Prostaglandin I2 is not a major metabolite of arachidonic acid in cultured endothelial cells from human foreskin microvessels

Prostaglandin I2 (PGI2), a potent vasodilator and inhibitor of platelet aggregation, is a major product of arachidonic acid metabolism in endothelial cells that are derived from large blood vessels (e.g., umbilical veins). We have examined whether PGI2 is also a major product of arachidonic acid metabolism in cultured endothelial cells that are derived from dermal microvessels in human newborn foreskin. Supernatants from confluent monolayers of endothelial cells that had been incubated for 20 min with [3H]arachidonic acid and the calcium ionophore A23187 (10 microM) were assayed for prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), and 6-keto-prostaglandin F1 alpha (PGF1 alpha) (the stable metabolite of PGI2) by using authentic standards and high performance liquid chromatography. Whereas supernates from stimulated umbilical vein endothelial cells contained 6-keto-PGF 1 alpha much greater than PGF 2 alpha much greater than PGE2, supernates from stimulated foreskin microvessel endothelial cells contained PGF 2 alpha congruent to PGE2 much greater than 6-keto-PGF 1 alpha. Similar results were obtained when supernates from stimulated, unlabeled endothelial cells were analyzed by radioimmunoassay. These data indicate that PGI2 is not a major metabolite of arachidonic acid in cultured endothelial cells from human foreskin microvessels.     

Elevated plasma 6-keto-prostaglandin F1 alpha in patients in septic shock

Central venous plasma concentrations of 6-keto-prostaglandin F1 alpha (PGF1 alpha), the stable hydrolysis product of prostacyclin (PGI2, a vasodilator and antiaggregatory metabolite of arachidonic acid), were determined in patients with septic shock. In eight nonsurvivors, the median plasma 6-keto-PGF1 alpha level was 229 pg/ml (range 31 to 21,998), compared to 30 pg/ml (range 22 to 194) in six survivors. In three control patients who were not septic or in shock, the levels were less than 4 pg/ml. This study demonstrates that human septic shock is associated with elevated plasma levels of 6-keto-PGF1 alpha, and raises the possibility that increased PGI2 formation may play a role in human septic shock.     

Glomerular prostaglandins: synthesis, mechanism of action and interaction with ACE inhibitors]

Prostaglandins (PG) play an important role in the regulation of the renal blood flow and glomerular filtration rate. This study was designed to examine PG synthesis in the presence and absence of the ACE inhibitor captopril, PG binding to specific receptors and the ability of PG to stimulate cAMP accumulation in isolated glomeruli. Glomeruli were isolated from rat kidneys by a passive mechanical sieving technique. PG synthesis was determined by RTLC and RIA. The main eicosanoids synthesized by glomeruli were PGF2 alpha, thromboxane (TX) A2 (measured as TXB2), PGI2 (measured as 6-keto-PGF1 alpha) and PGE2. Binding experiments were performed with PGE1, PGE2 and the PGI2 analogue iloprost. Scatchard analysis revealed that the specific binding was highest for PGE1, followed by iloprost and PGE2. Adenylate cyclase was preferentially stimulated by PGE1 and PGE2, and to a lesser extent by PGI2, whereas PGF2 alpha had almost no effect. Captopril reduced mainly TXB2 concentrations. Glomerular TXB2 reduction, therefore, seems to be an additional hypotensive effect of captopril medication.     

Plasma renin activity, angiotensin II, prostacyclin and thromboxane A2 concentrations in 139 preeclamptic patients

Plasma renin activity, plasma concentrations of angiotensin II (AngII), stable metabolites (6-keto-prostaglandin F1 alpha: 6-keto-PGF1 alpha) of prostacyclin (PGI2) and a metabolite (thromboxane B2: TXB2) of thromboxane A2 (TXA2) were measured with radioimmunoassay(RIA) in 107 normal pregnancy (control) and 139 preeclamptic patients in 28-41 gestational weeks. PRA and 6-keto-PGF1 alpha were significantly higher and AngII was slightly higher in preeclampsia than in control, and TXB2 was significantly lower in preeclampsia in control. The ratio of 6-keto-PGF1 alpha/TXB2 was significantly lower in preeclampsia than in control. These data suggest that the changes in the renin-angiotensin system may not be primary alterations in preeclampsia. It can be speculated that in preeclampsia the changes in absolute concentrations of 6-keto-PGF1 alpha and TXB2 are less important than the decrease in the ratio of the 6-keto-PGF1 alpha/TXB2.     

Effects of prostanoids on human and rabbit basilar arteries precontracted in vitro

The effect of a range of prostanoids on human and rabbit basilar arteries precontracted in vitro in the presence of the thromboxane receptor-blocking drug AH23848B was investigated. On the rabbit basilar artery and in the presence of AH23848B the thromboxane A2 mimetic U-46619 produced further concentration-related contractions of the tissue. All other prostaglandins (except ICI81008 and PGF2 alpha which had no effect) produced concentration-related relaxations with the rank order of relaxant potency being PGE2 greater than Iloprost greater than PGI2 = PGE1 = 16,16-dimethyl PGE2 = PGD2. On the human basilar artery PGI2 and iloprost produced concentration-related relaxations with iloprost being more potent than PGI2. At high concentrations both these compounds produced reduced relaxant responses. All other prostanoids (except ICI81008 and PGD2 which had no effect) contracted the tissue, the rank order of contractile potency being 16,16-dimethyl PGE2 greater than PGE2 greater than PGF2 alpha = PGE1 greater than U46619 much greater than ICI81008 and PGD2. It is concluded that the human basilar artery possesses two contractile prostanoid receptors, a TP receptor and one which may be of the EP-type in addition to a prostanoid receptor mediating relaxation which may be of the IP-type. The prostanoid receptor(s) mediating relaxation of the rabbit in vitro basilar artery is difficult to determine. The relevance of the observations to cerebrovascular disorders such as migraine and vasospasm is discussed.     

Effects of sodium depletion on renal prostanoid synthesis in rats: influence of the converting enzyme inhibitor captopril

1. The synthesis of prostaglandin (PG) E2, PGF2 alpha, 6-keto-PGF1 alpha and thromboxane (TX) B2 by isolated glomeruli, cortical tubules, inner medullary slices and outer medullary slices was measured in salt-depleted (LNa) rats and in salt-depleted rats receiving captopril (LNa-CEI). Animals were studied before and after 4, 9 and 15 days of Na+ depletion. 2. Na+ balance was reached in LNa rats after 4 days. Blood pressure and creatinine clearance remained stable. Serum Na+ decreased from 140 +/- 1 to 126 +/- 1 mmol/l (mean +/- SEM, P less than 0.01). In contrast, LNa-CEI rats were unable to conserve Na+ adequately: fractional excretion of Na+ and natriuresis were constantly greater than in LNa animals. As a consequence, LNa-CEI rats developed severe hyponatraemia, lost weight and their creatinine clearance decreased. 3. The glomerular synthesis of PGE2, PGF2 alpha and 6-keto-PGF1 alpha, but not of TXB2, was significantly increased in LNa rats. In LNa-CEI rats, the synthesis of PGE2 and 6-keto-PGF1 alpha was similar to control values, but PGF2 alpha and TXB2 synthesis was elevated at day 9. In cortical tubules, PGE2 and PGF2 alpha were unaffected by Na+ depletion, but 6-keto-PGF1 alpha and TXB2 were increased and a similar trend was observed in LNa-CEI rats. In outer medulla of LNa rats, a decrease in all the eicosanoids measured was observed at day 4. In LNa-CEI animals, the synthesis of PGE2 and PGF2 alpha, but not of 6-keto-PGF1 alpha and TXB2, was significantly depressed. In inner medulla, Na+ depletion only tended to decrease PGF2 alpha and 6-keto-PGF1 alpha, but in the presence of captopril, the synthesis of all prostanoids was significantly decreased.     

Angiotensin II-induced hypertension in the rat. Effects on the plasma concentration, renal excretion, and tissue release of prostaglandins.

We examined in rats the effects of intraperitoneal angiotensin II (AII) infusion for 12 d on urinary excretion, plasma concentration, and in vitro release of prostaglandin (PG) E2 and 6-keto-PGF1 alpha, a PGI2 metabolite. AII at 200 ng/min increased systolic blood pressure (SBP) progressively from 125 +/- 3 to 170 +/- 9 mmHg (P less than 0.01) and elevated fluid intake and urine volume. Urinary 6-keto-PGF1 alpha excretion increased from 38 +/- 6 to 55 +/- 5 and 51 +/- 7 ng/d (P less than 0.05) on days 8 and 11, respectively, of AII infusion, but urinary PGE2 excretion did not change. Relative to a control value of 129 +/- 12 pg/ml in vehicle-infused (V) rats, arterial plasma 6-keto-PGF1 alpha concentration increased by 133% (P less than 0.01) with AII infusion. Aortic rings from AII-infused rats released more 6-keto-PGF1 alpha (68 +/- 7 ng/mg) during 15-min incubation in Krebs solution than did rings from V rats (40 +/- 3 ng/mg); release of PGE2, which was less than 1% of that of 6-keto-PGF1 alpha, was also increased. Slices of inner renal medulla from AII-infused rats released more 6-keto-PGF1 alpha (14 +/- 1 ng/mg) during incubation than did slices from V rats (8 +/- 1 ng/mg, P less than 0.05), but PGE2 release was not altered. In contrast, AII infusion did not alter release of 6-keto-PGF1 alpha or PGE2 from inferior vena cava segments or from renal cortex slices. Infusion of AII at 125 ng/min also increased SBP, plasma 6-keto-PGF1 alpha concentration, and in vitro release of 6-keto-PGF1 alpha from rings of aorta and renal inner medulla slices; at 75 ng/min AII had no effect. SBP on AII infusion day 11 correlated positively with both 6-keto-PGF1 alpha plasma concentration (r = 0.54) and net aortic ring release (r = 0.70) when data from all rats were combined. We conclude that augmentation of PGI2 production is a feature of AII-induced hypertension. The enhancement of PGI2 production may be an expression of nonspecific alteration in vascular structure and metabolic functions during AII-induced hypertension, as well as the result of a specific effect of the peptide on the arachidonate-prostaglandin system.     

Endogenous vasoconstrictor prostanoids: role in serotonin and vasopressin-induced coronary vasoconstriction

A vasoconstrictor-induced prostacyclin (PGI2) production in a perfused rat heart was found, suggesting a mitigating role of PGI2 on coronary vasoconstriction. Treatment of the heart with cyclooxygenase inhibitors (aspirin or indomethacin) decreased PGI2 production by more than 90% and paradoxically reduced the vasoconstriction response. The attenuating effect of cyclooxygenase blockade suggested that endogenous prostanoids contribute to serotonin-, vasopressin- or U46619-induced vasoconstriction. Two prostaglandin (PG) H2/thromboxane A2 (TXA2) receptor antagonists, i.e., 13-azaprostanoic acid (13-APA) and SQ 29,548 were used to investigate putative endogenous vasoconstrictor prostanoids on the exogenously induced vasoconstriction. Retrogradely perfused (5-6 ml/min) rat hearts were rendered guiescent, yet responsive to stimuli, by local injection of lidocaine to the atrioventricular node. Changes in coronary vascular resistance (i.e., perfusion pressure at constant flow) were monitored and the cardiac effluent was collected for analysis of 6-keto PGF1 alpha (the stable metabolite of PGI2) as well as PGF2 alpha by radioimmunoassay. Three vasoconstrictors, i.e., serotonin, vasopressin and the TXA2/PGH2 analog U46619, as well as authentic PGD2, PGE2 and PGF2 alpha were infused. PGD2, PGE2 and PGF2 alpha exerted a dose-related coronary vasoconstriction, as did U46619, serotonin and vasopressin. Treatment with 13-APA (100 microM) or SQ 29,548 (100 nM) almost abolished U46619-induced vasoconstriction. The addition of PGH2/TXA2 receptor antagonists also significantly reduced the pressor effect of exogenously administered PGs, serotonin and vasopressin, with the exception that SQ 29,548 did not significantly antagonize PGE2-induced vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased renal vasodilator prostanoids prevent hypertension in mice lacking the angiotensin subtype-2 receptor

The angiotensin subtype-1 (AT(1)) receptor mediates renal prostaglandin E(2) (PGE(2)) production, and pharmacological blockade of the angiotensin subtype-2 (AT(2)) receptor potentiates the action of angiotensin II (Ang II) to increase PGE(2) levels. We investigated the role of the AT(2) receptor in prostaglandin metabolism in mice with targeted deletion of the AT(2) receptor gene. Mice lacking the AT(2) receptor (AT(2)-null) had normal blood pressure that was slightly elevated compared with that of wild-type (WT) control mice. AT(2)-null mice had higher renal interstitial fluid (RIF) 6-keto-PGF(1alpha) (a stable hydrolysis product of prostacyclin [PGI(2)]) and PGE(2) levels than did WT mice, and had similar increases in PGE(2) and 6-keto-PGF(1alpha) in response to dietary sodium restriction and Ang II infusion. In contrast, AT(2)-null mice had lower PGF(2alpha) levels compared with WT mice during basal conditions and in response to dietary sodium restriction or infusion of Ang II. RIF cAMP was markedly higher in AT(2)-null mice than in WT mice, both during basal conditions and during sodium restriction or Ang II infusion. AT(1) receptor blockade with losartan decreased PGE(2), PGI(2), and cAMP to levels observed in WT mice. To determine whether increased vasodilator prostanoids prevented hypertension in AT(2)-null mice, we treated AT(2)-null and WT mice with indomethacin for 14 days. PGI(2), PGE(2), and cAMP were markedly decreased in both WT and AT(2)-null mice. Blood pressure increased to hypertensive levels in AT(2)-null mice but was unchanged in WT. These results demonstrate that in the absence of the AT(2) receptor, increased vasodilator prostanoids protect against the development of hypertension.     

Prostaglandin and thromboxane synthesis by highly enriched rabbit proximal tubular cells in culture

Prostaglandin synthetic profiles were studied in monolayers of highly enriched rabbit renal proximal tubular cells cultured in serum-free, hormone-supplemented, defined media. The cultures were initiated from glomeruli-free cortical suspensions. Cells in culture demonstrated morphologic and functional characteristics highly suggestive of proximal tubular cells. The basal and stimulated synthesis of immunoassayable prostaglandin (PG) E2, PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane (Tx) B2 in response to various agonists, as well as the effect of two cyclooxygenase inhibitors, was assessed. Under both basal and stimulated conditions, PGE2 was the major product synthesized. PGF2 alpha and 6-keto-PGF1 alpha were synthesized to a lesser extent, and TxB2 was undetectable. The basal synthesis of PGE2 and PGF2 alpha in cultured cells was found to be higher than in isolated proximal tubular fragments by sevenfold and fivefold, respectively. Exogenous arachidonate, angiotensin II, and the divalent cation ionophore A23187 stimulated all three immunoassayable prostaglandins in a dose-dependent manner. Arginine vasopressin (10(-5) mol/L) had no stimulatory effect. In Ca++-free media or in the presence of 10(-5) mol/L Ca++ channel blocker, verapamil, the stimulatory effects of angiotensin II and A23187 were ameliorated. The stimulatory effect of angiotensin II was inhibited by saralasin (10(-5) mol/L), indicating that receptor binding could mediate PGE2 synthesis. Both indomethacin and sulindac sulfide (10(-5) mol/L) reversibly inhibited PGE2 synthesis.     

Effect of noradrenaline, vasopressin and angiotensin II on renal prostaglandins in man

To examine the response of renal prostaglandins (PG) to systemic and renal vasoconstriction noradrenaline (NA), arginine vasopressin (AVP) and angiotensin II (ANG II) were each infused into eight healthy female subjects for 3 h on different days. Urinary excretion of PGE2, PGF2 alpha and 6-keto-PGF1 alpha was determined hourly. NA and ANG II stimulated excretion of PGF2 alpha significantly, but not of PGE2 or 6-keto-PGF1 alpha. AVP stimulated renal PGF2 alpha and 6-keto-PGF1 alpha significantly, but not PGE2. A weak correlation was found between urinary PGF2 alpha and diastolic blood pressure during NA and ANG II infusions, but not during AVP infusion. The release of renal PG does not appear to constitute an obligatory and concomitant response to the blood pressure rise induced by the pressor agonists. The greater response of PGF2 alpha than of PGE2 may result from a preferential direct effect on PGF2 alpha secretion or from an increased conversion of PGE2 into F2 alpha.     

Hangover headache and prostaglandins: Prophylactic treatment with tolfenamic acid

Tolfenamic acid (TA), a potent inhibitor of prostaglandin (PG) biosynthesis and action, was tested prophylactically against hangover symptoms in 30 healthy volunteers in a double-blind cross-over study. One capsule of TA (200 mg) or placebo was taken before starting to drink alcohol and another before going to bed. The hangover symptoms were evaluated in the morning. TA was found significantly better than placebo in the subjective evaluation of drug efficacy (p less than 0.001) and in reducing the reported hangover symptoms in general (p less than 0.01). In the TA group, significantly lower symptom scores were obtained for headache (p less than 0.01), and for nausea, vomiting, irritation, tremor, thirst and dryness of mouth (all p less than 0.05). In a separate study with eight participants, plasma levels of PGs were followed during ingestion of alcohol with or without TA. The plasma concentrations of PGE2 and TXB2 (a metabolite of thromboxane A2) were lower in the TA group during alcohol ingestion, while PGF2 alpha and 6-keto-PGF1 alpha (a metabolite of prostacyclin) were unaffected. TXB2 correlated with blood alcohol levels in a U-shaped manner.     

Longitudinal study of renal prostaglandin excretion in cirrhotic rats: relationship with the renin-aldosterone system

1. A cross-sectional study (protocol A) was performed in 19 rats with cirrhosis, induced by carbon tetrachloride (CCl4), and ascites and in 10 control animals to assess renal prostaglandin (PG) excretion in experimental cirrhosis. In an additional group of animals, including nine rats chronically exposed to CCl4 (CCl4 rats) and six control rats, a longitudinal study (protocol B) was performed to investigate the temporal relationship between changes in renal PG excretion, the renin--aldosterone system and renal function. 2. Urinary PG excretion was assessed by specific radioimmunoassay of PGE2, PGF2 alpha, 6-keto-PGF1 alpha and thromboxane (TX) B2 after extraction with octadecyl silica cartridges and h.p.l.c. purification. Recoveries for each prostanoid (61 +/- 8% for PGE2, 64 +/- 12% for PGF2 alpha, 65 +/- 11% for 6-keto-PGF1 alpha and 66 +/- 17% for TXB2) were determined in every sample by adding tritiated standards, and the final values were corrected according to the individual recoveries. 3. Cirrhotic rats with ascites in protocol A showed a significantly higher plasma renin and aldosterone concentrations and urinary excretion of 6-keto-PGF1 alpha and TXB2 than did control animals. Urinary excretion of PGE2 and PGF2 alpha, however, was significantly reduced in cirrhotic animals as compared with controls. 4. In CCl4 rats included in protocol B, there was a close chronological relationship between the activation of the renin-aldosterone system, as estimated by urinary aldosterone excretion, the onset of sodium retention and the increase in urinary excretion of 6-keto-PGF1 alpha and TXB2. The urinary excretion of PGE2 and PGF2 alpha in CCl4 rats was reduced throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective inhibition of renal thromboxane biosynthesis increased sodium excretion rate in normal and saline-loaded rats

The excretion rates of renal thromboxane B2 (TXB2) and 6-ketoPGF1 alpha, the stable chemical metabolites of thromboxane A2 (TXA2) and prostaglandin I2 (PGI2) respectively, PGE2 and sodium were determined in normal and saline-loaded rats treated with the thromboxane synthetase inhibitor imidazole. In normal rats the administration of imidazole in doses which did not affect renal 6-keto-PGF1 alpha and PGE2 excretion but selectively inhibited renal TXB2 excretion, significantly increased the sodium excretion rate. Volume expansion with saline increased renal PGE2 and 6-ketoPGF1 alpha excretion but did not alter renal TXB2 excretion. The increase in renal prostaglandin excretion was accompanied by an increased sodium excretion rate. The administration of imidazole to saline-loaded animals also decreased renal TXB2 excretion but did not alter the increased excretion of renal PGE2 and 6-ketoPGF1 alpha. This reduction in renal thromboxane biosynthesis by imidazole further increased the sodium excretion rate. We suggest that TXA2 is a potent antinatriuretic factor as well as the most potent vasoconstrictor agent known.     

The potential role of thromboxane and prostacyclin in endotoxic and septic shock

The potential role of thromboxane (TxA2), a platelet aggregator and vasoconstrictor, and prostacyclin (PGI2) a platelet anti-aggregator and vasodilator, in endotoxic and septic shock was investigated. Early endotoxic shock in the rat is associated with marked elevations of plasma TxB2 (the stable metabolite of TxA2) and lesser increases in plasma 6-keto-PGF1 alpha (the stable metabolite of PGI2). Selective inhibition of TxA2 synthesis by several different chemical classes of Tx synthetase inhibitors was beneficial in endotoxic shock. In contrast, shock induced by acute intra-abdominal sepsis in the rat was characterized by high levels of plasma 6-keto-PGF1 alpha, which exceeded plasma TxA2 six- to eight fold at most time intervals studied. Tx synthetase inhibitors were not protective in this model of acute sepsis, but treatment with fatty acid cyclo-oxygenase inhibitors, an antibiotic (gentamicin), or reduction in arachidonic acid metabolism by essential fatty acid (EFA) deficiency significantly prolonged survival time. An important aspect of the latter study is that decreased arachidonic acid metabolism was an effective adjunct to antibiotic therapy. Conjoint administration of gentamicin in EFA-deficient rats or with indomethacin synergistically improved long-term survival, a result that was not evident with single treatment interventions. In addition to experimental studies, plasma TxB2 levels were measured during clinical sepsis. These studies demonstrated that plasma TxB2 levels were elevated tenfold in patients dying of septic shock compared with septic survivors or nonseptic controls. These composite experimental and clinical observations suggest that arachidonic acid metabolites play a role in the pathogenesis of endotoxic and septic shock.     

The behaviour of prostanoids during the course of acute experimental pancreatitis in rats

The behavior of two vasoactive prostanoids was studied in experimental acute pancreatitis (AP) in rats. The stable metabolites of prostacyclin (PGI2) and thromboxane A2 (TXA2), 6-keto-PGF1 alpha and TXB2, respectively, were measured during the course of experimental AP. Blood samples were taken at 3, 6, and 8 h after the induction of AP. In AP both plasma 6-keto-PGF1 alpha plasma TXB2 and serum TXB2 increased up to 6 h simultaneously (6-keto-PGF1 alpha from 271.1 +/- 77.2 pg/ml (mean +/- SD) to 459.4 +/- 192.6 pg/ml, plasma TXB2 from 752 +/- 350 pg/ml to 3640 +/- 2160 pg/ml and serum TXB2 from 22.3 +/- 14.8 micrograms/ml to 140.8 +/- 52.8 micrograms/ml). After 6 h 6-keto-PGF1 alpha remained elevated, whereas serum TXB2 dropped significantly. We suggest that in AP the balance of PGI2 and TXA2 is initially maintained, but later on an imbalance appears to favor vasodilatory PGI2. These agents may contribute to the regulation of the blood flow in the pancreas and thus play a role in the pathophysiology of AP.     

Mediator release from human lung under conditions of reduced oxygen tension

Although the mechanism underlying hypoxic pulmonary vasoconstriction remains undefined, various reports have suggested that mast cells and cell-derived mediators may be important in the production of this phenomenon. We investigated the effect of reducing oxygen tension on the release from human lung fragments of the mast cell-derived mediators histamine, prostaglandin (PG) D2 and peptide leukotrienes, as well as the release of the largely non-mast cell-derived mediators PGE2, PGF2 alpha, prostacyclin metabolite (6-keto-PGF1 alpha) and the thromboxane A2 metabolite (thromboxane B2). The effect of reducing oxygen tension on both basal mediator release and release triggered by goat antihuman immunoglobulin E was studied. Reducing pO2 of buffer in which lung fragments were placed from 161 to 54 mm Hg resulted in no spontaneous release of histamine, PGD2 or peptide leukotrienes. However, hypoxia had a marked effect on mediator release triggered by goat antihuman immunoglobulin E. Although net histamine release was relatively unaffected (control 13.9 +/- 2.7%, hypoxic 12.7 +/- 2.1%), hypoxic treatment resulted in an 89% inhibition of PGD2 release (control 47.7 +/- 17.4 ng/g of lung, hypoxic 5.26 +/- 1.91 ng/g of lung) and an 81% inhibition of peptide leukotriene release (control 22.5 +/- 7.6 ng/g of lung, hypoxic 4.37 +/- 2.4 ng/g of lung). Similar inhibition was seen for non-mast cell-derived mediators, including PGF2 alpha, prostacyclin metabolite and thromboxane B2, and probably for PGE2. We conclude that hypoxic treatment of human lung fragments in vitro results in no spontaneous release of preformed or newly formed mediators but that it markedly alters mediator release after goat antihuman immunoglobulin E triggering.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stimulation of peritoneal synthesis of vasoactive prostaglandins during peritonitis in patients on continuous ambulatory peritoneal dialysis

The peritoneal generation of arachidonic acid metabolites was studied in eight patients with end-stage renal disease undergoing continuous ambulatory peritoneal dialysis (CAPD) during infection-free periods and during bacterial peritonitis. The prostacyclin metabolite 6-keto-PGF1 alpha was found to be the major prostanoid generated by human peritoneal mesothelium (1090 ng (6h)-1, SEM 86, n = 8) followed by lesser amounts of PGE2 (142 ng (6 h)-1, SEM 26, n = 8), PGF2 alpha (162 ng (6 h)-1, SEM 27, n = 8) and TXB2 (59 ng (6 h)-1, SEM 5, n = 8). During peritonitis a significant increase of all prostaglandins and TXB2 occurred (P less than 0.001). The ratio of the vasodilating prostaglandins and their metabolites (PGE2 and 6-keto-PGF1 alpha) to the vasoconstrictors and their metabolites (PGF2 alpha and TXB2) increased from 6.6 to 10.5 during peritoneal inflammation. Augmented peritoneal clearances of creatinin and urea and increased losses of proteins during peritonitis as well as the enhanced peritoneal generation of prostanoids were reduced to basal values by adequate antibiotic therapy. The present results suggest that the increased peritoneal blood flow during peritonitis, probably responsible for the observed changes of peritoneal transport properties, may be induced by a change in the ratio of vasoactive prostaglandins generated by peritoneal mesothelial cells.     

Effects of selective COX-2 inhibition on prostanoids and platelet physiology in young healthy volunteers

BACKGROUND: Selective inhibitors of cyclooxygenase-2 (COX-2) called coxibs, are effective anti-inflammatory and analgesic drugs. Recently, these drugs were associated with an increased risk for myocardial infarction and atherothrombotic events. The hypothesis of thromboxane-prostacyclin imbalance has been preferred to explain these unwanted effects. METHODS: We studied the effects of 14 days intake of rofecoxib (25 mg q.d.), celecoxib (200 mg b.i.d.), naproxen (500 mg b.i.d.) and placebo in a randomized, blinded, placebo-controlled study in young healthy volunteers (median age 25-30 years, each group n = 10). We assessed prostanoid metabolite excretion (PGE-M, TXB(2), 6-keto-PGF(1alpha), 11-dehydro-TXB(2), 2,3-dinor-TXB(2), and dinor-6-keto-PGF(1alpha)), the expression of platelet activation markers (CD62P, PAC-1, fibrinogen), platelet-leukocyte formation, the endogenous thrombin potential, platelet cAMP content and plasma thrombomodulin level. RESULTS: Naproxen suppressed biosynthesis of PGE-M, prostacyclin metabolites and thromboxane metabolites and thrombomodulin levels. In contrast, both coxibs had an inhibitory effect only on PGE-M, 6-keto-PGF(1alpha), and on dinor-6-keto-PGF(1alpha), whereas TXB(2), 2,3-dinor-TXB(2) and 11-dehydro-TXB(2) excretion were unaffected. None of the coxibs exerted significant effects on the expression of platelet activation markers, cAMP generation, platelet-leukocyte formation, or on thrombomodulin plasma levels. Interestingly, platelet TXB(2) release during aggregation was enhanced after coxib treatment following arachidonic acid or collagen stimulation. CONCLUSION: In young healthy volunteers coxibs inhibit systemic PGE(2) and PGI(2) synthesis. Platelet function and expression of platelet aggregation markers are not affected; however, coxibs can stimulate TXB(2) release from activated platelets. Combined decrease in vasodilatory PGE(2) and PGI(2) together with increased TXA(2) in proaggregatory conditions may contribute to coxib side effects.     

Evidence that prostacyclin modulates the vascular actions of calcium in man.

Increases in extracellular calcium (Ca++) can alter vascular tone, and thus may result in increased blood pressure (Bp) and reduced renal blood flow (RBF). Ca++ can stimulate prostaglandin E2 (PGE2) and/or prostacyclin (PGI2) release in vitro, which may modulate Ca++ vascular effects. However, in man, the effect of Ca++ on PG release is not known. To study this, 14 volunteers received low-dose (2 mg/kg Ca++ gluconate) or high-dose (8 mg/kg) Ca++ infusions. The low-dose Ca++ infusion did not alter systemic or renal hemodynamics, but selectively stimulated PGI2, as reflected by the stable metabolite 6-keto-PGF1 alpha in urine (159 +/- 21-244 +/- 30 ng/g creatinine, P less than 0.02). The same Ca++ infusion given during cyclooxygenase blockade with indomethacin or ibuprofen was not associated with a rise in PGI2 and produced a rise in Bp and fall in RBF. However, sulindac, reported to be a weaker renal PG inhibitor, did not prevent the Ca++ -induced PGI2 stimulation (129 +/- 33-283 +/- 90, P less than 0.02), and RBF was maintained despite similar increases in Bp. The high-dose Ca++ infusion produced an increase in mean Bp without a change in cardiac output, and stimulated urinary 6-keto-PGF1 alpha to values greater than that produced by the 2-mg/kg Ca++ dose (330 +/- 45 vs. 244 +/- 30, P less than 0.05). In contrast, urinary PGE2 levels did not change. A Ca++ blocker, nifedipine, alone had no effect on Bp or urinary 6-keto-PGF1 alpha levels, but completely prevented the Ca++ -induced rise in Bp and 6-keto-PGF1 alpha excretion (158 +/- 30 vs. 182 +/- 38, P greater than 0.2). However, the rise in 6-keto-PGF1 alpha was not altered by the alpha 1 antagonist prazosin (159 +/- 21-258 +/- 23, P less than 0.02), suggesting that calcium entry and not alpha 1 receptor activation mediates Ca++ pressor and PGI2 stimulatory effects. These data indicate a new vascular regulatory system in which PGI2 modulates the systemic and renal vascular actions of calcium in man.