Compartmental prostaglandin release by angiotensin II and arginine-vasopressin in rabbit isolated perfused kidneys

The compartmental effects of angiotensin II (AII) and arginine-vasopressin (AVP) on renal prostaglandin (PG) formation were studied in the isolated perfused kidney of the rabbit by superfusion bioassay of venous and ureteral effluents (VE and UE) and radioimmunoassay (RIA). Comparable results were obtained with either bioassay or RIA when used to quantitate renal PG release. The effects on PG release into the VE were similar for AII and AVP, as were their pressor responses. However, their effects on PG release into the UE differed markedly. AII resulted in a 6-fold greater urinary efflux than venous of bioassayable PGs, whereas AVP-induced PG release into UE was slightly less than PG efflux into the VE at all doses of the peptide. The profile of released PGs varied according to the sampling source (VE or UE). Moreover, each peptide released a similar profile of PGs at all doses, i.e. UE PGE2 greater than PGF2 alpha greater than 6-keto PGF1 alpha; VE PGE2 greater than 6-keto PGF1 alpha greater than PGF2 alpha (TxB2 was not detected in either effluent). Thus, renal vascular PG release is similar for the vasoactive peptides, AII and AVP, whereas the urinary efflux of PGs is considerably greater in response to AII.     

ROLE OF PROSTAGLANDINS DURING REVERSAL OF ONE-KIDNEY, ONE-CLIP HYPERTENSION IN THE RAT

Unclipping the one-kidney, one-clip rat returned blood pressure to normotensive levels within 24 h and was associated with a substantial increase in urinary PGE2 and 6-keto PGF1 alpha excretion. Prior treatment with indomethacin (6.0 mg/kg) markedly reduced urinary prostaglandins after clip removal and attenuated the fall in blood pressure. Aspirin (100 mg/kg) treatment, which reduced 6-keto PGF1 alpha to a lesser degree without altering PGE2 excretion, had no significant effect on the blood pressure fall. It is suggested that in the one-kidney, one-clip rat prostaglandins are released as the result of exposing the unclipped kidney to elevated arterial pressure, and that these contribute to the subsequent fall in blood pressure.     

Indomethacin and cromolyn sodium alter ozone-induced changes in lung function and plasma eicosanoid concentrations in guinea pigs

Male Hartley guinea pigs were given either indomethacin (IN), cromolyn sodium (CS), or no drug (ND) and then exposed either to filtered air or to 1 ppm ozone (O3) for 1 hr. At 2 or 24 hr postexposure, ventilation, respiratory mechanics, lung volumes, carbon monoxide-diffusing capacity (DLCO), and alveolar volume (VA) were measured, and in separate groups of animals, plasma eicosanoids (EC) were measured. Both drugs blocked the increase in flow resistance noted at 2 hr after O3 and prevented O3-induced increases in the wet lung weight to body weight ratio seen at 2 and 24 hr in the ND group. In the ND animals O3 also decreased total lung capacity (TLC), vital capacity (VC), functional residual capacity (FRC), and residual volume (RV). IN as well as CS blocked reductions in FRC and RV at both 2 and 24 hr after O3. TLC was reduced by both drug treatments in air- and O3-exposed animals. CS treatment also decreased VC in all groups. IN blocked reductions in VA after O3 but did not prevent decreases in DLCO. CS blocked reductions in both VA and DLCO after O3, but the drug decreased DLCO in air-exposed animals. The prostaglandins PGF2 alpha and 6-keto PGF1 alpha were largely unaffected by O3 exposure or drug treatment. Prostaglandin E1 (PGE1) was not affected by O3, but both drugs significantly increased PGE1 in all exposure groups. Effects on plasma thromboxane B2 (TxB2) were variable although in most groups TxB2 was lower than in the O3-exposed ND groups. Although our findings suggest that both drugs block some effects of O3 exposure on the lungs and on plasma EC concentrations, the degree to which EC contribute to O3-induced pulmonary effects is not clearly apparent.     

Frusemide releases renin in the rat kidney when prostacyclin synthesis is suppressed.

The effect of inhibiting prostaglandin (PG) synthesis on basal and frusemide-stimulated renin secretion was examined in the rat isolated perfused kidney. The stable PGI2 derivative, 6-keto PGF1 alpha, was measured by radioimmunoassay in urine collected from the kidney. Treatment of rats with indomethacin (3.0 mg kg-1) reduced 6-keto PGF1 alpha excretion from 121.3 +/- 39.1 (n = 9) to 15.5 +/- 6.6 (n = 9) pg min-1 (P less than 0.02) but had no effect on basal renin secretion. Renal perfusion pressure, flow rate and vascular resistance were similar in treated and control rats. Mean urine flow was lower after treatment. Infusion of frusemide (250 micrograms min-1) did not alter 6-keto PGF1 alpha excretion in control or indomethacin-treated (P greater than 0.05) rats. Although renin secretion was increased during frusemide infusion, there was no significant difference between control (1,806 +/- 384 ng angiotensin I (AI) min-1) and treated (2,310 +/- 554 ng AI min-1) rats (P greater than 0.05). Propranolol, at a dose (8 micrograms min-1) which suppressed renin secretion after isoprenaline stimulation, had no effect on the response to frusemide in indomethacin-treated rats. These results demonstrate that frusemide-stimulated renin secretion in the rat kidney does not require intact renal PGI2 synthesis and is independent of beta-adrenergic mechanisms.     

Atrial natriuretic peptide and urinary prostaglandins in man.

1. In order to assess the effects of atrial natriuretic factor on the renal biosynthesis of prostaglandins (PG), the urinary excretion of PGE2, PGF2 alpha, 6-keto-PGF1 alpha and thromboxane (Tx)B2 were followed in eight salt-loaded healthy volunteers infused for 2 h with a non hypotensive dose of human atrial natriuretic peptide (hANP, 0.7 nmol min-1). 2. Within 1 h, hANP, infusion produced a marked increase in the urinary PG output, especially of PGE2 and 6-keto-PGF1 alpha (188 +/- 21% and 202 +/- 24% of the pre-infusion values respectively), followed by a significant decrease during the recovery period. 3. No correlations could be uncovered between the urinary excretion of sodium and that of any of the PGs. In contrast, during the infusion of hANP, the urinary output of PGE2 and of 6-keto-PGF1 alpha was found positively related to the urinary flow rate (r = 0.42; P less than 0.05; n = 32 and r = 0.43; P less than 0.05; n = 32 respectively) as well as during the recovery period (r = 0.66, P less than 0.001; n = 32 and r = 0.55; P less than 0.01; n = 32 respectively). 4. It was concluded that, in man, infusion of a non hypotensive dose of hANP is followed by a rise in urinary PG excretion presumably reflecting enhanced renal PG biosynthesis. This increased urinary PG excretion does not seem to be involved in the natriuretic action of hANP but might participate to its diuretic effect.     

The interaction of paracetamol with frusemide.

Following the administration of paracetamol (1 g 4 times per day) or placebo to 10 healthy female volunteers for 2 days, the pharmacological effects of intravenous frusemide (20 mg) were observed after a final dose of either paracetamol or placebo. Paracetamol pre-treatment had no effect on frusemide-induced diuresis or natriuresis. There was a significant reduction in the basal output of prostaglandin E2 (PGE2) with paracetamol pre-treatment (18.4 +/- 15.4 vs 7.6 +/- 5.0 ng h-1, P < 0.05; 95% confidence interval of the difference 0.2 to 21.8). Frusemide induced a transient increase in the urinary excretion rate of PGE2 and although this effect was reduced by paracetamol (46.6 +/- 50.9 vs 23.2 +/- 13.8) the differences in the change of excretion rate from baseline were not statistically significant (95% confidence interval of the difference -17.8 to 15.7). The basal level of 6-keto prostaglandin F1 alpha (PGF1 alpha) was less with paracetamol pre-treatment (61.7 +/- 41.1 vs 38.7 +/- 26.1 ng h-1, NS; 95% confidence interval of the difference -16.6 to 62.6) and the cumulative urinary output of PGF1 alpha in the 6 h after frusemide administration was significantly reduced (305.9 +/- 179.4 vs 181.8 +/- 100.2 ng h-1, P < 0.05; 95% confidence interval of the difference 32.2 to 216). The frusemide-induced rise in plasma renin activity was significantly less with paracetamol than placebo at 60 min (4.3 +/- 2.9 vs 2.7 +/- 1.9 ng ml-1 h-1, P < 0.01; 95% confidence interval of the difference 0.4 to 2.7).     

Exaggerated renal thromboxane and prostaglandin release by angiotensin II in suprarenal aortic coarctation hypertension

The ability of angiotensin II and arachidonic acid to release immunoreactive prostaglandins into venous and ureteral effluents of rabbit isolated perfused kidneys was examined 7 days after suprarenal aortic coarctation (SRAC) or sham operation (SHAM). Renal vascular responses to angiotensin II were significantly enhanced in SRAC and accompanied by an enhanced venous efflux of bioassayable prostaglandins. Angiotension II-induced release of immunoreactive PGE2, PGF2 alpha, 6-keto PGF1 alpha and TxB2 into the venous effluent was exaggerated in SRAC. As angiotensin II did not stimulate TxB2 efflux in the SHAM group the induction of TxB2 release by SRAC is particularly noteworthy. These changes in eicosanoid release in response to angiotensin II were not mimicked by arachidonic acid administration. These results suggest that in renovascular hypertension angiotensin II-induced prostaglandin release is primarily augmented in the vascular compartment and is consistent with the sensitivity of renal function to cyclooxygenase inhibitors in renovascular hypertension.     

Age-dependent changes in the synthesis and catabolism of 6 oxo PGE1 and other prostanoids by the rat kidney in vitro

Synthesis and catabolism of 6 oxo PGE1 was assessed in 100,000 g cell-free supernatant fractions of kidneys obtained from rats aged 20, 34 and 70 days. In addition the release of PGI2, TxA2 (measured as 6 oxo PGF1 alpha and TxB2, respectively), PGE2 and PGF2 alpha from kidney slices prepared from these three groups of rats was determined using specific radioimmunoassays. The conversion of PGI2 to 6 oxo PGE1 (but not 13,14 dihydro 15 oxo PGF2 alpha to 13,14 dihydro 15 oxo PGE2) was detected in supernatant fractions of kidneys from 20 day rats. Slices prepared from the kidneys of these animals spontaneously released significant amounts of three prostanoids (6 oxo PGF1 alpha greater than PGE2 greater than PGF2 alpha greater than TxB2 = 0). No formation of 6 oxo PGE1 from exogenous PGI2 was demonstrated in renal 100,000 g supernates from 34 and 70 day rats even though these supernates avidly oxidised 13,14 dihydro 15 oxo PGF2 alpha to 13,14 dihydro 15 oxo PGE2. In these animals the rank order of prostanoid release from kidney slices was PGE2 greater than 6 oxo PGF1 alpha greater than PGF2 alpha greater than TxB2 = 0. The catabolism of 6 oxo PGE1 is also age-dependent. In 20 and 34 day old rats 6 oxo PGE1 and PGE1 incubated with renal 100,000 g supernates undergo loss of biological activity as determined by the ability to inhibit ADP induced human platelet aggregation. In contrast, kidney 100,000 g supernates prepared from 70 day rats convert 6 oxo PGE1 to an unidentified metabolite with more potent anti-aggregatory activity. The possibility that 6 oxo PGE1 has a biological role in the developing rat kidney is discussed.     

Formation of 6-keto prostaglandin E1 in mammalian kidneys

1 The metabolism of prostacyclin (PGI2) and 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) was studied in cell-free homogenates of rat, rabbit and guinea-pig kidney. 2 Rabbit kidney converted both PGI2 and 6-keto PGF1 alpha to a stable metabolite with chromatographic and biological activity identical to that of authentic 6-keto PGE1. Activity was found in the kidney cortex but not medulla, was inhibited by NAD+ or NADP+ (5 mM) and showed an optimum temperature requirement of 37 degrees C. 3 Guinea-pig kidney converted PGI2 but not 6-keto PGF1 alpha to a labile, biologically active metabolite which was not 6-keto pge1. 4 No conversion of prostacyclin or 6-keto PGF1 alpha to biologically active metabolites occurred in cell-free homogenates of rat kidney, liver and colon or guinea-pig liver and colon. 5 6-keto PGE1 rapidly lost spasmogenic activity on the rat stomach strip following incubation with rabbit or guinea-pig kidney supernatant in the absence of added cofactors. No loss of activity occurred on incubation with rat kidney. 6 Rutin (50 microM) potently inhibited synthesis of 6-keto PGE1 from added PGI2 by rabbit kidney cortex. This reaction was potentiated by a similar concentration of sulphasalazine, carbenoxolone, imidazole, papaverine or indomethacin. 7 The relevance of these findings for the possible physiological and pathological roles of 6-keto PGE1 in the kidney is discussed.     

Systemic synthesis of prostaglandin I2 following sustained infusion of angiotensin II in conscious dogs

Acute infusion of pharmacological doses of angiotensin II stimulates the release of prostaglandin I2 (PGI2), which may modulate the vasoconstrictor response. It is uncertain whether sustained small increases in the plasma concentration of angiotensin II has the same effect. To investigate this further, low doses of angiotensin II were infused into conscious sodium replete dogs for 3 h. PGI2 synthesis was assessed by measurement of a major metabolite of PGI2, 2,3-dinor-6-keto PGF1 alpha, in urine and plasma, using gas chromatography mass spectrometry. Angiotensin II infusion (15 ng/min per kg body weight) resulted in a 3-fold increase in plasma angiotensin II (50.8 +/- 5.4 to 149 +/- 11.2 pg/ml, P less than 0.01). Mean blood pressure increased (84.8 +/- 4.3 to 108 +/- 4.7 mm Hg, P less than 0.02) and renal blood flow decreased (201 +/- 46 to 127 +/- 13 ml/min, P less than 0.01) throughout the infusion. However there was no change in either the plasma concentration (11.3 +/- 2.5 to 9.1 +/- 1.0 pg/ml) or rate of urinary excretion of dinor-6-keto PGF1 alpha (1.75 +/- 0.28 to 1.85 +/- 0.41 ng/30 min) during the angiotensin II infusion. The results suggest that small sustained elevations of the plasma concentration of angiotensin II such as are likely to occur in conscious animals, do not persistently stimulate release of PGI2 in the systemic circulation.     

Sulindac kinetics and effects on renal function and prostaglandin excretion in renal insufficiency

The purpose of this study was to evaluate the pharmacokinetics of sulindac, a purported "renal sparing" nonsteroidal anti-inflammatory drug, and its effects on renal function and prostaglandin excretion in patients with reduced glomerular filtration rate. Twelve female patients (glomerular filtration rate 37 +/- 4 mL/min) were treated with sulindac 200 mg bid for 11 days. Urinary PGE2, 6-keto-PGF1 alpha and serum thromboxane (TxB2) generation were measured by radioimmunoassay (RIA) following extraction on C-18 columns. Glomerular filtration rate and effective renal plasma flow were measured by 99TC-DPTA and 131I-para-aminohippuric acid clearance. In six patients serum and urine levels of sulindac and its metabolites were measured by high-pressure liquid chromatography (HPLC). Sulindac was rapidly absorbed and converted to sulindac sulfide with peak levels 2 hours after a single dose, but steady state levels were not reached prior to drug discontinuation. Sulindac sulfide AUC (0-5 hours micrograms min/mL) progressively increased from 382 to 3,030 on day 11. It did not appear in the urine. Baseline urinary PGE2 and 6-keto-PGF1 alpha excretion were 23.8 +/- 5.6 and 18.9 +/- 2.7 ng/hr respectively and were reduced by 68% and 47% by day 4 of therapy. TxB2 generation fell by 34% after one dose and by 67% by day 11. There was a significant increase in serum creatinine from 1.88 +/- 0.13 mg/dl before treatment to 2.16 +/- 0.15 mg/dL (P less than .05) after eleven days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Decrease of urinary prostaglandin E2 and prostaglandin F2 alpha excretion by nonsteroidal anti-inflammatory drugs in rats. Relationship to anti-inflammatory activity

An analytical method for measuring in vivo inhibition of prostaglandin (PG) synthesis by nonsteroidal anti-inflammatory drugs was developed for estimation of urinary prostaglandin levels in rats. Drugs were administered orally to rats (Wistar, male, 200-250 g), and water (2.5 ml/100 g body weight) was given 1 hr after drug administration to yield a constant volume of urine. Urine was collected for 4 hr after drug administration, and urinary PGE2 and PGF2 alpha were determined by radioimmunoassay. The urine volume in the 4-hr period was 5.0 +/- 0.30 ml per rat, and prostaglandin contents in the 4-hr urine were 4.56 +/- 0.56 ng PGE2 and 1.31 +/- 0.24 ng PGF2 alpha per rat in the no-drug control group. Administration of nonsteroidal anti-inflammatory drugs decreased the urinary PGE2 and PGF2 alpha dose dependently. The activities of ten typical nonsteroidal anti-inflammatory drugs in reducing urinary PGE2 excretion were compared with their anti-inflammatory activities in rats. A close correlation (r = 0.98, P less than 0.001) between the dose required for 50% reduction of urinary PGE2 excretion and the dose required for 50% inhibition of carrageenin edema was found for each drug. These drugs were also tested for their inhibitory effects on PGE2 biosynthesis in a cultured system of mouse 3T6 fibroblast cells and on prostaglandin synthesizing system in bovine seminal vesicle microsomes. No close correlation was observed between anti-inflammatory activities and inhibition of prostaglandin biosynthesis in vitro.     

Leukotrienes C4 and D4 induce prostaglandin and thromboxane release from rat peritoneal macrophages.

The present study examined the effect of leukotrienes C4 and D4, the products of the 5'lipoxygenase pathway on prostaglandins and thromboxane release from rat peritoneal macrophages. Incubation of rat peritoneal macrophages with leukotrienes C4 and D4 enhanced the release of prostaglandin E2 (PGE2), 6-keto PGF1 alpha and thromboxane B2 (TxB2) in a dose-dependent manner. The increase of PGE2 was more pronounced than that of 6-keto-PGF1 alpha and TxB2. Lipopolysaccharide, a known stimulator of these cells elicited a similar pattern of increase of the arachidonate metabolites assayed. These results suggest that leukotrienes C4 and D4 are potential activators of macrophages. Since leukotrienes C4 and D4 are produced by these cells, it is suggested that endogenous leukotrienes may be involved in activation of macrophages.     

Evidence that prostaglandins activate calcium channels to enhance basal and stimulation-evoked catecholamine release from bovine adrenal chromaffin cells in culture

The effects of prostaglandins (PGs) on catecholamine (CA) secretion and Ca2+ fluxes were studied in a primary culture of bovine chromaffin cells. PGD2, PGF2 alpha and PGE2 induced CA release from cultured bovine chromaffin cells in a concentration dependent manner (0.03-3 microM). PGD2, PGF2 alpha and PGE2 at 3 microM elicited maximum CA release of 0.043 +/- 0.001, 0.059 +/- 0.008, 0.062 +/- 0.002 micrograms/10(6) cells, respectively. Three micromolar of PGD2, PGF2 alpha and PGE2 enhanced CA release induced by acetylcholine (ACh) in a degree of 186 +/- 10, 206 +/- 6, 150 +/- 4% of control respectively. PGs also enhanced CA release induced by 20 mM K+, veratridine and A23187. In Ca2+-free medium, PGs failed to affect basal and caffeine (50 mM)-induced CA release. PGF2 alpha increased 45Ca uptake and showed additive effect with ACh on 45Ca uptake. Nicardipine (0.1-10 microM) suppressed CA release and 45Ca uptake induced by PGF2 alpha, while diltiazem and verapamil failed to affect these responses to PGF2 alpha. BAY K 8644 (1 microM) potentiated CA release and 45Ca uptake evoked by PGF2 alpha. These results suggest that PGs enhance basal and stimulation-evoked CA release from chromaffin cells possibly through facilitation of Ca2+ influx. The mechanisms of action of PGs in adrenal medulla are discussed.     

Characterization of the effects of isoprostanes on platelet aggregation in human whole blood

We tested the effects of 11 commercially-available isoprostanes on platelet aggregation directly or when triggered by the thromboxane receptor agonist U46619 or collagen in healthy human citrated blood using a whole blood aggregometer. None of the isoprostanes tested triggered aggregation alone, nor facilitated aggregation by a sub-threshold dose of U46619 or collagen. Five isoprostanes inhibited aggregation (rank order of potency 8-iso PGE(1)>8-iso PGE(2)>8-iso PGF(2alpha)>8-iso PGF(3alpha)>8-iso-13,14-dihydro-15-keto PGF(2alpha)). Blood incubated with LPS to induce a gross inflammatory response exhibited a time dependent (2 - 12 h) reduction in aggregation to U46619 but maintained a consistent response to collagen. Under these conditions, as in control blood, none of the isoprostanes tested induced aggregation. In fact, the inhibitory actions of isoprostanes on U46619-induced aggregation were enhanced in blood treated with LPS. L-NAME inhibited aggregation induced by U46619 in fresh blood and in blood treated with LPS. In the presence of L-NAME, (with or without LPS) none of the isoprostanes tested induced aggregation but retained their inhibitory action. Thus, in human whole blood the action of 8-iso PGE(1), 8-iso PGE(2), 8-iso PGF(2alpha), 8-iso PGF(3alpha), and 8-iso-13,14-dihydro-15-keto PGF(2alpha) is antiaggregatory. Moreover, this inhibitory capacity is still apparent and may be enhanced in blood subjected to inflammatory stimulation.     

Effect of nufenoxole on human colonic prostanoid synthesis, Na-K-ATPase and adenylate cyclase activities

To elucidate the possible mechanism whereby nufenoxole exerts its anti-diarrheal activity, its effects on human colonic prostanoid synthesis and on Na-K-ATPase and adenylate cyclase activity were determined. Colonic Na-K-ATPase activity was significantly different in the absence and presence of nufenoxole (50 ng/ml), 1.73 +/- 0.18 and 0.99 +/- 0.17 (x +/- S.E.; N = 18) mumol Pi/mg protein per h respectively. Nufenoxole (50-800 ng/ml) did not affect basal NaF-, VIP- or PGE2-stimulated colonic adenylate cyclase activity. 6-keto PGF1 alpha and TXB2 synthesis by cultured colonic mucosa was also not affected by nufenoxole (50-800 ng/ml). Nufenoxole (800 ng/ml) induced slight inhibition of PGE2 synthesis by cultured colonic mucosa. The results obtained do not suggest that the anti-diarrheal effects of nufenoxole are related to its in vitro effects on colonic prostanoid synthesis or adenylate cyclase activity. Inhibition of colonic Na-K-ATPase activity by nufenoxole also does not explain its anti-diarrheal effects. Further studies on nufenoxole effects on the respective jejunal enzyme systems and in human subjects treated with the drug may reveal its mechanism of action.     

Enhancement of carcinogen-induced malignant cell transformation by prostaglandin F(2 alpha)

The enhancement of carcinogen-induced malignant transformation of C3H/M2 mouse fibroblasts by the tumor promoters 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with the induction of cyclooxygenase expression and the stimulation of prostaglandin (PG) formation. Therefore, the potential of PGs, i.e., PGF(2alpha) and PGE(2), for tumor promotion was studied in the two-step C3H/M2 cell transformation assay, a model of the multi-step process of carcinogenesis. The transformation of fibroblasts was clearly enhanced by the addition of PGF(2alpha) in the promotion phase after pretreatment with a subthreshold dose of a carcinogen (3-methylcholanthrene or N-methyl-N'-nitro-N-nitrosoguanidine). No enhancement of cell transformation was observed in cells without carcinogen-pretreatment, i.e., PGF(2alpha) had no tumor initiating potential. The promotional effect was dose-dependent with a maximum at 16 nM PGF(2alpha). PGE(2) had no significant effect in this assay. Furthermore, PGF(2alpha) (but not PGE(2)) clearly reduced the inhibition of TPA-induced promotion by NS-398, an isozyme-specific inhibitor of cyclooxygenase-2. The inhibition of TPA- or TCDD-induced promotion by the non-specific cyclooxygenase inhibitor indomethacin was not affected by co-treatment with PGF(2alpha) and PGE(2). Our data suggest that PGF(2alpha) acts as an endogenous promoter of cell transformation implying that it may also be critically involved in tumor promoter-induced signalling transfer cascades ultimately triggering the process of carcinogenesis.     

Prostaglandins of the E series inhibit release of noradrenaline in rat hypothalamus by a mechanism unrelated to classical alpha 2 adrenergic presynaptic inhibition

The effects of eight different prostanoid derivatives (PGs) on the in vitro release of noradrenaline (NA) from rat hypothalamic slices are reported. Prostaglandin E2 (10(-8)-10(-5) M), which does not interfere with the [3H]NA uptake mechanism, inhibited [3H]NA release induced by K+-evoked depolarization. The rank order of inhibition of release of NA for the PGs was: PGE2 greater than PGE1 greater than PGA2 greater than 16, 16-dimethyl-PGE2 greater than 11-epi-PGE2 greater than or equal to 8-iso-PGE2 greater than PGF2 alpha greater than PGD2. It has recently been shown that PGs of the E series specifically bind with a high affinity to membrane preparations of rat hypothalamus. A similar rank order was found for the activity of these PGs in displacing [3H]PGE2 from its binding sites, suggesting that the effect of PGEs on release of NA is mediated by an interaction with PGE2 receptors. Under the same experimental conditions, 10(-6) M clonidine (an alpha 2 adrenoceptor agonist) diminished, and 10(-6) M yohimbine (an alpha adrenoceptor antagonist) increased [3H]NA release, supporting the existence of alpha 2 auto-inhibition. Exposure to 10(-6) M of the alpha 1, alpha 2 adrenergic receptor antagonist phentolamine, a concentration which by itself had no effect on overflow of [3H]NA, blocked the inhibitory effect of clonidine, but failed to antagonize the inhibitory action of PGE2. Moreover, the action of clonidine and yohimbine remained unaffected when PG synthesis was blocked with indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of two benzimidazoles as proton pump inhibitors on water immersion stress-induced gastric ulcers in rats.

This study was designed to clarify effects of proton pump inhibitors, E-3810(2-([4-(3-methoxypropoxy)-3methylpyridine-2-yl]methyl- sulfinyl)-1H-benzimidazol sodium salt) and omeprazole (CAS 73590-58-6), on water immersion stress-induced gastric ulcers in relation to mucosal prostaglandins (PGs) and leukotrienes (LTs). Mucosal PGs were measured by high performance liquid chromatography (HPLC). In untreated rats, 4 kinds of PGs, i.e., 6-keto-PGF1 alpha, PGF2 alpha, PGE2 and PGD2 were detected in gastric mucosa, but no LTs were detected. Water immersion stress for 6 h caused severe hemorrhagic lesions in the fundic portion and, concomitantly, significant decreases in mucosal PG levels. On the other hand, LTC4 and LTD4 were detected after 6 h stress treatment, though LTB4 and LTE4 were not detected throughout the experiments. Peptide-LT (the sum of LTC4 and LTD4) levels were 23.5 +/- 3.2 ng/g tissue 6 h after water immersion stress. Administration of 20 mg/kg of E-3810 or 20 mg/kg of omeprazole mitigated gastric lesions and increases in the mucosal peptide-LT levels, but dit not improve the decrease in mucosal PGs.     

CGS 15435A, a thromboxane synthetase inhibitor with an extended duration of action: a comparison with dazoxiben

CGS 15435A, a novel thromboxane (Tx) synthetase inhibitor (5-chloro-1-methyl-2-(3-pyridyl)-3-indolhexanoic acid HCl), had a selectivity for Tx synthetase 100,000-fold greater than that for cyclooxygenase, PGI2 synthetase and lipoxygenase enzymes. In conscious beagles, 1 h following a single 3 mg/kg p.o. dose, serum TxB2 was inhibited 95% by CGS 15435 and 82% by dazoxiben (DAZ). Unlike the short acting Tx synthetase inhibitor DAZ, CGS 15435A significantly inhibited TxB2 formation 4, 6, 12 and 24 h after dosing. Serum levels of 6-keto PGF1 alpha and PGE2 were significantly increased following the administration of either drug. CGS 15435A and DAZ were further examined in a model with known Tx involvement. Thrombotic sudden death, produced in anesthetized rabbits by injection of 0.75 mg/kg arachidonic acid (AA) i.v. resulted in a 45% fall in the platelet count and 0% survival. Pretreatment with DAZ (8.6 mumol/kg i.v.) at 0.25 or 2 h pre-AA resulted in 3 and 42% thrombocytopenia and 100 and 0% survival respectively. CGS 15435A (8.6 mumol/kg i.v.) prevented the increases in plasma TxB2 levels, thrombocytopenia and sudden death with pretreatment at 0.25 h (0% thrombocytopenia and 100% survival) or 24 h (11% thrombocytopenia and 83% survival) before AA. These data indicate that CGS 15435A is a potent and selective Tx synthetase inhibitor with a long duration of action, and suggest that the compound could be useful in chronic, non-symptomatic indications of Tx involvement.