Prostaglandin Release In Response Research Articles

Neuroaxonal and cellular damage/protection by prostanoid receptor ligands, fatty acid derivatives and associated enzyme inhibitors.

Cellular and mitochondrial membrane phospholipids provide the substrate for synthesis and release of prostaglandins in response to certain chemical, mechanical, noxious and other stimuli. Prostaglandin D2, prostaglandin E2, prostaglandin F2α, prostaglandin I2 and thromboxane-A2 interact with five major receptors (and their sub-types) to elicit specific downstream cellular and tissue actions. In general, prostaglandins have been associated with pain, inflammation, and edema when they are present at high local concentrations and involved on a chronic basis. However, in acute settings, certain endogenous and exogenous prostaglandins have beneficial effects ranging from mediating muscle contraction/relaxation, providing cellular protection, regulating sleep, and enhancing blood flow, to lowering intraocular pressure to prevent the development of glaucoma, a blinding disease. Several classes of prostaglandins are implicated (or are considered beneficial) in certain central nervous system dysfunctions (e.g., Alzheimer’s, Parkinson’s, and Huntington’s diseases; amyotrophic lateral sclerosis and multiple sclerosis; stroke, traumatic brain injuries and pain) and in ocular disorders (e.g., ocular hypertension and glaucoma; allergy and inflammation; edematous retinal disorders). This review endeavors to address the physiological/pathological roles of prostaglandins in the central nervous system and ocular function in health and disease, and provides insights towards the therapeutic utility of some prostaglandin agonists and antagonists, polyunsaturated fatty acids, and cyclooxygenase inhibitors.

Evaluation of the uterine environment early in pregnancy establishment to characterise cows with a potentially superior ability to support conceptus survival

During previous investigations, the capacity of the cow to secrete prostaglandin in response to oxytocin has been linked with pregnancy outcome. The objective of the present study was to evaluate the predictive value of prostaglandin release to identify groups of cows as potentially superior (SR, low prostaglandin release) or inferior (IR, high prostaglandin release) for pregnancy outcome and to utilise these cows to investigate factors that contribute to optimum uterine conditions for early pregnancy. Animals were synchronised and received an in vitro-derived blastocyst on Day 7 post-oestrus. Tissues (trophoblast and endometrial) and uterine luminal fluid (ULF) were recovered 10 days later. Pregnancy rates were 94 and 78% for SR and IR cows, respectively. Of the pregnant SR cows, 69% had larged conceptuses (>24 cm) in contrast to 43% IR of cows. IR cows with small conceptuses (<12 cm) had significantly lower mean Day 3 and 5 post-oestrous progesterone concentrations than cows with large conceptuses. The expression of factors involved in the prostaglandin pathway, pregnancy and conceptus development were analysed via quantitative RT-PCR and Western blot analysis. Investigation of 16 endometrial gene transcripts indicated no differences between IR and SR cows except for osteopontin expression which, in uteri with large conceptuses, was 2-fold greater in SR than IR cows (P=0.02). There was greater expression of CTGF, OXTR, PGES, PGHS2 and UTMP mRNA in uteri of SR and IR cows that had large compared with small conceptuses (P<0.05). More IFNT protein was recovered in SR compared with IR ULF (P<0.03). SR cows with large conceptuses had less TIMP2 and legumain protein in their gravid, compared with their non-gravid horns (P≤0.02) whereas IR cows did not. The predictive value of prostaglandin release in response to oxytocin challenge does not appear to be an effective indicator of subsequent pregnancy rates in cows. Differences between the two groups appear to be associated with subtle differences in progesterone and uterine protein concentrations that may be related to differences in conceptus size.

Fenofibrate Treatment of Diabetic Rats Reduces Nitrosative Stress, Renal Cyclooxygenase-2 Expression, and Enhanced Renal Prostaglandin Release

Renal cyclooxygenase (COX)-2 expression is increased in the diabetic rat and has been linked to increased glomerular filtration rate (GFR) and renal injury. Our studies indicate that oxidative stress in the form of peroxynitrite (ONOO) may be the stimulus for induction of COX-2. In this study, we addressed the effects of a peroxisome proliferator-activated receptor alpha agonist on renal COX-2 expression as fibrates exert renal protective effects. Forty-eight hours after the induction of diabetes with streptozotocin in male Wistar rats, fenofibrate treatment (100 mg/kg/day) was started, and the effects were compared with untreated diabetic rats and treated and untreated age-matched control rats (n = 5 per group). After 12 to 14 weeks of treatment, the right kidney was perfused to determine prostaglandin release in response to arachidonic acid (AA), and the left kidney was used to examine the expression of COX-2 and nitrotyrosine, an index of ONOO formation. Release of prostaglandin (PG) E(2) in response to AA was enhanced in the diabetic rat kidney compared with control (4.8 +/- 0.7 versus 1.9 +/- 0.7 ng/min) and reduced by fenofibrate to 0.6 +/- 0.2 ng/min. A similar pattern was obtained for AA-stimulated release of 6-ketoPGF(1alpha). The effects of fenofibrate were associated with reduced renal expression of COX-2 and nitrotyrosine in diabetic rats. We used creatinine clearance as an index of GFR, which was increased in the diabetic rat, 3.09 +/- 0.4 versus 1.15 +/- 0.1 ml/min for control, and reduced by fenofibrate treatment to 1.87 +/- 0.3 ml/min. These results show that fenofibrate treatment of diabetic rats decreases renal COX-2 expression, possibly by reducing nitrosative stress, and is associated with a reduction of the enhanced GFR.

Roles of gap junctions and hemichannels in bone cell functions and in signal transmission of mechanical stress.

Gap junctions formed by connexins (Cx) play an important role in transmitting signals between bone cells such as osteoblasts and osteoclasts, cells responsible for bone formation and bone remodeling, respectively. Gap junction intercellular communication (GJIC) has been demonstrated to mediate the process of osteoblast differentiation and bone formation. Furthermore, GJIC propagates Ca2+ signaling, conveys anabolic effects of hormones and growth factors, and regulates gene transcription of osteoblast differentiation markers. GJIC is also implicated to regulate osteoclast formation, survival and apoptosis. Compared with other bone cells, the most abundant type are osteocytes, which express large amounts of connexins. Mechanosensing osteocytes connect and form gap junctions with themselves and other cells only through the tips of their dendritic processes, a relatively small percent of the total cell surface area compared to other cells. Recent studies show that in addition to gap junctions, osteoblasts and osteocytes express functional hemichannels, the un-opposed halves of gap junction channels. Hemichannels are localized at the cell surface and function independently of gap junctions. Hemichannels in osteocytes mediate the immediate release of prostaglandins in response to mechanical stress. The major challenges remaining in the field are how the functions of these two types of channels are coordinated in bone cells and what the asserted, distinct effects of these channels are on bone formation and remodeling processes, and on conveying signals elicited by mechanical loading.

Effect of Tempol on Renal Cyclooxygenase Expression and Activity in Experimental Diabetes in the Rat

Renal cyclooxygenase (COX)-2 expression is increased in the streptozotocin (STZ)-diabetic rat and is associated with enhanced renal prostaglandin release in response to arachidonic acid (AA). Endoperoxide-mediated vasoconstrictor responses to AA were also enhanced in the diabetic rat kidney. Because oxidative stress is increased in diabetes and has been shown to induce COX-2, we assessed its contribution to prostaglandin release by treating diabetic rats with tempol (120 mg/kg/day) for 28 days. Release of AA-stimulated prostaglandins PGE(2) and 6-ketoPGF(1alpha) from the isolated perfused kidney was used as an index of COX activity, and Western analysis was used to determine COX-2 protein expression. In untreated diabetic rats, the release of prostaglandins in response to AA was markedly enhanced; the increase in release of both 6-ketoPGF(1alpha) and PGE(2) after AA was twice that in control rats. Renal cortical COX-2 expression in diabetic rats was 3-fold that of control rats. Tempol treatment reduced the AA-stimulated release of prostaglandins to levels seen in control rats; this was associated with reduced expression of COX-2 protein to levels not different from that in control rats. However, the enhanced vasoconstrictor response to AA in diabetic rats was unaffected by tempol treatment but abolished by inhibition of COX-1 with SC58560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole]. The addition of tempol to the perfusate of kidneys from diabetic and control rats had only a slight effect on prostaglandin release. We conclude that oxidative stress is an integral component of the mechanism involved in the induction of renal COX-2 in diabetes.

TGF-alpha reduces bradykinin-stimulated ion transport and prostaglandin release in human colonic epithelial cells.

The effect of chronic exposure to transforming growth factor-alpha (TGF-alpha) on bradykinin-stimulated acute prostanoid production and ion secretion in monolayers of HCA-7 colony 29 colonic epithelial cells has been studied. Monolayers synthesized prostaglandin E2 (PGE2) at a basal rate of 2.10 +/- 0.31 pg. monolayer-1. min-1 over 24 h. Bradykinin (10(-8)-10(-5) M) dose dependently increased acute PGE2 release by three orders of magnitude. This was associated with a rise in cAMP from 1.60 +/- 0.14 to 2.90 +/- 0.1 pmol/monolayer (P < 0.02) and a dose-dependent increase in short-circuit current (SCC). When monolayers were primed by a 24-h exposure to TGF-alpha, basal PGE2 release rose to 6.31 +/- 0.38 pg. monolayer-1. min-1 (TGF-alpha concn 10 ng/ml; P = 0.001). However, the stimulation of acute prostaglandin release, intracellular cAMP, and increased SCC by bradykinin was significantly reduced by preincubation with TGF-alpha. Priming with PGE2 (10(-8)-10(-6) M) over 24 h mimicked the effect of TGF-alpha on bradykinin-induced changes in cAMP and SCC. These data suggest that enhanced chronic release of prostaglandins in response to stimulation with TGF-alpha may downregulate acute responses to bradykinin. In vivo, TGF-alpha could have an important modulatory function in regulating secretion under inflammatory conditions.

Stimulation of endothelial cell prostaglandin production by angiotensin peptides. Characterization of receptors.

Angiotensin II stimulates prostaglandin release in blood vessels via activation of angiotensin receptors present in endothelium, vascular smooth muscle cells, or both. We evaluated the response of angiotensin II, angiotensin I, and [des-Phe8] angiotensin II [angiotensin-(1-7)] on prostaglandin release in porcine aortic endothelial cells. Incubation of cell monolayers with angiotensin I and angiotensin-(1-7), but not angiotensin II, stimulated the release of prostaglandin E2 and prostaglandin I2 in a dose-dependent manner (10(-10) to 10(-6) M) with an EC50 of approximately 1 nM. In addition, we characterized the angiotensin receptor subtypes mediating prostaglandin synthesis by using subtype-selective antagonists. Angiotensin I-stimulated prostaglandin synthesis was not altered by either of the nonselective classical angiotensin receptor antagonists [Sar1,Thr8]angiotensin II or [Sar1,Ile8]angiotensin II. In contrast, either the angiotensin subtype 1 (AT1) antagonist DuP 753 or the subtype 2 (AT2) antagonist CGP42112A significantly attenuated the prostaglandin release in response to angiotensin I. However, PD123177, another AT2 antagonist, did not inhibit angiotensin I-stimulated prostaglandin release. Angiotensin-(1-7)-induced prostaglandin release was significantly attenuated by [Sar1,Thr8]angiotensin II (10(-6) M) and PD123177 (10(-6) M) but not by [Sar1,Ile8]angiotensin II, DuP 753, or CGP42112A. Higher doses (10(-5) M) of DuP 753 and CGP42112A attenuated the angiotensin-(1-7) response. These data suggest that in porcine aortic endothelial cells, angiotensin I and angiotensin-(1-7) but not angiotensin II are potent stimuli for prostaglandin synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Human astrocytes contain two distinct angiotensin receptor subtypes.

The ability of angiotensin peptides to stimulate prostaglandin release and raise intracellular calcium levels by activating a phosphoinositide-specific phospholipase C was assessed in three human astrocytoma cell lines (CRTG3, STTG1, and WITG2). The addition of angiotensin II to CRTG3 cells resulted in a dose-dependent release of prostaglandin E2 and prostacyclin, the production of inositol 1,4,5-trisphosphate, and the mobilization of intracellular calcium. Angiotensin-(1-7), previously considered to be an inactive metabolite of angiotensin II, was as potent as angiotensin II for prostaglandin release but did not activate phospholipase C or mobilize intracellular calcium. In contrast, angiotensin-(2-8) caused only a slight increase in prostaglandin release, even though it was as effective as angiotensin II in augmenting inositol 1,4,5-trisphosphate production and calcium mobilization. Moreover, neither the release of prostaglandins in response to angiotensin II or angiotensin-(1-7) nor the mobilization of intracellular calcium in response to angiotensin II required extracellular calcium. Angiotensin II and angiotensin-(1-7) caused the release of prostaglandins from all three human astrocytoma cell lines, but changes in the level of intracellular calcium in response to angiotensin II only occurred in CRTG3 cells. Although previous studies have provided evidence for angiotensin receptor subtypes on the basis of selectivity of antagonists or signal transduction mechanisms, these data suggest that human astrocytes contain multiple angiotensin receptor subtypes on the basis of their response to different angiotensin heptapeptides--angiotensin-(1-7) and angiotensin-(2-8).(ABSTRACT TRUNCATED AT 250 WORDS)

Agonist-specific role for Na+-H+ antiport in prostaglandin release from microvessel endothelium

Rabbit coronary microvascular endothelial (RCME) cells synthesize prostaglandin (PG) I2 and PGE2 in response to stimulation with human thrombin, ATP, and the Ca2+ ionophore, A23187. Replacement of extracellular Na+ with choline or N-methylglucamine reduced thrombin-stimulated PG secretion but did not significantly affect either ATP- or A23187-stimulated PG secretion. Pretreatment of RCME cells with Na+ channel or Na+ -Ca2+ exchange blockers did not alter PG release in response to any of these three agonists. Pretreatment of RCME cells with the specific Na+ -H+ antiport blockers 5-(N-ethyl-N-isopropyl)-amiloride (EIPA, 10 microM) and 5-(N,N-hexamethylene)-amiloride (HMA, 0.1 microM) significantly reduced thrombin but not A23187- or ATP-stimulated PG secretion. Studies with the intracellular pH indicator dye 2,7-bis(carboxyethyl)-5(6)-carboxyfluorescein demonstrated thrombin activation of Na+ -H+ antiport, an effect blocked by either HMA or EIPA. Since manipulations known to inhibit Na+ -H+ exchange (EIPA, HMA, replacement of Na+ with choline or N-methylglucamine) reduced thrombin-stimulated RCME cell PG release, we conclude that activation of Na+ -H+ exchange is involved in the coupling of thrombin interaction with RCME cells to subsequent phospholipase activation and PG release.

Serotonin and the renal blood supply: Role of prostaglandins and the 5HT-2 receptor

Serotonin (5HT) has been reported to increase, to decrease, or not to change renal blood flow. We postulated that prostaglandin release in response to 5HT acted as a confusing variable, and tested the hypothesis by comparing infusions of serotonin and angiotensin into one renal artery of 14 anesthetized dogs before and after indomethacin administration. Renal blood flow (Q, by EM flow-meter) responses to 5HT were routinely biphasic, an initial sharp decrease followed by a gradual increase which stabilized well above baseline at three to six minutes. Indomethacin, 1 to 2 mg/kg, did not alter the acute Q decrement induced by 5HT but abolished the increase in Q at three to six minutes (P less than 0.001). Instead, sustained vasoconstriction became apparent. Ketanserin reversed the sustained vasoconstrictor effect of 5HT in indomethacin-treated dogs, leading to striking, serotonin-induced vasodilatation. The latter vasodilatation in turn was inhibited by methysergide. Four independent elements, two promoting vasoconstriction and two vasodilatation, are suggested. One vasodilator response is abolished by prostaglandin synthetase inhibition and the other by methysergide, a complex 5HT receptor blocker. The sustained vasoconstrictor response is blocked by ketanserin, suggesting an action on the 5HT-2 receptor. The initial, transient vasoconstrictor response is resistant to the blockers employed. These complex interactions may account for the variability in reported responses of the renal blood supply to serotonin.

Dynamic response of PG synthesis to peptide hormones and osmolality in renal tubular cells.

A superfusion technique was adapted to collagenase-dispersed renal medullary and cortical tubular cells to study prostaglandin (PG) synthesis in response to arginine vasopressin (AVP), angiotensin II (ANG II), bradykinin (BK), Ca2+ ionophore A23187, and to changes in osmolality. Medullary and cortical cells promptly responded to the stimuli by an increase in PGE2 and PGF2 alpha production, whereas 6-keto-PGF1 alpha was not detected. AVP and BK were active on medullary cells, and ANG II was active mainly on cortical cells. A23187 stimulated PG synthesis in both cells but predominantly in the medulla. PG synthesis was dependent on the presence of extracellular Ca2+. The Ca2+ entry blocking agents verapamil and lanthanum did not inhibit the PG response to AVP, BK, and ANG II. Thus peptide hormone-stimulated PG synthesis in renal tubular cells did not depend on Ca2+ influx through channels blocked by these agents. Hyperosmolar NaCl or mannitol stimulated PG synthesis in cortical and, more markedly, in medullary cells. Hyperosmolar urea inhibited PGE2 synthesis stimulated by peptide hormones, NaCl, and A23187 in both cell preparations. In conclusion, the superfusion of isolated tubular cells is a useful method to study the dynamic aspects of renal PG release in response to various sequentially applied stimuli.

Sites of lipase activation and prostaglandin synthesis in isolated, perfused rabbit hearts and hydronephrotic kidneys

The tissue lipids of isolated, perfused rabbit hearts and hydronephrotic kidneys were labelled with [ 14C]-arachidonic acid by two different techniques: direct infusion of [ 14C]-arachidonic acid in a protein free media into the perfused organ (method A), and recirculation of [ 14C]-arachidonic acid in a solution containing albumin (method B). Autoradiography of the labelled organs demonstrated that method A resulted in selective labelling of arteries and arterioles in both perfused organs as well as glomeruli in the kidney. Labelling with method B resulted in a non-specific radioisotope incorporation in both the vasculature and myocardial cells in the heart; and of the vasculature and renal tubules in the perfused kidneys. Analysis of the tissue lipids shows similar patterns of incorporation of radioactivity between methods A and B. Peptide hormone stimulation (bradykinin) and non-specific noxious stimulation (with transient ischemia) were employed to elicit lipase activation (i.e., release of [ 14C]-arachidonate) and prostaglandin (PG) synthesis. It was found that in both hearts and hydronephrotic kidneys, the radioactive PG release in response to bradykinin and ischemia was much higher with method A (vascular labelling) than with method B (diffuse labelling) despite the appearance of comparable amounts of bioassayable PG release, thus indicating the sites of PG synthesis in these organs is predominantly localized in the vascular tissue. Furthermore, the radioactive arachidonic acid release in response to bradykinin stimulation in the hydronephrotic kidneys was 3 times higher with method A than with method B, suggesting the predominant sites of hormone specific lipase activation in the renal cortex is also in the vasculature. However, the radioactive arachidonic acid release in response to ischemia was much higher with method B than with method A in both hearts and hydronephrotic kidneys, indicating the sites of non-specific lipase activation in these organs are more diffusely distributed, and present also in the myocardial cells and renal tubules.

Possible influence of intrarenal generation of kinins on prostaglandin release from the rabbit perfused kidney.

The effects of bradykinin and kininogen on renal prostaglandin release were studied in rabbit isolated kidneys perfused with oxygenated Krebs solution. The concentration of prostaglandin-like material in kidney effluent was determined by bioassay after extraction of the samples with organic solvents. In 7 experiments the samples were assayed after separation of prostaglandins E and F by thin layer chromatography. Addition of bradykinin to the perfusing fluid increased the venous and urinary effluxes of prostaglandin E-like substance by sixfold and fivefold, respectively, but efflux of prostaglandin F-like material was unaffected. Addition of kininogen to the perfusing fluid augmented the venous and urinary release of prostaglandin E-like substances by fifteenfold and ninefold respectively and caused a twofold increase in the efflux of prostaglandin F-like material into the venous effluent. Aprotinin, a kallikrein inhibitor, reduced the prostaglandin releasing action of kininogen but not of bradykinin. In contrast, inhibition of prostaglandin synthesis by indomethacin suppressed the release of prostaglandin evoked by either bradykinin or kininogen. This study suggests that augmented release of prostaglandins in response to kininogen is a consequence of renal generation of kinins. Thus, changes in the intrarenal activity of the kallikreinkinin system may modulate renal prostaglandin release.