Cloning of the rat and human prostaglandin F2 alpha receptors and the expression of the rat prostaglandin F2 alpha receptor

Aging-shifted prostaglandin profile in endothelium as a factor in cardiovascular disorders

Age-associated endothelium dysfunction is a major risk factor for the development of cardiovascular diseases. Endothelium-synthesized prostaglandins and thromboxane are local hormones, which mediate vasodilation and vasoconstriction and critically maintain vascular homeostasis. Accumulating evidence indicates that the age-related changes in endothelial eicosanoids contribute to decline in endothelium function and are associated with pathological dysfunction. In this review we summarize currently available information on aging-shifted prostaglandin profiles in endothelium and how these shifts are associated with cardiovascular disorders, providing one molecular mechanism of age-associated endothelium dysfunction and cardiovascular diseases.

The effect of prostaglandin analogues on central corneal thickness of patients with chronic open-angle glaucoma: a 2-year study on 129 eyes

PURPOSE

To evaluate the effect of prostaglandin analogues on the central corneal thickness (CCT) of patients with chronic open-angle glaucoma (COAG).

METHODS

One hundred and twenty-nine eyes were included in this study. Of these, 108 were treated with prostaglandin analogues (latanoprost, travoprost and bimatoprost), while 21 eyes treated with β-blockers were used as controls. CCT was measured before treatment and at 3-month intervals.

RESULTS

A slight but significant increase in CCT was recorded in the bimatoprost and latanoprost groups. Treatment with bimatoprost produced a constant increase (1.85-8.83 μm) in CCT at all time-points of the study. The CCT rise found in the latanoprost group was significant for the first year. Treatment with travoprost did not affect CCT.

CONCLUSION

The possibility of corneal thickening under prolonged, local prostaglandin treatment should be investigated further. However, in clinical practice, CCT changes may sometimes influence intraocular pressure measurements significantly.

Cyclic AMP-mediated chloride secretion is induced by prostaglandin F2alpha in human isolated colon

BACKGROUND AND PURPOSE

Prostaglandin F(2alpha) (PGF(2alpha)) is implicated in the pathogenesis of inflammatory bowel disease and colorectal cancer. This study investigates the effects of PGF(2alpha) on electrophysiological parameters in isolated human colonic mucosa.

EXPERIMENTAL APPROACH

Ion transport was measured as changes in short-circuit current across human colonic epithelia mounted in Ussing chambers. Colonic crypts were isolated by calcium chelation and cyclic adenosine monophosphate (cAMP) was measured by ELISA.

KEY RESULTS

PGF(2alpha) stimulated chloride secretion in a concentration-dependent manner with an EC(50) of 130 nM. The PGF(2alpha) induced increase in chloride secretion was inhibited by AL8810 (10 microM), a specific PGF(2alpha) receptor antagonist. In addition, PGF(2alpha) (1 microM) significantly increased levels of cAMP in isolated colonic crypts.

CONCLUSIONS AND IMPLICATIONS

PGF(2alpha) stimulated chloride secretion in samples of human colon in vitro through a previously unrecognizd cAMP-mediated mechanism. These findings have implications for inflammatory states.

Canine prostaglandin F2alpha receptor (FP) and prostaglandin F2alpha synthase (PGFS): molecular cloning and expression in the corpus luteum

In the dog luteolysis is not affected by hysterectomy. This observation led to the hypothesis that paracrine/autocrine rather than endocrine mechanisms of PGF2alpha are responsible for luteal regression in the dioestric bitch. The present experiments tested for the capacity of canine CL to produce and respond to PGF2alpha by qualitatively and quantitatively determining the expressions of PGFS, the enzyme converting PGH2 into PGF2alpha, and the PGF2alpha-receptor (FP) in CL of non-pregnant dogs during dioestrus. Canine PGFS and FP were isolated and cloned; both genes show a high homology (82-94%) when compared to those of other species. Relatively weak FP mRNA expression was detected on day 5 of dioestrus. It had increased by day 25 and remained constant thereafter. In situ hybridization (ISH) localized FP solely to the cytoplasm of the luteal cells, suggesting that these cells are the only luteal targets of PGF2alpha in this species. Only negative results were obtained for the expression of PGFS in canine CL by routine qualitative RT-PCR. When Real Time (TaqMan) PCR was applied, repetitively more negative than positive results were obtained at all timepoints. Any positive measurements observed at any point were neither repeatable nor related to the stage of dioestrus. This led us to conclude that expression of PGFS is either absent or present at very low level only. These data suggest that luteal regression in non-pregnant bitches is not modulated by PGF2alpha. However, the FP seems to be constitutionally expressed, explaining the receptivity of canine CL to exogenous PGF2alpha.

Cigarette smoke extract enhances oxytocin-induced rhythmic contractions of rat and human preterm myometrium

Although smoking during pregnancy is a major risk factor for preterm delivery, the underlying mechanism by which smoking stimulates uterine contractions is still poorly understood. In the present study, we tried to clarify the effects of smoking on myometrial contractility induced by oxytocin (OT) using cigarette smoke extract (CSE). Myometrial strips, which were taken from the rat on day 16 of pregnancy, and from human preterm and term delivery groups, were incubated overnight with several doses of CSE at 37 degrees C under non-hormonal conditions. The uterine contractile sensitivity and activity (force and frequency) upon exposure to OT were investigated. Furthermore, the expression levels of oxytocin receptor (OTR) mRNA in the myometrial strips were investigated by real-time PCR. Contractile sensitivity to OT in the rat CSE (10(-7) pieces/ml) group was found to be significantly higher than in the control group (P < 0.05). Contractile activity did not differ between the CSE and control groups. The expression levels of rat OTR mRNA in the CSE (10(-7) pieces/ml) group were significantly higher than in the control group (P < 0.01). Similarly, in preterm myometrial strips, the expression levels of human OTR mRNA in the CSE (10(-7) pieces/ml) group were significantly higher than in the control group (P < 0.05). These findings suggest that CSE directly increases the contractile sensitivity of preterm myometrium in response to OT by upregulating the expression of OTR mRNA and thereby increases the risk of preterm delivery in women, who smoke during pregnancy.

Effects of Antiglaucoma Drugs on Collagen Gel Contraction Mediated by Human Corneal Fibroblasts

PURPOSE

Measurement of intraocular pressure is affected by the shape and thickness of the cornea, and corneal shape is thought to be maintained by contraction of corneal fibroblasts. The effects of the antiglaucoma drugs latanoprost, timolol maleate, and pilocarpine on the contraction of corneal fibroblasts cultured in a 3-dimensional collagen gel were investigated. The effects of these drugs on collagen degradation by corneal fibroblasts and their possible cytotoxicity were also examined.

MATERIALS AND METHODS

Human corneal fibroblasts were cultured in a 3-dimensional gel of type I collagen and in the presence of various concentrations of latanoprost, timolol maleate, or pilocarpine for various times. Collagen gel contraction was evaluated by daily measurement of gel diameter. The extent of collagen degradation was determined by measurement of the amount of hydroxyproline generated by acid-heat hydrolysis of culture supernatants. The release of lactate dehydrogenase from corneal fibroblasts was determined as an index of drug cytotoxicity.

RESULTS

Latanoprost stimulated collagen gel contraction mediated by corneal fibroblasts in a concentration- and time-dependent manner, whereas timolol maleate and pilocarpine had no such effect. None of the 3 drugs affected collagen degradation by corneal fibroblasts or exhibited cytotoxicity at concentrations as high as 100 muM.

CONCLUSIONS

Among the antiglaucoma drugs examined, only latanoprost stimulated collagen gel contraction mediated by human corneal fibroblasts. This action of latanoprost might affect corneal shape and thereby influence measurement of intraocular pressure.

Prostaglandins E(2) and F(2alpha) enhance differentiation of cementoblastic cells

BACKGROUND

The prostaglandins (PG) E(2) and PGF(2alpha) are important cytokines in periodontal physiology and pathology. PGE(2) and PGF(2alpha) alter cell function by binding and activating the plasmamembrane G-protein-coupled PG receptors. In this study, we examined the PGE(2) and PGF(2alpha) effects on the immortalized cementoblastic OCCM cells.

METHODS

Confluent OCCM cells were treated with PGE(2), PGF(2alpha), specific activators/inhibitors of the EP prostanoid receptors, a specific activator of the FP prostanoid receptor, and direct activators/inhibitors of the protein kinase C (PKC) signaling pathway. Mineral nodule formation was assessed by the von Kossa stain.

RESULTS

PGE(2) and PGF(2alpha) significantly increased mineralization of OCCM cells. The EP1 and EP3 PG receptor activators 16,16-dimethyl-prostaglandin E(2) and sulprostone, also increased mineralization. In contrast, specific activators of the EP2 or the EP2/EP3/EP4 receptors did not have any effect. Fluprostenol, a specific activator of the FP receptor, significantly increased mineralization of OCCM cells. FP and EP (1 or 3) receptors signal through activation of the protein kinase C (PKC) pathway. Indeed, phorbol 12-myristate 13-acetate (PMA), a direct activator of the PKC pathway, significantly increase OCCM mineralization, while pre-treatment of OCCM cells with the PKC inhibitor GF109203x (bisindolylmaleimide) significantly decreased mineralization.

CONCLUSION

We conclude that PGE(2) and PGF(2alpha) exert an anabolic effect on OCCM mineralization through activation of PKC signaling.

Effects of PGF2alpha on human melanocytes and regulation of the FP receptor by ultraviolet radiation

Prostaglandins are potent lipid hormones that activate multiple signaling pathways resulting in regulation of cellular growth, differentiation, and apoptosis. In the skin, prostaglandins are rapidly released by keratinocytes following ultraviolet radiation and are chronically present in inflammatory skin lesions. We have shown previously that melanocytes, which provide photoprotection to keratinocytes through the production of melanin, express several receptors for prostaglandins, including the PGE2 receptors EP1 and EP3 and the PGF2alpha receptor FP, and that PGF2alpha stimulates melanocyte dendricity. We now show that PGF2alpha stimulates the activity and expression of tyrosinase, the rate-limiting enzyme in melanin synthesis. Analysis of FP receptor regulation showed that the FP receptor is regulated by ultraviolet radiation in melanocytes in vitro and in human skin in vivo. We also show that ultraviolet irradiation stimulates production of PGF2alpha by melanocytes. These results show that PGF2alpha binding to the FP receptor activates signals that stimulate a differentiated phenotype (dendricity and pigmentation) in melanocytes. The regulation of the FP receptor and the stimulation of production of PGF2alpha in melanocytes in response to ultraviolet radiation suggest that PGF2alpha could act as an autocrine factor for melanocyte differentiation.

Gene expression profiles in the rat central nervous system induced by JP-8 jet fuel vapor exposure

Jet propulsion fuel-8 (JP-8) is the predominant fuel for military land vehicles and aircraft used in the US and NATO. Occupational exposure to jet fuel in military personnel has raised concern for the health risk associated with such exposure in the Department of Defense. Clinical studies of humans chronically exposed to jet fuel have suggested both neurotoxicity and neurobehavioral deficits. We utilized rat neurobiology U34 array to measure gene expression changes in whole brain tissue of rats exposed repeatedly to JP-8, under conditions that simulated possible occupational exposure (6 h/day for 91 days) to JP-8 vapor at 250, 500, and 1000 mg/m(3), respectively. Our studies revealed that the gene expression changes of exposure groups can be divided into two main categories according to their functions: (1). neurotransmitter signaling pathways; and (2). stress response. The implications of these gene expression changes are discussed.

Proteinase-activated receptor-2 stimulates prostaglandin production in keratinocytes: analysis of prostaglandin receptors on human melanocytes and effects of PGE2 and PGF2alpha on melanocyte dendricity

Prostaglandins (PG) are key mediators of diverse functions in the skin and several reports suggest that PG mediate post-inflammatory pigmentary changes through modulation of melanocyte dendricity and melanin synthesis. The proteinase-activated receptor 2 (PAR-2) is important for skin pigmentation because activation of keratinocyte PAR-2 stimulates uptake of melanosomes through phagocytosis in a Rho-dependent manner. In this report, we show that activation of keratinocyte PAR-2 stimulates release of PGE(2) and PGF(2alpha) and that PGE(2) and PGF(2alpha) act as paracrine factors that stimulate melanocyte dendricity. We characterized the expression of the EP and FP receptors in human melanocytes and show that human melanocytes express EP1 and EP3, and the FP receptor, but not EP2 and EP4. Treatment of melanocytes with EP1 and EP3 receptor agonists resulted in increased melanocyte dendricity, indicating that both EP1 and EP3 receptor signaling contribute to PGE(2)-mediated melanocyte dendricity. Certain EP3 receptor subtypes have been shown to increase adenosine 3',5'-cyclic monophosphate (cAMP) through coupling to Gs, whereas EP1 is known to couple to Gq to activate phospholipase C with elevation in Ca(2+). The cAMP/protein kinase A system is known to modulate melanocyte dendrite formation through modulation of Rac and Rho activity. Neither PGF(2alpha) or PGE(2) elevated cAMP in human melanocytes showing that dendricity observed in response to PGE(2) and PGF(2alpha) is cAMP-independent. Our data suggest that PAR-2 mediates cutaneous pigmentation both through increased uptake of melanosomes by keratinocytes, as well as by release of PGE(2) and PGF(2alpha) that stimulate melanocyte dendricity through EP1, EP3, and FP receptors.

Nitrergic relaxation in rat gastric fundus: influence of mechanism of induced tone and possible role of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase

The aim of this study was to investigate the influence of the mechanism of induced tone and the role of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) in nitrergic relaxation of rat gastric fundus. Prostaglandin F(2alpha) (PGF(2alpha)), thapsigargin (TSG) and cyclopiazonic acid (CPA) were used in concentrations that induced a similar contraction (20 g force/g tissue). Nifedipine (3 x 10(-7) M) completely relaxed PGF(2alpha)-contracted tissues and relaxed tissues contracted by TSG and CPA by 20 +/- 6% and 56 +/- 12% respectively; contraction induced by the three contractile agents was fully reversed by a general Ca2+ entry blocker 1-[2-(4-methoxyphenyl)-2-[3-(4-metoxyphenyl)propoxy]ethyl-1H-imidazole HCl (SKF 96365; 10(-5) M). In the presence of nifedipine (3 x 10(-7) M) or verapamil (10(-5) M), PGF(2alpha) and CPA-induced contractions were still approximately 50% relaxed by SKF 96365. This suggests that contractions induced by PGF(2alpha) are related to Ca2+ entry through L-type voltage-operated Ca2+ channels and that contractions by TSG are mainly related to Ca2+ entry through store-operated Ca2+ channels. Relaxant responses to exogenous nitric oxide (NO), to endogenous NO released by electrical field stimulation, and to vasoactive intestinal polypeptide (VIP) were studied in tissues contracted by TSG and CPA and compared to responses in tissues contracted by PGF(2alpha). Responses to exogenous and endogenous NO were greatly attenuated in TSG-contracted tissues, but not in CPA-contracted tissues. When contraction was induced by CPA in the presence of nifedipine or verapamil, relaxations to exogenous and endogenous NO were also significantly reduced. Relaxation induced by VIP was reduced in tissues contracted by either TSG or CPA in the presence of nifedipine or verapamil. These results suggest that the ability of the nitrergic neurotransmitter to induce relaxation of rat gastric fundus is influenced by the mechanism used to induce tone and are indicative for a role for SERCA in nitrergic relaxation. However, activation of SERCA appears to not be unique for nitrergic relaxation, but might also be used by VIP, a co-transmitter of NO in this tissue.

Expression, localization and function of prostaglandin receptors in myometrium

Prostaglandins (PGs) play a role in the initiation and maintenance of labor, acting via specific relaxatory or contractile receptors on myometrium. Myometrial response to addition of PGs may be determined by the type and concentration of receptor expressed. Autoradiographic and ligand binding studies suggest a topographic distribution of receptors between fundus, lower segment, and cervix, and that hormonally regulated changes in expression occur with advancing gestation and labor. These receptors have now been cloned and sequenced allowing molecular studies. Current dogma suggests functional regionalization of the pregnant human uterus occurs with the lower segment displaying a contractile phenotype throughout gestation changing to a relaxatory phenotype at labor to allow passage of the fetal head whereas the upper segment has a relaxatory phenotype throughout most of gestation to accommodate the growing fetus and adopts a contractile phenotype for expulsion at labor. Studies to determine the role of PG receptors in this phenomenon are currently underway.

Smoking enhances oxytocin-induced rhythmic myometrial contraction

Although smoking during pregnancy is one of the major risk factors of premature delivery, the underlying mechanism by which smoking causes premature delivery is unknown. In the present study, we examined the effects of smoking on uterine contractility induced by oxytocin and prostaglandin F(2alpha). Rats inhaled either cigarette smoke or room air from Day 14 to Day 16 of pregnancy through an inhalation apparatus for experimental animals (type "Hamburg II"). After the rats were killed on Day 17 of pregnancy, the uterine contractile sensitivity and activity on exposure to oxytocin or prostaglandin F2alpha were investigated. The expression levels of oxytocin-receptor mRNA and prostaglandin F(2alpha) receptor mRNA in the uterus were investigated by reverse transcription-polymerase chain reaction. The contractile activity was assessed as the contractile force and the frequency of rhythmic contractions of myometrial strips that were treated with oxytocin or prostaglandin F(2alpha). The contractile sensitivity to oxytocin was significantly higher in the smoking group than in the control group (P < 0.01). Although the contractile force of oxytocin-induced contractions did not differ between the smoking and control groups, the frequency of contractions was significantly higher in the smoking group than in the control group (P < 0.01). On the other hand, no significant differences were found in the contractile sensitivity and activity in response to prostaglandin F(2alpha) between the smoking and control groups. The expression of oxytocin-receptor mRNA in the myometrium was significantly increased in the smoking group compared with the control group (P < 0.01). However, no significant difference was found in the level of expression of prostaglandin F(2alpha)-receptor mRNA between the two groups. These results suggest that smoking during pregnancy increases the contractile sensitivity and activity of the myometrium in response to oxytocin by up-regulating the expression of oxytocin-receptor mRNA. The effects of smoking on the contractile sensitivity and activity of the myometrium in response to oxytocin may increase the risk of premature delivery in smokers.

Prostaglandin F2(alpha) stimulates growth of skeletal muscle cells via an NFATC2-dependent pathway

Skeletal muscle growth requires multiple steps to form large multinucleated muscle cells. Molecules that stimulate muscle growth may be therapeutic for muscle loss associated with aging, injury, or disease. However, few factors are known to increase muscle cell size. We demonstrate that prostaglandin F2alpha (PGF2alpha) as well as two analogues augment muscle cell size in vitro. This increased myotube size is not due to PGF2alpha-enhancing cell fusion that initially forms myotubes, but rather to PGF2alpha recruiting the fusion of cells with preexisting multinucleated cells. This growth is mediated through the PGF2alpha receptor (FP receptor). As the FP receptor can increase levels of intracellular calcium, the involvement of the calcium-regulated transcription factor nuclear factor of activated T cells (NFAT) in mediating PGF2alpha-enhanced cell growth was examined. We show that NFAT is activated by PGF2alpha, and the isoform NFATC2 is required for PGF2alpha-induced muscle cell growth and nuclear accretion, demonstrating the first intersection between prostaglandin receptor activation and NFAT signaling. Given this novel role for PGF2alpha in skeletal muscle cell growth, these studies raise caution that extended use of drugs that inhibit PG production, such as nonsteroidal antiinflammatory drugs, may be deleterious for muscle growth.

Prostaglandin F2alpha- and FAS-activating antibody-induced regression of the corpus luteum involves caspase-8 and is defective in caspase-3 deficient mice

We recently demonstrated that caspase-3 is important for apoptosis during spontaneous involution of the corpus luteum (CL). These studies tested if prostaglandin F2alpha (PGF2alpha) or FAS regulated luteal regression, utilize a caspase-3 dependent pathway to execute luteal cell apoptosis, and if the two receptors work via independent or potentially shared intracellular signaling components/pathways to activate caspase-3. Wild-type (WT) or caspase-3 deficient female mice, 25-26 days old, were given 10 IU equine chorionic gonadotropin (eCG) intraperitoneally (IP) followed by 10 IU human chorionic gonadotropin (hCG) IP 46 h later to synchronize ovulation. The animals were then injected with IgG (2 micrograms, i.v.), the FAS-activating antibody Jo2 (2 micrograms, i.v.), or PGF2alpha (10 micrograms, i.p.) at 24 or 48 h post-ovulation. Ovaries from each group were collected 8 h later for assessment of active caspase-3 enzyme and apoptosis (measured by the TUNEL assay) in the CL. Regardless of genotype or treatment, CL in ovaries collected from mice injected 24 h after ovulation showed no evidence of active caspase-3 or apoptosis. However, PGF2alpha or Jo2 at 48 h post-ovulation and collected 8 h later induced caspase-3 activation in 13.2 +/- 1.8% and 13.7 +/- 2.2 % of the cells, respectively and resulted in 16.35 +/- 0.7% (PGF2alpha) and 14.3 PlusMinus; 2.5% TUNEL-positive cells when compared to 1.48 +/- 0.8% of cells CL in IgG treated controls. In contrast, CL in ovaries collected from caspase-3 deficient mice whether treated with PGF2alpha, Jo2, or control IgG at 48 h post-ovulation showed little evidence of active caspase-3 or apoptosis. CL of WT mice treated with Jo2 at 48 h post-ovulation had an 8-fold increase in the activity of caspase-8, an activator of caspase-3 that is coupled to the FAS death receptor. Somewhat unexpectedly, however, treatment of WT mice with PGF2alpha at 48 h post-ovulation resulted in a 22-fold increase in caspase-8 activity in the CL, despite the fact that the receptor for PGF2alpha has not been shown to be directly coupled to caspase-8 recruitment and activation. We hypothesize that PGF2alpha initiates luteolysis in vivo, at least in part, by increasing the bioactivity or bioavailability of cytokines, such as FasL and that multiple endocrine factors work in concert to activate caspase-3-driven apoptosis during luteolysis.

Function of prostanoid receptors: studies on knockout mice

Prostanoids consisting of the prostaglandins (PGs) and the thromboxanes (TXs) are the cyclooxygenase metabolites of arachidonic acid. They exert a range of actions mediated by their respective receptors expressed in the target cells. The receptors include the DP, EP, FP, IP and TP receptors for PGD, PGE, PGF, PGI and TXA, respectively. Furthermore, EP is subdivided into four subtypes, EP1, EP2, EP3 and EP4, which are encoded by different genes and differ in their responses to various agonists and antagonists. Recent developments in the molecular biology of the prostanoid receptors have enabled the investigation of physiological roles of each receptor by disruption of the respective gene. At this point, all the eight types and subtypes of the prostanoid receptors have been individually knocked out in mice, and various phenotypes have been reported for each strain. Here, we review the findings obtained in these studies. The results from these knockout mice studies may be useful in the development of novel therapeutics that can selectively manipulate actions mediated by each receptor.

Effects of prostaglandins on the aqueous humor outflow pathways

Topical treatments with certain prostaglandins (PGs), including FP receptor agonists, lower intraocular pressure by increasing uveoscleral outflow. Although the precise mechanism for the increased uveoscleral outflow is not known, there appears to be activation of a molecular transduction cascade and an increase in the biosynthesis of certain metalloproteinases. This leads to reduction of extracellular matrix components within the ciliary muscle, iris root, and sclera. It is possible that this reduction of extracellular matrix present within portions of the uveoscleral pathway may contribute to the mechanism of increased uveoscleral outflow. Additional mechanisms that may contribute to the PG-mediated increase of uveoscleral outflow include relaxation of the ciliary muscle, cell shape changes, cytoskeletal alteration, or compaction of the extracellular matrix within the tissues of the uveoscleral outflow pathway. Future studies should clarify the importance of these various responses that may contribute to increased uveoscleral outflow. At present, there is no compelling evidence for a substantial facility-increasing effect on the trabecular meshwork outflow for any of these compounds.

Response of rat thoracic aorta to F(2)-isoprostane metabolites

SUMMARY

This study was undertaken to investigate the vascular actions (contraction and relaxation) of the F(2)-isoprostane metabolites 15-keto-15-F(2t)-IsoP, 2,3-dinor-15-F(2t)-IsoP, and 2,3-dinor-5,6-dihydro -15-F(2t)-IsoP in comparison with 15-F(2t)-IsoP on the rat thoracic aorta. 15-keto-15-F(2t)-IsoP induced a vasoconstriction in a concentration-dependent manner with a pD(2) value of 5.80 +/- 0.05, whereas 2,3-dinor-15-F(2t)-IsoP and 2,3-dinor-5,6-dihydro-15-F(2t)-IsoP had no effect. The parent compound 15-F(2t)-IsoP was more potent (pD(2) value: 6.46 +/- 0.1). Endothelium removal had no influence on the contraction to 15-keto-15-F(2t)-IsoP. GR32191 (a TP-receptor antagonist) concentration-dependently inhibited the contraction induced by 15-keto-15-F(2t)-IsoP, with a significant decrease in the E(max) values for GR32191 10(-7) M. Pretreatment with 2,3-dinor-15-F(2t)-IsoP and 2,3-dinor-5,6-dihydro-15-F(2t)-IsoP induced no alteration of 15-F(2t)-IsoP concentration-response curves. In contrast, 15-keto-15-F(2t)-IsoP pretreatment competitively inhibited the response to 15-F(2t)-IsoP. When concentration ratios of EC(50) values were used, a Schild regression of this data was linear with a slope of 0.974 and a pA(2) value of 6.13. 15-keto-15-F(2t)-IsoP at high concentrations caused a weak concentration-dependent relaxation of rat aorta rings contracted with U46619 (3.10(-8) M) that was not modified in the absence of endothelium. In contrast, 2,3-dinor-15-F(2t)-IsoP and 2,3-dinor-5,6-dihydro-15-F(2t)-IsoP induced no vasodilation. In conclusion, among the F(2)-isoprostane metabolites, 2,3-dinor-15-F(2t)-IsoP and 2,3-dinor-5,6-dihydro-15-F(2t)-IsoP did not cause vasorelaxation or vasoconstriction on the rat thoracic aorta. In contrast, 15-keto-15-F(2t)-IsoP mediates contraction through activation of TP-receptors, probably as a partial agonist, and induces a weak endothelium-independent relaxation at high concentrations.

Expression and localization of the contractile prostaglandin F receptor in pregnant rat myometrium in late gestation, labor, and postpartum

A polyclonal antibody was raised against amino acids 7-18 in the first extracellular loop of rat prostaglandin F (FP) receptor to monitor expression and localization in pregnant rat myometrium at Gestational Days 16, 18, 20, 21, 21.5, 22 (delivery), and 23 (1-day postpartum; n = 5 per group). The antibody recognized a protein of approximately 43 kDa on Western blot analysis in both membrane (soluble and nonsoluble) and cytosolic fractions of myometrium on each day of gestation. Expression of FP protein increased significantly (P < 0.05) during late gestation in both soluble membrane and cytosolic fractions, being significantly greater at Day 21.5 than at Day 20 of gestation in the soluble membrane fraction and in the cytosolic fraction of tissues collected during labor compared with those obtained before labor. The total concentration of FP receptor in the membrane (soluble plus nonsoluble) remained high throughout late gestation and fell significantly (P < 0.05) in the postpartum period. The FP receptor in the soluble membrane fraction (compared to the total membrane FP receptor) was significantly (P < 0.05) higher in late gestation than earlier, whereas the ratio of FP protein in cytosolic to that in the total membrane was significantly (P < 0.05) higher on Day 23 than earlier in gestation, suggesting a dynamic movement of FP with advancing gestational age. Immunoreactive FP receptor localized to circular and longitudinal smooth muscle at all gestational ages, but changes in intracellular localization were observed in late gestation with a staining pattern similar to alpha-actin, suggesting an association with myofibrils. Our study suggests an increase in FP-receptor protein in myometrium with advancing gestation and a marked elevation at term. This supports a role for uterine FP receptors in mediation of uterine contractility at term.

Human granulosa-lutein cells express functional EP1 and EP2 prostaglandin receptors

Prostaglandin E(2) (PGE(2)) exerts mainly luteotrophic effects in the corpus luteum. In other tissues, PGE(2) acts via specific PGE(2) receptor subtypes including EP1, which modulates intracellular calcium ([Ca(2+)](i)) and EP2, which is coupled to cyclic AMP (cAMP) generation. We have therefore investigated the presence of functional EP1 and EP2 receptors using human granulosa-lutein (GL) cells. Reverse-transcription PCR revealed that GL cells expressed mRNA transcripts encoding both EP1 and EP2 receptors. When GL cells were challenged with ligands that can bind to both receptor subtypes (PGE(2) and 16,16 dimethyl PGE(2)) or exclusively to EP2 (butaprost), both cAMP formation and progesterone synthesis were stimulated. Furthermore, the cAMP response to these agonists could be significantly blocked by an EP1/2 antagonist AH6809 but not by an EP1-selective antagonist SC19220. Exposure of GL cells to 16,16-dm PGE(2) transiently raised [Ca(2+)](i) levels, which could be prevented by both AH6809 and SC19220. We therefore conclude that human GL cells express functional EP1 and EP2 receptors.

Prostaglandin F(2alpha) receptor in the corpus luteum: recent information on the gene, messenger ribonucleic acid, and protein

The prostaglandin (PG) F(2alpha) receptor (FPr) in the corpus luteum is essential for maintaining normal reproductive cyclicity in many species. Activation of this seven-transmembrane spanning receptor at the end of the cycle leads to a decrease in progesterone and the demise of the corpus luteum (luteolysis). Recently, the gene structure of the FPr in three mammalian species has been elucidated; however, promoter regulation of the gene is still poorly understood. The FPr mRNA is extremely low in steroidogenic follicular cells (theca or granulosa) but is expressed at high levels in the corpus luteum, particularly in the large luteal cells. Treatment with PGF(2alpha) decreased FPr mRNA expression in luteal cells in most species that have been studied. Key amino acids have been suggested to be critical for binding of FPr to PGF(2alpha) based on three-dimensional modeling and comparisons with other G-protein-coupled receptors. Moieties of the PGF(2alpha) molecule that are essential for binding or specificity of binding to the FPr have been identified by radioreceptor binding studies. In this article, recent information is reviewed on the structure of the FPr gene, regulation of luteal FPr mRNA, and receptor/ligand interaction requirements for the FPr protein.

Effects of gestational age and labor on expression of prostanoid receptor genes in baboon uterus

We determined the effect of gestational age and labor on the regional expression of prostanoid receptor genes in baboon myometrium. Cesarean hysterectomy was performed on 15 pregnant baboons of known gestational age in the last third of pregnancy, five of them during spontaneous term labor. Expression of prostanoid receptor genes was studied using Northern blot analysis. Transcripts of similar size to the human were detected for prostanoid EP(1), EP(2), EP(3), EP(4), IP, FP, and TP receptor genes using Northern blot analysis. There were no gestational age-related changes in expression of these genes. Expression of EP(1), EP(3), and IP receptor RNA mRNA was significantly higher in myometrium from the fundus (compared with the lower segment), whereas EP(2) gene expression was significantly lower in the fundus. Labor was associated with a reduction in the regional variation of both EP(2) and IP receptor gene expression, but not EP(1) and EP(3) expression. Labor was also associated with an overall lower level of expression of EP(2) receptor mRNA. We conclude that regional and labor-related variation in myometrial expression of prostanoid receptor genes may have a key role in primate parturition.

Effects of gestational age and labor on the expression of prostanoid receptor genes in pregnant baboon cervix

We sought to determine whether expression of genes encoding prostaglandin receptors varied with advancing gestational age and in association with the onset of spontaneous labor in the cervix of pregnant baboons. We performed cesarean hysterectomy on 14 pregnant baboons, five during spontaneous labor. Expression of genes was quantified by Northern analysis. Clear signals which were similar in estimated size to the human genes were detected by Northern analysis for the genes encoding the EP1, EP2, EP3, EP4, FP, IP and TP receptors. Expression of the gene encoding the prostanoid EP1 receptor increased with advancing gestational age prior to labor (r2 = 0.8, P = 0.007). There was a 4 fold lower level of expression of the EP2 receptor gene among animals in labor compared with animals not in labor (P = 0.006) and approximately 2-fold lower levels of expression of the FP and TP receptor genes (P < 0.0001 and P = 0.0002, respectively). We conclude that variation in the relative expression of prostanoid receptor types and sub-types may have a role in cervical dilatation in primate parturition.

Mitogen-activated protein kinase inhibitors suppress prostaglandin F(2alpha)-induced myosin-light chain phosphorylation and contraction in iris sphincter smooth muscle

The purpose of this study was to investigate the potential role of mitogen-activated protein (MAP) kinase in contraction by monitoring MAP kinase phosphorylation (activation) and contraction during agonist stimulation of cat iris sphincter smooth muscle. Changes in tension in response to prostaglandin F(2alpha), latanoprost, a prostaglandin F(2alpha) analog used as an anti-glaucoma drug, and carbachol were recorded isometrically, and MAP kinase activation was monitored by Western blot using a phosphospecific p42/p44 MAP kinase antibody. We found that treatment of the muscle with 2'-Amino-3'-methoxyflavone (PD98059) (10 microM), a specific inhibitor of MAP kinase kinase (MEK), inhibited significantly prostaglandin F(2alpha)- and latanoprost-induced phosphorylation and contraction, but had little effect on those evoked by carbachol. Prostaglandin F(2alpha) increased MAP kinase phosphorylation in a concentration-dependent manner with EC(50) value of 1.1 x 10(-8) M and increased contraction with EC(50) of 0.92 x 10(-9) M. The MAP kinase inhibitors PD98059, Apigenin and 1,4-Diamino-2,3-dicyano-1, 4bis(2-aminophenylthio)butadiene (UO126) inhibited prostaglandin F(2alpha)-induced contraction in a concentration-dependent manner with IC(50) values of 2.4, 3.0 and 4.8 microM, respectively. PD98059 had no effect on prostaglandin F(2alpha)- or on carbachol-stimulated inositol-1,4,5-trisphosphate (IP(3)) production. In contrast, the MAP kinase inhibitor inhibited prostaglandin F(2alpha)-induced myosin-light chain (MLC) phosphorylation, but had no effect on that of carbachol. N-[2-(N-(4-Chloro-cinnamyl)-N-methylaminomethyl)phenyl]-N-[2- hydroxyethyl]-4-methoxybenzenesulfonamide (KN-93) (10 microM), a Ca(2+)-calmodulin-dependent protein kinase inhibitor, and Wortmannin (10 microM), an MLC kinase inhibitor, inhibited significantly (by 80%) prostaglandin F(2alpha)- and carbachol-induced contraction. It can be concluded that in this smooth muscle p42/p44 MAP kinases are involved in the mechanism of prostaglandin F(2alpha)-, but not in that of carbachol, induced contraction. In addition, these data clearly indicate that the stimulation of the iris sphincter with prostaglandin F(2alpha) and carbachol activate two distinct pathways, the MAP kinase pathway and the Ca(2+) mobilization pathway.

Distribution and function of prostanoid receptors: studies from knockout mice

Recent developments in the molecular biology of the prostanoid receptors has allowed the investigation of the physiological roles of each individual receptor type and subtype. The following article reports the prostanoid receptor distributions deduced from Northern blot and in situ hybridization analyses, summarizes the phenotypes of each receptor knockout mice, and discusses recent studies investigating the effects of each receptor deficiency on the inflammatory response and female reproductive processes. The combination of expression pattern and knockout analyses enabled us to determine which receptor expressed in a particular cell is important for the maintenance of normal and/or pathological physiology. The results from these analyses may be useful in the development of novel therapeutics that can selectively manipulate prostanoid-mediated actions.

Prostanoid receptors: structures, properties, and functions

Prostanoids are the cyclooxygenase metabolites of arachidonic acid and include prostaglandin (PG) D(2), PGE(2), PGF(2alpha), PGI(2), and thromboxne A(2). They are synthesized and released upon cell stimulation and act on cells in the vicinity of their synthesis to exert their actions. Receptors mediating the actions of prostanoids were recently identified and cloned. They are G protein-coupled receptors with seven transmembrane domains. There are eight types and subtypes of prostanoid receptors that are encoded by different genes but as a whole constitute a subfamily in the superfamily of the rhodopsin-type receptors. Each of the receptors was expressed in cultured cells, and its ligand-binding properties and signal transduction pathways were characterized. Moreover, domains and amino acid residues conferring the specificities of ligand binding and signal transduction are being clarified. Information also is accumulating as to the distribution of these receptors in the body. It is also becoming clear for some types of receptors how expression of their genes is regulated. Furthermore, the gene for each of the eight types of prostanoid receptor has been disrupted, and mice deficient in each type of receptor are being examined to identify and assess the roles played by each receptor under various physiological and pathophysiological conditions. In this article, we summarize these findings and attempt to give an overview of the current status of research on the prostanoid receptors.

A novel biological role for prostaglandin D2 is suggested by distribution studies of the rat DP prostanoid receptor

We report the cloning, functional expression and cell-specific localization of the rat homologue of the prostaglandin D2 receptor (DP). In situ hybridization, utilizing multiple digoxigenin-labelled riboprobes and their complementary sense controls, was performed to determine the detailed distribution of DP receptor mRNA in the central nervous system and the gastrointestinal tract. Within the brain, the leptomeninges and choroid plexus expressed DP receptor mRNA. Transcripts detected in the spinal cord were localized to the sensory and motor neurons of the dorsal and ventral horns, respectively, suggesting a role for the DP receptor in the modulation of central nervous system processes, including pain transmission. Within the gastrointestinal tract (stomach, duodenum, ileum and colon) signals were highly localized to the mucous-secreting goblet cells and the columnar epithelium. These findings suggest a novel biological role for prostaglandin D2-mediated activity at the DP receptor, namely mucous secretion. In addition, radioligand binding assays (saturation analyses and equilibrium competition assays) and functional assays (measuring cAMP accumulation) were performed to characterize the recombinant rat DP receptor expressed in human embryonic kidney (HEK) 293(EBNA) cells. A single site of binding (K(D) = 14 nM, Bmax = 115 fmol/mg protein) was measured for prostaglandin D2-specific binding to the rat DP receptor. Prostaglandin D2 proved to be a potent agonist at the rat DP receptor (EC50 = 5 nM). The rank order of efficacy for DP receptor specific agonists [prostaglandin D2 = prostaglandin J2 = BW 245C (5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropylhydantoin)) > L-644,698 ((4-(3-(3-(3-hydroxyoctyl)-4-oxo-2-thiazolidinyl) propyl) benzoic acid) (racemate)] reflected the affinity with which the ligands bound to the receptor.

Prostaglandin F2 alpha upregulates intercellular adhesion molecule-1 expression in human gingival fibroblasts

Prostaglandin F2 alpha (PGF2 alpha) is a bioactive lipid mediator, which has been suggested to be involved in the pathogenesis of periodontal disease. However, the roles of PGF2 alpha in the disease are not well understood. In the present study, we investigated the effect of PGF2 alpha on intercellular adhesion molecule-1 (ICAM-1) expression in human gingival fibroblasts (HGF) and the effect of PGF2 alpha on ICAM-1 expression elicited by proinflammatory cytokines, interferon-gamma (IFN-gamma) and tumour necrosis factor alpha (TNF alpha) in the cells. PGF2 alpha-stimulated HGF expressed ICAM-1 expression in a time- and dose-dependent manner. IFN-gamma-elicited ICAM-1 expression was synergistically increased by PGF2 alpha, whereas TNF alpha-induced ICAM-1 expression was slightly inhibited by PGF2 alpha. Fluprostenol, a selective FP receptor agonist, could mimic PGF2 alpha-induced effect on ICAM-1 expression. Furthermore, signal transduction for the regulation of ICAM-1 by PGF2 alpha was investigated using N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7), a calcium calmodulin antagonist, and 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine (H-7), an inhibitor of protein kinase C (PKC). W-7 and H-7, remarkably, suppressed PGF2 alpha-induced ICAM-1 expression and synergistic increase of ICAM-1 expression by combination of PGF2 alpha and IFN-gamma, while IFN-gamma-elicited ICAM-1 expression was only partially inhibited by W-7 and H-7. From these data, we suggest that PGF2 alpha upregulates ICAM-1 expression in HGF and synergistically enhances IFN-gamma-induced ICAM-1 expression through FP receptor by calcium calmodulin-dependent and PKC-dependent pathways. PGF2 alpha may be involved in the pathology of periodontal disease by upregulating ICAM-1 expression in HGF.

Luteolysis: a neuroendocrine-mediated event

In many nonprimate mammalian species, cyclical regression of the corpus luteum (luteolysis) is caused by the episodic pulsatile secretion of uterine PGF2alpha, which acts either locally on the corpus luteum by a countercurrent mechanism or, in some species, via the systemic circulation. Hysterectomy in these nonprimate species causes maintenance of the corpora lutea, whereas in primates, removal of the uterus does not influence the cyclical regression of the corpus luteum. In several nonprimate species, the episodic pattern of uterine PGF2alpha secretion appears to be controlled indirectly by the ovarian steroid hormones estradiol-17beta and progesterone. It is proposed that, toward the end of the luteal phase, loss of progesterone action occurs both centrally in the hypothalamus and in the uterus due to the catalytic reduction (downregulation) of progesterone receptors by progesterone. Loss of progesterone action may permit the return of estrogen action, both centrally in the hypothalamus and peripherally in the uterus. Return of central estrogen action appears to cause the hypothalamic oxytocin pulse generator to alter its frequency and produce a series of intermittent episodes of oxytocin secretion. In the uterus, returning estrogen action concomitantly upregulates endometrial oxytocin receptors. The interaction of neurohypophysial oxytocin with oxytocin receptors in the endometrium evokes the secretion of luteolytic pulses of uterine PGF2alpha. Thus the uterus can be regarded as a transducer that converts intermittent neural signals from the hypothalamus, in the form of episodic oxytocin secretion, into luteolytic pulses of uterine PGF2alpha. In ruminants, portions of a finite store of luteal oxytocin are released synchronously by uterine PGF2alpha pulses. Luteal oxytocin in ruminants may thus serve to amplify neural oxytocin signals that are transduced by the uterus into pulses of PGF2alpha. Whether such amplification of episodic PGF2alpha pulses by luteal oxytocin is a necessary requirement for luteolysis in ruminants remains to be determined. Recently, oxytocin has been reported to be produced by the endometrium and myometrium of the sow, mare, and rat. It is possible that uterine production of oxytocin may act as a supplemental source of oxytocin during luteolysis in these species. In primates, oxytocin and its receptor and PGF2alpha and its receptor have been identified in the corpus luteum and/or ovary. Therefore, it is possible that oxytocin signals of ovarian and/or neural origin may be transduced locally at the ovarian level, thus explaining why luteolysis and ovarian cyclicity can proceed in the absence of the uterus in primates. However, it remains to be established whether the intraovarian process of luteolysis is mediated by arachidonic acid and/or its metabolite PGF2alpha and whether the central oxytocin pulse generator identified in nonprimate species plays a mediatory role during luteolysis in primates. Regardless of the mechanism, intraovarian luteolysis in primates (progesterone withdrawal) appears to be the primary stimulus for the subsequent production of endometrial prostaglandins associated with menstruation. In contrast, luteolysis in nonprimate species appears to depend on the prior production of endometrial prostaglandins. In primates, uterine prostaglandin production may reflect a vestigial mechanism that has been retained during evolution from an earlier dependence on uterine prostaglandin production for luteolysis.

Tyrosine kinase inhibitors suppress prostaglandin F2alpha-induced phosphoinositide hydrolysis, Ca2+ elevation and contraction in iris sphincter smooth muscle

We investigated the effects of the protein tyrosine kinase inhibitors, genistein, tyrphostin 47, and herbimycin on prostaglandin F2alpha- and carbachol-induced inositol-1,4,5-trisphosphate (IP3) production, [Ca2+]i mobilization and contraction in cat iris sphincter smooth muscle. Prostaglandin F2alpha and carbachol induced contraction in a concentration-dependent manner with EC50 values of 0.92 x 10(-9) and 1.75 x 10(-8) M, respectively. The protein tyrosine kinase inhibitors blocked the stimulatory effects of prostaglandin F2alpha, but not those evoked by carbachol, on IP3 accumulation, [Ca2+]i mobilization and contraction, suggesting involvement of protein tyrosine kinase activity in the physiological actions of the prostaglandin. Daidzein and tyrphostin A, inactive negative control compounds for genistein and tyrphostin 47, respectively, were without effect. Latanoprost, a prostaglandin F2alpha analog used as an antiglaucoma drug, induced contraction and this effect was blocked by genistein. Genistein (10 microM) markedly reduced (by 67%) prostaglandin F2alpha-stimulated increase in [Ca2+]i but had little effect on that of carbachol in cat iris sphincter smooth muscle cells. Vanadate, a potent inhibitor of protein tyrosine phosphatase, induced a slow gradual muscle contraction in a concentration-dependent manner with an EC50 of 82 microM and increased IP3 generation in a concentration-dependent manner with an EC50 of 90 microM. The effects of vanadate were abolished by genistein (10 microM). Wortmannin, a myosin light chain kinase inhibitor, reduced prostaglandin F2alpha- and carbachol-induced contraction, suggesting that the involvement of protein tyrosine kinase activity may lie upstream of the increases in [Ca2+]i evoked by prostaglandin F2alpha. Further studies aimed at elucidating the role of protein tyrosine kinase activity in the coupling mechanism between prostaglandin F2alpha receptor activation and increases in intracellular Ca2+ mobilization and identifying the tyrosine-phosphorylated substrates will provide important information about the role of protein tyrosine kinase in the mechanism of smooth muscle contraction, as well as about the mechanism of the intraocular pressure lowering effect of the prostaglandin in glaucoma patients.

Influence of a selective guanylate cyclase inhibitor, and of the contraction level, on nitrergic relaxations in the gastric fundus

1. The influence of the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ) on non-adrenergic non-cholinergic (NANC) relaxations and the possible role of a nerve-derived hyperpolarizing factor in NANC relaxation were investigated in the rat gastric fundus. 2. ODQ (10(-6) and 10(-5) M) concentration-dependently inhibited the short-lasting relaxations by NO (2 x 10(-6) M-10(-4) M) administered as a bolus without influencing the relaxation by 3 x 10(-8) M isoprenaline. The relaxation by an infusion of NO was reduced to the same extent by 10(-6) and 10(-5) M ODQ. 3. The electrically induced short-lasting and sustained relaxations (40 V, 1 ms, 0.5-16 Hz, 10 s trains at 2 min interval or cumulative increase in the frequency every 2 min) in NANC conditions were inhibited to a similar extent by 10(-6) and 10(-5) M ODQ, and by the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-4) M). 4. ODQ (10(-6) M) and L-NAME (3 x 10(-4) M), administered after 5, 10 or 20 min of long-term stimulation, reversed the relaxation to a similar extent (approximately 50% at 2 Hz and 20% at 8 Hz). 5. When the tissues were contracted to 40% of maximum by adapting the concentration of prostaglandin F2alpha (PGF2alpha), the inhibitory effect of 3 x 10(-4) M L-NAME on relaxations induced by train and cumulative stimulation was the same as when tissues were contracted with 3 x 10(-7) M PGF2alpha. 6. The findings of this study illustrate that the relaxation by exogenous and endogenous NO in the rat gastric fundus is due to activation of soluble guanylate cyclase. During long-term electrical stimulation, the partial contribution of NO to NANC relaxation is maintained but it is small at higher frequencies of stimulation. Evidence for the contribution of a nerve-derived hyperpolarizing factor to NANC relaxation was not obtained.

Stepwise activation of the gonadotropic signal transduction pathway, and the ability of prostaglandin F2alpha to inhibit this activated pathway

Through selective activation of the gonadotropic signal transduction pathway, we have determined the probable site of the antigonadotropic effects of prostaglandin F2alpha (PGF2alpha) in the human granulosa-luteal cell (hGLC). The gonadotropic signal transduction pathway was activated at the level of the receptor (luteinizing hormone and beta-adrenergic), stimulatory G protein (Gs), adenylate cyclase (AC), and protein kinase A (PKA) by human chorionic gonadotropin (hCG) and isoproterenol (Iso), cholera toxin (CTX), forskolin, and dibutryl cAMP (Db cAMP), respectively. Concomitantly, the ability of PGF2alpha to inhibit progesterone production in response to the activation of this cascade at these different levels was examined. hGLCs were obtained from in vitro fertilization patients and were precultured for 8 d in Medium 199 supplemented with fetal bovine serum (M199; 10% FBS). Following the preculture period, cells were treated with either vehicle or one of the above activators of the gonadotropic pathway, either in the absence or presence of PGF2alpha (in M199; No FBS). Following the treatment period, media were collected and assayed for progesterone by RIA. Prostaglandin F2alpha (10(-6) M) significantly inhibited hCG (1 IU/mL), Iso (10(-5) M), CTX (1 microg/mL), and forskolin- (10(-5) M) stimulated progesterone production. Conversely, PGF2alpha did not inhibit progesterone production stimulated by a saturating concentration of Db cAMP (10(-6) M). The ability of PGF2alpha to inhibit hCG- or CTX-stimulated progesterone production was attenuated by pertussis toxin (PTX; 50 ng/mL). In conclusion, through a pertussis toxin-sensitive G protein, PGF2alpha inhibits progesterone production at a level below AC, and above the activation of PKA by cAMP.

Regulation of a common, low-affinity binding site for primary prostanoids on bovine aortic endothelial cells

Bovine aortic endothelial cells contain a prostaglandin site which binds with similar low-affinity PGE2, PGF2alpha and the thromboxane agonist U-46619. Treatment of the cells with agents that increase the level of cellular cAMP such as forskolin, a direct activator of adenylate cyclase or IBMX, a phosphodiesterase inhibitor, decreased the binding of PGE2 to the cells. Addition of dibutyryl cAMP to intact cells caused a quick reduction in PGE2 binding with a half time of less than 2 min. The reduction in PGE2 binding was completely reversible after removing the dibutyryl cAMP. The reduction in PGE2 binding after addition of dibutyryl cAMP to the intact cells was also observed after a mechanical disruption of the cells or after permeabilization with digitonin. Incubation of the cells with myristoylated PKI(14-22) amide, a specific protein kinase A inhibitor, resulted in partial suppression of the reduction of PGE2 binding by dibutyryl cAMP. Pretreatment of intact cells for 24 h with 10(-6) M PGE2 or a PKC activator did not reduce the specific binding of [3H]-PGE2. These results suggest that PKA, but not PKC, is involved in a fast reversible regulation of the common prostanoid receptor on bovine endothelial cells.

Localization of the prostaglandin F2 alpha receptor in rat tissues

The localization of the prostaglandin F2alpha (FP) receptor was examined in rat tissues by immunohistochemistry and in situ hybridization. Immunohistochemistry on paraffin sections was performed with a rabbit polyclonal antiserum raised against a synthetic peptide derived from the rat FP receptor sequence. In situ hybridization on cryosections was done with 35S-labelled rat FP receptor antisense and sense riboprobes. The most intense FP receptor-like immunoreactivity was observed in granulosa luteal cells, muscle and epithelial cells, e.g. cardiac, skeletal and smooth muscle, and hepatocytes. Weaker immunoreactivity was found in connective tissue fibroblasts. In the eye, intense immunostaining was associated with the corneal and conjunctival epithelium and moderate staining with the ciliary body, retina, iris and connective tissues. In situ hybridization generally confirmed the results. The riboprobe hybridized weakly with the heart, skeletal muscle, uterus, liver, lung and corpus luteum. Thus, the prostaglandin FP receptor was found to be widely distributed in rat tissues.

Influence of endotoxin on contractility in the rat gastric fundus

The influence of in vivo treatment with E. coli lipopolysaccharide endotoxin on the contractility of the rat gastric fundus was studied. Four h after lipopolysaccharide treatment (20 mg/kg i.p.), the contractile responses to prostaglandin F2alpha in longitudinal muscle strips from the gastric fundus were not different from those in control animals, while the well-known decreased response to noradrenaline in rings of the thoracic aorta was confirmed. Incubation of the tissues with L-arginine did not depress the response to prostaglandin F2alpha in fundus strips of lipopolysaccharide-treated rats. Twelve h after lipopolysaccharide treatment (6.7 mg/kg i.p.), the prostaglandin F2alpha-induced contractions were consistently depressed. The impairment of the prostaglandin F2alpha-induced responses by lipopolysaccharide treatment was not reversed by the nitric oxide synthase inhibitors NG-nitro-L-arginine (L-NNA, 10(-4) M), NG-nitro-L-arginine methyl ester (L-NAME, 3 x 10(-4) M), aminoguanidine (10(-4) M) and L-N6-l-iminoethyl-lysine (L-NIL, 10(-4) M) nor by the cyclooxygenase inhibitor indomethacin (10(-5) M). The impairment was prevented by pretreating the animals with dexamethasone (5 mg/kg i.p.), which had no effect per se on the contractile response to prostaglandin F2alpha. Lipopolysaccharide treatment did not influence the contractile responses to KCl and serotonin. The nonadrenergic noncholinergic relaxant responses to transmural electrical stimulation were not influenced 4 h after lipopolysaccharide treatment but were moderately reduced after 12 h. The results illustrate that the selective impairment of prostaglandin F2alpha-induced contractions in the rat gastric fundus by lipopolysaccharide treatment is not mediated via generation of nitric oxide; downregulation of the prostaglandin F2alpha-receptor by lipopolysaccharide treatment might be involved.

Platelet prostanoid receptors

Prostaglandins (PGs) and thromboxanes are important modulators of platelet activation, and there is strong evidence to support the existence of distinct thromboxane, prostacyclin, PGD2 and PGE2 receptors on the platelet plasma membrane. In this review, each of these platelet prostanoid receptors is discussed in detail, with respect to their receptor pharmacology, molecular biology and signal transduction, and as to any therapeutic implications of the development of specific agonists and/or antagonists. In addition, it considers the possibility that there are separate vascular receptors for 8-epi PGF2 alpha, which are not present on the platelet.

Functional characterization of the ocular prostaglandin f2alpha (PGF2alpha) receptor. Activation by the isoprostane, 12-iso-PGF2alpha

Prostaglandin F2alpha (PGF2alpha) is a product of cyclooxygenase-catalyzed metabolism of arachidonic acid. Recently, PGF2alpha analogs have been hypothesized to reduce intraocular pressure via relaxation of the ciliary muscle. To investigate the molecular basis of PGF2alpha receptor (FP) activation in the eye, we cloned the FP from a human ciliary body (hcb) cDNA library. The open reading frame of the hcb-FP cDNA was identical to the uterine FP cDNA. The hcb-FP appeared to be predominantly membrane-localized, as visualized by an FP-specific peptide antibody, and coupled to inositol phosphate formation when stably expressed in HEK 293 cells. Interestingly, the hcb-FP could also be activated by the F2 isoprostane, 12-iso-PGF2alpha, in addition to its cognate ligand, PGF2alpha. 12-iso-PGF2alpha was less potent (EC50 = 5 microM) than PGF2alpha (EC50 = 10 nM) in generating inositol phosphates via the hcb-FP in HEK 293 cells. Both ligands also stimulated mitogenesis in NIH 3T3 cells. Although 12-iso-PGF2alpha caused a dose-dependent activation of the FP, it failed to activate the recombinant human prostacyclin receptor and caused only minimal activation of the thromboxane receptor isoforms stably expressed in HEK 293 cells. Four additional F2 isoprostanes, 8-iso-PGF2alpha, IPF2alpha-I, IPF2alpha-III, and 9beta,11beta-PGF2, caused trivial, or no, activation of the FP. Consistent with these observations, only PGF2alpha and 12-iso-PGF2alpha caused rapid homologous desensitization of FP and also exhibited cross-desensitization, with PGF2alpha resulting in a maximum of approximately 60% desensitization. The human FP may thus be activated specifically, by the free radical-catalyzed F2 isoprostane, 12-iso-PGF2alpha, in addition to the cyclooxygenase product, PGF2alpha. Incidental receptor activation by isoprostanes may complement the actions of PGF2alpha in clinical syndromes where oxidant stress and augmented prostaglandin biosynthesis coincide.

Detection of EP2, EP4, and FP receptors in human ciliary epithelial and ciliary muscle cells

We have examined the expression of three prostaglandin (PG) receptors, EP2, EP4, and FP, in a nonpigmented ciliary epithelial cell line (ODMCl-2) and in human ciliary muscle (HCM) cells. Total RNA preparations from either ODMCl-2 or HCM cells were subjected to reverse transcription-polymerase chain reaction (RT-PCR) with sense and antisense primers for each of the three PG receptors. The RT-PCR generated DNA products of predicted sizes corresponding to the EP2, EP4, and FP receptors in both ODMCl-2 and HCM cells. PCR products corresponding to each receptor were hybridized with specific 32P-labeled probes and, for further confirmation, digested with appropriate restriction enzymes. Pharmacological studies with the EP2 receptor-selective agonist butaprost resulted in a significant increase in the cyclic AMP level in ODMCl-2 cells. The stimulation of cyclic AMP in ODMCl-2 cells by PGE2 and 11-deoxy PGE1, the respective EP1/EP2/EP3/EP4 and EP2/EP3/EP4 receptor agonists, was concentration-dependently inhibited by the EP4 receptor-selective antagonist AH23848. These results conclusively demonstrate the presence of both mRNA and protein for EP2, EP4, and FP receptors in ODMCl-2 and HCM cells.

Prostaglandin F2alpha receptor (FP receptor) agonists are potent adipose differentiation inhibitors for primary culture of adipocyte precursors in defined medium

Prostaglandin F2alpha inhibits adipose differentiation of primary culture of adipocyte precursors and of the adipogenic cell line 1246 in defined medium. In the present paper, we investigated the effect of FP receptor agonists cloprostenol and fluprostenol on the differentiation of newborn rat adipocyte precursors in primary culture. The results show that cloprostenol and fluprostenol are very potent inhibitors of adipose differentiation. Dose response studies indicate that both agonists are more potent than PGF2alpha in inhibiting adipocyte precursors differentiation. 50% inhibition of adipose differentiation was observed at a concentration of 3 x 10(-12) M for cloprostenol and 3 to 10 x 10(-11) M for fluprostenol respectively whereas the PGF2alpha concentration required to elicit the same effect was 10(-8) M. In contrast compounds structurally related to PGE2 such as 17-phenyl trinor PGE2 had no effect on adipose differentiation except when added at a 10,000-fold higher concentration.

The lack of respiratory effects of the ocular hypotensive drug latanoprost in patients with moderate-steroid treated asthma

The use of beta blockers for glaucoma treatment may cause serious bronchoconstriction in patients with chronic obstructive pulmonary disease. The synthetic prostaglandin (PG) F2 alpha-analogue latanoprost (13,14,dihydro-17-phenyl-18,19,20-trinor-PGF-2-alpha-iso propylester) represents a new class of drugs for glaucoma treatment. In this study the pulmonary tolerability to latanoprost in 12 healthy volunteers and 11 (one withdrawal due to a sty before latanoprost treatment) subjects with moderate but stable steroid-treated intrinsic asthma was examined. Asthmatic subjects received 30 microliters of vehicle (placebo) at the scheduled administration times on baseline day. On a second day, a minimum of one week later, increasing concentrations (0.35, 115 and 350 micrograms/ml) of latanoprost were added to the vehicle and given topically to both eyes. Healthy volunteers were given latanoprost only. ECG, blood pressure, heart rate, forced expiratory volume (FEV1), peak expiratory outflow (PEF) and forced vital capacity (FVC) were recorded immediately prior to and 15, 30, 45 and 60 minutes after latanoprost. Asthmatic patients inhaled salbutamol (0.2 mg) at 60 minutes after the highest latanoprost dose. There were no significant differences in pulmonary function, blood pressure or heart rate after latanoprost in the healthy volunteers. Moreover, all parameters were unaffected in asthmatic patients on the day latanoprost was given compared to the baseline day. Latanoprost did not dampen the bronchodilator response to beta-2-adrenergic stimulation. It is concluded that latanoprost did not affect lung function in healthy subjects or in asthmatics after a total accumulated dose 10 times that clinically recommended for glaucoma treatment. Therefore, latanoprost appears to be safe for glaucoma treatment in patients with steroid-treated stable moderate intrinsic asthma.

The molecular biology and ocular distribution of prostanoid receptors

Enormous progress has been made in the characterization of prostanoid receptors during the past five years. Molecular biological studies have enabled structural identification of all the human prostanoid receptors that had been proposed according to pharmacological criteria. The pharmacological classification proposed different receptor subtypes for prostaglandins D2, E2, F2 alpha, I2 and thromboxane A2 which were termed DP, EP, FP, IP and TP, respectively. Further subdivision for only the EP receptor has been reported and EP1, EP2, EP3, and EP4 subtypes have been unequivocally identified. The molecular structure of all prostanoid receptors is typical of that for G protein-coupled receptors and consists of seven alpha-helical transmembrane domains, three extracellular loops and an amino terminus, and three intracellular loops and a carboxyl terminus. Interestingly, mRNA alternative splice variants of the carboxyl termini have been found to determine G protein interactions for the EP3 receptor. Application of molecular biological techniques is beginning to make an impact in ocular research, where precise localization of receptors is difficult by more traditional methods because of the diminutive size of most ocular tissues. In situ hybridization and immunohistochemical studies using antibodies against the cloned human FP receptor have already suggested an unexpectedly wide distribution in the monkey eye. Transgenic studies involving FP receptor knock-out animals may provide future insight into the role of this receptor in glaucoma. However, since prostaglandins are extraordinarily effective in reducing intraocular pressure, it follows that traditional physiological and pharmacological studies retain a key role in glaucoma research. Studies in perfused human anterior segment organ culture have revealed that although prostaglandin F2 alpha does not facilitate trabecular aqueous humor outflow, prostaglandin E1 does increase trabecular outflow. Thus, different prostanoids may lower intraocular pressure by distinctly different mechanisms of action. Recent studies also indicate that prostanoids may exert a beneficial effect on retinal blood perfusion and may even act as neuroprotective agents.

Signal transduction and gene expression in the eye: a contemporary view of the pro-inflammatory, anti-inflammatory and modulatory roles of prostaglandins and other bioactive lipids

Eye tissues respond to physiological and pathophysiological stimuli by the activation of phospholipases and the consequent release from membrane phospholipids of biologically active metabolites. These rapid events have profound effects on long-term ocular physiology. Activation of phospholipase A2 is the first step in the synthesis of two important classes of lipid second messengers, the eicosanoids and platelet-activating factor (PAF). PAF accumulates in the cornea in response to injury. It has been shown to stimulate metalloproteinase gene expression in the corneal epithelium, and is, thus, implicated in the extracellular matrix remodeling that accompanies wound healing and ulceration. PAF antagonists confer protection in animal models of acute and chronic anterior segment inflammation, and block the PAF-enhanced glutamate release from retina. The latter effect suggests a role for PAF in glaucomatous neuronal damage. The eicosanoids, in particular the prostaglandins, have long been implicated in the pathophysiology of ocular inflammation and there is pharmacological evidence for their role in the regulation of intraocular pressure. The induction by PAF of the inducible prostaglandin synthase in neurons and in the corneal epithelium provides a link between the actions of these two lipid second messengers. There may be thresholds of lipid second messenger concentrations which govern their activities as physiological, defensive, or harmful.

Expression and regulation of prostaglandin F receptor mRNA in rodent osteoblastic cells

The ability of prostaglandins to inhibit collagen synthesis and induce prostaglandin G/H synthase in bone cells appears to be mediated by the prostaglandin F2 alpha receptor (FPR). We have identified FPR mRNA in the osteoblastic cell lines, Py1a from rats and MC3T3-E1 from mice, as well as in the stem cell cultures, MN-7 and mouse marrow, using reverse transcriptase-polymerase chain reaction technology (RT-PCR). Expression of FPR mRNA was increased in Pyla, MN-7 and marrow cells with prolonged culture or dexamethasone treatment and decreased after treatment with fluprostenol, a selective FPR agonist.

Molecular cloning and characterization of the human prostanoid DP receptor

A cDNA encoding a functional human prostanoid DP (hDP) receptor has been constructed from a genomic clone and a fragment cloned by 3'-rapid amplification of cDNA ends-polymerase chain reaction. The hDP receptor consists of 359 amino acid residues with a predicted molecular mass of 40,276 and has the putative heptahelical transmembrane domains characteristics of G-protein-coupled receptors. The deduced amino acid sequence of the hDP receptor, when compared with all other members of the prostanoid receptor family, shows the highest degree of identity with the hIP and hEP2 receptors, followed by the hEP4 receptor. Radioreceptor binding studies using membranes prepared from mammalian COS-M6 cells transiently transfected with an expression vector containing the DP receptor cDNA showed that the rank order of affinities for prostaglandins and prostaglandin analogs, in competition for [3H]prostaglandin D2 (PGD2) specific binding sites, was as predicted for the DP receptor, with PGD2 >> PGE2 > PGF2 alpha = iloprost > U46619. The signal transduction pathway of the cloned hDP receptor was studied by transfecting the hDP expression vector in HEK 293(EBNA) cells. Activation of the hDP receptor with PGD2 resulted in an elevation of intracellular cAMP and in mobilization of Ca2+, but did not lead to generation of inositol 1,4,5-trisphosphate. Northern blot analysis of human tissue showed that the hDP receptor was a very discrete tissue distribution and was detectable only in retina and small intestine. In summary, we have cloned and expressed a functional cDNA for the hDP receptor.