Interactions between platelet activating factor and eicosanoids during endotoxic shock in anaesthetized pigs

The effects of platelet activating factor (PAF) on eicosanoid release during endotoxic shock was investigated in anaesthetized pigs receiving 5 mug kg(-1) Escherichia coli endotoxin (LPS) into the superior mesenteric artery over a 60 min period, by measuring plasma levels of a variety of mediators. Fifteen of the 31 animals infused with LPS and not treated with BN 52021, a PAF receptor antagonist, died within 30 min after the commencement of LPS infusion (non-survivors), while the other 16 survived the experimental period of 3 h, though in a state of shock (survivors). No alterations were observed in plasma concentrations of eicosanoids in the non-survivors. A significant, though transient, increase in eicosanoid concentrations occurred only in the survivors. Treatment with BN 52021 (4 mg kg-1, i.v.) injected 5 min prior to LPS infusion, failed to exert any effect on the survival rate. However, pretreatment with BN 52021 prevented circulatory collapse in the survivors and reduced the concentration of cyclooxygenase enzyme products, without affecting LTB(4) release. Exogenous administration of PAF (0.01 mug kg(-1)) caused hypotension and increased TXB(2) levels although 6-keto PGF(1alpha) and LTB(4) concentrations were unchanged. The data suggest that prostanoid formation may be secondary to PAF release in circulatory collapse evoked by LPS infusion in survivors, and give further support to the suggestion that PAF prostanoid interaction is important during endotoxic shock. However, their role in early death seems to be negligible, indicating the importance of other mediators.     

Zymosan-activated plasma-mediated thromboxane production by the perfused rabbit liver and isolated hepatocytes: involvement of calcium

The present study investigates the mechanism of zymosan-activated plasma (ZAP)-mediated eicosanoid production by the isolated, perfused rabbit liver and described ZAP-mediated eicosanoid stimulation in cultured hepatocytes. Perfused livers receiving untreated plasma demonstrated no significant changes in portal venous pressure or the rates of release of lactic dehydrogenase or acid phosphatase activity (indicators of cellular injury). The control group livers demonstrated stable rates of release for 6-keto PGF1 alpha and thromboxane B2 (TXB2). In contrast, the infusion of ZAP alone resulted in a rapid but transient release of TXB2 from the livers. No significant changes in perfusion pressure or enzyme release were observed following ZAP administration. Perfusion of livers with a calcium-free buffer decreased the basal rates of both 6-keto PGF1 alpha and TXB2 production and significantly, but not completely, attenuated the ZAP-mediated increase in hepatic TXB2 production. Perfusion of livers with nifedipine (3 microM) had no effect on ZAP-mediated TXB2 production in this model. Isolated hepatocytes responded to ZAP-treatment with significant increases in TXB2 production. These data suggest that activated fluid phase complement components induce thromboxane production by specific cells within the liver and that this stimulation is partially dependent upon the release of intracellular calcium but independent of complement-mediated cellular injury.     

Pancreas prostanoid production in ischemia and reperfusion.

This study was carried out to investigate the proportion of the 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) and thromboxane B2 (TXB2) alteration that is due to ischemia in pancreas transplantation against the proportion due to reperfusion. For this purpose, Lewis rats were divided in three experimental groups: Group I = Control, Group II = Donor pancreas subjected to 15 minutes of cold ischemia, Group III = Same as group II but pancreas were transplanted to the recipient individual and then subjected to reperfusion. The results indicate that increases in pancreas 6-keto PGF1 alpha occur as a consequence of cold ischemia while TXB2 remains unchanged. When blood flow was restored, 6-keto PGF1 alpha remained unchanged compared to the ischemic group while pancreatic levels of TXB2 were significantly increased. These results suggest a different induction of prostanoid metabolism during ischemia and reperfusion in pancreatic tissue.     

Defibrotide modulates prostaglandin production in the rat mesenteric vascular bed

Defibrotide 1 microM, a polydeoxyribonucleotide extracted from mammalian organs, reduced the contractile responses to noradrenaline (NA) in the rat isolated and perfused mesenteric vascular bed, in intact as well as in de-endothelialized preparations. Defibrotide was without effect on the acetylcholine-induced relaxations of U-46619-precontracted mesenteric vascular beds. Moreover, defibrotide increased 6-keto prostaglandin (PG) F(2alpha) (stable metabolite of prostacyclin) release sixfold in the presence, but not in the absence of the endothelium, with no modification on the release of other prostanoids. Defibrotide also inhibited the NA-induced increase in PGF(2alpha) release, in both intact and de-endothelialized mesenteric vascular beds. In conclusion, the present results show that defibrotide modulates PG production in the mesenteric bed and that the observed inhibition of the contractile responses should be due to the impairment of the NA-induced increase in PGF(2alpha) release.     

Enzyme immunoassay measurement of the urinary metabolites of thromboxane A2 and prostacyclin

We have used a recently developed enzyme immunoassay (EIA) method for measuring urinary concentrations of TXB2, 6-keto PGF1 alpha, 2,3-dinor-TXB2, 2,3-dinor-6-keto PGF1 alpha and 11-dehydro-TXB2 using acetylcholinesterase from Electrophorus Electricus coupled to TXB2, 6-keto PGF1 alpha and 11-dehydro-TXB2. Urinary PGI2 and TXA2 breakdown products and their metabolites were extracted from 3-40 ml of urine corresponding to 100 mumoles creatinine. Measurements were performed after Sep-Pak extraction and thin layer chromatography separation in a system that allows separation between dinor- and parent derivatives. Because of the relatively high cross reactivity (10-15%) of the anti-TXB2 serum with 2,3-dinor TXB2 and the anti-6-keto PGF1 alpha serum with 2,3-dinor-6-keto PGF1 alpha, measurements were done using 3 antisera (anti-TXB2 and anti-6-keto PGF1 alpha diluted 1/50,000, anti 11-dehydro-TXB2 diluted 1/200,000). The reproducibility of the technique was assessed by measuring the same urine stored frozen in aliquots together with each series of samples (Coefficient of variation 6-12% (n = 20), depending on the compound). In addition, the use of a different solvent system for the thin layer chromatography did not affect the results although the migration of the compounds was modified significantly. Determination of the urinary excretion of TXB2 and prostacyclin metabolites in 17 healthy individuals by this method provided results in agreement with those obtained by other methodologies. In addition, comparisons made between EIA and gas chromatography/mass spectrometry analysis showed good correlation between the urinary metabolites as determined by each technique (r = 0.98).     

Leukotriene F4 and the release of arachidonic acid metabolites from perfused guinea pig lungs in vitro

Radioimmunoassay and bioassay techniques have been used to investigate the ability of leukotriene (LT)F4 to release products of arachidonic acid metabolism from guinea pig isolated lungs perfused via the pulmonary artery. Also, the abilities of LTC4, LTD4, LTE4 and LTF4 to contract guinea pig ileal smooth muscle (GPISM) was studied. Each of the LT's contracted GPISM. The rank order of potency was LTD4 greater than LTC4 greater than LTE4 much greater than LTF4 in a ratio of 1:7:170:280 respectively. Bioassay of pulmonary effluents indicated the passage of LTF4 through the lungs caused a contraction of rabbit aorta as well as an FPL-55712 sensitive contraction of GPISM. The contractions of rabbit aorta were inhibited by pretreatment of the lungs with Indomethacin but not with the thromboxane synthetase inhibitor Dazoxiben. Radioimmunoassay of the lung effluents indicated LTF4 to cause a 70-fold increase in thromboxane B2 (TXB2), 4-fold increase in prostaglandin (PG)E2 and a 16-fold increase in 6-keto PGF1 alpha levels. The LTF4-induced increments of these immunoreactive metabolites was inhibited by pretreatment of the lungs with Indomethacin. Pretreatment of lungs with Dazoxiben inhibited the LTF4-induced increment in TXB2 and enhanced the effluent levels of PGE2 24-fold (compared with untreated lungs). There were no detectable differences in either immunoreactive LTC4 or immunoreactive LTB4 levels. It is concluded LTF4 is a relatively weak agonist on GPISM and can induce the release of cyclooxygenase products of arachidonic acid metabolism from guinea pig perfused lung.     

Plasma levels of nitrites, PGF1α and nitrotyrosine in LPS-treated rats: functional and histochemical implications in aorta

We investigated the effects of lipopolysaccharide (LPS) administration on plasma nitrite, nitrotyrosine and 6-keto prostaglandin F1alpha, (PGF1alpha) levels and the related resultant changes in function and histochemistry of aorta in rats. Plasma nitrite and PGF1alpha nitrotyrosine levels were analysed after 5 mg/kg intravenous LPS was administered to rats compared with those in non-treated rats. The distribution of nitrotyrosine in the aorta was studied immunohistochemically. The contractile responses of aortic rings to phenylephrine (PE) from both the LPS-treated and control rats were studied in the organ baths. There were increases in plasma nitrite, PGF1alpha, and nitrotyrosine concentrations of LPS-treated rats compared to non-treated rats. Immunoreactivity of nitrotyrosine residues were detected in the endothelial and smooth muscle cells in LPS-treated but not in control rat aorta. The contractile responses to PE of the LPS-treated rat aortic rings were significantly reduced as compared with those of control rat's. Incubation of the aortic rings from LPS-treated rats with cyclooxygenase inhibitor indomethacine or with a combination of indomethacine and nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) increased the contractile responses to the levels observed in control rats suggesting that both prostanoids and particularly nitric oxide (NO) are involved in the reduced contractile responses in LPS-treated rats. These results supported the view that LPS might cause an increment in both NO and PGI2 levels. This increase in the NO and PGI2 levels may be responsible from the reduction in responses of aorta to contractile agents in LPS-treated rats. Increased peroxynitrite formation in LPS-treated rats may lead to nitration of the tyrosil residues of the proteins in the aorta.     

Effects of leukotriene B4 on permeability, prostacyclin and thromboxane release by normal and oxygen-preexposed isolated, perfused rat lungs

This study assessed the hemodynamic and permeability effects of exogenous, synthetic leukotriene B4 (LTB4) on normal rat lungs and lungs from rats preexposed to oxygen for 48 h, which were isolated and perfused at constant flow in vitro. Adult, Sprague-Dawley rats were exposed to air or greater than 97% O2 for 48 h. After exposure, their lungs were removed from the thorax, ventilated with normoxic gas, and perfused at 12 ml/min with Krebs-Ringer bicarbonate buffer which contained 5 mM glucose and 3 mg/ml albumin. A total of 5.55 micrograms of synthetic LTB4 was infused in three separate boluses over 15 minutes. Perfusion and airway pressures were monitored, and the lungs release of 6-ketoprostaglandin F1 alpha and thromboxane B2 (TXB2) into the effluent from the pulmonary vasculature was measured by radioimmunoassay. The LTB4 had no measureable effects on pulmonary vascular pressures. LTB4 infusion caused a pronounced increase in permeability, indicated by increased albumin concentrations in alveolar lavage fluid from O2-preexposed lungs. Release of TXB2 from both air- and O2-preexposed lungs was increased after LTB4 infusion, while the change in 6-ketoprostaglandin F1 alpha release was not statistically significant. Both the increase in permeability enhanced TXB2 released after LTB4 infusion were inhibited by 10 microM indomethacin in the perfusate. These data indicate that exogenous LTB4 increases microvascular permeability in O2-exposed lungs in association with increased release of TXB2 into the pulmonary vascular effluent.     

High glucose levels modulate eicosanoid production in uterine and placental tissue from non-insulin-dependent diabetic rats during late pregnancy

Severe uterine and placental disturbances have been described in diabetes pathology. The relative severity of these changes appears to correlate with high glucose levels in the plasma and incubating environment. In order to characterize changes in eicosanoid production we compared uterine and placental arachidonic acid conversion from control and non-insulin-dependent diabetes mellitus (NIDDM) rats on day 21 of pregnancy, into different prostanoids, namely PGE2, PGF22alpha, TXB2 (indicating the production of TXA2) and 6-keto-PGF1 (indicating the generation of PGI2). PGE2, PGF2alpha and TXB2 production was higher and 6-keto-PGF1alpha was similar in diabetic compared to control uteri. PLA2 activity was found diminished in the NIDDM uteri in comparison to control. A role for PLA2 diminution as a protective mechanism to avoid prostaglandin overproduction in uterine tissue from NIDDM rats is discussed. Placental tissues showed an increment in TXB2 generation and a decrease in 6-keto PGF1alpha level in diabetic rats when compared to control animals. Moreover, when control uterine tissue was incubated in the presence of elevated glucose concentrations (22 mM), similar generation of 6-keto PGF1alpha and elevated production of PGE2, PGF2alpha and TXB2 were found when compared to those incubated with glucose 11 mM. Placental TXB2 production was higher and 6-keto PGF1alpha was lower when control tissues were incubated in the presence of high glucose concentrations. However, high glucose was unable to modify uterine or placental prostanoid production in diabetic rats. We conclude that elevated glucose levels induced an abnormal prostanoid profile in control uteri and placenta, similar to those observed in non-insulin-dependent diabetic tissues.     

Evidence for separate PGD2 and PGF2 alpha receptors in the canine mesenteric vascular bed.

Potential interactions between PGD2 and PGF2 alpha in the mesenteric and renal vascular beds were investigated in the anesthetized dog. Regional blood flows were measured with electromagnetic flow probes. PGD2, PGF2 alpha and Norepinephrine (NE) were injected as a bolus directly into the appropriate artery, and responses to these agents were obtained before, during and after infusion of either PGD2 or PGF2 alpha into the left ventricle. In each case, the infused prostaglandin caused vascular effects of its own. Left ventricular infusion of PGD2 reduced responses to local injections of PGD2 in the intestine, and a similar effect was observed for PGF2 alpha, suggesting significant receptor or receptor-like interactions for each of the prostanoids. However, systemic infusion of prostaglandin F2 alpha (20--100 ng/kg/min) had no effect on renal or mesenteric vascular responses to local injection of prostaglandin D2. Similarly, PGD2 administration (100 ng/kg/min) did not affect responses to PGF2 alpha in the intestine. The present results therefore suggest that these prostaglandins, i.e., D2 and F2 alpha, act through separate receptors in the mesenteric and renal vascular beds. In addition, increased prostaglandin F2 alpha levels produced by infusion of F2 alpha reduced mesenteric but not renal blood flow, suggesting that redistribution of cardiac output might participate in side effects often observed with clinical use of this prostaglandin, such as nausea and abdominal pain.     

Effect of prostaglandins against alloxan-induced diabetes mellitus

Previously, we observed that alloxan-induced in vitro cytotoxicity and apoptosis in an insulin secreting rat insulinoma, RIN, cells was prevented by prior exposure to prostaglandin (PG) E(1), PGE(2), PGI(2), PGF(1)(alpha), and PGF(3)(alpha) (P<0.05 compared to alloxan), whereas thromboxane B(2) (TXB(2)) and 6-keto-PGF(1)(alpha) were ineffective. In an extension of these studies, we now report that prior intraperitoneal administration of PGE(1), PGE(2), PGF(1)(alpha), and PGF(3)(alpha) prevented alloxan-induced diabetes mellitus in male Wistar rats, whereas PGI(2), TXB(2), and 6-keto PGF(1)(alpha) were not that effective. PGE(1), PGE(2), PGF(1)(alpha), and PGF(3)(alpha) not only attenuated chemical-induced diabetes mellitus but also restored the antioxidant status to normal range in red blood cells and pancreas. These results suggest that PGE(1), PGE(2), PGF(1)(alpha), and PGF(3)(alpha) can abrogate chemically induced diabetes mellitus in experimental animals and attenuate the oxidant stress that occurs in diabetes mellitus.     

Effect of 3-methylindole on the plasma and lung concentrations of prostaglandins and thromboxane B2 in goats

1. The role of prostanoids in 3-methylindole (3MI)-induced lung disease was investigated. Goats were infused with 3MI in propylene glycol at a dose of 35 mg 3MI/kg body weight. Control goats were infused with propylene glycol alone. 2. Blood was collected at regular intervals starting 24 hr before and ending 72 hr following 3MI infusion. In a second experiment, 3MI-treated goats were killed at 2, 6, 12, 24, 48 and 72 hr post-infusion. The concentrations of PGF2 alpha, PGE, 6-keto PGF1 alpha and TXB2 in plasma and lung of 3MI-infused and control goats were determined by radioimmunoassay. 3. Comparison of individual prostanoid concentrations showed that 3MI-infused and control goats exhibited similar plasma profiles for all four prostanoids measured. 4. In addition, prostanoid concentrations in lungs did not seem to be affected by 3MI infusion. 5. Thus, plasma and lung prostaglandin and TXB2 concentrations do not appear to be altered in 3MI-induced lung disease.     

Metabolism of prostacyclin. III. Urinary metabolite profile of 6-keto PGF1 alpha in rat.

The in vivo metabolism of 6-keto PGF1 alpha was investigated in rats. Following continuous intravenous infusion for 14 days the urinary metabolites were isolated and identified. A substantial amount of unchanged 6-keto PGF1 alpha was recovered in the urine. The metabolic pattern very closely resembles that of PGI2 in rats. Metabolites were found which represented 15-dehydrogenation, beta-oxidation, omega and omega-1-hydroxylation and oxidation. Previous work showed that 6-keto PGF1 alpha is very poorly oxidized by 15-PGDH. We administered 15-[H3]-PGI2 and 15-[H3]-6-keto PGF1 alpha to rats and measured urinary tritiated water as an index for in vivo 15-PGDH activity. The results showed that PGI2 and 6-keto PGF1 alpha were both oxidized to the 15-keto product, although the rate of oxidation of PGI2 was greater than that of 6-keto PGF1 alpha. We concluded that the administered PGI2 was oxidized by 15-PGDH before hydrolysis to 6-keto PGF1 alpha. A portion of the dose is probably hydrolzyed before 15-dehydrogenation.     

Dissociation of beta-adrenergic stimulation of renin secretion and prostacyclin synthesis in the rabbit kidney

The effect of inhibition of prostaglandin (PG) synthesis with indomethacin on basal and isoproterenol-stimulated renin secretion was examined in the isolated perfused rabbit kidney. 6-keto PGF1 alpha' the stable metabolite of prostacyclin, was measured in urine by radioimmunoassay using 125I labelled histamine coupled to 6-keto PGF1 alpha as ligand. The level in urine, prior to isolation and perfusion of the kidney, was 10.7 +/- 5.6 ng/min, and this was reduced to 0.32 +/- 0.25 ng/min (P less than 0.05) in rabbits treated with 2.0 mg/kg of indomethacin. Renin release was markedly stimulated by intrarenal infusion of isoproterenol (0.1 microgram/min) but urinary 6-keto PGF1 alpha did not change. These responses were not affected by indomethacin treatment. Renal perfusion pressure, perfusate flow rate and consequently renal vascular resistance, remained relatively constant during the course of perfusion and were unaltered by indomethacin treatment. These results therefore do not support a role for PGs, and in particular prostacyclin, in the renin response to beta-adrenergic stimulation with isoproterenol.     

Beneficial haemodynamic effect of indomethacin during endotoxin shock in anaesthetized pigsputative involvement of nitric oxide?

Endotoxin shock was induced in 31 anaesthetized pigs by infusion of 5 mug/kg of Escbeicbia coli endotoxin (LPS) over 60 min into the superior mesenteric artery. Fifteen of these pigs died within 30 min of the start of LPS infusion whereas the remaining 16 survived the experimental period of 2 h. In a group of nine pigs indomethacin (2 mg/kg, i.v.)was inected 20-25 rain after the start of LPS infusion at which time mean arterial blood pressure (MABP) had decreased below 40 mmHg indicating imminent death. Indomethacin immediately reversed the hypotension. In another group of five pigs, N(G)-nitro L-arginine-methyl ester (L-NAME, 1 and 3 mg/kg)was iniected 10 and 5 min, respectively, before the expected death without any beneficial effect on the hypotension. Three rain after the last dose of L-NAME, indomethacin (2 mg/kg, i.v.) was iniected. In three animals the hypotension was reserved by indomethacin, although this beneficial effect was delayed in comparison with the LP-Streated group not receiving L-NAME. Four pigs were pretreated with L-NAME, 3 mg/kg, i.v., 10 min prior to LPS infusion. All pretreated animals tended to die within 30 min of the start of the LPS infusion. Five rain before the expected death (20-25 rain after the start of LPS infusion) indomethacin (2 mg/kg) was inected. In three of these animals indomethacin reversed hypotenston and prevented death. Interestingly, this rise in the MABP developed very slowly. These results suggest that the beneficial effect of indomethacin in endotoxin shock might be related partially to interference with nitric oxide, which is not the only factor determining blood pressure levels during endotoxic shock.     

Zymosan-activated plasma-mediated thromboxane production by the perfused rabbit liver and isolated hepatocytes: Involvement of calcium

The present study investigates the mechanism of zymosan-activated plasma (ZAP)-mediated eicosanoid production by the isolated, perfused rabbit liver and describes ZAP-induced eicosanoid stimulation in cultured hepatocytes. Perfused livers receiving untreated plasma demonstrated no significant changes in portal venous pressure or the rates of release of lactic dehydrogenase or acid phosphatase activity (indicator of cellular injury). The control group livers demonstrated stable rates of release for 6-keto PGF1α and thromboxane B2 (TXB2). In contrast, the infusion of ZAP alone resulted in a rapid but transient releaes of TXB2 from the livers. No significant changes in perfusion pressure or enzyme release were observed following ZAP administration. Perfusion of livers with a calcium-free buffer decreased the basal rates of both 6-keto PGF1α and TXB2 production and significantly, but not completely, attenuated the ZAP-mediated increase in hepatic TXB2 production. Perfusion of livers with nifedipine (3 μM) had no effect on ZAP-mediated TXB2 production in this model. Isolated hepatocytes responded to ZAP-treatment with significant increases in TXB2 production. These data suggest that activated fluid phase complement components induce thromboxane production by specific cells within the liver and that this stimulation is partially dependent upon the release of intracellular calcium but independent of complement-mediated cellular injuiry.     

Dietary soy protein reduces early renal disease progression and alters prostanoid production in obese fa/fa Zucker rats

With the rising incidence of obesity and the metabolic syndrome, obesity-associated nephropathy also has increased. One of the earliest pathologies in the development of this nephropathy is glomerular hyperfiltration and hypertrophy. Dietary soy protein (SP) ameliorates disease progression in several models of renal disease, and vegetable sources of protein, as compared to animal sources of protein, alter renal hemodynamics. Therefore, the effect of dietary SP on early renal disease and prostanoid production was examined in the obese fa/fa Zucker rat. Rats, 6 weeks of age, were given diets containing 17% protein from either SP or egg white (EW) for 8 weeks. Feed consumption and body and kidney weights were significantly greater in fa/fa rats as compared to lean rats. The fa/fa rats also had 139% more proteinuria and kidneys with 43% larger glomeruli. SP feeding did not alter body weights or proteinuria but did result in 6% lower kidney weights (g/100 g body weight) and 16% smaller glomeruli in fa/fa rats. Cyclooxygenase activity as determined by 6-keto prostaglandin F(1alpha) (6-keto PGF(1alpha)) synthesis was lower in fa/fa rats given SP-based diets as compared to those given EW-based diets. Ratios of renal thromboxane (TX) B(2)/6-keto PGF(1alpha) and PGE(2)/6-keto PGF(1alpha) were higher, while TXB(2)/PGE(2) levels were not different in rats given SP diets as compared to those given EW diets, also indicating that dietary SP reduced renal 6-keto PGF(1alpha) levels. These findings suggest that attenuation of early glomerular hypertrophy in young obese fa/fa rats by dietary SP may be mediated by the lower levels of 6-keto PGF(1alpha) since this would be expected to reduce glomerular hyperfiltration.     

Prostaglandin synthesis by the cochlea

The exogenous and endogenous syntheses of prostaglandins (PG's) by the cochlea of adult mongolian gerbils were studied in vitro. After incubation of the whole membraneous cochlea with [3H]-arachidonic acid (AA), syntheses of PGF2 alpha, 6-keto PGF1 alpha, PGE2, thromboxane (TX) P2 and PGD2 were evidenced in this order. The synthesis of radioactive PG's was almost completely inhibited by incubation with 10(-5) M indomethacin. No significant amounts of those PG's were detected by radioimmunoassay (RIA) in the cochlea obtained from animals killed by microwave irradiation at 5.0 kw for 0.8 sec. However, when the homogenate of the whole membraneous cochlea obtained from animals without microwave irradiation was incubated at 37 degrees C for 0-15 min, PGD2, PGE2, PGF2 alpha and 6-keto PGF1 alpha were found to be formed from endogenous AA in the cochlea by RIA. PG's were formed already at 0 time to considerable level (PGD2, PGF2 alpha and 6-keto PGF1 alpha, 90-120 pg/cochlea; PGE2, 370 pg/cochlea), reached to the maximum level (PGD2, PGF2 alpha and 6-keto PGF1 alpha, 170-200 pg/cochlea; PGE2, 500 pg/cochlea) at a 5-min incubation, and then gradually decreased. On the other hand, the amount of TXB2 was lower than the detection limit by RIA (less than 50 pg/cochlea) even after the incubation. The cochlea was dissected into three parts: organ of Corti + modiolus (OC + M), lateral wall (LW), and cochlear nerve (CN), and then PG's formed by these tissues were determined after a 5-min incubation of the homogenates. In the CN and OC + M, PGE2 was the major PG (100 and 160 pg/tissue, respectively), and the amounts of PGD2, PGF2 alpha and 6-keto PGF1 alpha were about 1/3 of those of PGE2. In the LW, the amounts of PGD2, PGE2, PGF2 alpha and 6-keto PGF1 alpha were about the same level (70-100 pg/LW).     

Time-course of the alterations in prostanoid production and in contractile responses of mesenteric beds isolated from streptozotocin diabetic rats.

The prostanoid production and the effect of indomethacin on the noradrenaline-induced contractions were studied in the mesenteric bed of rats at different times (1-8 weeks) after the administration of streptozotocin (STZ). The production of prostacyclin (measured as 6-keto-PGF1alpha) and prostaglandin (PG) E2 was unchanged one week after STZ, but it was reduced to 50% of control values 4 weeks after STZ without further changes 8 weeks after the treatment. The release of thromboxane (TX) A2 (measured as TXB2) and PGF2alpha, increased by 100% one week after STZ and returned to basal values at 3 weeks. TX release was below control values 8 weeks after STZ. The ratio 6-keto-PGF1alpha/TXB2 was reduced one week after STZ, recovered to control values at 4 weeks and augmented at 8 weeks. Indomethacin (10 microM) reduced the contractile responses to noradrenaline in the controls, whereas in STZ-treated rats this effect was observed solely 8 weeks after the treatment. Since this recovery coincided with an increase of the vasodilator/vasoconstrictor prostanoid ratio, a time-dependent compensation of the vascular alterations caused by STZ can be proposed from the present results.     

Zonal heterogeneity of prostaglandin and thromboxane release in the dog kidney

The release of prostaglandin(PG) and thromboxane(TX) was examined in the six different areas of the normal dog kidney, i.e., renal arterial and venous strips(RA and RV), superficial and deep cortical slices (SC and DC) and outer and inner medullary slices(Om and IM). These tissues were incubated in Krebs-bicarbonate buffer(pH 7.4, 37°C), and the released PGE2, PGF2α, 6-keto-PGF1α and TXB2(as stable metabolites of PG12 and TXA2, respectively) were determined by radioimmunoassay. In RA, RV, SC and DC, 6-keto-PGF1α was predominant, however, there were no quantitative differences between RA and RV, or SC and DC. The release of 6-keto-PGF1α reached a maximum in IM, similar to findings on the release of PGE2 and PGF2α. The release of TXB was uniform in OM and IM. The amount of PGE2, PGF2α, 6-keto-PGF1α and TXB2 released from IM was 2800, 400, 60 and 50 times higher, respectively, than the extent of the release from the cortical slices.These results suggest that PG12 as well as PGE2 and PGF2α, may be involved in renal PG, and that TXA2 is biosynthesized in the normal dog kidney.