Metabolism of prostacyclin in Cynomolgus monkey

The metabolism of prostacyclin (PGI2) in vivo was investigated in Cynomolgus monkey. Following intravenous infusion of 11-[3H]-PGI2 for three days, pooled urine was extracted with Amberlite XAD-2, then chromatographed and purified by Sephadex LH-20, and reverse phase column chromatography. Radioactive fractions were converted to appropriate derivatives for identification by gas chromatography mass spectrometry. Twelve metabolites were characterized, the major of which was 6-keto-PGF1 alpha, accounting for 13% of the urinary radioactivity. The metabolic pathways are similar to those observed earlier in the rat. The excretion of substantial amounts of unchanged 6-keto-PGF1 alpha indicated that the monkey was not able to metabolize PGI2 as avidly as the rat.

Prostacyclin production by isolated adipocytes

Isolated rat adipocytes produce prostacyclin (PGI2) in relatively large quantities during norepinephrine (NE)-induced lipolysis. The endogenous NE-induced production rate of PGI2, calculated from the NE-induced production rate of PGI2 observed in our studies (2.2 ng/10(6) cells/2 h) and from the number of fat cells in the normal organism, is 1.46 ng/kg/min for rats, 4.46 ng/kg/min for men, and 11.86 ng/kg/min for women. These rates are comparable to the exogenous PGI2 infusion rate that alters platelet aggregation and blood pressure in rats and humans. Exogenous PGI2 failed to modify the rate of NE-induced lipolysis. Inhibition of endogenous PGI2 production by indomethacin had no effect on the rate of NE-induced lipolysis when either a maximal or submaximal lipolytic concentration of NE was used. PGI2 [rather than prostaglandin (PG) E2] may be the substance that accounts for the functional vasodilatation that accompanies hormone-induced lipolysis. PGI2 is produced in large quantities than PGE2 during NE-induced lipolysis and is a more potent vasodilator than PGE2. Its instability can account for the inability of previous investigators to detect a vasodilator substance in the venous effluent of adipose tissue. The production of PGI2 by adipocytes may be an important modulator of the regulation of vascular tone and platelet aggregation by catecholamines in the vascular bed of adipose tissue and perhaps other tissues. PGI2 produced by adipocytes, by virtue of its ability to cause vasodilatation and inhibit platelet aggregation, may contribute to the maintenance of luminal patency in the vascular bed of adipose tissue and possibly other tissue as well.

Extractive alkylation of prostaglandins

The simultaneous extraction and esterification of prostaglandins in aqueous solution is described. High yield of esters can be achieved in a one minute reaction time. The specificity of the alkylation can be controlled by the counterion. Thus, a long chain carboxylic acid can be selectively extracted and derivatized in the presence of PGF2 alpha.

The impermeability of the basic cell membrane to thromboxane-B2' prostacyclin and 6-keto-PGF 1 alpha

Washed rabbit red blood cells (RBCs) were suspended in electrolyte solution containing 3H-labeled prostacyclin (PGI2), thromboxane (TxB2) or 6-keto-PGF 1 alpha and 14C-labeled sucrose or thiourea. following 1 to 30 min incubation with 14C-sucrose, 3H-TxB2 or 3H-6-keto-PGF 1 alpha, the 14C or 3H space of packed RBCs remained essentially constant, yielding mean values (+/- S.E.) for all time periods of 6.1 +/- 0.3, 9.5 +/- 0.5 and 6.5 +/- 0.4%, respectively. After 1 min of incubation at 4 degrees or 23 degrees C at a pH of 7.4 or 8.5 with trace amounts (10(-9)M) of 3H-PGI2 or in the presence of added PGI2 (10(-5)M) or ethacrynic acid (1.6 x 10(-4)M), the apparent PGI2 space of packed RBCs ranged from 16 to 27%, decreasing to about 7% by 30 min. When RBCs were resuspended in fresh 3H-PGI2 every 5 min, their 3H content increased very slowly (apparent PGI2 space less than 40% at 30 min) as compared to thiourea (distribution space greater than 80% within 5 min). Over 90% of this 3H activity was lost from the RBCs in less than 2 min during elution at 4 degrees or 23 degrees C. It is concluded that RBC membranes and thus, presumably, the basic cell membrane in general, is not fundamentally permeable to PGI2, 6-keto-PGF 1 alpha or TxB2. Hence, the effective entry of these cyclooxygenase products into some cells or their passage across tight-junctional capillaries or epithelial membranes must require facilitated or active transport processes as was shown to be the case for E, F and A PGs. This implies that the distribution, pharmacological action and metabolism of these and presumably all related cyclooxygenase products are selective rather than unrestricted.

Prostacyclin and blood glucose levels in humans and rabbits

In patients with peripheral vascular disease and in healthy rabbits, infusion of PGI2 but not of 6-keto PGF1 alpha induced a rise in blood glucose level and a pathological deviation in glucose tolerance test. In experiments in vitro, the increased concentrations of glucose produced dose-dependent inhibition of PGI2 release from isolated rat aortic rings. The link between PGI2 and carbohydrate metabolism is discussed.

High performance liquid chromatography and UV detection for the separation and quantitation of prostaglandins

A fast and reliable method for the separation and quantitation of arachidonic acid metabolites PGF1 alpha, PGF2 alpha, PGD2, PGE1, PGE2, PGB2, PGA2, 6-keto PGE1, 6-keto PGF1 alpha, TxB2 and 15-keto PGE2 by high-performance liquid chromatography has been developed. Utilizing a single reverse-phase column and a UV spectrophotometer, sensitivity as little as 30 nanograms of each of these prostaglandins can be separated and subsequently detected. Although this study was performed using standards, it is highly promising for future application to biological fluids.

Increased prostacyclin synthesizing activity in human ripening uterine cervix

Homogenate of human uterine cervix at delivery were incubated with radioactive arachidonic acid. A major metabolite (conversion rate, approx. 20%) was identified with 6-ketoprostaglandin F1 alpha, a metabolite of prostacyclin. The 6-ketoprostaglandin F1 alpha production in the ripening cervix was more than 6 times per wet weight and 37 times per DNA as much as that in the non-pregnant cervix.

Effect of RNA and protein synthesis inhibitors on the release of inflammatory mediators by macrophages responding to phorbol myristate acetate

The interaction of phorbol myristate acetate with resident populations of mouse peritoneal macrophages causes an increased release of arachidonic acid followed by increased synthesis and secretion of prostaglandin E2 and 6-keto-prostaglandin F1 alpha. In addition, phorbol myristate acetate causes the selective release of lysosomal acid hydrolases from resident and elicited macrophages. These effects of phorbol myristate acetate on macrophages do not cause lactate dehydrogenase to leak into the culture media. The phorbol myristate acetate-induced release of arachidonic acid and increased synthesis and secretion of prostaglandins by macrophages can be inhibited by RNA and protein synthesis inhibitors, whereas the release of lysosomal hydrolases is unaffected. 0.1 microgram/ml actinomycin D blocked the increased prostaglandin production due to this inflammatory agent by more than 80%, and 3 microgram/ml cycloheximide blocked prostaglandin production by 78%. Similar results with these metabolic inhibitors were found with another stimulator of prostaglandin production, zymosan. However, these inhibitors do not interfere with lysosomal hydrolase releases caused by zymosan or phorbol myristate acetate. It appears that one of the results of the interaction of macrophages with inflammatory stimuli is the synthesis of a rapidly turning-over protein which regulates the production of prostaglandins. It is also clear that the secretion of prostaglandins and lysosomal hydrolases are independently regulated.

Enhanced 6-oxo-PGF1 alpha levels in plasma during hemodialysis

The activation of platelets due to foreign surface interaction is a well known fact. Earlier, we found an increase of circulating platelet microaggregates (method of Wu and Hoak) during hemodialysis. Since this phenomenon might cause a PGI2-release by lung and/or vascular tissue, we studied the plasma 6-oxo-PGF 1 alpha-levels in 6 patients during hemodialysis. We found an initial increase of plasma 6-oxo-PGF 1 alpha. Coincidently, hypoxemia, fall in platelet and lekocyte count and a decrease in platelet count ratio were observed. An effect of heparin was excluded in a control group. The findings support the hypothesis that PGI2 acts as a defense mechanism against platelet deposition on vascular wall by a temporary increased synthesis which could be monitored by a temporarily enhanced plasma 6-oxo-PGF 1 alpha-level during the initial phase of hemodialysis.

Metabolism of prostacyclin and 6-keto-prostaglandin F1 alpha in man

Labeled and unlabeled prostacyclin and 6-keto-PGF1 alpha were infused into healthy volunteers; urine was chromatographed on different systems including high pressure liquid chromatography. The peaks obtained by the latter method were derivatized to the methoxime methyl ester trimethyl silyl ether and analyzed by gas-liquid chromatography-mass spectrometry. After infusion of prostacyclin the following metabolites could be identified: dinor-4-keto-7,9,13-trihydroxy-prosta-11,12-enoic acid (20.5%), dinor-4,13-diketo-7,9-dihydroxy-prostanoic acid (6.8%), dinor-4,13-diketo-7,9-dihydroxy-prostan-1,18-dioic acid (19.7%), and 6-keto-PGF1 alpha (14.2%), the in vitro hydrolysis product of prostacylin. 6-Keto-PGF1 alpha infusion resulted in the same metabolites with the relative amounts of 22.4, 5.4, 7.0, and 6.8%, respectively. Additionally, 6,15-diketo,13,14-dihydro-PGF1 alpha (5.7%) could be identified. These data show that the metabolic pathway of prostacyclin involves hydrolysis to 6-keto-prostaglandin F1 alpha, subsequent beta-oxidation, dehydrogenation at C-15, reduction of the double bond between C-13 and C14, and omega-oxidation to the dicarboxyl metabolite. We conclude that dinor-4-keto-7,9,13-trihydroxy-prosta-11,12-enoic acid and dinor-4,13-diketo-7,9-dihydroxy-prostan-1,18-dioic acid represent the major urinary metabolites of prostacyclin in man. 6-keto-PGF1 alpha is a minor urinary excretory product following the administration of prostacyclin or 6-keto-PGF1 alpha.

Quantitative determination of 6-Oxo-PGF1 alpha in biological fluids by gas chromatography mass spectrometry

A selected ion monitoring method for the determination of 6-oxo-PGF1 alpha, the stable end-product of prostacyclin, in biological fluids has been developed. In this method, biosynthetically prepared [2H6]-6-oxo-PGF1 alpha is used as internal standard. The method involves extraction, thin-layer chromatography purification and derivatization into the methyl ester, methoxime, trimethylsilyl ether derivatives by carrying out the methoximation first. Quantitative gas chromatographic mass spectrometric analysis is performed in the electron impact mode by monitoring the [M - (TMSOH + CH3O)]+ fragment ions. The use of this method in the measurement of 6-oxo-PGF1 alpha in serous fluids and in incubation media of serous tissues is described.

Quantitative determination of 6-keto-PGF1 alpha released by rat aorta: comparison of mass fragmentography and high resolution gas chromatography with electron capture detection

Mass fragmentography (MF) and high resolution gas chromatography with electron capture detection (HRGC-ECD) were used for measuring 6-keto-PGF1 alpha, the stable hydrolysis product of prostacyclin (PGI2) released by fresh rings of rat aorta, incubated in the absence of the precursors arachidonic acid or prostaglandin endoperoxide (PGH2). The incubation medium was acidified, extracted, chromatographed on silicic acid column and derivatized. Comparable results were obtained analyzing each sample by MF and HRGC-ECD. Both methods proved to be suitable in terms of sensitivity and specificity for the measurement of 6-keto-PGF1 alpha produce by individual rat aortae.

Prostaglandin production by minced carrageenin granuloma tissue of rats and its inhibition by dexamethasone and cycloheximide

Seven-day-old carrageenin granuloma tissue of rats, when incubated in organ culture, produced 6-keto-prostaglandin F1 alpha, prostaglandin E2, prostaglandin F2 alpha, and thromboxane B2 in ratios of 16/7/1/1, respectively. Indomethacin (1 microgram/ml) inhibited this cyclooxygenase-mediated arachidonic acid metabolism. Dexamethasone (1 microgram/ml) also inhibited this metabolic cascade. Its inhibitory effect was not immediate; preincubation of the tissue with dexamethasone potentiated its inhibitory effectiveness. Cycloheximide (0.1 to 10 microgram/ml) also inhibited prostaglandin production. The inhibitory mechanism by cycloheximide of prostaglandin production was discussed in relation to that by dexamethasone.

The effects of prostacyclin (PGI2) and 6-keto-PGF1 alpha on bovine plasma progesterone and LH concentrations

Injections of 1 mg PGI2 directly into the bovine corpus luteum significantly increased peripheral plasma progesterone concentrations within 5 min. Concentrations were higher in the PGI2-treated heifers than in saline-injected controls between 5 and 150 min and at 3.5, 4, 5, and 7 h post-treatment. Levels tended to remain elevated through 14 h. Saline and 6-keto-PGF1 alpha were without effect on plasma progesterone levels. The luteotrophic effect of PGI2 was not due to alterations in circulating LH concentrations. An in vitro experiment assessed the effects of either PGI2 alone or in combination with LH on progesterone production by dispersed luteal cells. Progesterone accumulation over 2 h for control, 5 ng LH, 1 microgram PGI2, 10 micrograms PGI2, and 10 micrograms PGI2 plus 5 ng LH averaged 99 +/- 42, 353 +/- 70, 152 +/- 35, 252 +/- 45, and 287 +/- 66 ng/ml (n = 4), respectively. Thus PGI2 has luteotrophic effects on the bovine CL both in vivo and in vitro.

Preparation of two dinor-PGI2 metabolites from 6-keto-PGF1 alpha by Mycobacterium rhodochrous

The transformation of 6-keto-PGF1 alpha to two prostacyctin metabolites, 2,3-dinor-6-keto-PGF1 alpha (I) and 2,3-dinor-6,15-diketo-13,14-dihydro-PGF1 alpha (II) by Mycobacterium rhodochrous UC-6176 is described. The finding that the bacterium oxidized 6-keto-PGF1 alpha to the 6,15-diketo metabolite II shows that it contains 15-hydroxy prostaglandin dehydrogenase and delta 13 reductase enzyme systems.

Prostaglandins in the human fetal circulation in mid-trimester and term pregnancy

Concentrations of prostaglandins in fetal and maternal plasma during mid-pregnancy and fetal plasma at term have been measured. Fetal levels at both gestations were higher than found in maternal blood. The stable chemical breakdown product of prostacyclin, 6-keto-prostaglandin F1 alpha, was consistently considerably higher in the fetus during mid-pregnancy compared with at term. Prostaglandin F levels were also significantly higher in mid-pregnancy, though there was no difference in the concentrations of the major circulating prostaglandin F metabolite, PGFM. Concentrations of prostaglandin E were similar at the two stages of pregnancy. The physiological significance of these findings is discussed.

Bronchodilator effects of prostacyclin (PGI2) in dogs and guinea pigs

prostacyclin (PGI2), a recently discovered unstable product in the biosynthetic conversion of prostaglandin endoperoxides, was examined for bronchopulmonary actions. in anesthetized dogs, PGI2 given i.v. (0.3-30.0 microgram/kg) and by aerosol (0.002-0.2%) inhibited significantly PGF2 alpha-induced increases in pulmonary resistance and decreases in dynamic lung compliance in a dose-related fashion. Intrinsically, PGI2 affected resting bronchopulmonary and cardiac functions minimally, but decreased peripheral and pulmonary vascular pressures. PGI2 (0.1-10 mg/kg, i.p.) afforded protection against histamine-induced asphyxial collapse in normal guinea pigs and ovalbumin-induced anaphylaxis in sensitized animals. Cumulative concentrations of PGI2 (1.0 x 10(-9)--3.0 x 10(-4) M) relaxed contractions of the isolated guine pig trachea produced by carbachol. These bronchodilator and hemodynamic effects could not be ascribed to the stable metabolic product of PGI2, because 6-keto-PGF1 alpha was inactive or markedly less active than PGI2 in these test systems. The results of this investigation suggest that PGI2 possesses considerable bronchodilator and vasodilator activity in experimental animal systems.

Identification of the major metabolite of prostacyclin and 6-ketoprostaglandin F1 alpha in man

Human volunteers were infused with 3H- and 2H-labeled prostacyclin or 3H-labeled 6-ketoprostaglandin F1 alpha and, in separate experiments, with the unlabeled prostanoids. The urine was purified by different chromatographic steps and finally separated into several fractions by high-performance liquid chromatography. The major fractions contained 20.5 and 23.0% of the eluted readioactivity for the metabolites of prostacyclin and 6-ketoprostaglandin F1 alpha, respectively. The structure of both metabolites was identified by gas-liquid chromatography-mass spectrometry as dinor-6-ketoprostaglandin F1 alpha. It is concluded that the major metabolite of prostacyclin and 6-ketoprostaglandin F1 alpha in man is dinor-6-ketoprostaglandin F1 alpha.

Synthesis of thromboxane B2 and 6-keto-prostaglandin F1 alpha by bovine gastric mucosal and muscle microsomes

Bovine gastric mucosal and muscle microsomes synthesize prostaglandins and thromboxane b/ (TXB2) from aratchidonic acid (AA). TXB2 and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were the majro products synthesized by pylorus, body, and cardiac region of the gastric mucosa. Gastric muscle mainly synthesized 6-keto-PGF1 alpha. TXB2 and 6-keto-PGF1 alpha synthesis occurs at an appreciable rate from endogenous precursors but more rapidly with added arachidonate. Prostaglandins E2, F2 alpha and D2 were synthesized in smaller amounts under the conditions studied.

Differential production of PGF and 6-keto-PGF1 alpha by the rat endometrium and myometrium in response to oxytocin, catecholamines and calcium ionophore

Uterine horns for castrated, estrogen-treated rats wee superfused for 6 hours in 95% O2/5% CO2 at 37 degrees C. The method of superfusion in which medium flows separately over the inner and outer surfaces of the horn allows prostaglandin synthesis in the myometrium and endometrium to be measured independently while their anatomical relationship is undisturbed. Prostaglandins were measured by radioimmunoassay. They myometrium formed more 6-keto-PGF1 alpha than PGF whereas the opposite was true of the endometrium. Production rates of TxB2 in both tissues were relatively low. The addition of inophore A-23187, oxytocin or phenylephrine to the superfusion medium not only increased the myometrial production rates of both 6-keto-PGF1 alpha and PGF but also increased the ratio of 6-keto-PGF1 alpha:PGF. Neither ionophore nor phenylephrine affected the rate of prostaglandin synthesis in the endometrium whereas oxytocin caused a significant increase in the production rate of PGF. We conclude that the large amounts of 6-keto-PGF1 alpha in the myometrial superfusate probably originate in both the smooth-muscle cells of the myometrium and the endothelium of the myometrial blood vessels. The differential responses to ionophore A-23187, phenylephrine and oxytocin suggest differences in the mode of their regulation of prostaglandin synthesis.

Prostaglandins and prostaglandin metabolites in human gastric juice

Human gastric juice contains higher concentrations of PG metabolites than of unmetabolized PG indicating that local metabolism might play a role in limiting the biological activity of PG in gastric mucosa and has to be considered when investigating endogenous gastric PG. A major fraction of the 15-keto-13,14-dihydro-PGE2 (KH2PGE2) formed in gastric mucosa and released into the gastric lumen seems to be rapidly dehydrated to a compound co-chromatographing with KH2PGA2, while the amounts of the bicyclic degradation product 11-deoxy-13,14-dihydro-15-keto-11,16-cyclo-PGE2 (11-deoxy-KH2-cyclo-PGE2), as measured by radioimmunoassay, in freshly extracted gastric juice are negligible. Stimulation of secretion with pentagastrin does not influence significantly the concentrations of PG and PG metabolites in human gastric juice, but total output tends to increase parallel to the increase in secretion volume. Levels of immunoreactive 6-keto-PGF1 alpha in human gastric juice are much lower than those of PGE2. Since human gastric mucosa synthesizes conciderable amounts of PGI2 and 6-keto-PGF1 alpha in vitro, the low levels of 6-keto-PGF1 alpha in gastric juice might indicate that PGI2 formed by gastric mucosa in vivo is, like PGE2 and PGF2 alpha, rapidly metabolized and/or removed preferentially via the blood stream.

Prostaglandin I2 synthesis and elevation of cyclic AMP levels in 3T3 fibroblasts

Arachidonic acid and prostaglandin H2 elevate the levels of adenosine 3':5'-monophosphate (cyclic AMP) in Balb/c 3T3 fibroblasts. This effect was inhibited by 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid, an inhibitor of prostaglandin I2 synthase (Claesson, H.-E., Lindgren, J.A. and Hammarstr!om, S. (1977) FEBS Lett. 81, 415-418). After addition of arachidonic acid to 3T3 cultures, cellular cyclic AMP levels and growth medium concentrations of 6-ketoprostaglandin F1 alpha (degradation product of prostaglandin I2) were quantitatively determined. The stimulatory effect of exogenously-added prostaglandin I2 on cellular cyclic AMP levels was also determined. The results indicate that the endogenous production of prostaglandin I2 is sufficient to explain the stimulatory action of arachidonic acid on cyclic AMP formation in 3T3 fibroblasts.

Lidocaine increases prostacyclin in the rat

In the rat, the effect of intravenous lidocaine was evaluated on plasma prostacyclin concentration as well as the concentration of prostacyclin in aortic ring incubation chambers and in the effluent of isolated perfused lungs. Prostacyclin was assayed using a radioimmunoassay for its stable product 6-Keto PGF1 alpha. Lidocaine in therapeutic doses (2 mg/kg) will significantly increase 6-Keto PGF1 alpha in plasma as well as in aortic ring incubation chambers and in the effluent of isolated perfused lungs when compared to saline treated controls.

The differential inhibition of prostaglandin synthesis in platelets and vascular tissue in response to aspirin

Since aspirin inhibits the platelet as well as vascular prostaglandin synthesis it may therefore, paradoxically induce a thrombotic tendency when used as an antithrombotic agent. The in vivo effect of therapeutic doses of aspirin on the prostaglandin synthetic capacity of the rat platelets and vascular tissue was therefore studied to determine the significance of this paradoxical aspirin effect. A single aspirin dose of 5 mg/kg or greater was found to significantly decrease the synthesis of prostaglandin E by rat platelets. Even the normal augmentation of PGE synthesis by N-ethyl maleimide was significantly reduced by this single aspirin dose. In contrast, doses as high as 20 mg/kg of aspirin failed to reduce the production of 6-keto PGF1 alpha by aortic slices from rats pretreated with aspirin. These results indicate that the cyclo-oxygenase enzyme (CO) system in the prostaglandin biosynthetic pathway within blood vessel walls has the capacity to recover from this inhibitory effect of aspirin or it is less susceptible to inhibition than the CO in platelets. This relative resistance of CO to the inhibitory effects of aspirin may serve to protect the organism from excessive thrombotic tendencies brought about by the effect of aspirin on the vascular prostaglandin generating system. These results indicate that an aspirin dose of 5-10 mg/kg would be optimal if aspirin were to be used as an antithrombotic agent.

Prostaglandin synthetase activity in vascular tissue of male and female rats

1. Isolated perfused lungs from mature male rats show greater conversion of 14C Arachidonic Acid to cyclo-oxygenase products than females. 2. Following unlabelled arachidonate infusion, the male lungs release more 6-K-PGF1 alpha and TxB2 than females. 3. Aortic rings from male rats release more PGI2-like material and 6-K-PGF1 alpha than the females. 4. These data indicate an elevated PG synthetase activity in male rats as compared with females.

Conversions of prostaglandin endoperoxides by prostacyclin synthase from pig aorta

Partially purified prostacyclin synthase from pig aorta converted the prostaglandin (PG) endoperoxide PGH2 to prostacyclin (PGI2), and PGH1 to 12-hydroxy-8,10-heptadecadienoic acid (HHD). Both reactions were inhibited by 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HP) in a dose-dependent rashion. However, the reactions PGH2 leads to PGI2 and PGH1 leads to HHD appeared to differ: substrate availability was rate limiting in the latter reaction, while the enzyme became rapidly saturated witth PGH2 and a steady rate of prostacyclin formation was observed at higher substrate levels.

Radioimmunological assay of prostacyclin synthetase activity

A radioimmunoassay for 6-oxoprostaglandin F1 alpha has been developed. 6-Oxoprostaglandin F1 alpha antiplasma was produced in rabbits by repeated immunization with 6-oxoprostaglandin F1 alpha coupled to bovine serum albumin. [125I] -labelled hapten with high specific radioactivity was prepared by radioiodination of 6-oxoprostaglandin F1 alpha-tyrosine methyl ester conjugate followed by purification with thin layer chromatography. The antibodies showed good specificity toward 6-oxoprostaglandin F1 alpha and crossreacted only significantly with prostaglandin F1 alpha. The radioimmunoassay was applied to the determination of prostacyclin synthetase activity in swine aorta microsomes using arachidonic acid and prostaglandin H2 as indirect and direct substrates. The enzyme assay was validated by the criteria that the formation of 6-oxoprostaglandin F1 alpha, immunoreactivity from either substrates was both time and enzyme protein dependent, and was inhibitable by specific inhibitors of the enzyme system.

Human plasma transforms prostacyclin (PGI2) into a platelet antiaggregatory substance which contracts isolated bovine coronary arteries

Prostacyclin (PGI2) incubated in Human Platelet Rich Plasma (PRP); in Platelet Poor Plasma (PPP) or in Krebs-Ringer-Bicarbonate (KRB) during different periods of time on contractions of bovine coronary arteries and on the ADP platelet aggregative capacity of human PRP, were explored. It was documented that incubates in PRP or in PPP retain an antiaggregatory activity at higher levels and during a longer time than in KRB. On the other hand, PGI2 incubates in KRB exhibited only a relaxing activity on isolated bovine coronary arteries, whereas when incubated in PRP or in PPP presented a biphasic influence. The initial effects (evoked by incubates of 30 minutes) were distinctly relaxing but those obtained with later incubates (60--150 minutes) stimulated clearly the resting basal tone of the arteries. The possibility that the human plasma might have an enzyme(s) able to transform prostacyclin into a more stable material with human antiaggregatory platelet function and bovine coronary contracting capacity is discussed.

Production of 6-oxo-prostaglandin F1 alpha, PGF2 alpha and PGE2 by sheep uterine tissue

Incubation in vitro of sheep uterine tissue revealed that although both caruncular and non-carunuclar endometrium can synthesize appreciabel quantities of PGF2 alpha, PGE2 and 6-oxo-PGF2 alpha, the myometrium synthesizes predominantly 6-oxo-PGF1 alpha. Non-caruncular endometrium contained more 6-oxo-PGF1 alpha than either the myometrium or the caruncles, while myometrial tissue possessed less PGF2 alpha than either caruncular or non-caruncular endometrium.

Blood levels of 6-oxo-prostaglandin F 1 alpha during endotoxin-induced hypotension in rabbits

Levels of 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha), the non-enzymic degradation product of prostacyclin, were measured in arterial blood from anaesthetized rabbits, before and after intravenous (i.v.) administration of endotoxin (Lipopolysaccharine W E. coli 0111:B4, 5 mg/kg). 6-Oxo-PGF1 alpha was assessed by radioimmunoassay after extraction and separation by thin-layer chromatography. The basal concentration of 6-oxo-PGF1 alpha in blood was less than 100 mg/ml in 19 out of 20 rabbits. This indicates that the level of circulating prostacyclin is generally below 100 pg/ml. The administration of endotoxin induced a biphasic hypotension, and increased levels of 6-oxo-PGF1 alpha were found in all endotoxin-treated animals during the secondary hypotension after 60 and 120 min. Pretreatment with indomethacin (2.5 mg/kg) prevented the secondary fall in arterial blood pressure and significantly suppressed the rise in 6-oxo-PGF1 alpha. However, indomethacin failed to alter the endotoxin-induced thrombocytopenia and did not modify the endotoxin-induced platelet aggregation in vitro. It is concluded that prostacyclin contributed to the secondary hypotension which accompanied the i.v. administration of endotoxin. Thromboxane A2 seems not to be of primary importance in the endotoxin-platelet interaction.

Production rates of prostaglandin F, 6-keto-PGF1 alpha and thromboxane B2 by perifused human endometrium

Human endometrium obtained from fresh hysterectomy specimens was perifused for 7 hr in 95% O2/5% CO2 at 37 degrees C. The phase of the menstrual cycle was determined by histological examination. The concentrations of PGF, 6-keto-PGF1 alpha and TxB2 in 20 min fractions of the perifusion medium were measured by radioimmunoassay and production rates were calculated in terms of dry weight of tissue. Biphasic patterns of production were observed; high initial values fell to about 20% at 2 hr and then increased to relatively stable values at about 4 hr which were maintained for the next 2 hr. During this latter period, production rates in endometria taken at different phases of the cycle differed markedly from each other; the production rates of PGF in secretory and early proliferative endometria were low (15.8 +/- 2.6, mean +/- SEM and 67.2 +/- 8.3 ng/min/g respectively) whereas they were high in late proliferative and premenstrual endometria (188.0 +/- 16.7 and 196.4 +/- 16.9 ng/min/g respectively). The patterns of production of 6-keto-PGF1 alpha and TxB2 were similar to those of PGF but the absolute values were much lower (less than 10%). We conclude that the observed rates of production of prostaglandins by perifused human endometrium are consistent with synthesis being stimulated either by estrogen or withdrawal of hormonal support and being inhibited by progesterone.

Inhibition of vasoconstrictor responses by 6-keto-PGE1 in the feline mesenteric vascular bed

The effects of 6-keto-PGE1 on vascular resistance and vascular responses to sympathetic nerve stimulation and vasoconstrictor hormones were investigated in the feline mesenteric vascular bed. Infusions of 6-keto-PGE1 into the superior mesenteric artery dilated the mesenteric vascular bed and markedly inhibited vasoconstrictor responses to sympathetic nerve stimulation, norepinephrine and angiotensin II. The effects of 6-keto-PGE1 and PGE1 on vascular resistance and vasoconstrictor responses were quite similar and both substances inhibited responses to nerve stimulation and pressor hormones in a reversible manner. Responses to nerve stimulation, norepinephrine and angiotensin II were inhibited to a similar extent during infusion of 6-keto-PGE1 and PGE1. Results of these studies suggest that 6-keto-PGE1, a newly identified prostaglandin metabolite, and PGE1 possess the ability to inhibit the vasoconstrictor effects of sympathetic nerve stimulation and pressor hormones by a non-specific action on vascular smooth muscle in the feline small intestine.

A radioimmunoassay for 6-keto-prostaglandin F1 alpha utilizing an antiserum against 6-methoxime-prostaglandin F1 alpha. Application to study renal in vitro synthesis of prostacyclin

PGI2 and 6-keto-PGF1 alpha were converted to 6-methoxime-PGF1 alpha (6-MeON-PGF1 alpha) by treatment with methoxyamine HCl in acetate buffer. The formed 6-MeON-PGF1 alpha was measured by radioimmunoassay. Antisera were raised in rabbits after immunization against 6-MeON-PGF1 alpha-BSA conjugate. Diluted 1:20.000 to bind 50% of the tracer (3H-6-MeON-PGF1 alpha, 100 Ci/mmol), the antiserum cross reacted 0.8% with PGE2, 1% with PGF2 alpha and less than 0.2% with PGD2, PGF1 alpha, PGF2 beta and TXB2. The radioimmunoassay was used to estimate release of PGI2 and 6-keto-PGF1 alpha from chopped rabbit renal medulla and cortex incubated in Krebs-Ringer bicarbonate buffer (37 degrees C, 30 min). The 6-keto-PGF1 alpha radioimmunoassay was validated in biological samples by mass fragmentography. The chopped medulla (n = 5) released 38-+9 ng/g/min and the cortex (n = 5) 4.7-+2-0 ng/g/min, while the release of immunoreactive PGE2 (iPGE2) and iPGF2 alpha was 171-+26 and 74-+13 ng/g/min from the medulla and 4.3-+1.3 and 2.7-+0.3 ng/g/min from the cortex, respectively. The results confirm previous findings, which indicate that in the renal medulla prostaglandin endoperoxides are mainly transformed to prostaglandins, while in the cortex transformation to PGI2 seems to be of greater relative importance.

Correction of increased prostacyclin synthesis in Bartter's syndrome by indomethacin treatment

The role of prostacyclin and thromboxane A2 in the pathogenesis of Bartter's syndrome was investigated by measurement of the urinary excretion of 6-keto-PGF1 alpha and thromboxane B2, respectively, in five patients. The prostaglandin metabolites were extracted from urine by a reproducible method and measured by specific radioimmunoassays. The patients with Bartter's syndrome excreted about four-times as much 6-keto-PGF1 alpha as the normal controls. In contrast, there was no significant difference in the urinary excretion of thromboxane B2 between the patients and the controls. In a second part of the study, three patients were treated with indomethacin (150 mg/day for four days), an inhibitor of prostaglandin synthesis. This regimen suppressed urinary excretion of 6-keto-PGF1 alpha by 43% and that of thromboxane B2 by 46%. It is suggested that the increase in prostacyclin production is responsible for both the hyperreninemia and and the other endocrine derangements as well as the hyporesponsiveness of blood pressure to intravenous infusion of vasopressors in patients with Bartter's syndrome.

Prostaglandin profiles in nervous tissue and blood vessels of the brain of various animals

The endogenous formation of prostaglandin (PG) D2, E2, F2 alpha, and 6-keto-PGF1 alpha was determined in homogenates of mouse, rat, and rabbit brain, and of rat cerebral blood vessels, using gas chromatography mass spectrometry. In all species tested, 6-keto-PGF1 alpha could be identified in the brain homogenates, but was a minor component in relation to other PGs. In contrast 6-keto-PGF1 alpha was the most abundant PG in the blood vessels, being present in about 40-fold higher levels than in the brain tissue. PGD2 was the most abundant PG in rat and mouse brains, but was below detection limits in the analyzed blood vessels. These studies indicating differential metabolism of PG endoperoxides in nervous and vascular tissue, provide a biochemical basis for further studies on the role of the PGs in brain circulation and neuronal activity.

Evidence for 6-keto-PGF1 alpha in adrenal cortex of the rat and effects of 6-keto-PGF1 alpha and PGI2 on adrenal cAMP levels and steroidogenesis

Both intact cortical tissue and isolated cortical cells from the adrenal gland of the rat were analyzed for 6-keto-PGF1 alpha, the hydrolysis metabolite of PGI2, using high-performance liquid chromatography and gas chromatography-mass spectrometry. 6-Keto-PGF1 alpha was present in both incubations of intact tissue and isolated cells of the adrenal cortex, at higher concentrations than either PGF2 alpha or PGE2. Thus, the cortex does not depend upon vascular components for the synthesis of the PGI2 metabolite. Studies in vitro, using isolated cortical cells exposed to 6-keto-PGF1 alpha (10(-6)-10(-4)M), show that this PG does not alter cAMP levels or steroidogenesis. Cells exposed to PGI2 (10(-6)-10(-4)M), however, show a concentration-dependent increase of up to 4-fold in the levels of cAMP without altering cortico-sterone production, ACTH (5-200 microU/ml) increased cAMP levels up to 14-fold, and corticosterone levels up to 6-fold, in isolated cells. ACTH plus PGI2 produced an additive increase in levels of cAMP, however, the steroidogenic response was equal to that elicited by ACTH alone. Adrenal glands of the rat perfused in situ with PGI2 showed a small decrease in corticosterone production, whereas ACTH greatly stimulated steroid release. Thus, while 6-keto-PGF1 alpha is present in the rat adrenal cortex, its precursor, PGI2, is not a steroidogenic agent in this tissue although it does stimulate the accumulation of cAMP.

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.