Comparison of plasma prostanoid levels in the human cord artery in normal and fetal distressed deliveries

Prostaglandin E2 (PGE2), thromboxane B2 (TXB2; as a stable metabolite of TXA2), prostaglandin F2 alpha (PGF2 alpha) and 6-keto-PGF1 alpha (as a stable end product of prostacyclin) have been measured by using specific radioimmunoassay in the plasma of the cord artery immediately after delivery before the cord was clamped. Plasma prostanoid concentrations in normal deliveries (n = 8, as controls) were 24.8 +/- 2.6 (PGE2), 246.8 +/- 37.0 (TXB2), 122.2 +/- 13.3 (PGF2 alpha) and 82.1 +/- 7.7 (6-keto-PGF1 alpha) respectively (pg/ml, mean +/- s.e). On the other hand, in fetal distressed deliveries showing continuous bradycardia (n = 6), they increased significantly to 275.4 +/- 20.1 (PGE2), 948.6 +/- 102.5 (TXB2), 218.0 +/- 21.4 (PGF2 alpha) and 1498.6 +/- 298.4 (6-keto-PGF1 alpha) respectively (pg/ml, mean +/- s.e, p less than 0.005). However, both PGF2 alpha/PGE2 and TXB2/6-keto-PGF1 alpha ratios declined significantly from 4.70 +/- 0.33 to 0.68 +/- 0.05 and from 3.07 +/- 0.37 to 0.68 +/- 0.12 respectively (mean +/- s.e, p less than 0.005) in the fetal distressed group compared with those of the controls. From these results, it may be concluded that the cord artery, which is known as the patent source for the production of PGE2 and prostacyclin, did exert a sufficiently strong reaction to overcome the undesirable haemodynamic changes to maintain the fetal well-being in utero.     

Dual actions of prostacyclin (PGI2) on the rat pregnant uterus.

Using strips of rat pregnant uterus, treated with indomethacin to suppress spontaneous contractility, the oxytocic activity of prostacyclin was compared with other prostaglandins. A prostacyclin concentration of 32 ng/ml elicited uterine contractions in all experiments. In this respect prostacyclin was 80 times more active than 6-oxo-PGF1 alpha but less active than PGE2 or PGF2 alpha. Apart from a direct stimulant effect, prostacyclin also exhibited an indirect potentiating action. In threshold concentrations prostacyclin caused a 3-fold potentiation of threshold doses of oxytocin. A lesser 1.5-fold potentiation of PGE2 alpha was also observed. The implications of these findings in relation to prostacyclin playing a role in parturition are discussed.     

Renal production of thromboxane and prostaglandins in a rat model of type 2 diabetes

In an investigation of the involvement of prostanoids in the pathogenesis of nephropathy in type 2 diabetes, we repeatedly measured the urinary excretion of prostanoids in both diabetic and healthy rats as the rats aged. Seven rats of the Otsuka Long-Evans Tokushima Fatty strain were used as rats with a model of type 2 diabetes and seven rats of the Long-Evans Tokushima Otsuka strain were used as rats without diabetes. Thromboxane (TX) B2 and 6-keto-prostaglandin (PG) F1alpha, the amounts of which reflect renal production of TXA2 and PGI2, respectively, and PGE2 in urine collected in metabolic cages were assayed when rats were 14, 30, 46, and 54 weeks old. Plasma glucose and urinary protein excretion also were measured periodically. The mean plasma glucose concentration of the diabetic rats was higher than that of the healthy rats throughout the study. At 30 weeks and later, urinary protein excretion by the diabetic rats was greater than that of the healthy rats, and it increased with age. Urinary excretion of TXB2 by the diabetic rats was higher than that of the healthy rats at 14 weeks (52.4+/-23.5 vs. 27.0+/-2.6 ng/day; mean +/- SD, P = .015) and the difference continued to the end of the experiment. Urinary excretion of 6-keto-PGF1alpha by the diabetic rats was high at 14 weeks (52.3+/-12.8 vs. 26.9+/-4.6 ng/day; mean +/- SD, P<.001) but decreased with age and was the same as that of the healthy rats at 54 weeks. The urinary excretion of PGE2 by the two groups of rats was not significantly different. These results suggest that altered renal production of TXA2 and PGI2 is involved in the pathogenesis of diabetic nephropathy in rats with type 2 diabetes.     

Transepithelial prostacyclin gradient in isolated canine trachea

Cyclooxygenase products of arachidonic acid, potential modulators of airway smooth muscle, have recently been described in bronchoalveolar lavage from canine lungs. To evaluate the possibility that airway epithelium represents a barrier to movement of prostacyclin (PGI2), an important bronchodilator synthesized by isolated airway, we measured the concentrations of 6-oxoprostaglandin F1 alpha (6-oxo-PGF1 alpha), the stable degradation product of PGI2, on the mucosal and serosal sides of isolated canine tracheal segments (CTS) mounted in Ussing chambers. 6-oxo-PGF1 alpha was measured by radioimmunoassay after purification by high-performance liquid chromatography. The concentration of 6-oxo-PGF1 alpha was significantly higher on the serosal than the mucosal side of CTS (1,262 +/- 252 vs. 390 +/- 168 pg.min-1.g-1, n = 8, P less than 0.05). A significant correlation was present between 6-oxo-PGF1 alpha measured on both sides of each CTS (r = 0.778, n = 26, P less than 0.01). 6-oxo-PGF1 alpha production from CTS stripped of mucosa was significantly greater than from isolated mucosa. Radiochromatograms obtained after incubation with [3H]arachidonic acid and calcium ionophore A23187 confirmed PGI2 as the predominant cyclooxygenase product of the submucosa, whereas the mucosa produced only small amounts of PGI2 in proportion to other cyclooxygenase products. PGI2 (10(-8) to 10(-6) M) applied to the mucosal surface of closed tracheal segments precontracted with histamine resulted in no significant relaxation, whereas serosal application showed a concentration-dependent effect. Radiolabeled 6-oxo-PGF1 alpha did not cross the isolated epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of 6-oxo-PGF1 alpha in human plasma using gas chromatography-mass spectrometry.

The plasma concentration of the prostacyclin (PGI2) hydration product 6-oxo-PGF1 alpha has been assayed by stable isotope dilution GC-MS in six normal volunteers infused with increasing doses of PGI2 intravenously. The predosing levels of 6-oxo-PGF1 alpha ranged between 114 and 266 pg/ml. Infusion of PGI2 increased 6-oxo-PGF1 alpha concentration in plasma but the increments were lower than expected suggesting less conversion of the PGI2 to 6-oxo-PGF1 alpha at high infusion rates.     

Factors regulating the production of prostaglandin E2 and prostacyclin (prostaglandin I2) in rat and human adipocytes.

The regulation of PGE2 (prostaglandin E2) and PGI2 (prostaglandin I2; prostacyclin) formation was investigated in isolated adipocytes. The formation of both PGs was stimulated by various lipolytic agents such as isoproterenol, adrenaline and dibutyryl cyclic AMP. During maximal stimulation the production of PGE2 and PGI2 (measured as 6-oxo-PGF1 alpha) was 0.51 +/- 0.04 and 1.21 +/- 0.09 ng/2 h per 10(6) cells respectively. Thus PGI2 was produced in excess of PGE2 in rat adipocytes. The production of the PGs was inhibited by indomethacin and acetylsalicylic acid in a concentration-dependent manner. The half-maximal effective concentration of indomethacin was 328 +/- 38 nM and that of acetylsalicylic acid was 38.5 +/- 5.3 microM. The PGs were maximally inhibited by 70-75% after incubation for 2 h. In contrast with their effect on PG production, the two agents had a small potentiating effect on the stimulated lipolysis (P less than 0.05). The phospholipase inhibitors mepacrine and chloroquine inhibited both PG production and triacylglycerol lipolysis and were therefore unable to indicate whether the PG precursor, arachidonic acid, originates from phospholipids or triacylglycerols in adipocytes. Angiotensin II significantly (P less than 0.05) stimulated both PGE2 and PGI2 production in rat adipocytes without affecting triacylglycerol lipolysis. Finally, it was shown that PGE2 and PGI2 were also produced in human adipocytes, although in smaller quantities than in rat adipocytes. It is concluded that the production of PGs in isolated adipocytes is regulated by various hormones. Moreover, at least two separate mechanisms for PG production may exist in adipocytes: (1) a mechanism that is activated concomitantly with triacylglycerol lipolysis (and cyclic AMP) and (2) an angiotensin II-sensitive, but lipolysis (and cyclic AMP)-independent mechanism.     

Pharmacological modulation of prostacyclin and thromboxane production of rat and cat venous tissue slices.

To reveal a potential modulating effect of vasoactive pharmacological agents on the prostanoid production of the venous wall, prostacyclin and thromboxane release from venous tissue slices was studied. Aortic and caval vein samples from 20 rats as well as from 21 cats were studied. Prostacyclin and thromboxane productions were determined by radioimmunoassay as 6-keto-PGF1 alpha and TxB2 released into the incubation medium. Venous tissue produced significantly less prostacyclin per unit weight than arterial tissue in rats (30.7 +/- 4.6 vs. 52.1 +/- 8.2 pg/mg/min), while in cats an opposite situation was found (16.6 +/- 3.2 vs. 7.06 +/- 1.9 pg/mg/min). Thromboxane production of venous tissue was consequently higher than corresponding values for aortic tissue (3.72 +/- 0.46 vs. 1.54 +/- 0.14 in rats and 3.4 +/- 0.6 vs. 1.33 +/- 0.19 in cats, all values in pg/mg/min). Norepinephrine and dopamine significantly increased both the prostacyclin and the thromboxane release from venous tissue, while isoproterenol had no effect. Vasopressin significantly increased thromboxane release and decreased the ratio of prostacyclin vs. thromboxane production (from 10.4 +/- 1.6 to 7.5 +/- 1.6, in acetylsalicylic acid pretreated cats). Angiotensin and thrombin had no significant effects. Bradykinin (0.5 microgram/ml) significantly augmented prostacyclin release from venous tissue (14.4 +/- 2.6 from 10.9 +/- 2.4 pg/mg/min) and decreased thromboxane release (0.65 +/- 0.18 from 1.35 +/- 0.22 pg/mg/min). Methionine-enkephalin (5 micrograms/ml) significantly reduced the thromboxane release from venous tissue slices. The presented material demonstrates that several vasoactive agents modulate the vasoactive prostanoid release of the venous wall. In some cases, the prostacyclin and the thromboxane productions are influenced separately, which in turn will have its impact on smooth muscle activity and thrombocyte aggregation.     

The effects of prostacyclin (PGI2) on tissues which detect prostaglandins (PG'S).

The effects of prostacyclin (PGI2) and its stable metabolite 6-oxo-PGF1alpha on various bioassay tissues are compared with those of PGE2 and PGF2alpha, using the cascade superfusion method. On vascular smooth muscle, PGI2 caused relaxation of all tissues tested except the rabbit aorta. PGE2 relaxed rabbit coeliac and mesenteric artery but contracted bovine coronary artery and had no effect on rabbit aorta. 6-oxo-PGF1alpha was ineffective at the concentrations tested. On gastro-intestinal smooth muscle, PGI2 contracted strips of rat and hamster stomach and the chick rectum. It was less potent than PGE2 or PGF2alpha. None of these substances contracted the cat terminal ileum. 6-oxo-PGF1alpha was inactive on these tissues at the doses tested. PGI2 was less active than PGE2 or PGF2alpha in contracting guinea-pig trachea and rat uterus; 6-oxo-PGF1alpha was active only on the rat uterus. Thus, PGI2 can be distinguished from the other stable prostaglandins using the cascade method of superfusion.     

Impaired responsiveness of renal sensory nerves in streptozotocin-treated rats and obese Zucker diabetic fatty rats: role of angiotensin

Increasing afferent renal nerve activity decreases efferent renal nerve activity and increases urinary sodium excretion. Activation of renal pelvic mechanosensory nerves is impaired in streptozotocin (STZ)-treated rats (model of type 1 diabetes). Decreased activation of renal sensory nerves would lead to increased efferent renal nerve activity, sodium retention, and hypertension. We examined whether the reduced activation of renal sensory nerves in STZ rats was due to increased renal angiotensin activity and whether activation of the renal sensory nerves was impaired in obese Zucker diabetic fatty (ZDF) rats (model of type 2 diabetes). In an isolated renal pelvic wall preparation from rats treated with STZ for 2 wk, PGE2 failed to increase the release of substance P, from 5 +/- 1 to 6 +/- 1 pg/min. In pelvises from sham STZ rats, PGE2 increased substance P release from 6 +/- 1 to 13 +/- 2 pg/min. Adding losartan to the incubation bath increased PGE2-mediated release of substance P in STZ rats, from 5 +/- 1 to 10 +/- 2 pg/min, but had no effect in sham STZ rats. In pelvises from obese ZDF rats (22-46 wk old), PGE2 increased substance P release from 12.0 +/- 1.2 to 18.3 +/- 1.2 pg/min, which was less than that from lean ZDF rats (10.3 +/- 1.6 to 22.5 +/- 2.4 pg/min). Losartan had no effect on the PGE2-mediated substance P release in obese or lean ZDF rats. We conclude that the mechanisms involved in the decreased responsiveness of the renal sensory nerves in STZ rats involve activation of the renin angiotensin system in STZ but not in obese ZDF rats.     

Effect of dipyridamole on prostanoid production in rat isolated atria.

The effect of 0.01 microM dipyridamole on prostanoid production was studied in atria from normal, acute diabetic and insulin-treated diabetic rats. Diabetes was induced by i.v. administration of 65 mg/kg of streptozotocin (STZ) and the rats were killed 5 days later. Atria were incubated during 60 min in Krebs solution. The prostanoids 6-keto-prostaglandin (PG) F1alpha (6-keto-PGF1alpha) and thromboxane (TX) B2, stable metabolites of prostacyclin and TXA2, respectively, as well as PGE2 were measured by reversed phase high-performance liquid chromatography-UV. In diabetic atria, 6-keto-PGF1alpha production was reduced by 50% whereas TXB2 release was increased two-fold compared to the controls, with a significant decrease in the 6-keto-PGF1alpha/TXB2 ratio. The preincubation with 0.01 microM dipyridamole for 30 min increased 6-keto-PGF1alpha production in control, diabetic and insulin-treated diabetic atria whereas TXB2 release was not modified. This effects provoked an significant increase in the 6-keto-PGF1alpha/TXB2 ratio. In conclusion, STZ diabetes reduces the 6-keto-PGF1alpha/TXB2 ratio impairing the functional status of the atria. Dipyridamole increased this ratio in atria from diabetic and insulin-treated diabetic rats, thus opposing the effects of STZ diabetes. This fact suggests the possibility of a participation of the drug in pathologies characterized by an imbalance in the production of vasodilator and vasoconstrictor prostanoids.     

The renal haemodynamic and excretory actions of prostacyclin and 6-oxo-PGF1 alpha in anaesthetized dogs.

Intrarenal arterial (i.a.) infusions of prostacyclin (PGI2) at 30-300 ng/min to anaesthetized dogs reduced renal vascular resistance (RVR) and filtration fraction (FF), increased mean renal blood flow (MRBF) but did not alter mean arterial pressure (MAP)or glomerular filtration rate (GFR). The urinary excretion of sodium (UNaV), potassium (UKV) and chloride ions (UC1V) were increased through inhibition of net tubular ion reabsorption. PGI2 (3000 ng/min, i.a.) reduced MAP and increased heart rate. Intravenous (i.v.) infusions of PGI2 (3000 gn/min) reduced MAP, GFR, FF, urine volume and ion excretion, with elevation of heart rate. The measured variables were unaltered by 6-oxo-PGF1 alpha (10,000 ng/min i.a.). Treatment of the dogs with the PG synthetase inhibitor meclofenamic acid (2.5 mg/kg i.v.) did not antagonise the elevation of MRBF to PGI2 (300 ng/min i.a.). Thus the renal effects of PGI2 were due to a direct action rather than through conversion to 6-oxo-PGF1 alpha or through stimulation of endogenous renal PG biosynthesis and release.     

Effect of subcutaneous pancreatic tissue transplants on streptozotocin-induced diabetes in rats. II. Endocrine and metabolic functions.

The present study examines the effect of subcutaneous pancreatic tissue grafts (SPTG) on endocrine and metabolic functions in streptozotocin (STZ)-induced diabetic rats using radioimmunoassay and biochemical techniques. SPTG survived even after 15 weeks of transplantation and significantly improved the weight of STZ-diabetic rats over a 15-week period. Although blood glucose-, cholesterol-, and glycosylated-haemoglobin (GHb) levels were not significantly lower in STZ-diabetic rats treated with SPTG, the values of these biochemical parameters were lower than those in untreated diabetic rats. Plasma and pancreatic immunoreactive C-peptide (IRCP) levels did not improve after SPTG (IRCP expressed as mean +/- standard deviation were 0.22 +/- 0.07, 0.072 +/- 0.02 and 0.08 +/- 0.03 pg ml-1 in the plasma non-diabetic diabetic and treated rats respectively, while IRCP levels in the pancreas of the non-diabetic, diabetic and treated rats were 433.8 +/- 0.1, 22.9 +/- 0.01 and 10.4 +/- 0.01 pg mg tissue-1 respectively). SPTG, however, improved plasma immunoreactive insulin (IRI) levels in both plasma and pancreas. IRI values in plasma were 54.7 +/- 13.6, 18.0 +/- 5.0 and 22.1 +/- 4.3 microUI ml-1 in non-diabetic, diabetic and treated rats respectively and were 277.3 +/- 37.1, 14.7 +/- 1.8 and 30.3 +/- 15.9 microIU micrograms tissue-1 in the pancreas of non-diabetic, diabetic and treated rats respectively. There was improvement in immunoreactive glucagon (IRG) levels after SPTG. IRG values in the plasma of non-diabetic, diabetic and treated rats were 147.0 +/- 10.7, 408.0 +/- 76.5 and 247.7 +/- 3 pg ml-1 respectively whereas, IRG measured in the pancreas was 1642.25 +/- 424.23, 1899.0 +/- 290.4 and 1714.1 +/- 301.98 pg micrograms tissue-1 in non-diabetic, diabetic and treated rats, respectively. The pancreas:plasma ratio of pancreatic hormones was deranged in untreated diabetes but improved after SPTG. In conclusion, SPTG significantly improved the weight gain, pancreatic insulin content, plasma IRG and pancreas: plasma ratio of IRCP, IRI and IRG. It also reduced blood glucose-, cholesterol-, and glycosylated-hemoglobin levels in STZ-diabetic rats.     

Effects of experimental diabetes on spontaneous contractions, on the output of prostaglandins and on the metabolism of labelled arachidonic acid, in uteri isolated from ovariectomized rats. Influences of estradiol

Spontaneous changes in isometric developed tension (IDT) as a function of time after isolation (contractile constancy) in uteri from control-castrated and castrated chronic streptozotocin-diabetic rats, were explored. The effects of injecting 17-beta estradiol (Eo) were also studied. No differences in the minor changes of contractile constancy, between control and diabetic preparations, during a period of 60 min, were detected, whereas uteri from non-diabetic Eo injected animals (0.5 + 1.0 ug, prior to sacrifice), exhibited a profound reduction of IDT, significantly greater than in tissues obtained from Eo injected-diabetic rats. Moreover, basal generation and outputs into the suspending solution of prostaglandins (PGs) E1, E2 and F2 alpha, were explored in the same groups, at 60 min following tissue isolation. The basal outputs of these three PGs were similar in castrated control rats, but preparations from castrated-diabetics released significantly more PGE1. The administration of Eo to castrated-diabetics, failed to alter the releases of the three PGs explored. In addition, the metabolism of labelled arachidonic acid (AA) into different prostanoids (6-keto-PGF1, PGF2, PGE2 and thromboxane B2-TXB2), was also investigated. The non-diabetic spayed rat uterus converted AA into these four prostanoids, the transformation into 6-keto-PGF1 alpha (as an index of PGI2 formation) being the most prominent. In preparations from diabetic rats the formation) being the most prominent. In preparations from diabetic rats the formation of 6-keto-PGF1 alpha, PGF2 alpha and PGE2, was significantly smaller than in controls, whereas a greater % of TXB2 formation (as an index of TXA2), was detected. On the other hand uterine preparations from non-diabetic spayed rats injected with Eo formed less 6-keto-PGF1 alpha and PGE2 and similar amounts of PGF2 alpha or of TXB2 from AA, than Eo injected controls, whereas uteri from castrated diabetic animals injected with Eo, formed a similar % of 6-keto-PGF1 alpha, PGF2 alpha and PGE2 from AA, than tissue preparations from non-estrogenized controls. However, the enhanced transformation of the labelled fatty acid precursor (AA) into TXB2 in the diabetic group, was significantly reduced by the steroid. The role of the augmented generation and release of PGE1 in uteri from diabetic rats is discussed in terms of precedents indicating the relevance of PGs type E supporting rat uterine motility. In addition the influence of Eo is attractive, because its reducing effect on TX production, in diabetes, a disease known to be accompanied by enhanced synthesis of vasoconstrictor and platelet aggregation TXA2, and by frequent obstructive circulat     

Effects of fish oil on glomerular function in rats with diabetes mellitus

The mechanisms responsible for hyperfiltration in diabetes mellitus (DM) as well as for the initiation and progression of diabetic nephropathy are not fully elucidated. Enhanced prostaglandin E2 (PGE2) production has been invoked in the former and thromboxane (TXB2) and hyperlipidemia in the latter. Fish oil (FO)-enriched diets can favorably alter eicosanoid synthesis and serum lipid profiles. We therefore examined the effects of a FO-enriched diet on glomerular filtration (GFR), proteinuria, glomerular eicosanoid production, and serum lipids in rats with streptozotocin-induced DM (STZ-DM). Groups of 5-8 rats with STZ-DM were maintained on low insulin and then pair-fed with isocaloric diets enriched with either FO (20% w/w) or beef tallow (BT; 20% w/w). GFR was determined in the same animals at onset of diet and after 8 and 20 weeks on the respective diets by [14C]inulin clearance using implanted osmotic minipumps each time. Significant hyperfiltration was present initially and GFR did not change on either diet for 20 weeks, in spite of a significant and greater than 50% decrease in all prostaglandins (PGE2, TXB2, PGF2 alpha, 6-keto, PGF1 alpha) produced by glomeruli isolated from DM/FO as compared to DM/BT or control rats. FO diet completely corrected the hypertriglyceridemia of diabetes and significantly reduced the mild and early proteinuria of DM. The decrease in proteinuria and the correction of hyperlipidemia of DM by a FO-enriched diet may be beneficial in the long term not only for the development of diabetic glomerulopathy, but also for the accelerated atherosclerosis of DM.     

Prostacyclin and thromboxane in diabetes.

Concentrations of the stable antiaggregatory prostacyclin metabolite 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and of the proaggregatory thromboxane A2 metabolite thromboxane B2 were measured by radioimmunoassay in plasma from 53 diabetics. In 33 of these patients the ability of platelets to produce thromboxane B2 during spontaneous clotting was also studied. Plasma 6-keto-PGF1 alpha concentrations were higher (p less than 0.05) in the diabetics (mean 107.7 +/- SE 7.6 ng/l) than in non-diabetic controls matched for age and sex (87.5 +/- 4.7 ng/l), and diabetics with microangiography (n = 28) and higher (p less than 0.01) concentrations (124.3 +/- 10.8 ng/l) than those without microangiography (n = 25; 89.2 +/- 9.3 ng/l). Plasma thromboxane B2 concentrations were also higher (p less than 0.01) in the diabetics (mean 218.5 +/- SE 25.3 ng/l) than in the controls (127.7 +/- 9.8 ng/l), but this increase was not related to microangiography. The ability of platelets to generate thromboxane B2 did not differ between the diabetics (181.4 +/- 16.4 microgram/l) and controls (195.8 +/- 11.8 microgram/l). Platelets of diabetics with microangiopathy or taking oral hypoglycaemic agents (n = 19), however, produced decreased amounts of thromboxane B2 during clotting. Plasma concentrations of 6-keto-PGF1 alpha and thromboxane B2 were not related to concentrations of glucose, haemoglobin A1, high-density lipoprotein cholesterol, cholesterol, triglycerides, magnesium, or creatinine. These results suggest that in diabetics with microangiopathy a balance between prostacyclin and thromboxane A2 is shifted to dominance by prostacyclin.     

Effect of angiotensin ii and norepinephrine on release of prostaglandins E2 and I2 by the perfused rat mesenteric artery

Prostaglandin E2 (PGE2) and 6 keto-PGF1 alpha, the stable metabolite of prostacyclin (PGI2), have been measured in the effluent of perfused rat mesenteric arteries by the use of a sensitive and specific radioimmunoassay (RIA) method. The PGE2 and 6 keto-PGF1 alpha were continuously released by the unstimulated mesenteric artery over a period of 145 min. After 100 min of perfusion the release of PGE2 and 6 keto-PGF1 alpha was 45.1 +/- 8.4 pg/min and 254 +/- 75 pg/min respectively, which is in accord with the general belief that PGI2 is the major PG synthesized by arterial tissue. Angiotensin II (AII) (5 ng/ml) induced an increase of PGE2 and 6 keto-PGF1 alpha release without changing the perfusion pressure. The effect of norepinephrine (NE) injections on release of PGs depended on the duration of the stabilization period. The changes of perfusion pressure induced by NE were not related to changes in release of PGs. Thus, it seems that the increase of PG release induced by AII and NE was due to a direct effect of the drugs on the vascular wall. This may represent an important modulating mechanism in the regulation of vascular tone.     

Responsiveness of renal glomeruli to adenosine in streptozotocin-induced diabetic rats dependent on hyperglycaemia level.

Glomerular filtration rate (GFR) in response to adenosine precursor, NAD, and glomeruli contractility in response to adenosine were evaluated in streptozotocin-induced diabetic rats with severe (blood glucose 27.8 +/- 1.2 mmol/L) and moderate hyperglycaemia (18.2 +/- 0.9 mmol/L) compared with nondiabetic (ND)-rats. In anaesthetised rats, basal GFR was greater in moderately diabetic rats compared with severely diabetic rats (p < 0.05) and ND-rats (p < 0.02). Intravenous infusion of 5 nmol x min(-1) x kg(-1) NAD reduced GFR and renal plasma flow (RPF) in diabetic rats but had no effect on these parameters in ND-rats. Moreover, NAD-induced reduction of GFR and RPF was greater in rats with severe diabetes (41% and 30%, respectively) than in with moderate diabetes (25% and 26%, respectively). Theophylline (0.2 micromol x min(-1) x kg(-1) ) abolished renal response to NAD. Isolated glomeruli contraction in response to adenosine, assessed by glomerular 3H-inulin space reduction, was lowered in moderately diabetic-group and enhanced in severely diabetic-group. compared with ND-group (p < 0.05). Adenosine A1-receptor antagonist DPCPX inhibited adenosine-induced glomeruli contraction. This differential response of diabetic renal glomeruli to adenosine suggests that impaired glomerular contractility in response to adenosine could be responsible for hyperfiltration in moderate diabets, whereas, the increased adenosine-dependent contractility of glomeruli in severe diabetes may increase the risk of acute renal failure in this condition.     

Investigation of the vascular actions of arachidonate lipoxygenase and cyclo-oxygenase products on the isolated perfused stomach of rat and rabbit

The vascular actions of several prostanoids and arachidonate lipoxygenase products were investigated on the gastric circulation of rat and rabbit in vitro perfused with Krebs' solution. Under resting conditions, prostacyclin and PGE2 produced small decreases in perfusion pressure with prostacyclin being the more potent. During vasoconstriction induced by infusion of noradrenaline, vasopressin or angiotensin II, prostacyclin was 20-40 times as active as PGE2 as a gastric vasodilator in rat or rabbit stomach. PGF2 alpha was a less potent vasoconstrictor than noradrenaline, while the epoxy-methano endoperoxide analogue produced a long-lasting vasoconstriction. The putative metabolite, 6-oxo-PGE1 was less active than prostacyclin as a vasodilator, having comparable activity to PGE1, whereas 6-oxo-PGF1 alpha had very little activity. The endoperoxide, PGH2 reduced perfusion pressure, this effect being inhibited by concurrent infusion of 15-HPETE. The vasodilation induced by arachidonic acid was likewise reduced by 15-HPETE, and abolished by indomethacin infusion. The arachidonate lipoxygenase hydroperoxides were vasodilator in the gastric circulation, the rank order of potency being 12-HPETE greater than 11-HPETE greater than 5-HPETE greater than 15-HPETE in both rat and rabbit stomach. It is possible that such vasoactive lipoxygenase products, may play modulator roles in the gastric mucosa.     

Uteroplacental production of eicosanoids in ovine pregnancy

Dramatic cardiovascular alterations occur during normal ovine pregnancy which may be associated with increased prostaglandin production, especially of uteroplacental origin. To study this, we examined (Exp 1) the relationships between cardiovascular alterations, e.g., the rise in uterine blood flow and fall in systemic vascular resistance, and arterial concentrations of prostaglandin metabolites (PGEM, PGFM and 6-keto-PGF1 alpha) in nonpregnant (n = 4) and pregnant (n = 8) ewes. To determine the potential utero-placental contribution of these eicosanoids in pregnancy, we also studied (Exp 2) the relationship between uterine blood flow and the uterine venous-arterial concentration differences of PGE2, PGF2 alpha, PGFM, 6-keto-PGF1 alpha, and TxB2 in twelve additional late pregnant ewes. Pregnancy was associated with a 37-fold increase in uterine blood flow and a proportionate (27-fold) fall in uterine vascular resistance (p less than 0.01). Arterial concentrations of PGEM were similar in nonpregnant and pregnant ewes (316 +/- 19 and 245 +/- 38 pg/ml), while levels of PGFM and PGI2 metabolite 6-keto-PGF1 alpha were elevated 23-fold (31 +/- 14 to 708 +/- 244 pg/ml) and 14-fold (12 +/- 4 to 163 +/- 78 pg/ml), respectively (p less than 0.01). Higher uterine venous versus uterine arterial concentrations were observed for PGE2 (397 +/- 36 and 293 +/- 22 pg/ml) and 6-keto-PGF1 alpha (269 +/- 32 and 204 +/- 32 pg/ml), p less than 0.05, but not PGF2 alpha or TxB2. Although PGFM concentrations appeared to be greater in uterine venous (1197 +/- 225 pg/ml) as compared to uterine arterial (738 +/- 150 pg/ml) plasma, this did not reach significance (0.05 less than p less than 0.1). In normal ovine pregnancy arterial levels of PGI2 are increased, which may in part reflect increased uteroplacental production. Moreover the gravid ovine uterus also appears to produce PGE2 and metabolize PGF2 alpha.     

Predominance of locally-produced prostaglandin E2 over prostacyclin in skin incisions in man

Blood was collected from skin incisions made by the 'Simplate' technique in 8 healthy men. Prostaglandin (PG) E2, but not 6-oxo-PGF1 alpha, the stable hydrolysis product of prostacyclin (PGI2), was tentatively identified using capillary column gas chromatography/electron capture mass spectrometry. It was not possible to quantify PGE2 because of the small volumes of blood generated by this method. Larger blood samples were then collected from 22 skin incisions in 13 patients undergoing cardiothoracic surgery. Concentrations of PGE2 were substantially greater than 6-oxo-PGF1 alpha in every sample. 13,14-Dihydro-15-oxo-PGF2 alpha, a pulmonary metabolite of PGE2, was not elevated, indicating that the PGE2 was synthesised locally at the site of incision. In 6 further patients undergoing cardiac surgery, blood sampled from an antecubital vein before and during operation contained little or no PGE2. We conclude that a substantial proportion of the PGE2 in blood emerging from skin incisions may be formed locally by the traumatised microvessels, consistent with the hypothesis that PGE2 is the principle prostaglandin synthesised by human cutaneous microvessels in vivo.