Role of prostaglandins in acute phase proteins in inflammation

Prostaglandin E1, a mediator of inflammation, was investigated for its effects on serum acute phase proteins, alpha 2 macroglobulin (alpha 2M). Induction of carrageenin inflammation in rats caused an elevation of alpha 2M to a maximum level (100%) at 1 day. Similarly, administration of PGE1 (1 mg/kg) was found to increase serum alpha 2M levels in normal rats. On the other hand, sc injection of PGE1 into inflamed rats significantly reduced the alpha 2M in serum as well as edema. In vitro studies with liver slices showed increasing rates of incorporation of [14C]leucine into alpha 2M with the addition of PGE1 to the medium. It was followed by the secretion of alpha 2M-bound radioactivity into media. But addition of higher doses (greater than 100 ng/ml) of PGE1 resulted in the suppression of incorporation and secretion of alpha 2M-bound radioactivity. Incubation of inflamed liver slices with PGE1, however, showed only decreased incorporation and secretion of alpha 2M-bound radioactivity. These results indicate that (a) primary prostaglandins, like PGE1, generated during inflammation may be responsible for the increase of alpha 2M in serum, and (b) PGE1 enhanced the synthesis of alpha 2M in liver and its secretion into the medium, so the anti-inflammatory drugs which decrease levels of PGs are likely to alter alpha 2M levels.     

The dynamic content of prostaglandins and cyclic nucleotides in the blood of irradiated dogs and monkeys

In experiments with dogs and monkeys a study was made of the dynamics of the content of prostaglandins (PG) and cyclic nucleotides after gamma irradiation. In dogs irradiation with lethal doses (3.1 and 50 Gy) caused a short-term, evidently stress growth of cAMP, PGE and PGF2 alpha levels. At the height of radiation sickness PGF2 alpha and cGMP content decreased considerably. Irradiation of monkeys with a nonlethal dose of 3.2 Gy changed PGE and PGF2 alpha levels to a lesser extent, while concentrations of cyclic nucleotides varied but their ratio remained stable.     

Hypotensive response to prostacyclin and 6-keto-PGE1 following hepatectomy in the rat

Prostacyclin (PGI2) is metabolized to 6-keto-prostaglandin E1 (6-keto-PGE1) which is more stable yet equipotent to PGI2 in lowering systemic arterial blood pressure in the dog. In this study, partial hepatectomy was performed to determine the role of the liver in the vasodepressor response to both intravenously administered PGI2 and 6-keto-PGE1. The magnitude and the duration of systemic hypotensive responses were measured in hepatectomized and sham-operated male Wistar rats following less than maximal, equidepressor doses of PGI2 (0.3 microgram/kg), 6-keto-PGE1 (1.0 microgram/kg), and also PGE1 (3.0 micrograms/kg) and PGE2 (3.0 micrograms/kg). Hepatectomy did not significantly alter the magnitude of the systemic hypotensive response to any of the prostaglandins tested. This indicates that the liver and hepatic circulation do not contribute significantly to the hypotensive effect of these prostaglandins by alterations of systemic vascular resistance, venous pooling of blood, or the generation of additional vasoactive metabolites as may be expected following administration of these prostaglandins. However, hepatectomy did significantly increase the duration of the hypotensive response to PGI2 and 6-keto-PGE1 but not PGE1 or PGE2. We conclude that in vivo, the liver has a more significant role in PGI2 and 6-keto-PGE1 inactivation than in the inactivation of PGE1 and PGE2 when administered intravenously. These results also support the relatively greater significance of the lung in the inactivation of PGE1 and PGE2 in vivo.     

Radiation-induced alterations in prostaglandin excretion in the rat

Dose-related alterations in the levels of prostaglandins (PGF2 alpha and PGE) and thromboxane B2 (TxB2) were observed in the urine of unanesthetized rats following whole-body gamma radiation. Exposure doses of 100 and 900 rads resulted in significant changes in urinary levels of these cyclooxygenase products. These findings suggest the potential use of radioimmunoassay measurement of urinary prostaglandins and thromboxane as a noninvasive indicator of radiation exposure.     

The effects of certain vasodilating prostaglandins on the coronary and hindlimb vascular beds of the conscious sheep

Vasodilating prostaglandins were injected, in bolus doses, into the lower abdominal aorta or left circumflex coronary artery (LCCA) of conscious sheep. Local blood flow, mean arterial pressure (MAP), heart rate (HR) and ECG were monitored continuously. 6-Keto PGF1 alpha had no effect on either vascular bed in doses up to 100 micrograms. PGE2 was more potent than PGI2 in dilating hindlimb vasculature and PGE2 induced a more persistent hyperaemia whereas PGD2 elicited a biphasic response (constriction-dilation). PGE1, PGE2, PGD2 and PGI2 all produced dose-dependent vasodilation, the order of potency being PGD2 greater than PGI2 greater than PGE1 greater than or equal to PGE2. The effect of PGI2 was more transient and PGE1 and PGD2 caused small but consistent decreases in MAP and HR, respectively.     

Effect of prostaglandin E2 on urea synthesis and hepatic hemodynamics in rat livers. An in vivo/in vitro study

The study was carried out on 30 rats. PGE2 was found to inhibit both the ammonium uptake and urea formation by hepatocytes, i.e. PGE2 inhibited the ornithine cycle in a non-recirculating perfusion of the liver. Simultaneously PGE2 inhibited liver oxygen uptake and raised portal pressure. Inhibition of urea synthesis in the liver and decrease of hepatic hemodynamics by PGE2 were also found in experiments in vivo. The PGE2 inhibiting effect on urea synthesis may be achieved mainly through decreasing hepatic blood flow and perhaps, by hypoxia.     

Plasma concentration of 13,14-dihydro-15-keto-PGE2 (PGEM) after various ways of cervix ripening with PGE2

PGEM concentration was determined radioimmunologically in a non-pregnant woman, in whom PGE2 was infused intravenously at increasing rates and in women, in whom labor was induced by various methods for local application of PGE2. There was excellent correlation between the amount of PGE2 infused intravenously and the levels of PGEM determined in the peripheral plasma. The following methods of local application of PGE2 were included in the study: 0.4 mg PGE2 gel placed retroamnially by means of a balloon catheter, 0.4 and 0.5 mg PGE2 applied endocervically and 3 mg PGE2 placed intravaginally in form of a single vaginal tablet; also included was a control-group, where only vaginal examination was performed. Bloods were drawn before, 30 minutes, 1, 2 and 3 hours after PGE2 administration. Mean levels of PGEM in the maternal peripheral plasma did not change neither within nor between the various groups. It is concluded from the present study, that local application of doses currently used to soften the cervix and/or induce labor at term do not lead to the same PGEM-concentration in the maternal blood as after intravenous infusion of PGE2 in doses normally used to induce labor.     

Regulation of breathing movements in fetal sheep by prostaglandin E2

In fetal sheep, plasma prostaglandin (PG) E2 concentrations are high, and fetal breathing movements (FBM) occur intermittently, primarily during low-voltage fast electrocortical activity (LVFA). There is evidence suggesting that prostaglandins, specifically PGE2, may regulate FBM. To define the physiological role of PGE2 in regulation of FBM, we infused meclofenamate (0.9 mg X kg-1 X h-1), a prostaglandin synthetase inhibitor, into six fetal sheep to suppress endogenous prostaglandin production. Afterward, PGE2 was added in mean doses of 9, 18, 36, and 90 ng X kg-1 X min-1. Meclofenamate decreased PGE2 concentrations and increased FBM, especially during high-voltage slow electrocortical activity (HVSA). Addition of PGE2 reversed the effects of meclofenamate, increasing PGE2 concentrations and decreasing FBM, especially during HVSA. The response to PGE2 was dose dependent; the overall incidence of FBM and incidences of FBM during HVSA and LVFA were inversely correlated with both the infused PGE2 dose and the mean PGE2 concentration. At higher doses of PGE2, FBM occurred intermittently and only during LVFA; thus PGE2 infusion restored the physiological pattern of FBM. These results indicate that PGE2 regulates FBM by inhibiting FBM during HVSA.     

Differential sensitivity of osteoclasts and osteoblasts suggests that prostaglandin E1 effects on bone may be mediated primarily through the osteoclasts

Prostaglandin E (PGE) stimulates resorption in bone. Since osteoblast-like osteosarcoma cells secrete PGE2, the possibility that osteoclasts were the major target for PGE was considered. To study this question, it was first established that in isolated bone cells enriched for either osteoclastic (OC) or osteoblastic (OB) characteristics, PGE1 can induce biochemical effects similar to those seen with bovine parathyroid hormone 1-84 (PTH), another potent stimulator of bone resorption. These changes include increased cAMP and hyaluronate synthesis in OC cells, and increased cAMP but decreased citrate decarboxylation in OB cells. By following these markers, it is demonstrated that PGE1 can activate OC cells at doses as low as 1 nM, whereas OB cells require 250 nM. Bone cell responses to various doses of PTH and PGE1 were also compared. In OC cells the lowest effective dose of PGE1 and PTH was similar (1 nM), but increasing response to PGE1 was seen up to 1000 nM in contrast to PTH response which peaked at 20 nM. In addition, the magnitude of PGE1-induced OC cell hyaluronate was two to four times greater than that of PTH at all doses tested. In OB cells, PTH induced significant decreases in citrate decarboxylation at 0.1 nM, compared to 250 nM for PGE1. Half-maximal inhibition of citrate decarboxylation (19% of control) by PTH occurred at 0.5 nM, whereas 500 nM of PGE1 was required for an equivalent effect. Thus, (i) OC cells responded to PGE1 doses that were approximately 200 times lower than the minimum required by OB cells, and (ii) OB cells responded to 100 times lower doses of PTH than PGE1.     

The hyperalgesic effects of prostacyclin and prostaglandin E2.

Hyperalgesia induced in rat paws or dog knee joints by prostacyclin (PGI2) and prostaglandin E2 was measured by a modification of the Randall-Selitto method (1) or by the degree of incapacitation (2). In both species PGI2 induced an immediate hyperalgesic effect but the effect of PGE2 had a longer latency. Low doses of PGI2 caused a short lasting effect but PGE2, large doses of PGI2 or successive administration of small doses of PGI2 caused a long lasting effect. It is suggested that prostacyclin mediates rat paw hyperalgesia induced by carrageenin. The long lasting hyperalgesic effect of PGE2 and high doses of PGI2 is possibly an indirect effect caused by stimulation of a sensory nerve sensitising mechanism.     

Oral PGE2 inhibits gastric acid secretion in man

The effect of oral prostaglandin E2 (PGE2) on gastric acid secretion was examined in healthy subjects. The gastric secretion was stimulated by a modified shamfeeding procedure. Each subject underwent one control test and three tests with intragastrically administered graded doses of PGE2: 0.5, 1.0 and 2.0 mg. Oral PGE2 significantly suppressed the peak and total acid response to vagal stimulation. The total acid output in controls was 27.5 +/- 3.2 mmol/90 min and 20.8 +/- 2.8, 15.8 +/- 2.2 (p less than 0.01) and 15.9 +/- 3.8 (p less than 0.005) mmol/90 min in test series with 0.5, 1.0 and 2.0 mg PGE2 respectively. The two higher doses were equally inhibitory to an average 40%. Gastric outputs of sodium and potassium in response to modified shamfeeding were reduced by PGE2. In controls there was a significant release of plasma-gastrin in response to shamfeeding. Plasma-gastrin was apparently suppressed after the two lower doses of PGE2 but 2.0 mg PGE2 gave an elevation similar to controls. Thus the study demonstrates that oral natural PGE2 suppresses the gastric acid secretion in man. The absence of such an effect in prior studies has been one of the objections against an acid regulatory action of endogenously formed prostaglandins. The present results do not support this argument.     

Tumor necrosis factor alpha down-regulates the Na+-K+ ATPase and the Na+-K+2Cl- cotransporter in the kidney cortex and medulla

The effect of TNF-alpha on the renal Na+-K+ pump and the Na+-K+2Cl- cotransporter was investigated in the rat. Animals were injected with the cytokine, and 4h later, a homogenate from the cortical and medullary tissues was prepared and used to assay the activity of the Na+-K+ ATPase and the protein expression of the pump and symporter. TNF-alpha reduced the activity and expression of the pump in both cortex and medulla, and its effect disappeared when animals were pre-treated with indomethacin, suggesting that TNF-alpha acts via PGE2. Higher levels of PGE2 were detected by enzyme immunoassay, in kidney tissues isolated from rats treated with PGE2, thus confirming this hypothesis. The cytokine also down-regulated the Na+-K+2Cl- cotransporter but this effect was not abrogated by indomethacin. PGE2, injected into animals, exerted a dose-dependent effect. Low doses did not have any effect on the two transporters in the cortex while high doses inhibited and down-regulated the pump and up-regulated the cotransporter. In the medulla low doses increased the activity and expression of the pump but down-regulated the cotransporter while high doses exerted an exactly opposite effect on the two transporters. It was concluded that the effect of TNF-alpha on the pump is mediated via PGE2 which is released at relatively high doses. The effect of the cytokine on the cotransporter is, however, independent of PGE2.     

In situ structural analysis of microsomal UDP-glucuronyltransferases by radiation inactivation

The structure of the UDP-glucuronyltransferases in microsomes from guinea pig and rat liver was examined in situ by radiation inactivation analysis. The p-nitrophenol conjugating activity of guinea pig microsomes increased at lower doses of radiation; at higher doses (greater than or equal to 36 megarads), activity showed a first order decline yielding a target size of 71 +/- 9 kDa. Treating microsomes with Triton X-100 eliminated the activation seen at lower doses of radiation and yielded a simple exponential decrease in activity which gave a larger target size (95 +/- 18 kDa). A monoexponential decrease in activity was seen in sonicated microsomes, at greater than or equal to 36 megarads. The same response was obtained when the reaction was assayed in the reverse direction. The estrone conjugating activity of guinea pig microsomes was similarly activated at lower doses of radiation and declined at higher doses (greater than or equal to 36 megarads), with a target size of 57 +/- 11 kDa. Allosteric activation of the enzyme by UDP-N-acetylglucosamine was eliminated by lower doses of radiation. Thus, activation of the enzyme by radiation, detergent, sonication, and UDP-N-acetylglucosamine appear to be interdependent. These activations are postulated to be due to the existence of the enzyme in an oligomeric form which can be dissociated into monomers with higher activity. The same biphasic activation-inactivation curves were obtained for p-nitrophenol conjugation in rat liver microsomes. The target sizes were 54 +/- 8 kDa (p-nitrophenol in the forward direction) and 66 +/- 10 kDa (p-nitrophenol in the reverse direction). Thus, the enzyme appears to be smaller in rat liver as compared with guinea pig liver. Lithocholate glucuronidating activity in rat liver microsomes (at greater than 36 megarads) gave a target size of 74 +/- 1 kDa.     

Effects of PGE1 or PGE2 on luteal function in pseudopregnant rats

Effects of PGE1 or PGE2 on luteal function were studied in 163 pseudopregnant rats. PGE1 (10, 100, or 300 micrograms) given intrauterine every 6 hr did not shorten pseudopregnancy (P greater than 0.05), however, the same doses of PGE2 given intrauterine every 6 hr advanced luteolysis (P less than 0.05). PGE1 (100 or 300 micrograms) given every 4 hr intramuscular maintained levels of progesterone in peripheral blood above controls (P less than 0.05) while 100 or 300 micrograms of PGE2 hastened the decline in progesterone (P less than 0.05). The antiluteolytic effect of PGE1 was not via an inhibition of PGF secretion (P greater than 0.05) by the uterus or by induction of ovulation in treated animals. Moreover, PGE1 (100, 200, or 500 micrograms) given intramuscular every 4 hr from day 4 of pseudopregnancy until the next proestrus delayed luteal regression around 3 days (P less than 0.05). PGE2 at doses of 100, 200, or 500 micrograms every 4 hr given intramuscular consistently shortened pseudopregnancy (P less than 0.05). Lower doses were without effect (P greater than 0.05). Based on the above data it is concluded that PGE2 is consistently luteolytic whereas PGE1 is not luteolytic in pseudopregnant rats and that PGE1 may be an antiluteolysin.     

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

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

Regulation of oxygen radical release from murine peritoneal macrophages by pharmacologic doses of PGE2

The ability of pharmacologic doses of PGE2 to alter the release of superoxide (O2-) and hydrogen peroxide (H2O2) from elicited peritoneal macrophages (M theta) was studied. Twice-daily administration of 200 or 100 micrograms of PGE2 to mice during accumulation of peritoneal M theta resulted in a significant reduction in M theta recovery and in the triggered release of H2O2, but not O2-. Cultivation of elicited M theta from normal mice with concentrations of PGE2 in excess of 10(-7) M for 24-48 h resulted in a significant reduction in the triggered release of H2O2, but not O2-. Cultivation for shorter periods of time or with lower concentrations of PGE2 failed to alter H2O2 release. This effect of PGE2 was reproduced by the phosphodiesterase inhibitor theophylline. The ability of PGE2 to inhibit H2O2 release in the presence of normal production of O2- was not prevented by the addition of superoxide dismutase. Cultivation of peritoneal M theta with 10(-5) M PGE2 for 48 h failed to increase intracellular catalase, although increased H2O2 scavenger activity was demonstrated. The inhibition of extracellular release of H2O2, but not O2-, by pharmacologic doses of PGE2 may be one mechanism for the anti-inflammatory action of this compound.     

Effect of small doses of gamma radiation on the activity of marker enzymes in the plasma membranes of chick embryo liver

A study was made of marker enzyme activity in plasma membranes of chick liver during embryogenesis in normal conditions and after exposure to ionizing radiation. It was shown that irradiation with small doses of eggs prior to incubation and of chick embryos during different periods of the prenatal ontogenesis caused essential changes in activity of membrane-bound enzymes of liver plasmolemma. Stimulation with small radiation doses was most effective with preincubation irradiation of eggs and most manifest at later stages of the prenatal ontogenesis. Thus, the marker enzymes were shown to play a significant role in the realization of the stimulatory effect of low-level radiation.     

Effects of selective COX-2 and 5-LOX inhibition on prostaglandin and leukotriene synthesis in ductal pancreatic cancer in Syrian hamster

Selective inhibition of eicosanoid synthesis seems to decrease carcinogenesis, however, the effect on liver metastasis in pancreatic cancer is still unknown. Ductal pancreatic adenocarcinoma was chemically induced by weekly injection of N-nitrosobis-2-oxopropylamine (BOP) in Syrian hamster. Animals received selective inhibition of cyclooxygenase-2 (Celebrex) and 5-lipoxygenase (Zyflo). In week 33, hamsters were sacrificed and incidence of pancreatic carcinomas as well as liver metastases were examined. Furthermore, size and number of liver metastases per animal were determined and concentration of PGF1alpha, PGE2 and leukotrienes was measured in hepatic and pancreatic tissue. Combined therapy (Celebrex+Zyflo) significantly decreased incidence, number and size of liver metastases. Furthermore extra- and intrametastatic concentration of PGE2 was reduced by this treatment in hepatic tissue. Single Cox-2-inhibition (Celebrex) decreased intrametastatic hepatic PGF1alpha and PGE2 concentration while PGF1alpha concentration was reduced in non-metastatic liver (nml). Moreover 5-LOX-inhibition (Zyflo) decreased intrametastatic PGE2 concentration as well as PGF1alpha and PGE2 in nml. In pancreatic carcinomas highest LT-concentration was found after combined treatment and this therapy group was the only one revealing a significantly higher amount of LTs in carcinomas compared to tumour-free tissue. Hepatic LT-concentration was significantly lower in the control groups than in nml of the tumour groups. Combination of Cox-2-inhibition and 5-Lox-inhibition might be a suitable adjuvant therapy to prevent liver metastasis in human ductal pancreatic adenocarcinoma.     

Distribution of radioactivity of tritiated prostaglandins E2 and A2 in rat tissues including a renal autoradiographic study.

Distribution of radioactivity in different tissues has been studied by liquid scintillation counting 60 sec after administration of [3H] PGE2 and [3H] PGA2 in the rat. In addition, renal autoradiographs were prepared 15 sec and 60 sec after tritiated PG administration. In some experiments, [3H] PGE2 was accompanied by a large dose of PGE2 (isotopic dilution). 60 sec after [3H] PGE2 administration, radioactivity concentrates principally in the kidney, followed by the liver and the lung. Within the kidney, radioactivity concentrated predominantly in the cortex. Isotopic dilution diminished radioactivity due to [3H] PGE2 in all regions of the kidney. Renal autoradiographs 15 sec after [3H] PGE2 administration showed cortical radioactivity to be higher in glomeruli than in tubules. After [3H] PGA2 radioactivity also concentrates in the kidney, liver and lung but to a lesser extent than after [3H] PGE2 and no glomerular concentration of radioactivity was found.