Elevation of prostaglandin and cyclic AMP levels by arachidonic acid in primary epithelial cell cultures of C3H mouse mammary tumors

Arachidonic acid causes a sharp transient increase in cyclic AMP levels in primary epithelial cell cultures obtained from C3H mouse mammary tumors. The effect is evident within two minutes and is enhanced by theophylline or 3-isobutyl-1-methylxanthine. Maximum increase in cyclic AMP levels are observed with a dose of 100 μg/ml of arachidonic acid (AA). At higher dose levels the increase in cyclic AMP levels is reduced. Naproxen, an inhibitor of prostaglandin synthesis in this system markedly reduces the stimulation of cyclic AMP by arachidonic acid but it does not affect the increase in cyclic AMP levels observed after the addition of prostaglandin E's, epinephrine or cholera enterotoxin.Arachidonic acid, under the same conditions, also causes a significant elevation of PGE and PGF media levels which is slower and more sustained than the cAMP response. The data strongly suggest that a metabolite of arachidonic acid is responsible for the cyclic rise, however, it is not certain whether this is due to PGE₂ or some other product.     

Prostaglandin I2 synthesis and elevation of cyclic AMP levels in 3T3 fibroblasts

Arachidonic acid and prostaglandin H2 elevate the levels of adenosine 3':5'-monophosphate (cyclic AMP) in Balb/c 3T3 fibroblasts. This effect was inhibited by 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid, an inhibitor of prostaglandin I2 synthase (Claesson, H.-E., Lindgren, J.A. and Hammarstr!om, S. (1977) FEBS Lett. 81, 415-418). After addition of arachidonic acid to 3T3 cultures, cellular cyclic AMP levels and growth medium concentrations of 6-ketoprostaglandin F1 alpha (degradation product of prostaglandin I2) were quantitatively determined. The stimulatory effect of exogenously-added prostaglandin I2 on cellular cyclic AMP levels was also determined. The results indicate that the endogenous production of prostaglandin I2 is sufficient to explain the stimulatory action of arachidonic acid on cyclic AMP formation in 3T3 fibroblasts.     

Beta-adrenergic stimulation of prostaglandin production by human amnion tissue

Arachidonic acid is released from specific glycerophospholipids in human amnion and is used to synthesize prostaglandins that are involved in parturition. In an investigation of the regulation of prostaglandin production in amnion, the effects of isoproterenol on discs of amnion tissue maintained in vitro were examined. Isoproterenol caused a large but transitory increase in the amount of cyclic AMP in amnion discs and this was accompanied by a sustained stimulation of the release of arachidonic acid (but not palmitic acid or stearic acid) and prostaglandin E2. The dependencies of cyclic AMP accumulation, arachidonic acid mobilization and prostaglandin E2 release on the concentration of isoproterenol were similar, each response was maximal at 10(-6) M isoproterenol and was inhibited by propranolol. Dibutyryl cyclic AMP stimulated the release of prostaglandin E2 from amnion discs. Although prostaglandin E2, when added to amnion discs caused an accumulation of cyclic AMP, it did not appear to mediate isoproterenol-induced accumulation of cyclic AMP since the latter effect was insensitive to indomethacin in concentrations at which prostaglandin production was inhibited greatly. These data support the proposition that catecholamines, found in increasing amounts in amniotic fluid during late gestation, may be regulators of prostaglandin production by the amnion.     

Beta-adrenergic stimulation of prostaglandin production by human amnion tissue

Arachidonic acid is released from specific glycerophospholipids in human amnion and is used to synthesize prostaglandins that are involved in parturition. In an investigation of the regulation of prostaglandin production in amnion, the effects of isoproterenol on discs of amnion tissue maintained were examined. Isoproterenol caused a large but transitory increase in the amount of cyclic AMP in amnion discs and this was accompanied by a sustained stimulation of the release of arachidonic acid (but not palmitic acid or stearic acid) and prostaglandin E₂. The dependencies of cyclic AMP accumulation, arachidonic acid mobilization and prostaglandin E₂ release on the concentration of isoproterenol were similar, each response was maximal at 10⁻⁶ M isoproterenol and was inhibited by propranolol. Dibutyryl cyclic AMP stimulated the release of prostaglandin E₂ from amnion discs. Although prostaglandin E₂, when added to amnion discs caused an accumulation of cyclic AMP, it did not appear to mediate isoproterenol-induced accumulation of cyclic AMP since the latter effect was insensitive to indomethacin in concentrations at which prostaglandin production was inhibited greatly. These data support the proposition that catecholamines, found in increasing amounts in amniotic fluid during late gestation, my be regulators of prostaglandin production by the amnion.     

Effects of prostaglandins F alpha on dog thyroid cyclic AMP level and function

Prostaglandins F1 alpha and F2 alpha, at high concentrations (greater than or equal to 28 microM) enhanced cyclic AMP accumulation in dog thyroid slices. At lower concentrations, they inhibited the cyclic AMP accumulation induced by thyrotropin (TSH), prostaglandin E1, and cholera toxin. This effect was rapid in onset and of short duration, calcium-dependent and suppressed by methylxanthines. Prostaglandin F alpha also inhibited TSH-induced secretion and activated iodide binding to proteins. These characteristics are similar to those of carbamylcholine action, except that prostaglandins F did not enhance cyclic GMP accumulation. The effect of prostaglandin F alpha was not inhibited by atropine, phentolamine and adenosine deaminase and can therefore not be ascribed to an induced secretion of acetylcholine, norepinephrine or adenosine. It is suggested that prostaglandins F act by increasing influx of extracellular Ca2+. Arachidonic acid also inhibited the TSH-induced cyclic AMP accumulation. However this effect was specific for TSH, it was enhanced in the absence of calcium and was not inhibited by methylxanthines or by indomethacin at concentrations which completely block its conversion to prostaglandin F alpha. Arachidonic acid action is sustained. This suggests that arachidonic acid inhibits thyroid adenylate cyclase at the level of its TSH receptor and that this effect is not mediated by prostaglandin F alpha or any other cyclooxygenase product.     

The involvement of prostaglandin endoperoxide formation in the elevation of cyclic GMP levels during platelet aggregation.

Arachidonic acid- or collagen-induced aggregation was accompanied by a progressive elevation in the level of cyclic GMP in washed human platelets with no significant alteration in the concentration of cyclic AMP. The extent of the increase in cyclic GMP was proportional to the concentration of arachidonic acid added. Enhanced accumulation of cyclic GMP produced by arachidonic or collagen was prevented by prior exposure of platelets to aspirin or indomethacin. Prostaglandin endoperoxide G2 caused platelet aggregation and an increase in cyclic GMP concentration; neither event was blocked by prostaglandin synthesis inhibitors. These results indicate that the generation of prostaglandin endoperoxides is a step in the sequence of events in platelet aggregation leading to the enhanced accumulation of cyclic GMP.     

Effect of acetaminophen on prostaglandin E2 and prostaglandin F2α synthesis in the renal inner medulla of rat

Effects of acetaminophen on the renal inner medullary production of prostaglandin E₂ and F_2α were compared with the well-known effects of aspirin on this process. Acetaminophen was found to elicit a dose-dependent inhibition of both prostaglandin E₂ and F_2α accumulation in media with a K_i of 100–200 μM. This inhibition could not be accounted for by increased accumulation of prostaglandins within slices. Acetaminophen inhibition was reversed by removal of acetaminophen during the incubation or by addition of arachidonic acid. Similar manipulations did not reverse aspirin or indomethacin-mediated inhibition of prostaglandin synthesis. Thin-layer and gas chromatographic analysis of acetaminophen following incubation with slices demonstrated that this material was identical to authentic acetaminophen. This, in addition to the lack of an effect of glutathione on inhibition, suggests that acetaminophen does not have to be metabolized to exert this inhibition. Arachidonic acid did not alter the metabolism or increase the efflux of acetaminophen. Lower levels of prostaglandin E₂ observed with 5 mM acetaminophen and 1 mM aspirin caused a corresponding decrease in cyclic AMP content. Removal of acetaminophen from the second incubation or addition of arachidonic acid caused increases in both prostaglandin E₂ and cyclic AMP. Aspirin inhibition of cyclic AMP content was not reversed by similar manipulations. In vivo inhibition of inner medullary prostaglandin E₂ and prostaglandin F_2α synthesis was observed 2 h after a 375 mg/kg, intraperitoneal injection of acetaminophen. These data suggest that acetaminophen, like aspirin, is capable of reducing tissue prostaglandin synthesis. However, the mechanisms by which these two analgesic and antipyretic agents elicit their inhibition of prostaglandin synthesis are quite different.     

Differences in size, structure and function of free and membrane-bound polyribosomes of rat liver. Evidence for a single class of membrane-bound polyribosomes.

PG (prostaglandin) E1 inhibits the uptake of iridine, thymidine, 2-deoxy-D-glucose and L-isoleucine into human diploid WI38 fibroblasts. The inhibition occurs within seconds of the addition of the prostaglandin to the culture. PGE2, PGF1alpha and PGF2alpha behave similarly. Arachidonic acid and 8,11,14-eicosatrienoic acid also decrease uptake in the presence or absence of indomethacin. Other unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid are essentially inactive. Ricinoleic acid (the 9-hydroxyoleic acid), however, inhibits uptake to about the same degree, at concentrations similar to those of the prostaglandins. Results indicate that this rapid blockage by the prostaglandins and certain fatty acids is not cyclic AMP-mediated. For example, although PGF1alpha and PGF2alpha are much poorer stimulators of cyclic AMP formation than are PGE1 and PGE2, they are nevertheless effective inhibitors of substrate uptake. Adrenaline, a very effective stimulator of cyclic AMP formation in the cells, is not inhibitory. Also, the addition of 8-methylthioadenosine 3':5'-cyclic monophosphate (methylthio cyclic AMP) to the culture, methylthio cyclic AMP decreases the uptake of nucleotides into cultures undergoing active cell division, approximately to values found in quiescent cultures. PGE1 also has this effect on cells undergoing active growth. This gradual decrease is substrate uptake caused by PGE1 appears to be a separate event from its initial rapid inhibition of uptake.     

Unsaturated fatty acid effect on cyclic amp levels in human embryo lung fibroblasts

The addition of arachidonic acid at 250 μM to cultures of human embryo lung fibroblasts (IMR-90) increases cellular cyclic AMP levels within 5 minutes to approximately 15-fold over basal. Other unsaturated fatty acids, 11, 14, 17-eicosatrienoic, linoleic, 8, 11, 14-eicosatrienoic and oleic also cause similar rapid elevation of cellular cyclic AMP. During this time interval, no detectable conversion of the added linoleic or arachidonic acids to prostaglandin is observed. These cells produce prostaglandins at measurable concentrations in response to treatment with ascorbic acid or bradykinin. Saturated fatty acids have no influence on cyclic AMP levels in these cells. This effect of unsaturated fatty acids on cellular cyclic AMP levels varies with the cell type. For example, smooth muscle and endothelial cells obtained from the calf pulmonary artery show very little or no increase in cellular cyclic AMP upon exposure to arachidonic acid.     

Unsaturated fatty acid effect on cyclic AMP levels in human embryo lung fibroblasts.

The addition of arachidonic acid at 250 muM to cultures of human embryo lung fibroblasts (IMR-90) increases cellular cyclic AMP levels within 5 minutes to approximately 15-fold over basal. Other unsaturated fatty acids, 11, 14, 17-eicosatrienoic, linoleic, 8, 11, 14-eicosatrienoic and oleic also cause similar rapid elevation of cellular cyclic AMP. During this time interval, no detectable conversion of the added linoleic or arachidonic acids to prostaglandin is observed. These cells produce prostaglandins at measurable concentrations in response to treatment with ascorbic acid or bradykinin. Saturated fatty acids have no influence on cyclic AMP levels in these cells. This effect of unsaturated fatty acids on cellular cyclic AMP levels varies with the cell type. For example, smooth muscle and endothelial cells obtained from the calf pulmonary artery show very little or no increase in cellular cyclic AMP upon exposure to arachidonic acid.     

Differentiation of Human Neuroblastoma Cells: Marked Potentiation of Prostaglandin E-Stimulated Accumulation of Cyclic AMP by Retinoic Acid

Neuroblastoma cells in culture contain low levels of cyclic AMP, a second messenger which plays a major role in neuronal maturation. In this study, human neuroblastoma cells, SK-N-SH-SY5Y, were induced to differentiate by treatment with either nerve growth factor (50 ng/ml), retinoic acid (10 microM), dibutyryl cyclic AMP (1 mM), or 12-O-tetradecanoylphorbol-13-acetate (0.1 microM), and the ability of several neurotransmitters or hormones to stimulate adenylyl cyclase was tested. Although all four differentiation factors caused morphological changes towards a neuronal phenotype, only retinoic acid dramatically enhanced cyclic AMP accumulation, specifically upon stimulation with prostaglandin E1 (PGE1). PGE2 was also active, but less potent, than PGE1, whereas the other cyclic AMP-stimulating agents tested were largely unaffected. Further, the rapid desensitization of the PGE1-cyclic AMP response observed in control cells after 20 min of PGE1 exposure did not occur in retinoic acid-treated cells, and the EC50 values for PGE1 were reduced from approximately 240 to 14 nM after retinoic acid treatment. The increased sensitivity to PGE was associated with an increase of high-affinity PGE1 binding sites, whereas the Gs coupling proteins and adenylyl cyclase were not measurably affected. A similar enhancement of the PGE1-cyclic AMP response by retinoic acid was also observed in two additional human neuroblastoma cell lines tested, Kelly and IMR-32, suggesting that up-regulation of the prostaglandin response by retinoic acid is common among neuroblastoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cyclic AMP and platelet prostaglandin synthesis.

The present study has investigated the influence of agents which elevate intracellular levels of endogenous platelet adenosine 3'5'-cyclic monophosphate (cyclic AMP), and the effect of the exogenous cyclic AMP analog, dibutyryl cyclic AMP, on the conversion of 14C-arachidonic acid by washed platelets. Prostaglandin E1 (PGE1), PGE1 with theophylline, or dibutyryl cyclic AMP incubated with washed platelets prevented arachidonic acid induced platelet aggregation, but had no effect on the conversion of arachidonic acid to 12L-hydroxy-5,8,10, 14-eicosatetraenoic acid (HETE), 12L-hydroxy-5,8,10 heptadecatrienoic acid (HHT), or thromboxane B2. Ultrastructural studies of the platelet response revealed that agents acting directly or indirectly to increase the level of cyclic AMP inhibited the action of arachidonic acid on washed platelets and prevented internal platelet contraction as well as aggregation. The influence of PGE1 with theophylline, and dibutyryl cyclic AMP on the thrombin induced release of 14C-arachidonic acid from platelet membrane phospholipids was also investigated. These agents were found to be potent inhibitors of the thrombin stimulated release of arachidonic acid from platelet phospholipids, due most likely to an inhibition of platelet phospholipase A activity. The results show that dibutyryl cyclic AMP and agents which elevate intracellular cyclic AMP levels act to inhibit platelet activation at two steps 1) internal contraction and 2) release of arachidonic acid from platelet phospholipids.     

Effects of prostaglandins Fα on dog thyroid cyclic AMP level and function

Prostaglandins F_1α and F_2α, at high concentrations (≥28 μM) enhanced cyclic AMP accumulation in dog thyroid slices. At lower concentrations, they inhibited the cyclic AMP accumulation induced by thyrotropin (TSH), prostaglandin E₁, and cholera toxin. This effect was rapid in onset and of short duration, calcium-dependent and suppressed by methylxanthines. Prostaglandin F_α also inhibited TSH-induced secretion and activated iodine binding to proteins. These characteristics are similar to those of carbamylcholine action, except that prostaglandins F did not enhance cyclic GMP accumulation. The effect of prostaglandin F_α was not inhibited by atropine, phentolamine and adenosine deaminase and can therefore not be ascribed to an induced secretion of acetylcholine, norepinephrine or adenosine. It is suggested that prostaglandins F act by increasing influx of extracellular Ca²⁺. Arachidonic acid also inhibited the TSH-induced cyclic AMP accumulation. However this effect was specific for TSH, it was enhanced in the absence of calcium and was not inhibited by methylxanthines or by indomethacin at concentrations which completely block its conversion to prostaglandin F_α. Arachidonic acid action is sustained. This suggests that arachidonic acid inhibits thyroid adenylate cyclase at the level of its TSH receptor and that this effect is not mediated by prostaglandin F_α or any other cyclooxygenase product.     

Multiple signal transduction pathways lead to extracellular ATP-stimulated mitogenesis in mammalian cells: II. A pathway involving arachidonic acid release, prostaglandin synthesis, and cyclic AMP accumulation.

We have previously shown that extracellular ATP acts as a mitogen via protein kinase C (PKC)-dependent and independent pathways (Wang, D., Huang, N., Gonzalez, F.A., and Heppel, L.A. Multiple signal transduction pathways lead to extracellular ATP-stimulated mitogenesis in mammalian cells. I. Involvement of protein kinase C-dependent and independent pathways in the mitogenic response of mammalian cells to extracellular ATP. J. Cell. Physiol., 1991). The present aim was to determine if metabolism of arachidonic acid, resulting in prostaglandin E2 (PGE2) synthesis and elevation of cAMP levels, plays a role in mitogenesis mediated by extracellular ATP. Addition of ATP caused a marked enhancement of cyclic AMP accumulation in 3T3, 3T6, and A431 cells. Aminophylline, an antagonist of the adenosine A2 receptor, had no effect on the accumulation of cyclic AMP elicited by ATP, while it inhibited the action of adenosine. The accumulation of cyclic AMP was concentration dependent, which corresponds to the stimulation of DNA synthesis by ATP. The maximal accumulation was achieved after 45 min, with an initial delay period of about 15 min. That the activation of arachidonic acid metabolism contributed to cyclic AMP accumulation and mitogenesis stimulated by ATP in 3T3, 3T6, and A431 cells was supported by the following observations: (a) extracellular ATP stimulated the release of [3H]arachidonic acid and PGE2 into the medium; (b) inhibition of arachidonic acid release by inhibitors of phospholipase A2 blocked PGE2 production, cyclic AMP accumulation, and DNA synthesis activated by ATP, and this inhibition could be reversed by adding exogenous arachidonic acid; (c) cyclooxygenase inhibitors, such as indomethacin and aspirin, diminished the release of PGE2 and blocked cyclic AMP accumulation as well as [3H]thymidine incorporation in response to ATP; (d) PGE2 was able to restore [3H]thymidine incorporation when added together with ATP in the presence of cyclooxygenase inhibitors; (e) pertussis toxin inhibited ATP-stimulated DNA synthesis in a time- and dose-dependent fashion as well as arachidonic acid release and PGE2 formation. Other evidence for involvement of a pertussis toxin-sensitive G protein(s) in ATP-stimulated DNA synthesis as well as in arachidonic acid release is presented. In A431 cells, the enhancement of arachidonic acid and cyclic AMP accumulation by ATP was partially blocked by PKC down-regulation, implying that the activation of PKC may represent an additional pathway in ATP-stimulated metabolism of arachidonic acid. In all of these studies, ADP and AMP-PNP, but not adenosine, were as active as ATP.(ABSTRACT TRUNCATED AT 400 WORDS)     

Urinary excretion of cyclic nucleotides, creatinine prostaglandin E2 and thromboxane B2 from mice exposed to whole-body irradiation from an enhanced neutron field

Urine volume and excretion of cyclic AMP, cyclic GMP, prostaglandin E2 (PGE2), thromboxane B2 (TxB2) and creatinine were evaluated as potential indicators of radiation damage in mice given 2-5 Gy to the whole body from an enhanced neutron field. In general, urinary cyclic AMP, cyclic GMP, creatinine and urine volumes were positively correlated across time postexposure, for each radiation dose. TxB2 levels positively correlated with urine volume and cyclic AMP excretion only in animals given 2.0 Gy. None of these parameters suggests their use as a prognostic indicator of the extent of radiation damage. Urinary excretion of PGE2 was negatively correlated with other urinary parameters. Biphasic increases in urinary PGE2 were also observed. The initial transient elevation 2-3 days postexposure was not correlated with the dose (2-5 Gy). The second elevation of PGE2 excretion occurred at 6-10 days. The magnitude of the latter increase suggests that urinary PGE2 excretion may be a useful indicator of whole-body or kidney exposure to neutron fields.     

Action of luteinizing hormone-releasing hormone and synthesis of prostaglandin in the pituitary gland.

The possibility that prostaglandin E2 (PGE2) may play a role in luteinizing hormone (LH) release was examined using an in vitro model. Addition of luteinizing hormone-releasing hormone (LH-RH) to the culture medium stimulated cyclic AMP accumulation and LH-release by incubated hemipituitaries, but did not affect the level of PGE2 or prostaglandin synthetase activity in the gland. Aspirin and indomethacin reduced both prostaglandin synthetase activity and PGE2 or prostaglandin synthetase activity in the gland. Aspirin and indomethacin reduced both prostaglandin synthetase activity and PGE2 content in the pituitary, but did not impair the stimulatory action of LH-RH on either cyclic AMP accumulation or LH-release. Flufenamic acid on its own caused LH-release, but the drug abolished the effect of LH-RH on cyclic AMP accumulation. The mechanism of this action of flufenamic acid is not understood. It is concluded that the stimulatory action of LH-RH on pituitary cyclic AMP production and LH release is not mediated by prostaglandins.     

Requirement and role of arachidonic acid in the differentiation of pre-adipose cells.

The terminal adipose differentiation of Ob1771 cells, characterized by glycerol-3-phosphate dehydrogenase activity and triacylglycerol accumulation, was studied in serum-free hormone-supplemented medium containing growth hormone, tri-iodothyronine, insulin, transferrin and fetuin. Arachidonic acid was able to substitute for a crude adipogenic fraction isolated from fetal bovine serum but not for growth hormone or tri-iodothyronine. Arachidonic acid was also able to increase in a rapid and dramatic manner cyclic AMP production; moreover it was able to amplify the adipose conversion promoted by other agents elevating cyclic AMP concentrations and to induce inositol phospholipid breakdown. Both phorbol 12-myristate 13-acetate, a protein kinase C activator and ionomycin, a Ca2+-mobilizing agent, showed potent synergy with agents elevating cyclic AMP concentrations for the promotion of adipose conversion, whereas 8-bromo cyclic GMP and 4 alpha-phorbol 12,13-dibutyrate were ineffective. The triggering of both the cyclic AMP and inositol phospholipid pathways was accompanied by a single round of cell division, and within a few days all the cells became differentiated. Similar results were obtained, after exposure to arachidonic acid, with preadipose 3T3-F442A cells and with rat adipose precursor cells in primary culture. The availability of arachidonic acid from intracellular stores and/or of exogenous origin should play a major role for the onset of critical mitoses leading to terminal differentiation in pre-adipose cells.     

Cyclic-AMP inhibits neither A23187-stimulated [14C]-arachidonic acid release from prelabelled lipids nor phospholipase A2 activity in resident rat peritoneal macrophages

8-Bromo cyclic AMP inhibited A23187-stimulated PGE2 production in adherent resident rat peritoneal macrophages by 50% when this was assessed by radioimmunoassay. In contrast, neither exogenous 8-bromo cyclic AMP nor elevation of endogenous cyclic AMP with cholera toxin inhibited 14C-arachidonic acid release or labelled prostaglandin formation by [1-14C]-arachidonic acid-prelabelled macrophages stimulated with either A23187 or melittin. Inhibition by cyclic AMP appears to be confined to PGE2 originating from a pool of endogenous phosphoglyceride that does not readily exchange with isotopically-labelled arachidonic acid. Phospholipase A2 activity, assessed as calcium-dependent [1-14C]-arachidonic acid release from exogenous 1-stearoyl, 2-[1-14C]-arachidonyl phosphatidyl choline at pH 8.6, was activated by melittin but not by A23187 in 1000 x g supernates from sonicated cells. Neither melittin nor calcium activation of phospholipase A2 was inhibited by preincubation of the cells prior to breakage with 8-bromo-cyclic AMP, nor by inclusion of either 8-bromo cyclic AMP or the catalytic subunit of cyclic AMP-dependent kinase in the assay. The results are inconsistent with the hypothesis that inhibition of A23187-stimulated PGE2 production by cyclic AMP in peritoneal macrophages is due to inhibition of a calcium-stimulated phospholipase A2.     

Hydrocortisone inhibition of the bradykinin activation of human synovial fibroblasts.

Human synovial fibroblasts in culture respond to bradykinin with a 20-fold increment in intracellular cyclic AMP concentrations, however bradykinin does not directly activate adenylate cyclase activity in a particulate fraction derived from these cells. Bradykinin evokes a release of labeled arachidonic acid and prostaglandins E and F from synovial fibroblasts pre-labeled with 3H-arachidonic acid. Hydrocortisone inhibits the bradykinin induced increment in cyclic AMP and the release of arachidonic acid and prostaglandins E and F from synovial fibroblasts. Indomethacin, which also inhibits the cyclic AMP response to bradykinin, has no effect on the release of arachidonic acid from synovial fibroblasts. Indomethacin does, however, inhibit the quantity of prostaglandins released into the medium. These studies support the hypothesis that bradykinin does not activate human synovial fibroblast adenylate cyclase, but presumably activates a phospholipase whose products in turn result in the synthesis of prostaglandins. These and other investigations also suggest that a product(s) of the prostaglandin pathway causes the increment in cyclic AMP.     

Cardiac effects of prostaglandins E1 and F1 alpha

The effects of prostaglandin E1 (PGE1) and prostaglandin F1 alpha (PGF1 alpha) were studied on perfused rat hearts and isolated rat atria. Both PGE1 and PGF1 alpha produced dose-dependent increases in right atrial rate but had no effect on left atrial tension development. PGE1 (10(-4) M) increased right atrial cyclic AMP content without changing phosphorylase a activity. PGF1 alpha (10(-4) M) did not change right atrial cyclic AMP or cyclic GMP content. Both prostaglandins had no effect on left atrial cyclic nucleotide content. When infused at a rate of 1 microgram/min, PGE1 produced a time-dependent increase in cyclic AMP content in the Langendorff perfused hearts but did not alter contractile force development or phosphorylase a activity. An infusion of PGF1 alpha produced a dose-dependent increase in tension development which was secondary to a negative chronotropic effect. PGF1 alpha (1 microgram/min) did not produce any changes in cyclic nucleotide levels or phosphorylase a activity in the Langendorff perfused hearts. These results show that PGE1 can selectively increase myocardial cyclic AMP content without altering contractile force or phosphorylase activity and that PGF1 alpha does not increase rat cardiac AMP levels.