Prostaglandin E2 increases cardiac fibroblast proliferation and increases cyclin D expression via EP1 receptor.

PGE(2) affects growth of many cell types. Thus, we hypothesized that PGE(2) would stimulate growth of cardiac fibroblasts. To test our hypothesis we used neonatal rat ventricular fibroblasts (NVF). RT-PCR demonstrated the presence of all 4 PGE(2) receptor (EPs) mRNAs in NVF. Using flow cytometry, we found that PGE(2) decreased the percentage of cells in G0/G1 and increased the number of cells in S phase. PGE(2) also increased expression of cyclin D3, a known regulator of the cell cycle and this effect was mimicked by the EP1/EP3 agonist sulprostone. Next, we found that treatment of NVF with PGE(2) increased phosphorylation of p42/44 MAPK and Akt and that PGE(2)-stimulation of cyclin D3 was antagonized with both a MEK inhibitor and a PI3 kinase inhibitor. In conclusion, PGE(2) stimulates cardiac fibroblast proliferation via EP1 and/or EP3, p42/44 MAPK and Akt-regulation of cyclin D3. These results may be relevant to cardiac fibrosis.

Lack of microsomal prostaglandin E synthase-1 reduces cardiac function following angiotensin II infusion.

Our laboratory previously reported that inducible PGE(2) synthase, mPGES-1, contributes to micromolar production of PGE(2) in neonatal ventricular myocytes in vitro, which stimulates their growth. We therefore hypothesized that mPGES-1 contributes to cardiac hypertrophy following angiotensin II (ANG II) infusion. To test this hypothesis, we used 10- to 12-wk-old mPGES-1 knockout mice (mPGES-1 KO) and C57Bl/6 control mice infused for 8 wk with either 1.4 mg · kg(-1) · day(-1) ANG II or vehicle subcutaneously. Blood pressure [systolic blood pressure (SBP)] was measured throughout the study, and cardiac function was assessed by M-mode echocardiography at baseline and at 8 wk of infusion. At the conclusion of the study, immunohistochemistry was used to evaluate collagen fraction, myocyte cross-sectional area (MCSA), and apoptosis. At baseline, there was no difference in SBP between mPGES-1 KO mice and C57BL/6 controls. ANG II infusion increased SBP to similar levels in both strains. In control mice, infusion of ANG II increased MCSA and posterior wall thickness at diastole (PWTd) but had little effect on cardiac function, consistent with compensatory hypertrophy. In contrast, cardiac function was worse in mPGES-1 KO mice after ANG II treatment. Ejection fraction declined from 76.2 ± 2.7 to 63.3 ± 3.4% after ANG II, and left ventricular dimension at systole and diastole increased from 1.29 ± 0.02 to 1.78 ± 0.15 mm and from 2.57 ± 0.03 to 2.90 ± 0.13 mm, respectively. Infusion of ANG II increased both the LV-to-body weight and the mass-to-body weight ratios to a similar extent in both strains. However, PWTd increased by a lesser extent in KO mice, suggesting an impaired hypertrophic response. ANG II infusion increased collagen staining similarly in both strains, but TdT-dUTP nick end labeling staining was greater in mPGES-1 KO mice. Overall, these results are consistent with a beneficial effect for mPGES-1 in the maintenance of cardiac function in ANG II-dependent hypertension.

PKA, Rap1, ERK1/2, and p90RSK mediate PGE2 and EP4 signaling in neonatal ventricular myocytes.

We have previously reported that 1) inhibition of cyclooxygenase-2 and PGE(2) production reduces hypertrophy after myocardial infarction in mice and 2) PGE(2) acting through its EP4 receptor causes hypertrophy of neonatal ventricular myocytes (NVMs) via ERK1/2. It is known that EP4 couples to adenylate cyclase, cAMP, and PKA. The present study was designed to determine interactions between the cAMP-PKA pathway and ERK1/2 and to further characterize events downstream of ERK1/2. We hypothesized that PKA and the small GTPase Rap are upstream of ERK1/2 and that 90-kDa ribosomal S6 kinase (p90RSK) is activated downstream. Treatment of NVMs with PGE(2) activated Rap, and this activation was inhibited in part by an EP4 antagonist and PKA inhibition. Transfection of a dominant negative mutant of Rap reduced PGE(2) activation of ERK1/2. PGE(2) activation of p90RSK was also dependent on EP4, PKA, and Rap. We also tested the involvement of Rap, ERK1/2, and p90RSK in PGE(2) regulation of gene expression. PGE(2) stimulation of brain natriuretic peptide promoter activity was blocked by either ERK1/2 inhibition or a dominant negative mutation of p90RSK. PGE(2) stimulation of c-Fos was dependent on EP4, PKA, ERK1/2, and p90RSK, whereas only the latter two kinases were involved in PGE(2) regulation of early growth response-1. Finally, we tested the involvement of EP4-dependent signaling in the NVM growth response and found that the overexpression of EP4 increased NVM cell size. We conclude that EP4-dependent signaling in NVMs in part involves PKA, Rap, ERK1/2, and p90RSK and results in the increased expression of brain natriuretic peptide and c-Fos.

Gene expression profiling of dilated cardiomyopathy in older male EP4 knockout mice.

Using a line of mice with cardiac-specific knockout (KO) of the EP4 receptor gene, experiments were designed to determine whether a cardiac phenotype developed with age. Cardiac function was assessed by echocardiography in 23- to 33-wk-old male and female KO and littermate controls (WT) mice. After echocardiography, hearts were removed to assess weight, and then some were further processed for histology [myocyte cross-sectional area (MCSA), interstitial collagen fraction (ICF), and macrophage infiltration] and some for extraction of total RNA and protein. Older male KO mice had reduced ejection fraction (EF) coupled with left ventricular dilatation. MCSA and infiltrating macrophages were not different between groups, but ICF increased by 39% in KO mice. In contrast to male KO mice, 30- to 32-wk-old female KO mice had only a slight reduction in EF. To understand gene expression differences between male WT and KO mice, we performed whole genome gene expression profiling (Illumina BeadChips) on hearts of 30-to 32-wk-old mice. Data indicated that 156 genes were overexpressed in the KO hearts more than twofold, including genes involved in remodeling, inflammation, and oxidative stress. Overexpressed chemokines/cytokines were further examined in hearts of 10- to 12-wk-old male KO mice, and we found that growth differentiation factor-15 (GDF-15) expression was higher in KO than in WT hearts. In conclusion, EP4 knockdown in cardiac myocytes in aged male KO mice is in part associated with increased fibrosis, reduced EF, and dilated cardiomyopathy. Early overexpression of GDF-15 in hearts of male KO mice may contribute to or be a marker of the disease phenotype. The absence of serious cardiac dysfunction in aged female mice suggests a sexual dimorphism in the phenotype.

Reduced cardiac remodeling and function in cardiac-specific EP4 receptor knockout mice with myocardial infarction.

We have shown previously that cyclooxygenase-2 inhibition reduces cardiac hypertrophy and fibrosis postmyocardial infarction (MI) in a mouse model and that prostaglandin E(2) stimulates cardiomyocyte hypertrophy in vitro through its EP(4) receptor. Because the role of cardiac myocyte EP(4) in cardiac function and hypertrophy in vivo is unknown, we generated mice lacking EP(4) only in cardiomyocytes (CM- EP(4) knockout [KO]). Twelve- to 14-week-old mice were evaluated using echocardiography and histology. There were no differences in ejection fraction, myocyte cross-sectional area, and interstitial collagen fraction between KO mice and littermate controls. To test the hypothesis that EP(4) is involved in cardiac remodeling after MI, we induced MI by ligating the left anterior descending coronary artery. Two weeks later, the mice were subjected to echocardiography, and hearts were removed for histology and Western blot. There was no difference in infarct size between KO mice and controls; however, KO mice showed less myocyte cross-sectional area and interstitial collagen fraction than controls. Also, CM-EP4 KO mice had reduced ejection fraction. Because the transcription factor Stat-3 is involved in hypertrophy and protection from ischemic injury, we tested whether it was activated in control and KO mouse hearts after MI. Western blot indicated that Stat-3 was activated in control hearts after MI but not in KO hearts. Thus, CM-EP4 deletion decreased hypertrophy, fibrosis, and activation of Stat-3. However, cardiac function was unexpectedly worsened in these mice. We conclude that cardiac myocyte EP(4) plays a role in hypertrophy via activation of Stat-3, a process that seems to be cardioprotective.

Tadalafil, a long-acting type 5 phosphodiesterase isoenzyme inhibitor, improves neurological functional recovery in a rat model of embolic stroke.

Sildenafil, a type 5 phosphodiesterase isoenzyme (PDE5) inhibitor with a short half-life, increases brain cyclic guanosine monophosphate (cGMP) levels and improves neurological functional recovery when administered after stroke. In the present study, we investigated the effects of tadalafil (Cialis), a long acting PDE5 inhibitor, on brain cGMP levels, neurogenesis, angiogenesis, and neurological function during stroke recovery in a rat model of embolic stroke. Male Wistar rats (n=28) were subjected to embolic middle cerebral artery (MCA) occlusion. Tadalafil was orally administered every 48 h at a dose of 2 mg/kg or 10 mg/kg for 6 consecutive days starting 24 h after stroke onset. Control animals received the equivalent volume of saline at the same time points. For mitotic labeling, bromodeoxyuridine (BrdU, 100 mg/kg) was administered twice a day at 5, 6, and 7 days after stroke. ELISA assays were performed to evaluate the specificity of the effect of tadalafil on cGMP. Treatment with tadalafil at a dose of 2 or 10 mg/kg significantly improved neurological functional recovery compared with saline-treated rats. In addition, tadalafil treatment increased cerebral vascular density and the percentage of BrdU-positive endothelial cells around the ischemic boundary compared with saline-treated rats. Moreover, tadalafil-treated rats showed greater ipsilateral SVZ cell proliferation than saline-treated rats. However, treatment with tadalafil did not reduce infarct volume when compared to the saline group. Tadalafil selectively increased cGMP but not cyclic adenosine monophosphate (cAMP) in brain. Our data demonstrate that treatment of ischemic stroke with tadalafil improved functional recovery, which was associated with increases of brain cGMP levels and enhancement of angiogenesis and neurogenesis.

PGE2 stimulates human brain natriuretic peptide expression via EP4 and p42/44 MAPK.

Brain natriuretic peptide (BNP) produced by cardiac myocytes has antifibrotic and antigrowth properties and is a marker of cardiac hypertrophy. We previously showed that prostaglandin E2 (PGE2) is the main prostaglandin produced in myocytes treated with proinflammatory stimuli and stimulates protein synthesis by binding to its EP4 receptor. We hypothesized that PGE2, acting through EP4, also regulates BNP gene expression. We transfected neonatal ventricular myocytes with a plasmid encoding the human BNP (hBNP) promoter driving expression of a luciferase reporter gene. PGE2 increased hBNP promoter activity 3.5-fold. An EP4 antagonist reduced the stimulatory effect of PGE2 but not an EP1 antagonist. Because EP4 signaling can involve adenylate cyclase, cAMP, and protein kinase A (PKA), we tested the effect of H-89, a PKA inhibitor, on PGE2 stimulation of the hBNP promoter. H-89 at 5 muM decreased PGE2 stimulation of BNP promoter activity by 100%. Because p42/44 MAPK mediates the effect of PGE2 on protein synthesis, we also examined the role of MAPKs in the regulation of BNP promoter activity. PGE2 stimulation of the hBNP promoter was inhibited by a MEK1/2 inhibitor and a dominant-negative mutant of Raf, indicating that p42/44 MAPK was involved. In contrast, neither a p38 MAPK inhibitor nor a JNK inhibitor reduced the stimulatory effect of PGE2. Involvement of small GTPases was also studied. Dominant-negative Rap inhibited PGE2 stimulation of the hBNP promoter, but dominant-negative Ras did not. We concluded that PGE2 stimulates the BNP promoter mainly via EP4, PKA, Rap, and p42/44 MAPK.

Molecular regulation of the brain natriuretic peptide gene.

After brain natriuretic peptide (BNP) was isolated in 1988, rapid progress was made in cloning its cDNA and gene, facilitating studies of tissue-specific expression and molecular regulation of gene expression. This review focuses on the molecular determinants of regulation of the rat and human BNP genes, including signaling pathways that impact on changes in gene expression and cis regulatory elements responsive to these signaling pathways. For both rat and human genes, elements in the proximal promoter (-124 to -80), including GATA, MCAT, and AP-1-like, have been shown to contribute to basal and inducible regulation. More distal elements in the human BNP gene respond to calcium signals (an NF-AT site at -927), thyroid hormone (a thyroid-responsive element at -1000), and mechanical stretch (shear stress-responsive elements at -652 and -162). Understanding how BNP is regulated by signaling molecules that are activated in the hypertrophied and ischemic heart should be useful in understanding the underlying pathology. This may lead to therapeutic strategies that prevent hypertrophy while allowing for the beneficial effects of BNP production.

PGE2-induced hypertrophy of cardiac myocytes involves EP4 receptor-dependent activation of p42/44 MAPK and EGFR transactivation.

Upon induction of cyclooxygenase-2 (COX-2), neonatal ventricular myocytes (VMs) mainly synthesize prostaglandin E2 (PGE2). The biological effects of PGE2 are mediated through four different G protein-coupled receptor (GPCR) subtypes (EP(1-4)). We have previously shown that PGE2 stimulates cAMP production and induces hypertrophy of VMs. Because the EP4 receptor is coupled to adenylate cyclase and increases in cAMP, we hypothesized that PGE2 induces hypertrophic growth of cardiac myocytes through a signaling cascade that involves EP4-cAMP and activation of protein kinase A (PKA). To test this, we used primary cultures of VMs and measured [3H]leucine incorporation into total protein. An EP4 antagonist was able to partially block PGE2 induction of protein synthesis and prevent PGE2-dependent increases in cell surface area and activity of the atrial natriuretic factor promoter, which are two other indicators of hypertrophic growth. Surprisingly, a PKA inhibitor had no effect. In other cell types, G protein-coupled receptor activation has been shown to transactivate the epidermal growth factor receptor (EGFR) and result in p42/44 mitogen-activated protein kinase (MAPK) activation and cell growth. Immunoprecipitation of myocyte lysates demonstrated that the EGFR was rapidly phosphorylated by PGE2 in VMs, and the EP4 antagonist blocked this. In addition, the selective EGFR inhibitor AG-1478 completely blocked PGE2-induced protein synthesis. We also found that PGE2 rapidly phosphorylated p42/44 MAPK, which was inhibited by the EP4 antagonist and by AG-1478. Finally, the p42/44 MAPK inhibitor PD-98053 (25 micromol/l) blocked PGE2-induced protein synthesis. Altogether, we believe these are the first data to suggest that PGE2 induces protein synthesis in cardiac myocytes in part via activation of the EP4 receptor and subsequent activation of p42/44 MAPK. Activation of p42/44 MAPK is independent of the common cAMP-PKA pathway and involves EP4-dependent transactivation of EGFR.

Regulation of the membrane-localized prostaglandin E synthases mPGES-1 and mPGES-2 in cardiac myocytes and fibroblasts.

The proinflammatory mediator cyclooxygenase (COX)-2 and its product PGE(2) are induced in the ischemic heart, contributing to inflammatory cell infiltration, fibroblast proliferation, and cardiac hypertrophy. PGE(2) synthesis coupled to COX-2 involves two membrane-localized PGE synthases, mPGES-1 and mPGES-2; however, it is not clear how these synthases are regulated in cardiac myocytes and fibroblasts. To study this, we used primary cultures of neonatal ventricular myocytes (VM) and fibroblasts (VF) treated with IL-1beta for 24 h. To test for involvement of MAPKs in IL-1beta regulation of mPGES-1 and-2, cells were pretreated with the pharmacological inhibitors of p42/44 MAPK, p38 MAPK, and c-Jun kinase (JNK). mRNA was analyzed by RT-PCR. Protein was analyzed by densitometry of Western blots. mPGES-1 was undetectable in untreated VF but induced by IL-1beta; inhibition of either p42/44 MAPK or JNK, but not p38 MAPK, was almost completely inhibitory. In VM, inhibition of the three MAPKs reduced IL-1beta-stimulated mPGES-1 protein by 70-90%. mPGES-2 was constitutively synthesized in both VM and VF and was not regulated by IL-1beta or MAPKs. Confocal microscopy revealed colocalization of both mPGES-1 and mPGES-2 with COX-2 in the perinuclear area of both VF and VM. Finally, PGE(2) production was higher in VM than VF. Our data show that 1) mPGES-1 is induced in both VF and VM, 2) regulation of mPGES-1 by MAPK family members is different in the two cell types, 3) mPGES-2 is constitutively synthesized in both VM and VF and is not regulated, and 4) mPGES-1 and mPGES-2 are colocalized with COX-2 in both cells. Thus differences in activity of mPGES-1 and COX-2 or coupling of COX-2 with mPGES-1 may contribute to differences in PGE(2) production by myocytes and fibroblasts.

Inhibition of cyclooxygenase-2 improves cardiac function after myocardial infarction in the mouse.

Cyclooxygenase (COX)-2 is expressed in the heart in animal models of ischemic injury. Recent studies have suggested that COX-2 products are involved in inflammatory cell infiltration and fibroblast proliferation in the heart. Using a mouse model, we questioned whether 1). myocardial infarction (MI) in vivo induces COX-2 expression chronically, and 2). COX-2 inhibition reduces collagen content and improves cardiac function in mice with MI. MI was produced by ligation of the left anterior descending coronary artery in mice. Two days later, mice were treated with 3 mg/kg NS-398, a selective COX-2 inhibitor, or vehicle in drinking water for 2 wk. After the treatment period, mice were subjected to two-dimensional M-mode echocardiography to determine cardiac function. Hearts were then analyzed for determination of infarct size, interstitial collagen content, brain natriuretic peptide (BNP) mRNA, myocyte cross-sectional area, and immunohistochemical staining for transforming growth factor (TGF)-beta and COX-2. COX-2 protein, detected by immunohistochemistry, was increased in MI versus sham hearts. MI resulted in increased left ventricular systolic and diastolic dimension and decreased ejection fraction, fractional shortening, and cardiac output. NS-398 treatment partly reversed these detrimental changes. Myocyte cross-sectional area, a measure of hypertrophy, was decreased by 30% in the NS-398 versus vehicle group, but there was no effect on BNP mRNA. The interstitial collagen fraction increased from 5.4 +/- 0.4% in sham hearts to 10.4 +/- 0.9% in MI hearts and was decreased to 7.9 +/- 0.6% in NS-398-treated hearts. A second COX-2 inhibitor, rofecoxib (MK-0966), also decreased myocyte cross-sectional area and interstitial collagen fraction. TGF-beta, a key regulator of collagen synthesis, was increased in MI hearts. NS-398 treatment reduced TGF-beta immunostaining by 40%. NS-398 treatment had no effect on infarct size. These results suggest that COX-2 products contribute to cardiac remodeling and functional deficits after MI. Thus selected inhibition of COX-2 may be a therapeutic target for reducing myocyte damage after MI.

PPARgamma inhibition of cyclooxygenase-2, PGE2 synthase, and inducible nitric oxide synthase in cardiac myocytes.

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear receptor superfamily. They regulate lipid metabolism, glucose homeostasis, cell proliferation, and differentiation and modulate inflammatory responses. We examined whether PPARgamma is functional in cultured neonatal ventricular myocytes and studied its role in inflammation. Western blots revealed PPARgamma in myocytes. When myocytes were transfected with a PPAR response element reporter plasmid (PPRE-TK-luciferase), the PPARgamma activator 15-deoxy-Delta12,14-prostaglandin J2 (15dPGJ2) increased promoter activity, whereas cotransfection of a dominant negative PPARgamma inhibited it. To determine the role of 15dPGJ2 in expression of proinflammatory genes, we tested its effect on interleukin-1beta induction of cyclooxygenase-2 (COX-2). 15dPGJ2 decreased interleukin-1beta stimulation of COX-2 by 40% and PGE2 production by 73%. We next questioned whether 15dPGJ2 was modulating the expression of inducible prostaglandin E2 synthase (PGES) and found that it completely blocked interleukin-1beta induction of PGES. Use of a second PPARgamma agonist, troglitazone, and the selective PPARgamma antagonist GW9662 demonstrated that the effects seen were PPARgamma-dependent. In addition, we found that 15dPGJ2 blocked interleukin-1beta stimulation of inducible nitric oxide synthase (iNOS). We concluded that 15dPGJ2 may play an anti-inflammatory role in a PPARgamma-dependent manner, decreasing COX-2, PGES, and PGE2 production, as well as iNOS expression.

Left ventricular targeting of reporter gene expression in vivo by human BNP promoter in an adenoviral vector.

To selectively introduce genes into the mouse myocardium, we used a recombinant adenovirus encoding a transgene composed of a cardiac-specific promoter [the proximal human brain natriuretic peptide (hBNP) promoter] coupled to a luciferase reporter gene (Ad.hBNPLuc). Activity in vitro and in vivo was compared with Ad.CMVLuc, which contained the cytomegalovirus (CMV) enhancer/promoter. We tested cell-specific and inducible regulation of Ad.hBNPLuc in vitro. Expression was higher in neonatal cardiac myocytes than in a fibroblast cell line and was induced by interleukin-1beta, phenylephrine, and isoproterenol in myocytes. For in vivo experiments, Ad.hBNPLuc, Ad.CMVLuc, or vehicle was injected into the left ventricular (LV) free wall of the mouse heart. In Ad.hBNPLuc-injected mice, luciferase activity was only detected in the heart. In contrast, Ad.CMVLuc-injected mice had detectable luciferase activity in all tissues examined. Our studies indicate that 1) the cardiac-specific hBNP promoter and direct cardiac injection limit expression of the transgene to the LV free wall; and 2) transgene expression in vitro is inducible and cardiac myocyte specific. Thus the use of the proximal hBNP promoter in recombinant adenoviral vectors may allow cardiac-specific and inducible expression of therapeutic genes in vivo and prevent some of the side effects of systemic adenovirus administration.

Regulation of the human brain natriuretic peptide gene by GATA-4.

Brain natriuretic peptide (BNP) is a cardiac hormone constitutively expressed in the adult heart. We previously showed that the human BNP (hBNP) proximal promoter region from -127 to -40 confers myocyte-specific expression. The proximal hBNP promoter contains several putative cis elements. Here we tested whether the proximal GATA element plays a role in basal and inducible regulation of the hBNP promoter. The hBNP promoter was coupled to a luciferase reporter gene (1818hBNPLuc) and transferred into neonatal ventricular myocytes (NVM), and luciferase activity was measured as an index of hBNP promoter activity. Mutation of the putative GATA element at -85 of the hBNP promoter [1818(mGATA)hBNPLuc] reduced activity by 97%. To study transactivation of the hBNP promoter, we co-transfected 1818hBNPLuc with the GATA-4 expression vector. GATA-4 activated 1818hBNPLuc, and this effect was eliminated by mutation of the proximal GATA element. Electrophoretic mobility shift assay showed that an oligonucleotide containing the hBNP GATA motif bound to cardiomyocyte nuclear protein, which was competed for by a consensus GATA oligonucleotide but not a mutated hBNP GATA element. The beta-adrenergic agonist isoproterenol and its second messenger cAMP stimulated hBNP promoter activity and binding of nuclear protein to the proximal GATA element. Thus the GATA element in the proximal hBNP promoter is involved in both basal and inducible transcriptional regulation in cardiac myocytes.

Trophic effects of the cyclooxygenase-2 product prostaglandin E(2) in cardiac myocytes.

Interleukin-1beta (IL-1beta), a proinflammatory cytokine, induces cyclooxygenase-2 (COX-2) in cultured neonatal ventricular myocytes (NVMs), resulting in the preferential production of prostaglandin E(2) (PGE(2)). To explain the preferential PGE(2) release by myocytes, we studied whether its specific synthase, PGE(2) synthase (PGES), is also induced by IL-1beta. Because COX-2 has been extensively associated with cell growth, we questioned whether PGE(2) plays a role in cardiac cell growth. IL-1beta--treated myocytes showed induction of PGES protein and mRNA by Western blot and reverse transcription--polymerase chain reaction, respectively. Immunofluorescence studies revealed perinuclear localization of COX-2 and PGES in IL-1beta--treated myocytes. Exogenous PGE(2) increased protein synthesis in NVMs, as indicated by a 1.6-fold increase in [(3)H]leucine incorporation, comparable to the known hypertrophic factor phenylephrine (1.6-fold). Because PGE(2) exerts different effects through 4 receptor subtypes (EP(1), EP(2), EP(3), and EP(4)), we investigated whether these receptors are functional in myocytes. Treatment of NVMs with the selective EP(1)/EP(3) agonist sulprostone significantly increased protein synthesis (1.7-fold), whereas the EP(1)/EP(2) antagonist AH6809 blocked this effect by 43%. In contrast, AH6809 had no effect on PGE(2)-induced protein synthesis. Regarding second messengers, sulprostone had no effect on cAMP, whereas PGE(2) increased it. We concluded that (1) PGE(2) production requires the induction of its specific synthase; (2) in myocytes, the inducible enzymes COX-2 and PGES are perinuclear; and (3) PGE(2) and sulprostone induce cardiac myocyte growth but seem to activate a different subset of EP receptors.