic mucosa, whereas 3H-6-keto prostaglandin F1 alpha, 3H-prostaglandin F2 alpha, and 3H-prostaglandin D2 were not catabolized to any appreciable extent. The rate of catabolism of PGs was not significantly different in prostaglandin E2-immunized rabbits and control rabbits, with the exception of prostaglandin F2 alpha which was catabolized slightly more rapidly in prostaglandin E2-immunized rabbits. These results indicate that development of gastric ulcers in prostaglandin E2-immunized rabbits is not associated with an alteration in the capacity of the gastric mucosa to synthesize or catabolize prostaglandins.     

On the metabolism of prostaglandins by human gastric fundus mucosa.

1.Specific radioimmunoassays for the prostaglandins E2, F2alpha and A2 and the metabolites 13,14-dihydro-15-keto-prostaglandin E2, 15-keto-prostaglandin F2alpha and 13,14-dihydro-15-keto-prostaglandin F2alpha were used to study the metabolism of prostaglandins by gastroscopically obtained small biopsy specimens of human gastric fundus mucosa. 2.Three prostaglandin-metabolizing enzymes were found in the 100 000 X g supernatant of human gastric fundus mucosa, 15-hydroxy-prostaglandin-dehydrogenase, delta13-reductase and delta9-reductase. The specific activity was highest for 15-hydroxy-prostaglandin-dehydrogenase and lowest for delta9-reductase. 3.Formation of prostaglandin A2 (or B2) was not observed under the same conditions. 4.None of the three enzyme activities detected in the 100 000 X g supernatant was found in the 10 000 X g and 100 000 X g pellets of human gastric fundus mucosa. 5.The results indicate that high speed supernatant derived from human gastric mucosa can rapidly metabolize prostaglandin E2 and prostaglandin F2alpha to the 15-keto and 13,14-dihydro-15-keto-derivatives. Furthermore, prostaglandin E2 can be converted to prostaglandin F2alpha, the biological activity of which, on gastric functions, differs from that of prostaglandin E2.     

Effective use of rabbit gastric antral mucosal slices in prostaglandin synthesis and metabolism studies

Intact slice preparations of rabbit stomach (antral mucosa, corporal mucosa, antral muscle and corporal muscle) were incubated and the released prostaglandins (PGs) were measured by reverse-phase high-performance liquid chromatography using 9-anthryldiazomethane for derivatization. With respect to total PG production, the highest amounts were generated by antral mucosal slices. Antral mucosal slices produced PGE2, 6-keto PGF1 alpha, thromboxane B2, PGF2 alpha and PGD2 (in descending order of magnitude) and possessed a high capacity for producing 13,14-dihydro-15-keto derivatives of both PGE2 and PGF2 alpha. Studies utilizing aspirin, EGTA or Ca2+ revealed that PG release by antral mucosal slices in the present in vitro system reflects a composite of the activities of phospholipase A3, PG cyclooxygenase and PG-metabolizing enzymes. These results show that antral mucosal slices will be useful in physiological and pharmacological studies on PG synthesis and metabolism of the stomach.     

On the synthesis of prostaglandins by human gastric mucosa and its modification by drugs.

1. Specific radioimmunoassays for the prostaglandins E2, A2 and F2alpha were used to study the synthesis of prostaglandins by gastroscopically obtained small biopsy specimens of human gastric corpus mucosa. 2. Both prostaglandin E2 and prostaglandin F2alpha were found to be synthesized from arachidonic acid by themicrosomal fraction of human gastric mucosa. The synthesis of prostaglandin E2 exceeded that of prostagladin F2alpha by a factor of about 10. 3. Synthesis of prostaglandin A2 or prostaglandin B2 was not observed under the same incubation conditions. 4. Indometacin effectively inhibited synthesis of both prostaglandin E2 (ID50 4.2 microng/ml) and prostaglandin F2alpha (ID50 1.8 microng/ml) by human gastric mucosa, while paracetamol even in a concentration of 310 microng/ml did not influence prostaglandin synthesis. The anti-ulcer agent carbenoxolone, which has been shown to inhibit prostaglandin inactivation, at the same concentration only slightly inhibited (about 20%) prostaglandin synthesis. 5. The results support the hypothesis that the gastro-intestinal effects or side effects of several drugs are mediated by an influence on the enzymes of prostaglandin synthesis or inactivation.     

Biosynthesis and metabolism of prostaglandins in chick epiphyseal cartilage.

Microsomal fractions of cells isolated from chick epiphyseal cartilage catalyzed the synthesis of prostaglandins from radiolabeled delta8,11,14-eicosatrienoic and from arachidonic acids. In addition, the microsomal supernatants contained both 15-hydroxyprostaglandin dehydrogenase and prostaglandin 15-keto delta13,14-reductase activities. Two major classes of prostaglandins (E and F) were synthesized; however, a major product which chromatographically behaves as PGA was also isolated. Synthetase activities were analyzed for pH optima and response to known stimulators and inhibitors of prostaglandin systhesis. The different activators had varying stimulatory effects on prostaglandin synthesis; the anti-inflammatory drugs were all strongly inhibitory. Synthetase activity in the growth plate was highest in the zone of hypertrophy, declining substantially in the more heavily calcified regions. Degradative enzyme activities were highest in the zone of maturation and significantly lower in the adjacent hypertrophic zone. The net effect of these opposing activities would be to elevate prostaglandin levels at the zone of hypertrophy, a finding which suggests that prostaglandins may play a role in the modulation of epiphyseal cartilage metabolism.     

Impaired generation of prostaglandins from isolated gastric surface epithelial cells in portal hypertensive rats

We studied generation of prostaglandins E2 and 6-keto F1a by surface epithelial cell isolated from the gastric mucosa of portal hypertensive and sham-operated rats. Oxygenated cell suspensions containing 80 +/- 3% of surface epithelial cells were incubated for 30 min at 37 degrees C and the concentration of prostaglandin E2 and 6-keto-prostaglandin F1a in medium was measured by radioimmunoassay. Viability of the cells was assessed with Fast green exclusion at baseline and after 30-min and 60-min incubation. Within 30 minutes the surface epithelial cells obtained from portal hypertensive rats generated 22.0 +/- 1.6 (mean +/- SE) pg prostaglandin E2 and 40.7 +/- 4.7 pg 6-keto prostaglandin F1a, per 10(6) cells. These were significantly less than prostaglandin generation by cells obtained from sham-operated rats. The viability of the surface epithelial cells from portal hypertensive rats was also significantly reduced compared with sham-operated rats after 60 minute incubation. Reduced ability of the surface epithelial cells to generate prostaglandins may be one mechanism for increased susceptibility of portal hypertensive gastric mucosa to injury by noxious agents.     

Biosynthesis and metabolism of prostaglandins in chick epiphyseal cartilage

Microsomal fractions of cells isolated from chick epiphyseal cartilage catalyzed the synthesis of prostaglandins from radiolabeled Δ^8,11,14-eicosatrienoic and from archidonic acids. In addition, the microsomal supernatants contained both 15-hydroxyprostaglandin dehydrogenase and prostaglandin 15-keto Δ^13,14-reductase activities. Two major classes of prostaglandins (E and F) were synthesized; however, a major product which chromatographically behaves as PGA was also isolated. Synthetase activities were analyzed for pH optima and response to known stimulators and inhibitors of prostaglandin synthesis. The different activators had varying stimulatory effects on prostaglandin synthesis; the anti-inflammatory drugs were all strongl inhibitory. Synthetase activity in the growth plate was highest in the zone of hypertrophy, declining substantially in the more heavily calcified regions. Degradative enzyme activities were highest in the zone of maturation and significantly lower in the adjacent hypertrophic zone. The net effect of these opposing activities would be to elevate prostaglandin levels at the zone of hypertrophy, a finding which suggests that prostaglandins may play a role in the modulation of epiphyseal cartillage metabolism.     

Bradykinin and electrical stimulation increase prostaglandin production in the rat vas deferens

The epididymal portion of the rat vas deferens produced prostaglandins (PG) E(2), F(2alpha)and 6-keto F(1alpha). Electrical stimulation (ES, 0.1 Hz, 1 ms) increased such production by 100%, and similar results were obtained in the presence of 1.0 microM bradykinin (Bk). When both stimuli were applied simultaneously, the increases in PG production were 1100% for PGE(2), 800% for PGF(2alpha)and 400% for PG6-keto F(1alpha). Prazosin abolished the effect of ES on PG production. A selective Bk B(2)-receptor antagonist abolished the increase in PG production induced by Bk, both in non-stimulated and in ES tissues. Bk (1.0 microM) elicited contractile responses in non-stimulated as well as in ES tissues, responses that were not modified in the presence of 10 microM indomethacin. In conclusion, the effects of Bk on prostaglandin production appears to depend on the activation of B(2) receptors, while the increase in prostaglandin release induced by ES, and the effects observed with both stimuli simultaneously, should be mediated by the release of noradrenaline and the subsequent activation of alpha(1) adrenoceptors.     

Effects of isolation and culture on prostaglandin synthesis by porcine aortic endothelial and smooth muscle cells

Freshly isolated neonatal porcine aortic tissue (smooth muscle with or without endothelium present) produced approximately 30 ng/mg wet tissue of 6-oxo-prostaglandin F1 alpha (the stable hydrolysis product from prostacyclin) and approximately 15 ng/mg of prostaglandin E2, as measured by radioimmunoassay after 24 h incubation in culture medium. Primary cultures of porcine endothelial and smooth muscle cells (isolated by enzymic digestion of aortic tissue) exhibited the same pattern of prostaglandin production, but absolute values were greater than for fresh tissue, particularly in the case of endothelium. Subcultures of endothelium produced smaller amounts of prostaglandins, although the pattern remained similar. In contrast, subcultures of smooth muscle cells produced a greater total amount of prostaglandins than did primary cultures, and the main product was prostaglandin E2. Experiments with [14C] prostaglandin H2 or [14C]arachidonic acid confirmed that aortic tissue, cultured endothelium, and primary cultures or aortic smooth muscle cells synthesized prostacyclin, and demonstrated that subcultured smooth muscle cells enzymically isomerised prostaglandin H2 to prostaglandin E2. Kinetic studies showed that prostaglandin production by cultured vascular cells was transiently increased by subculture or changing the growth medium, and that production per cell declined with increasing cell density. The change in pattern of prostaglandin production during culture was shown to be due to a rapid decline in the rate of prostacyclin production (which apparently began immediately after tissue isolation), together with a more gradual rise in prostaglandin E2 production. These results indicate that the amounts and ratios of prostaglandins produced by vascular endothelial and smooth muscle cells are greatly affected by the conditions used to isolate and culture the cells; vascular cells in vivo may similarly alter their pattern of prostaglandin production in response to local changes in their environment.     

Prostaglandin 9-hydroxydehydrogenase activity in the adult rat kidney. Identification, assay, pathway, and some enzyme properties.

Prostaglandin F2alpha is converted to 15-keto-13,14-dihydroprostaglandin E2 by adult rat kidney homogenates. A variety of substrates labeled as either the 9beta position alone or at several other positions in the prostaglandin molecule were used to define the step at which the crossover from the F type to the E type prostaglandins takes place. Time course studies further confirmed that 15-keto-13,14-dihydroprostaglandin F2alpha is the immediate substrate for this enzyme which we have termed prostaglandin 9-hydroxydehydrogenase. An assay system based on specific loss of tritium from 9beta-tritiated prostaglandin F2alpha is described. Enzyme activity with prostaglandin F2alpha as substrate is linear with time up to 10 min, stimulated by NAD+, saturable at low concentrations of substrate, stable to storage at minus 25 degrees in phosphate buffer (up to 3 weeks), and has a broad pH optimum around 7.5. The product, 15-keto,13,14-dihydroprostaglandin E2 was identified by mass spectrometry through a sodium borohydride-sodium borodeuteride reduction method.     

Bovine placental prostaglandin synthesis: principal cell synthesis as modulated by the binucleate cell

Bovine placentomes were collected during late gestation, prepartum, and immediately postpartum. Postpartum tissues were collected prior to fetal placental release. A procedure for separating fetal placental principal cells from fetal binucleate cells (BNC) was developed. Dispersed fetal placental cells (mixed types), principal cells, and BNC were each examined for their ability to produce prostaglandins (PGs) from arachidonic acid (AA) and to metabolize prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) in vitro. Dispersed fetal placental cells obtained prepartum produced predominantly PGs of the E series (PGEs) from AA (p less than 0.05). PGE synthesis predominated (p less than .05) in cells from postpartum tissue if the fetal placental membranes were subsequently retained, whereas synthesis of PGs of the F series (PGFs) predominated (p less than 0.05) if the fetal membranes were subsequently released. Principal cells were the primary source of fetal placental PG synthesis from AA (p less than 0.05). BNC exhibited a lesser ability to synthesize PGs from AA (p less than 0.05), but were able to convert PGF2 alpha to PGE2. Dispersed fetal placental cells exhibited greater ability to convert PGF2 alpha to PGE2 (p less than 0.05) than did the separated cells. These data suggest the function of a two-cell system within the fetal villi such that the BNC modulate the output of principal cell PG synthesis and/or metabolism.     

Prostanoid synthesis in peripheral nerve

The transformation of [1-14C]arachidonic acid into radiolabeled prostanoids was studied with homogenates and desheathed sciatic nerves of rats and frogs. All of the preparations studied were shown to synthesize prostaglandins; the specific prostanoids made were characterized by their migration on thin-layer chromatograms in three separate solvent systems. Both desheathed rat nerve and homogenates synthesize prostaglandin E2, prostaglandin F2 alpha, prostaglandin D2, 6-ketoprostaglandin F1 alpha and thromboxane B2. With preparations from frog nerve, prostaglandin E2 was the major prostanoid product formed. Several conditions were able to modulate the production of prostaglandin E2 with desheathed frog nerve. Electrical stimulation at high frequency (100 Hz) for 30 min increased the formation of labeled prostaglandin E2. Inclusion of glutathione also affected prostaglandin E2 formation. A lower concentration (0.1 mM) stimulated prostaglandin synthesis, while 1 mM glutathione was partially inhibitory. In both the rat and frog system, prostanoid synthesis was suppressed by indomethacin and aspirin.     

Effect of sodium cloprostenol and flunixin meglumine on luteolysis and the timing of birth in bitches.

At birth, the physiological role of prostaglandins in bitches is unclear. Bitches were treated before parturition with either saline, the prostaglandin analogue, sodium cloprostenol, or the prostaglandin synthetase inhibitor, flunixin meglumine. The animals were examined regularly to determine the onset of parturition and a series of blood samples were taken to define the hormonal profiles before, during and after birth. Animals treated with cloprostenol whelped earlier than did controls. In addition, the prostaglandin F2 alpha metabolite surge and decrease in plasma progesterone concentration and rectal temperature were earlier than in controls. Flunixin meglumine disrupted the normal 13,14-dihydro-15-keto prostaglandin F2 alpha profile but did not abolish prostaglandin synthesis completely or delay the onset of labour in treated animals. This study confirms that prostaglandins induce luteolysis and the onset of labour in the bitch. However, the partial inhibition of prostaglandin synthesis does not prevent parturition.     

Stimulation of prostaglandin synthesis in rabbit gastric antral mucosal slices by desferrioxamine in vitro.

Desferrioxamine is an iron-chelating agent used in the treatment of iron overload. It is a powerful inhibitor of iron-dependent radical reactions. The effect of desferrioxamine of prostaglandin (PG) synthesis and metabolism in rabbit gastric antral mucosal slices has been examined. Desferrioxamine significantly enhanced the production of PGE2 and PGF2 alpha. The formation of 13,14-dihydro-15-keto PGE2 and 13,14-dihydro-15-keto PGF2 alpha was also increased slightly by desferrioxamine. The addition of Fe3+ or Al3+ blocked the stimulatory action of desferrioxamine on PGE2 and PGF2 alpha production. Desferrioxamine appears to be stimulating the activity of PG cyclooxygenase through the removal of endogenous antral mucosal iron. These results suggest that desferrioxamine has the potential to increase the PG levels in gastric mucosa by primarily stimulating PG biosynthesis. The possibility that desferrioxamine may be of therapeutic value in the treatment of ischemic injury in the stomach is discussed.     

The purification and properties of NADPH-dependent carbonyl reductases from rat ovary

Two carbonyl reductases have been highly purified from rat ovary to apparent homogeneity. Though they have similarities in terms of molecular weight (33,000), substrate specificities, inhibitor sensitivities, amino acid composition, and immunological properties, they differed in pI values (6.0 and 5.9). Both enzymes reduced aromatic aldehydes, ketones, and quinones at higher rates, compared to prostaglandins and 3-ketosteroids, whereas they showed higher affinity for prostaglandins and 3-ketosteroids. The enzymes also catalyzed oxidation of the 9-hydroxy group of prostaglandin F2 alpha. Moreover, they showed the remarkable characteristic of catalyzing the reduction of not only the 9-keto group of prostaglandin E2 but also the 15-keto group of 13,14-dihydro-15-keto-prostaglandin F2 alpha. Both enzymes were inhibited by SH-reagents, quercitrin, indomethacin, furosemide, and disulfiram. The results of immunoinhibition, using antibody against the purified enzymes, indicated that the enzymes were solely responsible for the overall catalytic activities of prostaglandin E series reduction, as well as 13,14-dihydro-15-keto-prostaglandin F2 alpha reduction and prostaglandin F2 alpha oxidation in rat ovarian cytosol. Western-blot analysis revealed that immunoreactive proteins were present in adrenal gland and various reproductive tissues except uterus of rats.     

Leukotriene synthesis by human gastrointestinal tissues

The prostaglandin and leukotriene synthesizing capacity of human gastrointestinal tissues obtained at surgery was investigated using radioimmunoassay for prostaglandin E2, leukotriene B4 and sulfidopeptide leukotrienes. The leukotriene immunoassay data were validated by high-pressure liquid chromatography (HPLC). During incubation at 37 degrees C, fragments of human gastric, jejuno-ileal and colonic mucosa released considerably larger amounts of prostaglandin E2 than of leukotriene B4 and sulfidopeptide leukotrienes. Gastrointestinal smooth muscle tissues released even larger amounts of prostaglandin E2, but smaller amounts of leukotrienes than the corresponding mucosal tissues. Adenocarcinoma tissue released larger amounts of leukotriene B4, sulfidopeptide leukotrienes and prostaglandin E2 than normal colonic mucosa. Ionophore A23187 (5 micrograms/ml) did not stimulate release of prostaglandin E2 from any of the tissues investigated, but enhanced release of leukotriene B4 and sulfidopeptide leukotrienes. HPLC analysis demonstrated that immunoreactive leukotriene B4 co-chromatographed almost exclusively with standard leukotriene B4, while immunoreactive sulfidopeptide leukotrienes consisted of a mixture of leukotrienes C4, D4 and E4. Leukotriene synthesis by human gastrointestinal tissues was inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the dual enzyme inhibitor BW755C (3-amino-1-(trifluoromethylphenyl)-2-pyrazoline hydrochloride). Synthesis of prostaglandin E2 was inhibited by the cyclooxygenase inhibitor indomethacin as well as by BW755C. Incubation of gastrointestinal tissues in the presence of glutathione decreased the amounts of leukotrienes D4 and E4, while release of leukotriene C4 was simultaneously increased. On the other hand, incubation of tritiated leukotriene C4 with incubation media from human gastric or colonic mucosa resulted in conversion of the substrate to [3H]leukotriene D4 and [3H]leukotriene E4. The results indicate the capacity of human gastrointestinal tissues to synthesize the 5-lipoxygenase-derived products of arachidonate metabolism, leukotriene B4 and sulfidopeptide leukotrienes, in addition to larger amounts of prostaglandin E2. Furthermore, considerable activities of the sulfidopeptide leukotriene-metabolizing enzymes gamma-glutamyl transpeptidase and dipeptidase were detected in human gastrointestinal tissues. These enzymes might play an important role in biological inactivation and/or change of biological profile of sulfidopeptide leukotrienes generated in the human gastrointestinal tract.     

Follicular and uterine prostaglandin levels in relation to uterine contraction and the first ovulation of a sequence in the hen

Changes in the concentration of progesterone, estrone, estradiol, prostaglandins (PG) E2, 6-keto F1 alpha and 13,14-dihydro-15-keto F2 alpha (PGFM) were measured in peripheral plasma, and in venous effluent from the shell gland and the largest (F1) and the second largest (F2) preovulatory follicles. Tissue concentrations in the F1, F2 and the most recently ruptured follicle and the shell gland also were determined. Changes in these criteria were compared to changes in uterine contraction before the first ovulation of a sequence. Significant increases of PGF2 alpha and PGFM in the peripheral plasma were observed when the frequency of uterine contraction reached a maximum, about 1 h before ovulation. Relative to peripheral plasma, the concentrations in F1 plasma of progesterone, PGF2 alpha and PGFM were increased 20-fold, 150-fold and 15-fold, respectively, at the time of the maximum frequency of uterine contraction. The highest tissue concentrations of PGs were also observed in the F1 follicle. These results suggest that the largest preovulatory follicle is the major source of PG synthesis and release. These PGs may stimulate uterine contraction and may also play a role in follicular rupture and release of the ovum.     

Prostaglandin profile and synthetic capacity of the colon: comparison of tissue sources and subcellular fractions.

Although there has been intense interest in the physiology and pathophysiology of prostaglandins (PGs) synthesized in the colon, little is known about the PG profile and synthetic capacity of different tissue sources and subcellular fractions as enzyme sources. Subcellular fractions prepared from the mucosa and muscle layer of rat colon were incubated with or without exogenous arachidonic acid ([3H]20:4n-6) for 30 min. In experiments with exogenous [3H]20:4n-6, the prostaglandin synthetic capacity of the colonic muscle layer was significantly higher than that of the mucosa. Among the subcellular fractions, microsomes had the highest PG synthetic capacity in both mucosa and muscle. The major PG product was PGI2 and PGD2 in the mucosal microsomes and PGI2 and PGE2 in the muscularis microsomes. However, production of PGI2 in the mucosa and PGE2 in the muscle was significantly reduced in the fractions containing both cytosol and microsome, resulting in an alteration of the PG profile. Substrate availability (exogenous vs endogenous supply) appears to influence the PG profile of the colon. In the colonic mucosa with exogenous [3H]20:4n-6, the production of PGI2 was 5 times higher than that of PGE2, whereas the production of PGE2 was twice higher than that of PGI2 in experiments with endogenous 20:4n-6. These observations indicate: 1) different PG profile and synthetic capacity of tissue sources and subcellular fractions; 2) alteration of PG profile due to the variation of 20:4n-6 availability. Thus, the outcome of experiments on the physiological role of PG in the colon may be determined, in part, by the tissue source and subcellular fraction selected for analysis. The present study also suggests that the variation of substrate availability in physiological and pathophysiological processes may affect the PG profile of the colon.     

Radioimmunologic identification of prostaglandins produced by serum-stimulated mouse embryo palate mesenchyme cells

High-performance liquid chromatography and radioimmunoassay were used to identify the prostaglandins synthesized by mouse embryo palate mesenchyme cells. Serum stimulated the release of several different metabolites of arachidonic acid including 6-ketoprostaglandin F1 alpha (the stable product of prostacyclin, prostaglandin I2), prostaglandin E2 and prostaglandin F2 alpha. Compared to control cells, the serum-stimulated cells produce elevated levels of prostaglandin E2 (36-fold), 6-ketoprostaglandin F1 alpha (15-fold) and prostaglandin F2 alpha (7-fold). The acetylenic analogue of arachidonic acid, 5,8,11,14-eicosatetraynoic acid prevented this accelerated synthesis.