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.     

Renal prostaglandins in cirrhosis of the liver

Urinary prostaglandin excretion was studied in 42 patients with liver cirrhosis and in nine control subjects on restricted sodium intake and on bed rest. Creatinine clearance (CCr), sodium excretion (UNaV), plasma renin activity (PRA) and plasma aldosterone were also evaluated. Patients without ascites and ascitic patients without renal failure showed increased urinary excretion of immunoreactive 6-ketoprostaglandin F1 alpha (i6-keto-PGF1 alpha), prostaglandin E2 (iPGE2) and thromboxane B2 (iTXB2) when compared with controls, while immunoreactive PGF2a (iPGF2 alpha) levels did not differ from those in the control group. Patients with functional renal failure (FRF) presented a significant reduction of vasodilator prostaglandins but urinary excretion of iTXB2 was higher than in controls. On the whole, cirrhotic patients with higher urinary excretion of prostaglandins had normal or nearly normal PRA and aldosterone levels. i6-keto-PGF1 alpha and iPGE2 inversely correlated with PRA and aldosterone. The relationship between i6-ketoPGF alpha alpha and CCr was found to be highly significant in cirrhotic patients but not in the control group. On the other hand, iPGE2 significantly correlated with UNaV and with the fractional excretion of sodium (FENa). We concluded that: (a) enhanced renal prostaglandin synthesis in cirrhosis, inversely related to PRA and aldosterone, may be dependent on volume status; and (b) preserved renal function in these patients is associated with the ability to synthesize prostacyclin and PGE2.     

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.     

Prostaglandin synthesis elicited by adrenergic stimuli is mediated via alpha-2C and alpha-1A adrenergic receptors in cultured smooth muscle cells of rabbit aorta.

This study was performed to characterize the subtype of adrenergic receptor(s) (AR) involved in prostacyclin synthesis [measured as 6-keto-prostaglandin (PG)F1 alpha] elicited by AR agonists in cultured vascular smooth muscle cells of rabbit aorta. Both alpha-1 and alpha-2 AR agonists enhanced 6-keto-PGF1 alpha synthesis in a dose-dependent manner with the following order of potency: norepinephrine greater than BHT 933 greater than UK 14304 greater than xylazine greater than phenylephrine greater than or equal to methoxamine greater than cirazoline. Isoproterenol and oxymetazoline did not alter 6-keto-PGF1 alpha synthesis. Methoxamine-induced 6-keto-PGF1 alpha synthesis was not reduced by the alpha-2 AR antagonist rauwolscine. The affinities of AR antagonists (PA2 value) in inhibiting methoxamine-induced 6-keto-PGF1 alpha synthesis were of the following order: prazosin greater than WB 4101 greater than corynanthine greater than yohimbine. Administration of WB 4101 and the irreversible alpha-1B AR antagonist chloroethylclonidine reduced norepinephrine (in the presence of rauwolscine, 10(-8) M)- or methoxamine-induced 6-keto-PGF1 alpha synthesis; WB 4101 was more potent than chloroethylclonidine. UK 14304-induced 6-keto-PGF1 alpha synthesis was not reduced by chloroethylclonidine or BRL 44408, a selective alpha-2A AR antagonist, but it was inhibited by other alpha AR antagonists. The affinities of AR antagonists (PA2 values) in inhibiting UK 14304-induced 6-keto-PGF1 alpha synthesis were of the following order: rauwolscine greater than yohimbine greater than BAM 1303 greater than BRL 41992 greater than WB 4101 greater than ARC 239 greater than or equal to prazosin greater than SKF 104078 greater than or equal to corynanthine. The order of affinity of alpha-2 AR antagonists in inhibiting UK 14304-induced 6-keto-PGF1 alpha synthesis in vascular smooth muscle cells was similar to that derived from radioligand binding studies in opossum kidney cell line receptors classified as alpha-2C receptors. These data suggest that 6-keto-PGF1 alpha synthesis elicited by adrenergic stimuli in cultured vascular smooth muscle cells of rabbit aorta is mediated primarily via alpha-2C and to a lesser extent alpha-1A receptors.     

Comparison of signal transduction mechanisms of alpha-2C and alpha-1A adrenergic receptor-stimulated prostaglandin synthesis.

Prostaglandin (PG) synthesis elicited by adrenergic transmitter in the vascular smooth muscle cells (VSMC) of rabbit aorta is primarily mediated through activation of alpha-2C and alpha-1A adrenergic receptors (ARs). We have now investigated and compared the signal transduction mechanisms involved in alpha-2C and alpha-1A AR-stimulated prostacyclin (PGI2) production, measured as 6-keto-PGF1 alpha, in vascular smooth muscle cells. Norepinephrine, methoxamine (an alpha-1 AR agonist) and UK-14304 (an alpha-2 AR agonist) enhanced 6-keto-PGF1 alpha production. UK-14304 and norepinephrine (in the presence of propranolol), but not methoxamine, reduced basal adenosine 2':3'-cyclic monophosphate (cyclic AMP) as well as forskolin- and isoproterenol-stimulated cyclic AMP accumulation. Forskolin and isoproterenol did not alter basal 6-keto-PGF1 alpha production and alpha AR agonist-induced 6-keto-PGF1 alpha production. Alpha-2C and alpha-1A AR-stimulated 6-keto-PGF1 alpha production was independent of cyclic AMP levels in vascular smooth muscle cells. Both alpha-2C and alpha-1A AR-stimulated 6-keto-PGF1 alpha production required extracellular Ca++. Pertussis toxin prevented inhibition of cyclic AMP accumulation and reduced 6-keto-PGF1 alpha production in response to AR agonists. Guanosine 5'-O-(3-thiotriphosphate) potentiated 6-keto-PGF1 alpha production induced by norepinephrine and UK-14304 but not by methoxamine, whereas at a higher Mg++ concentration (4 mM), guanosine 5'-O-(3-thiotriphosphate) potentiated 6-keto-PGF1 alpha production by all three agonists. In contrast, the effect of UK-14304 on cyclic AMP was prevented in the presence of 4 mM Mg++. These data suggest that the pertussis toxin-sensitive G protein(s) mediated the stimulation of PG synthesis by alpha-1A and alpha-2C AR activation and the decrease in cyclic AMP accumulation by alpha-2C AR activation.     

Effect of the converting enzyme inhibitor SQ-20881 on urinary excretion of prostaglandin E2 in the rat: influence of pretreatment with deoxycorticosterone

The effect of SQ-20881, an inhibitor of the peptidyl dipeptidase that degrades kinins and converts angiotensin I to angiotensin II, on the urinary excretion of immunoreactive prostaglandin E2 (iPGE2) was studied in rats receiving either deoxycorticosterone (DOCA, 5 mg/day s.c.) or sesame oil vehicle for 10 days before and then during the study, DOCA-treated animals had higher urinary excretion of iPHE2 and kallikrein, and lower plasma renin, than did animals injected with oil only. In rats pretreated with DOCA, infusion of SQ-20881 (1.2 mg/day s.c.) for 6 days increased iPGE2 excretion from 87.3 +/- 1.9 to 150.9 +/- 14.5 ng/day (P < .05). In contrast, in rats pretreated with vehicle, SQ-20881 had no significant effect on urine iPGE2. The enzyme inhibitor did not affect the intake of fluid, the volume of urine or the urinary excretion of kallikrein and electrolytes in either DOCA- or vehicle-treated animals. The blood pressure reduction elicited by a bolus injection of bradykinin (1.0 microgram i.v.) was greater in rats receiving SQ-20881 than in vehicle-infused controls, both in the DOCA- and in the sesame oil-treated groups, suggesting inhibition of kinin degradation by the converting enzyme inhibitor. These results indicate that DOCA or the consequences of its administration are required for SQ-20881 to increase iPHE2 excretion in the rat. Such an effect of the inhibitor probably relates to stimulation of renal prostaglandin synthesis consequent to elevation of kinin levels.     

Arachidonic acid metabolism and urinary excretion of prostaglandins and thromboxane in rats with experimental diabetes mellitus

Urinary prostaglandins (PGs) and thromboxane excretion, measured by radioimmunoassay, were examined in male Wistar rats made diabetic with streptozotocin, 70 mg/kg. In addition, immunoreactive (i) 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) production by aortic rings was studied as well as conversion of [14C] arachidonic acid (AA) by aortic rings, polymorphonuclear leukocytes, and macrophages isolated from diabetic and age-matched control rats. The profile of urinary eicosanoid excretion changed after induction of diabetes. iPGF2 alpha excretion transiently increased, reaching a peak at 7 days and declining to control values by 48 days. iPGE2 excretion declined with time after induction of diabetes while marked increases in i thromboxane B2 and i6-keto-PGF1 alpha excretion occurred within 48 h and were maintained for the duration of the study, up to 176 days. However, serum i thromboxane B2 levels were similar in control and diabetic rats. Formation of i6-keto-PGF1 alpha by aortic rings obtained from diabetic rats was approximately one-half that of aortic rings from control rats. Similarly, conversion of [14C]AA revealed a diminished capacity of aortic rings from diabetic rats to synthesize prostacyclin (PGI2) measured as 6-keto-PGF1 alpha. Conversion of [14C]AA by polymorphonuclear leukocytes and macrophages obtained from diabetic rats did not differ from those obtained from control rats. In conclusion, experimental diabetes mellitus is accompanied by temporal alterations in AA metabolism, the functional significance of which is unknown at this time.     

Differential inhibition by aspirin of platelet thromboxane and renal prostaglandins in the rat

Aspirin (ASA) beside inhibiting platelet thromboxane A2 (TxA2) can suppress the formation of renal prostacyclin (PGI2) and prostaglandin E2 (PGE2) which play a crucial role in the control of renal hemodynamics. Previous studies based on urinary PG measurements have suggested that p.o. ASA can spare renal cyclooxygenase. We wanted to establish by direct measurement whether p.o. ASA has a renal sparing effect and to establish to which extent changes in renal cyclooxygenase activity can be predicted measuring urinary excretion of 6-keto-PGF1 alpha and PGE2. Our results showed that in normal rats 10 mg/kg of ASA given p.o. partially inhibits platelet TxA2 formation (measured as serum TxB2) and does not inhibit glomerular and medullary PGI2 and PGE2 synthesis. Higher doses of ASA (30-200 mg/kg) effectively and completely inhibit platelet TxA2 independently if given p.o. or i.v., and also inhibit glomerular and medullary PG synthesis. The kinetics of the effect of ASA on platelet vs. renal cyclooxygenase is different: the inhibition being irreversible in platelets, but rapidly reversible in glomeruli and medulla. Six hours after the administration of 10 and 30 mg/kg i.v. and 30 mg/kg p.o., kidney cyclooxygenase activity recovers completely. This transient inhibition of renal cyclooxygenase is not reflected by urinary excretion of 6-keto-PGF1 alpha and PGE2 (6- and 24-hr collection periods). In conclusion our present results indicate that doses of ASA enough to inhibit platelet TxA2, transiently inhibit glomerular and medullary PGI2 and PGE2. Although the inhibitory effect on platelets is long lasting, the effect on renal cyclooxygenase is transient and rapidly reversible.(ABSTRACT TRUNCATED AT 250 WORDS)     

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)     

Increased prostaglandin PGE2 and 6-keto-PGF1 alpha immunoactivity in incubates of gastric mucosa and forestomach of nephrectomized rats.

Prostaglandin E2 (PGE2)- and 6-keto-PGF1 alpha-like immunoactivity was measured in incubates of forestomach and gastric corpus mucosa in (a) unoperated rats, (b) rats with sham-operation of the kidneys and (c) rats with bilateral nephrectomy. In addition the mean ulcer area in the forestomach and gastric mucosa was assayed in all three groups of rats. The PGE2- and 6-keto-PGF1 alpha-like immunoactivity in gastric mucosa incubates and 6-keto-PGF1 alpha in the forestomach incubates was almost the same in unoperated and sham-operated rats. Increased 6-keto-PGF1 alpha in the forestomach and of PGE2 and 6-keto-PGF1 alpha in the gastric mucosa was found in rats with bilateral nephrectomy before gastric lesions were seen. A higher mean ulcer area occurred in the forestomach and gastric mucosa 24-48 h after bilateral nephrectomy. We conclude, that the increased PGE2- and 6-keto-PGF1 alpha production by the gastric mucosa and forestomach was associated with the loss of normal renal tissue function. Despite the protection of PGE2 and PGI2 by gastric tissue, gastric lesions nevertheless occur in acute uraemic rats.     

Gentamicin and indomethacin in the treatment of septic shock: effects on prostacyclin and thromboxane A2 production

We investigated the effects of the thromboxane synthetase inhibitor 7-(1-imidazolyl)heptanoic acid (7-IHA) and the fatty acid cyclooxygenase inhibitors indomethacin or ibuprofen in the treatment of fecal peritonitis in the rat. The effects of gentamicin alone and in combination with reduction of arachidonic acid metabolism by either treatment with indomethacin or essential fatty acid deficiency was also investigated. 7-IHA (60 mg/kg), administered i.p. 30 min before i.p. instillation of a fecal suspension, significantly reduced the plasma levels of immunoreactive (i) TxB2 from 1066 +/- 194 pg/ml (N = 14) to nondetectable (less than 200 pg/ml; N = 9) (P less than .01) at 1 hr and from 1695 +/- 218 (N = 16) to 508 +/- 56 pg/ml (N = 6) (P less than .01) at 4 hr after instillation of feces. In contrast, the levels of i6-keto-prostaglandin (PG)F1 alpha, the stable metabolite of prostacyclin, were significantly elevated by 7-IHA pretreatment from vehicle-treated septic control levels of 3777 +/- 414 (N = 16) to 5185 +/- 467 pg/ml (N = 9) (P less than .05) at 1 hr. Plasma i6-keto-PGF1 alpha at 4 hr in 7-IHA-treated rats (5503 +/- 665 pg/ml) (N = 6) was not different from vehicle-treated controls. Survival associated with fecal peritonitis was not altered by 7-IHA pretreatment. Indomethacin (10 mg/kg) or ibuprofen (5 mg/kg) administered i.p. 30 min before the fecal suspension significantly decreased both iTxB2 and i6-keto-PGF1 alpha, plasma levels when measured at 4 hr and prolonged survival time (P less than .05). Fibrinogen/fibrin degradation products were elevated (P less than .01) during fecal peritonitis and were reduced by indomethacin (P less than .01) or 7-IHA (P less than .05). Gentamicin significantly increased mean survival time from 8.6 +/- 0.2 (N = 50) to 23.8 +/- 2.6 hr (N = 16) (P less than .01). Gentamicin in combination with indomethacin or essential fatty acid deficiency further improved mean survival time and resulted in long-term survivals (greater than 48 hr) of 35 (N = 17) and 30% (N = 7), respectively (P less than .01 compared with gentamicin). Gentamicin pretreatment did not significantly alter plasma iTxB2 levels, but decreased i6-keto-PGF1 alpha from 9465 +/- 792 (N = 7) to 3096 +/- 1,174 pg/ml (N = 5; P less than .01) at 6 hr after induction of fecal peritonitis. These studies raise the possibility that inhibition of fatty acid cyclooxygenase may be a useful adjunct to antibiotic therapy in the treatment of septic shock.     

Renal response to 9 alpha, 11 beta-prostaglandin F2 in the rat

9 alpha, 11 beta-Prostaglandin F2 (9 alpha, 11 beta-PGF2) is a novel PG formed from PGD2 by the action of 11-ketoreductase which has been shown to exist in the liver, lung and kidneys. 9 alpha, 11 beta-PGF2 has been reported to possess platelet antiaggregatory, vasoconstrictor and bronchoconstrictor properties. To define further the biological activity of 9 alpha, 11 beta-PGF2, with respect to kidney function, studies were conducted in anesthetized male Sprague-Dawley rats prepared for renal clearance measurements. Intravenous infusion of highly-purified 9 alpha, 11 beta-PGF2 (2.5 micrograms/min, n = 9) elevated urine flow (28 +/- 6 microliter/min, P less than .05), urinary sodium/potassium (0.96 +/- 0.31, P less than .05), hematocrit (0.5 +/- 0.3, volumes/100 ml, P less than .05) and urinary sodium excretion (2.3 +/- 1.0 microEq/min). Similar responses but of greater magnitude were obtained with PGF2 alpha (2.5 micrograms/min). Glomerular filtration rate (GFR) and mean arterial pressure (MAP) were unaffected. In contrast, PGD2 (2.5 micrograms/min) resulted in decreases in MAP and concomitant reductions in GFR, urine flow and sodium excretion. Abrupt and pronounced increases in urine flow and sodium excretion were observed on administration of 9 alpha, 11 beta-PGF2 at 7.5 micrograms/min. 9 alpha, 11 beta-PGF2 (2.5 micrograms/min) produced consistent increases in urine flow and the excretion of sodium and chloride in rats treated with meclofenamate, 2 mg/kg/hr i.v., indicating that these responses were not dependent on endogenous PG synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stereospecific radioimmunoassay for propranolol isomers.

Antisera against propranolol were produced in rabbits immunized with propranolol conjugated to bovine serum albumin. The antiserum against dl-propranolol recognized both d- and l-propranolol to the same degree. However, antiserum against l-propranolol was able to discriminate the l-propranolol selectively. The antisera were used to develop radioimmunoassays for dl-propranolol and l-propranolol. The assay can detect as little as 10 pg of propranolol. Metabolites of propranolol do not interfere with the assay unless concentrations are very high. Serum and heart levels of l-propranolol and the d-isomer were determined in the rat after i.v. injection (1 mg/kg) of dl-propranolol. l-Propranolol declines rapidly in the blood after the injection. Concomitantly, there is a rapid accumulation of l-propranolol by the heart. The d-form of propranolol remains in the blood and is metabolized rapidly as reflected by a shorter half-life (23.8 minutes) than the one found for l-propranolol (5.20 minutes).     

Sodium salicylate inhibits prostaglandin formation without affecting the induction of cyclooxygenase-2 by bacterial lipopolysaccharide in vivo.

The mechanisms underlying the anti-inflammatory properties of salicylate are not well understood. In particular, while salicylate inhibits prostaglandin production in vivo it only weakly inhibits cyclooxygenase (COX)-1 or -2 activity in vitro. Thus, it has often been suggested that in vivo salicylate may inhibit the expression rather than the activity of COX, particularly COX-2. Using a model of acute COX-2 expression in the rat, we show that salicylate inhibits COX-2 activity in vivo without affecting COX-2 expression. In anesthetized rats LPS (6 mg kg(-1), i.p.) increased the expression of COX-2 as evidenced by increased circulating levels of 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha), a stable breakdown product of PGI(2)), greatly exaggerated formation of 6-keto-PGF(1alpha) following arachidonic acid (AA) challenge (3 mg kg(-1), i.v.), and increased expression of COX-2, but not COX-1, protein. Diclofenac (3 mg kg(-1), i.p.) or the COX-2 selective agent diisopropyl fluorophosphate (10 mg kg(-1), i.p.) decreased the LPS-induced increase in circulating 6-keto-PGF(1alpha) and the exaggerated 6-keto-PGF(1alpha) production following AA challenge. Sodium salicylate (20 or 120 mg kg(-1), i.p.) (administered either 1 h prior, or once per day for 3 days prior, to LPS injection) reduced only the LPS-induced increase in circulating 6-keto-PGF(1alpha), but not the exaggerated 6-keto-PGF(1alpha) production following AA challenge or the expression of COX-2. Thus, salicylate inhibits LPS-induced COX-2 activity in a manner that is overcome by provision of excess substrate and independent of effects on COX-2 expression. In conclusion, our results exclude mechanisms other than direct enzyme inhibition as responsible for the anti-COX effects of salicylate.     

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.     

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.     

Neuropeptide Y stimulates renal prostaglandin synthesis in the isolated rat kidney: contribution of Ca++ and calmodulin

We have investigated the effects of neuropeptide Y (NPY) on vascular tone and renal output of prostaglandins (PGs) and the mechanism underlying these actions by examining the effects of Ca++ depletion, Ca++ channel blockers and calmodulin inhibitors in the isolated Tyrode's perfused rat kidney. Administration of NPY (0.23-2.3 nmol) into the kidney produced a dose-related renal vasoconstriction and an increase in the output of PGE2 and 6-keto-PGF1 alpha, the stable hydrolysis product of PGI2. Omission of Ca++ (1.8 mM) or addition of Ca++ channel blockers, diltiazem (60 microM) or nifedipine (1.4 microM), to the perfusion fluid abolished the effects of NPY to promote renal vasoconstriction and PG synthesis. Infusion of calmodulin inhibitors, trifluoperazine (2 microM), W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide] (20 microM) or calmidazolium (0.2 microM), attenuated the renal vasoconstriction and the increase in PG output produced by NPY (0.7 nmol). In kidneys perfused with normal Tyrode's solution, infusion of NPY, in a concentration (1.7 X 10(-8) M) that produced only a small transient increase in renal vascular tone and failed to alter the renal output of PGs, enhanced the rise in PGE2 and 6-keto-PGF1 alpha elicited by norepinephrine (0.25 nmol) but not by arginine vasopressin (0.004 nmol) or angiotensin II (0.09 nmol). The renal vasoconstriction elicited by norepinephrine and arginine vasopressin as well as by angiotensin II was enhanced by NPY.(ABSTRACT TRUNCATED AT 250 WORDS)     

The antiproteinuric action of enalapril in stroke-prone spontaneously hypertensive rats is unrelated to alterations in urinary prostaglandins.

We examined whether the renal protective effect of the angiotensin I converting enzyme inhibitor enalapril in stroke-prone spontaneously hypertensive rats (SHRSP) is dose-related and associated with alterations in the urinary excretion of prostaglandin (PG) E2 and 6-keto-PGF1 alpha, a stable breakdown product of prostacyclin. Enalapril maleate at 1.5, 5 and 15 mg/kg/day or vehicle was chronically administered to saline-drinking SHRSP (six per group) starting at 8.1 weeks of age. Vehicle-treated SHRSP developed severe hypertension, proteinuria and strokes (age at death, 14 +/- 1 weeks; mean +/- S.E.). Enalapril prolonged survival dose-dependently and reduced proteinuria; all SHRSP given 15 mg/kg/day lived beyond 23 weeks of age without evidence of stroke or proteinuria. There was no effect of enalapril at any dose on systolic arterial blood pressure in spite of variable levels of urinary protein excretion and onset of stroke in the different groups. Likewise, urinary 6-keto-PGF1 alpha and PGE2 excretion did not differ among the groups except for an increase in 6-keto-PGF1 alpha in the 15 mg/kg/day group at one week after initiation of enalapril therapy. These results are consistent with a dose-related renal protective action of enalapril in saline-drinking SHRSP that is not closely associated with sustained alterations in urinary excretion of renal vasodilatory PGs.     

The contribution of PGI2 to the effects of captopril in conscious dogs in differing states of sodium balance

There is some evidence that increased prostaglandin synthesis may mediate some of the effects of the angiotensin converting enzyme inhibitor captopril. The potential role of prostaglandin (PG)I2 in this process was assessed by measurement of changes in urinary 6-keto-PGF1 alpha excretion after captopril in eight sodium replete and depleted conscious dogs. In sodium replete animals captopril induced a small decrease in blood pressure, transient increases in effective renal plasma flow and urinary 6-keto-PGF1 alpha excretion, and progressive increases in plasma renin activity (PRA) and urinary sodium excretion. By contrast, during sodium depletion captopril induced a large decrease in blood pressure, a transient increase in effective renal plasma flow and urinary 6-keto-PGF1 alpha excretion, an early large but transient increase in PRA and small progressive increase in sodium excretion. The time course of changes after captopril suggested that increased PGI2 synthesis may contribute to the transient decrease in renal vascular resistance. The increase in PRA during sodium depletion was not associated with any change in urinary 6-keto-PGF1 alpha excretion.     

Renal eicosanoids and renal hemodynamics in early borderline hypertension.

To study the modulatory role of renal eicosanoids on renal hemodynamics and electrolyte excretion, pressor doses of norepinephrine (NE) were infused in 10 control subjects (mean age, 26 y) and 13 patients (mean age, 25 y) with borderline hypertension. The highest NE dose used (150 ng/kg/min) produced comparable increases in mean blood pressure in control subjects (20 +/- 2 mmHg) and in patients (23 +/- 3 mmHg). NE induced a significant increase in renal vascular resistance (p less than 0.01, both groups), with a smaller decrease in glomerular filtration rate resulting in a concomitant increase in filtration fraction (p less than 0.01, both groups). The renal hemodynamic changes tended to be more pronounced in borderline hypertension. NE infusion led to similar decreases in electrolyte clearances in the two groups. Urinary prostaglandin (PG)E2, PGF2 alpha (p less than 0.01), and 6-keto-PGF1 alpha increased with NE infusion. Urinary thromboxane (TX)B2 increased slightly in control subjects and decreased in borderline hypertension (p less than 0.05). The 6-keto-PGF1 alpha/TXB2 ratio, an index of vasodilation, was significantly increased (p less than 0.05) in borderline hypertension. These results demonstrate that in both groups pressor infusion of NE induced significant modifications in renal hemodynamics and in urinary electrolyte and eicosanoid excretion. The vasodilatory component of the renal eicosanoid system appears hyperresponsive in borderline hypertension, which may represent an early antihypertensive defense mechanism.