Roles of prostaglandin E2-EP1 receptor signaling in regulation of gastric motor activity and emptying

Effect of central and peripheral injection of prostaglandin E2 and F2α on feeding and the crop-emptying rate in chicks

Prostaglandins (PGs) have been shown to cause several physiological changes in mammals including anorexia, awakening and sleeping, change in digestive function, and activation of the hypothalamus-pituitary-adrenal gland (HPA) axis. However, there is a paucity of information about the effect of PGs on physiological parameters in birds. The purpose of the present study was to clarify whether intracerebroventricular (ICV) and intraperitoneal (IP) injections of prostaglandin E2 (PGE2) and prostaglandin F2α (PGF2α) affect feeding, voluntary movement, crop-emptying rate, and corticosterone release in chicks (Gallus gallus). ICV injection of either PGE2 or PGF2α (2 and 4μg) significantly decreased food intake in chicks. The anorexigenic effect was also observed after IP injection of the PGs. Voluntary movement was significantly suppressed by ICV injection of PGE2 or PGF2α, although the time-course change was different between the two. In contrast, IP injection of the PGs had no or less effect on voluntary movement. Both ICV and IP injection of PGE2 significantly retarded the crop-emptying rate, whereas PGF2α significantly lowered the crop-emptying rate only after IP injection. The plasma corticosterone concentration significantly increased after ICV and IP injection of PGE2, whereas PGF2α had no effect. These results suggest that central and peripheral PGs are involved in the regulation of appetite, voluntary movement, food passage in the digestive tract, and activation of the HPA axis in chicks, although the effects depend on the site of action and type of PGs.

Lipopolysaccharide reduces food passage rate from the crop by a prostaglandin-independent mechanism in chickens

1. We examined the effect of lipopolysaccharide (LPS), a component of Gram-negative bacteria, on food passage in the digestive tract of chickens (Gallus gallus) in order to clarify whether bacterial infection affects food passage in birds.

2. Food passage in the crop was significantly reduced by intraperitoneal (IP) injection of LPS while it did not affect the number of defecations, suggesting that LPS may affect food passage only in the upper digestive tract.

3. Similar to LPS, prostaglandin E2 (PGE2), one of the mediators of LPS, also reduced crop-emptying rate in chickens while it had no effect on the number of defecations.

4. Pretreatment with indomethacin, which is an inhibitor of cyclooxygenase (COX), a prostaglandin synthase, had no effect on LPS-induced inhibition of crop emptying.

5. IP injection of LPS did not affect the mRNA expression of COX2 in the upper digestive tract of chickens.

6. It is therefore likely that LPS and PGE2 reduced food passage rate in the crop by a prostaglandin-independent pathway in chickens.

The mechanistic basis of prostacyclin and its stable analogues in pulmonary arterial hypertension: Role of membrane versus nuclear receptors

Pulmonary arterial hypertension (PAH) is a progressive disease of distal pulmonary arteries in which patients suffer from elevated pulmonary arterial pressure, extensive vascular remodelling and right ventricular failure. To date prostacyclin (PGI2) therapy remains the most efficacious treatment for PAH and is the only approved monotherapy to have a positive impact on long-term survival. A key thing to note is that improvement exceeds that predicted from vasodilator testing strongly suggesting that additional mechanisms contribute to the therapeutic benefit of prostacyclins in PAH. Given these agents have potent antiproliferative, anti-inflammatory and endothelial regenerating properties suggests therapeutic benefit might result from a slowing, stabilization or even some reversal of vascular remodelling in vivo. This review discusses evidence that the pharmacology of each prostacyclin (IP) receptor agonist so far developed is distinct, with non-IP receptor targets clearly contributing to the therapeutic and side effect profile of PGI2 (EP3), iloprost (EP1), treprostinil (EP2, DP1) along with a family of nuclear receptors known as peroxisome proliferator-activated receptors (PPARs), to which PGI2 and some analogues directly bind. These targets are functionally expressed to varying degrees in arteries, veins, platelets, fibroblasts and inflammatory cells and are likely to be involved in the biological actions of prostacylins. Recently, a highly selective IP agonist, selexipag has been developed for PAH. This agent should prove useful in distinguishing IP from other prostanoid receptors or PPAR binding effects in human tissue. It remains to be determined whether selectivity for the IP receptor gives rise to a superior or inferior clinical benefit in PAH.

Morin protects gastric mucosa from nonsteroidal anti-inflammatory drug, indomethacin induced inflammatory damage and apoptosis by modulating NF-κB pathway

BACKGROUND

Deregulation in prostaglandin (PG) biosynthesis, severe oxidative stress, inflammation and apoptosis contribute to the pathogenesis of nonsteroidal anti-inflammatory drug (NSAID)-induced gastropathy. Unfortunately, most of the prescribed anti-ulcer drugs generate various side effects. In this scenario, we could consider morin as a safe herbal potential agent against IND-gastropathy and rationalize its action systematically.

METHODS

Rats were pretreated with morin for 30 min followed by IND (48 mgkg(-1)) administration for 4 h. The anti-ulcerogenic nature of morin was assessed by morphological and histological analysis. Its effects on the inflammatory (MPO, cytokines, adhesion molecules), ulcer-healing (COXs, PGE(2)), and signaling parameters (NF-κB and apoptotic signaling) were assessed by biochemical, RP-HPLC, immunoblots, IHC, RT-PCR, and ELISA at the time points of their maximal changes due to IND administration.

RESULTS

IND induced NF-κB and apoptotic signaling in rat's gastric mucosa. These increased proinflammatory responses, but reduced the antioxidant enzymes and other protective factors. Morin reversed all the adverse effects to prevent IND-induced gastric ulceration in a PGE2 independent manner. Also, it did not affect the absorption and/or primary pharmacological activity of IND.

CONCLUSIONS

The gastroprotective action of morin is primarily attributed to its potent antioxidant nature that also helps in controlling several IND-induced inflammatory responses.

GENERAL SIGNIFICANCE

For the first time, the study reveals a mechanistic basis of morin mediated protective action against IND-induced gastropathy. As morin is a naturally abundant safe antioxidant, future detailed pharmacokinetic and pharmacodynamic studies are expected to establish it as a gastroprotective agent.

Cloning and expression of prostaglandin E2 receptor subtype 1 (ep 1 ) in Bostrichthys sinensis

Our previous studies suggested that prostaglandin E2 (PGE2) is a putative sex pheromone in Chinese black sleeper Bostrichthys sinensis, a fish species that inhabits intertidal zones and mates and spawns inside a muddy burrow. We found immunoreactivities of PGE2 receptor subtypes (Ep1-3) expressed in the olfactory sac, but only Ep1 presented higher density of immunoreactivity in mature fish than that in immature fish in both sexes. To gain a better understanding of the underlying molecular mechanism for the detection of PGE2 in the olfactory system, we cloned an ep 1 cDNA from the adult olfactory sac. The open-reading frame of the ep 1 consisted of 1,134-bp nucleotides that encoded a 378-amino acid-long protein with a seven-transmembrane domain, typical for the G protein-coupled receptors superfamily. Expression of ep 1 mRNA was observed in all tissues examined, with higher levels obtained in the olfactory sacs and testes. The expression of ep 1 mRNA in the olfactory sacs and gonads was significantly higher in both sexes of mature fish than in those of immature ones. Taken together, our results suggested that Ep1, which is highly expressed in the olfactory sacs and gonads of mature fish, is important for the control of reproduction and may be involved in PGE2-initiated spawning behavior in B. sinensis.

Molecular characterization of prostaglandin F receptor (FP) and E receptor subtype 1 (EP₁) in zebrafish

Prostaglandins E (PGE) and F (PGF) mediate diverse physiological functions via their cell surface receptors - prostaglandin E receptor (EP) subtypes 1, 2, 3 and 4 (EP(1); EP(2); EP(3); EP(4)) and F receptor (FP). In teleost fishes, PGE was implicated in gill epithelium ion transport, while both PGE and PGF were involved in oocyte maturation, follicular rupture and coordination of reproductive behaviors. However, little is known about the mechanisms behind their actions. In present study, we first identified the full-length ORF cDNA clones of three zebrafish prostaglandin E receptor subtype 1 (zEP(1)) isoforms - zEP(1a), zEP(1b) and zEP(1c) - and FP (zFP) from adult ovary. RT-PCR showed that zEP(1a), zEP(1b) and zFP are widely expressed in adult tissues, while zEP(1c) mRNA expression is mainly confined in brain and kidney. Using a pGL3-NFAT-RE luciferase reporter system, both zEP(1a) and zEP(1b) expressed in DF-1 cells were shown to be activated by PGE(2) potently while zEP(1c) and zFP were activated by PGF(2a) effectively, suggesting that the four receptors are functionally coupled to intracellular Ca(2+)-signaling pathway. Furthermore, EP1a and EP1b, but not EP1c were suggested to couple to cAMP-PKA signaling pathway using a pGL3-CRE luciferase reporter assay. Although zEP(1c) might originate as a paralog to zEP(1a) and zEP(1b), its functional coupling to PGF(2α) instead of PGE(2) suggested that zEP(1) isoforms might have sub-functionalized in their ligand binding and G protein coupling specificity, in addition to differential tissue distribution. Characterization of these receptors undoubtedly furthered our understanding on the diverse yet highly target-specific responses of prostaglandins in teleosts.

At last, a truly selective EP₂ receptor antagonist

Ever since the discovery of prostaglandin E(2)(PGE(2)), this lipid mediator has been the focus of intense research. The diverse biological effects of PGE(2) are due, at least in part, to the existence of four distinct receptors (EP(1-4)). This can complicate the analysis of the biological effects produced by PGE2. While there are currently selective pharmacological tools to explore the roles of the EP(1,3,4) receptors in cellular and tissue responses, analysis of EP(2) receptor-induced responses has been hampered by the lack of a selective EP(2) receptor antagonist. The recent publication in this journal by af Forselles et al. suggests that such a tool compound is now available. In their manuscript, the authors describe a series of experiments that show PF-04418948 to be a potent and selective EP(2) receptor antagonist. The discovery of this tool compound will interest many scientists and through collaborations with Pfizer they may have access to PF-04418948 to facilitate further investigation of the biology of this fascinating lipid mediator.

Roles of prostaglandin E2 in cardiovascular diseases

Prostaglandin E2 (PGE(2)) is produced in inflammatory responses and regulates a variety of immunological reactions through 4 different receptor subtypes; EP1, 2, 3 and 4. However, the precise role of each receptor in cardiovascular disease has not yet been elucidated. Enhanced expression of some EPs has been observed in clinical and experimental cardiovascular diseases. EP agonists have been developed to clarify the role of each receptor. Recently, we developed a novel selective agonist to examine the effects of EP4 on cardiac transplantation, myocardial ischemia, and myocarditis. Of note, a selective EP4 agonist attenuated inflammatory cytokines and chemokines via attenuation of macrophage activation in inflammatory heart diseases. In this review article, we discuss the effects of PGE(2) receptor agonists on the development of cardiovascular diseases.