Metabolism of prostacyclin in rat.

Following a single intravenous administration of [11-3H]prostacyclin in rat, 77% of the administered dose was excreted within 3 days with 33% in urine and 44% in feces. Urinary metabolites were accumulated by chronic intravenous infusions of [11-3H]prostacyclin for 14 days. The drug was extensively metabolized and the structures of seven metabolites were elucidated by combined gas chromatography and mass spectrometry. The urinary products include the dinor and 19-hydroxy dinor derivatives of 6-keto-PGF1alpha and 13,14-dihydro-6,15-diketo-PGF1alpha, omega-hydroxy and omega-carboxyl dinor derivates of dihydro-6,15-diketo-PGF1alpha, and a dihydrodiketotetranordicarboxylic acid. The metabolic pathways of PGI2 in rat are similar to that of PGF2alpha.     

Metabolism of prostacyclin in the rabbit kidney.

In the isolated rabbit kidney perfused with Tyrode's solution, we examined the metabolism of radiolabeled prostacyclin. [9-3H]Prostacyclin was infused into the kidney and the radiolabeled products from the renal venous effluent were separated by thin layer chromatography and identified by gas chromatography-mass spectrometry. The major products were 7,9-dihydroxy-4,13-diketo-dinor-prostanoic acid and dinor-6-keto-prostaglandin F1alpha. They represented 25% and 10% of the total radioactivity, respectively. Metabolism of prostacyclin by the kidney may be an important determinant of the effects of prostacyclin on renal function.     

Metabolism of prostacyclin in cynomolgus monkey

The metabolism of prostacyclin (PGI₂) $\text{in vivo}$ 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-PGF_1α, 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-PGF_1α indicated that the monkey was not able to metabolize PGI₂ as avidly as the rat.     

Potassium and blood vessels.

Intraarterial infusion of potassium causes vasodilation whereas reduction of the potassium concentration in the inflowing blood causes vasoconstriction. These responses have always been puzzling since the predicted effects from the Nernst equation are just the reverse. Recent evidence suggests that they result form effects on the activity of sarcolemmal Na, K ATPase in the vascular smooth muscle cell which influence the electrogenic NaK pump. The possible relevance of these findings is discussed.     

Metabolism of prostacyclin. Oxidation by rhesus monkey lung 15-hydroxyl prostaglandin dehydrogenase.

Partially purified rhesus monkey lung 15-hydroxyl prostaglandin dehydrogenase (15-OH PGDH) catalyzed the NAD-dependent oxidation of prostacyclin (PGI₂) and 6-keto-PGF_1a to 6,15-diketo-PGF_1a. The product was identified by gas chromatography-mass spectroscopy. Prostacyclin was oxidized four to six times faster than 6-keto-PGF_1a under identical reaction conditions, suggesting that the metabolism of prostacyclin probably proceeds through a bicyclic 15-keto intermediate before chemically decomposing to the final stable product, 6,15-diketo-PGF_1a. Prostacyclin has a good affinity for the 15-OH PGDH enzyme. A Lineweaver-Burke plot gave an apparent K_m value of 7.4 μm, which compares very favorably with the K_m values for PGE₁ and PGE₂.     

Metabolism of linoleic acid by prostaglandin endoperoxide synthase from adult and fetal blood vessels

Linoleic acid (18:2) is converted by prostaglandin endoperoxide synthase in particulate fractions and homogenates of fetal calf aorta to its 9- and 13-hydroperoxy metabolites. These intermediates are then either dehydrated to the corresponding oxo compounds or reduced to monohydroxy products. Alternatively, the hydroperoxyoctadecadienoic acids can be converted to epoxyhydroxyoctadecenoic acids, which are hydrolyzed to trihydroxy metabolites by epoxide hydrolases present in both particulate and cytosolic fractions from aorta. Linoleic acid (Km, 442 microM) is a much poorer substrate for prostaglandin endoperoxide synthase than is arachidonic acid (20:4) (Km, 48 microM). However, the oxygenation of 18:2 by particulate fractions from aorta is linear with time for at least 5 min, whereas the oxygenation of 20:4 is linear for only 15 s. Arachidonic acid strongly inhibits the conversion of 18:2 to monohydroxy (ID50, 10 microM) and trihydroxy (ID50, 140 microM) products. Linoleic acid has a similar, but much weaker effect on the formation of 6-oxoprostaglandin F1 alpha from 20:4. Substantial amounts of both the monohydroxy (9-hydroxy-10, 12-octadecadienoic acid and 13-hydroxy-9,11-octadecadienoic acid) and trihydroxy (9,10,11-trihydroxy-12-octadecenoic acid, 9,10,13-trihydroxy-11-octadecenoic acid and 9,12,13-trihydroxy-10-octadecenoic acid) metabolites of 18:2 were shown by gas chromatography-mass spectrometry to be formed from endogenous substrate during incubation of slices of fetal calf aorta in physiological medium. This raises the possibility that some of these products or their hydroperoxy precursors may have some biological significance.     

PGI2 production by rat blood vessels: Diminished prostacyclin formation in veins compared to arteries

Homogenates of eleven different blood vessels from normal Sprague-Dawley rats varied in their ability to produce PGI₂ (i.e., 6-keto-PGF_1α) from [1−¹⁴C]PGH₂. The most notable difference was seen between arteries and veins. Arterial tissues produced more 6-keto-PGF_1α from exogenous PGH₂ than veins at all enzyme (i.e., protein) concentrations tested. Similar results were obtained utilizing different homogenization techniques or arterial and venous rings, indicating this difference was real and not due to homogenization artifacts. In addition, the thoracic segment of the inferior vena cava was more active in converting added [1−¹⁴C]PGH₂ to 6-keto-PGF_1α than the abdominal segment of added inferior vena cava suggestive of a possible segmental distribution of the enzyme activity in blood vessels. These results may be interpreted as indicating that PGI₂ may have a vasomotor function for blood vessels in addition to its proposed antithrombotic role.     

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.     

Isolation of prostacyclin from whole blood

A method was developed for the isolation of prostacyclin (PGI₂) from whole blood in a fraction suitable for high pressure liquid chromatography (HPLC) separation of PGI₂ and 6-keto-prostaglandin F_1α (6-K-PGF_1α). Prostacyclin was stabilized in whole blood by rapidly raising the pH to 10 with Na₂CO₃ and cooling the samples to 0°C. Under these conditions, 2.9% hydrolysis was observed after 20 min. Reverse phase extraction columns were used to directly extract both PGI₂ and 6-K-PGF_1α from the alkaline plasma with recoveries of greater than 95% using an acetonitrile/2mM Na₂B₄O₇, pH 10, elution solvent mixture. An additional 1.7% hydrolysis was found during the column extraction procedure. Final separation of PGI₂ and 6-K-PGF_1α was performed with HPLC using an alkaline solvent system. This method is capable of rapidly and efficiently extracting and separating PGI₂ and 6-K-PGF_1α from whole blood or plasma. It introduces less than 5% hydrolysis of PGI₂, thus providing a means of applying highly sensitive 6-K-PGF_1α assays to the determination of PGI₂ levels in physiological samples.     

Adrenergic innervation of human mesenteric blood vessels.

A fluorescent histochemical technique has been applied to study the adrenergic innervation of human superior mesenteric arteries obtained at autopsy. Specific catecholamine fluorescence was demonstrated in the smaller branches of this artery taken from three infants and one child. No specific fluorescence was seen in arteries from three adult subjects.     

LUMENating blood vessels

The acquisition of a lumen is an essential step in vascular morphogenesis. In this issue of Developmental Cell, Xu et?al. (2011) show that the small GTPase Rasip is a critical regulator of cytoskeleton dynamics and cell adhesion, which together drive the emergence of vascular lumens.     

Nitric oxide as a signal in blood vessels.

In the five years since the discovery that nitric oxide is produced as a signal in blood vessels, a great deal has been discovered about the processes involved. This article reviews current knowledge about the vascular cell synthesis, effects and subsequent destruction of this messenger molecule.     

Effect of prostacyclin on the cerebral vessels and its pharmacological modification

The ability of prostacyclin to relax human brain arteries contracted by different vasotropic agents has been investigated. Prostacyclin relaxation effect was less marked in atherosclerotically damaged vessels. Nifedipine was demonstrated to potentiate relaxation effect of prostacyclin at the level of sarcolemmal calcium transport, while cavinton and dipyridamole had an analogous influence, redistributing calcium in the intracellular stores. The potentiating effect of these drugs was also less pronounced in affected vessels, which might be connected to the depression of transport ATPase activity in the vascular smooth muscle cells.     

Superficial anastomoses of blood vessels in the human heart.

We investigated superficial interarterial, intra-arterial, arterio-venous and veno-venous anastomoses in 100 hearts from men and women taken at random who died at 20-85 years of age. By means of careful dissection and injection into the blood vessels of a differently stained 12% solution of vinilit in acetone, we studied the number and localization of the anastomoses and their appearance. Interarterial anastomoses, i.e. anastomoses between the ramification of the left and the right coronary artery, were detected in 33 hearts. Intra-arterial anastomoses, i.e. anastomoses between the ramifications of one and the same artery, were seen in 5 hearts. Arterio-venous anastomoses were found in 39 hearts. Veno-venous anostomoses were found in 49 hearts. The veno-venous anastomoses display a great many variations, being commonly the regular finding in human veins.     

Maternal cigarette smoking increases F2-isoprostanes and reduces prostacyclin and nitric oxide in umbilical vessels.

The objective of this study was to evaluate the influence of smoking on F2-isoprostanes, prostacylin and nitric oxide in human umbilical vessels. Umbilical cords from 13 babies of smoking mothers and from 28 babies of non-smoking mothers were examined for levels of F2-isoprostanes, prostacyclin, L-arginine, and L-citrulline. Forty-one umbilical arteries and eleven umbilical veins were analyzed. Statistical analysis of data was done using modified t-test. Cigarette smoking increased F2-isoprostane levels and reduced the generation of prostacyclin, L-arginine and L-citrulline comparably in umbilical arteries and veins. Notably, in umbilical cords of babies of non-smoking mothers the F2-isoprostane level was significantly higher in arteries. Cigarette smoking correlates with a direct vasoconstrictive effect. We suggest that smoking might enhance the vasoconstrictory capacity in umbilical arteries by increased F2-isoprostanes and by a simultaneous decrease in the production of the vasodilatory compounds, prostacyclin, and nitric oxide.