The effect of prostacyclin on the human umbilical artery

Prostacyclin was tested on human umbilical artery obtained after spontaneous delivery or by Cesarean section. Isometric and isotonic responses were measured on spiral preparations in Krebs-bicarbonate buffer at 37°C equilibrated with 95% O₂ and 5% CO₂. Spiral artery strips, whether superfused or mounted in organ baths isometrically or isotonically, responded in a dose-dependent manner to both prostacyclin and serotonin; the PGI₂ response was biphasic in that low doses (2.5 × 10^-8 M - 1.0 × 10^-6 M) elicited a dose-dependent relaxation which changed with higher concentrations (1.0 × 10^-6 M - 2.53 × 10⁵ M) to a contractile response. The maximum tension exerte was 50% less than that elicited by serotonin. The data indicate that the human umbilical artery is responsive to prostacyclin and may be involved in the regulation of fetal placenta blood flow.     

The effect of prostacyclin on the human umbilical artery.

Prostacyclin was tested on human umbilical artery obtained after spontaneous delivery or by Cesarean section. Isometric and isotonic responses were measured on spiral preparations in Krebs-bicarbonate buffer at 37 degrees C equilibrated with 95% O2 and 5% CO2. Spiral artery strips, whether superfused or mounted in organ baths isometrically or isotonically, responded in a dose-dependent manner to both prostacyclin and serotonin; the PGI2 response was biphasic in that low doses (2.5 x 10(-8) M -1.0 x 10(-6) M) elicited a dose-dependent relaxation which changed with higher concentrations (1.0 x 10(-6) M -2.53 X 10(-5) M) to a contractile response. The maximum tension exerted was 50% less than that elicited by serotonin. The data indicate that the human umbilical artery is responsive to prostacyclin and may be involved in the regulation of fetal placenta blood flow.     

Human recombinant lipocortin 1 inhibits prostacyclin production by human umbilical artery

Submicromolar concentrations of human recombinant Lipocortin 1 inhibit the release of prostacycin from human umbilical artery rings in a dose-dependent fashion. This is the first demonstration that the recombinant protein is effective in human cells.     

Human recombinant lipocortin 1 inhibits prostacyclin production by human umbilical artery in vitro

Submicromolar concentrations of human recombinant Lipocortin 1 inhibit the release of prostacyclin from human umbilical artery rings in a dose-dependent fashion. This is the first demonstration that the recombinant protein is effective in human cells.     

Macromolecules mediate prostacyclin release from human umbilical artery

Previous reports regarding the modulation of prostaglandin release from tissues by serum components did not identify these components. We have found that inhibition of prostacyclin release from human umbilical artery by human serum is attributable to serum macromolecules. We demonstrate that such inhibitory activity depends on macromolecular size and may result from macromolecule/cell surface interactions.     

Effect of ethanol on thromboxane and prostacyclin synthesis by fetal platelets and umbilical artery

The effect of ethanol (10-500 mmol/l) on platelet thromboxane production and on vascular thromboxane and prostacyclin was studied in human fetal tissues. The release of thromboxane B2 (a metabolite of thromboxane A2) during thrombin-induced spontaneous aggregation of fetal platelets was inhibited by ethanol concentrations of 50 mmol/l or higher. Ethanol at concentration from 100 mmol/l also inhibited umbilical artery production of thromboxane B2 and that of 6-keto-prostaglandin F1 alpha (a metabolite of prostacyclin). However, it stimulated the conversion of exogenous arachidonic acid to thromboxane B2 in fetal platelets and to 6-keto-prostaglandin F1 alpha in the umbilical artery. This suggests that ethanol inhibits phospholipase A2, but stimulates the enzymes distal from phospholipase A2 in the prostaglandin-synthesizing enzyme cascade.     

Cocaine: its use in otolaryngology

A review of 120 patients who had a discharge diagnosis of intermediate coronary syndrome showed 12 patients with documented transient ST elevation during spontaneous rest pain consistent with Prinzmetal''s angina. Coronary arteriography showed severe proximal occlusive coronary atherosclerosis in nine of the patients, and normal or minimal disease in the other three patients. In two of these three, there was documented coronary arterial spasm with reproduction of symptoms during arteriography. Although a shorter history of chest pain, presence of an old myocardial infarction and a positive finding on electrocardiogram treadmill test tended to predict the patients with severe occlusive coronary artery disease, these methods were inadequate to select candidates for arteriography. All patients responded well to nitroglycerine while in the hospital. Five of the nine patients with coronary artery disease had coronary bypass operations, with two excellent, two fair and one poor result. One of the three patients with normal findings on coronary arteriograms died with refractory ventricular arrhythmia six months after study. The other two have had good-to-moderate relief of symptoms on long-acting vasodilators and propranolol. Current concepts of the syndrome of Prinzmetal''s angina and ST elevation are reviewed. It appears that this syndrome has a wide spectrum of clinical presentations and coronary arteriographic anatomies.     

Acyl chain-dependent effect of lysophosphatidylcholine on endothelial prostacyclin production

Previously we identified palmitoyl-lysophosphatidylcholine (16:0 LPC), linoleoyl-LPC (18:2 LPC), arachidonoyl-LPC (20:4 LPC), and oleoyl-LPC (18:1 LPC) as the most prominent LPC species generated by the action of endothelial lipase (EL) on high-density lipoprotein. In the present study, the impact of those LPC on prostacyclin (PGI₂) production was examined in vitro in primary human aortic endothelial cells (HAEC) and in vivo in mice. Although 18:2 LPC was inactive, 16:0, 18:1, and 20:4 LPC induced PGI₂ production in HAEC by 1.4-, 3-, and 8.3-fold, respectively. LPC-elicited 6-keto PGF1α formation depended on both cyclooxygenase (COX)-1 and COX-2 and on the activity of cytosolic phospholipase type IVA (cPLA2). The LPC-induced, cPLA2-dependent ¹⁴C-arachidonic acid (AA) release was increased 4.5-fold with 16:0, 2-fold with 18:1, and 2.7-fold with 20:4 LPC, respectively, and related to the ability of LPC to increase cytosolic Ca²⁺ concentration. In vivo, LPC increased 6-keto PGF_1α concentration in mouse plasma with a similar order of potency as found in HAEC. Our results indicate that the tested LPC species are capable of eliciting production of PGI₂, whereby the efficacy and the relative contribution of underlying mechanisms are strongly related to acyl-chain length and degree of saturation.     

Comparison of umbilical vein models for measurement of relative prostacyclin and thromboxane production

There is growing evidence that blood vessels generate TXA₂ in addition to PGI₂. We examined effluents from continously perfused human umbilical vein and supernatants from umbilical vein rings for TXB₂ and 6-keto-PGF_1α measurements (stable metabolites of TXA₂ and PGI₂, respectively). TXB₂ and 6-keto-PGF_1α were identified in all samples. 6-keto-PGF_1α to TXB₂ ratio was higher in intact vein effluents than in the venous ring supernatants (112:1 and 28:1, respectively, P<0.01). Arachidonate stimulation increased 6-keto-PGF_1α and TXB₂ levels similarly in the intact vein effluent. In contrast, stimulation of the venous rings resulted in a relatively larger increase in TXB₂ than in 6-keto-PGF_1α. This caused 6-keto-PGF_1α to TXB₂ ratio to decline (p<0.01). The identity of TXB₂ was confirmed in several different ways. These data suggest that 1) human umbilical veins produce TXA₂ in addition to PGI₂, 2) TXA₂ release is more by venous rings than by the intact vein probably reflecting contribution from non-endothelial layers, and 3) arachidonate stimulation causes relatively greater release of TXA₂ than of PGI₂ from the venous rings, whereas release of PGI₂ and TXA₂ is similar from the intact vein.     

Effect of hypoxia on prostacyclin production in cultured pulmonary artery endothelium

Exposure of cultured bovine pulmonary artery endothelial cells to varying levels of hypoxia (10% or 0% O2) for 4 hours resulted in a significant dose-dependent inhibition in endothelial prostacyclin synthesis (51% and 98%, at the 10% and 0% O2 levels respectively, p less than 0.05, compared to 21% O2 exposure values). Release of 3H-arachidonic acid from cellular pools was not altered by hypoxia. Some of the cells were incubated with arachidonic acid (20 microM for 5 min) or PGH2 (4 microM for 2 min) immediately after exposure. Endothelium exposed to 0% O2, but not to 10% O2, produced significantly less prostacyclin after addition of either arachidonic acid (25 +/- 5% of 21% O2 exposure values, n = 6, p less than 0.01) or PGH2 (31 +/- 3% of 21% O2 exposure values, n = 6, p less than 0.05). These results suggest that hypoxia inhibits cyclooxygenase at the 10% O2 level and both cyclooxygenase and prostacyclin synthetase enzymes at the 0% O2 exposure levels. Exposure of aortic endothelial cells resulted in a 44% inhibition of prostacyclin at the 0% exposure level. No significant alteration in prostacyclin production was found in pulmonary vascular smooth muscle cells exposed to hypoxia. These data suggest that the increased prostacyclin production reported in lungs exposed to hypoxia is not due to a direct effect of hypoxia on the main prostacyclin producing cells of the pulmonary circulation.     

Effect of hypoxia on prostacyclin production in cultured pulmonary artery endothelium

Exposure of cultured bovine pulmonary artery endothelial cells to varying levels of hypoxia (10% or 0% O₂) for 4 hours resulted in a significant dose-dependent inhibition in endothelial prostacyclin synthesis (51% and 98%, at the 10% and 0% O₂ levels respectively, p <0.05, compared to 21% O₂ exposure values). Release of ³H-arachidonic acid from cellular pools was not altered by hypoxia. Some of the cells were incubated with arachidonic acid (20 μM for 5 min) or PGH₂ (4 μM for 2 min) immediately after exposure. Endothelium exposed to 0% O₂, but not to 10% O₂, produced significantly less prostacyclin after addition of either arachidonic acid (25 ± 5% of 21% O₂ exposure values, n=6, p <0.01) or PGH₂ (31 ± 3% of 21% O₂ exposure values, n=6, p <0.05). These results suggest that hypoxia inhibits cyclooxygenase at the 10% O₂ level and both cyclooxygenase and prostacyclin synthetase enzymes at the 0% O₂ exposure levels. Exposure of aortic endothelial cells resulted in a 44% inhibition of prostacyclin at the 0% exposure level. No significant alteration in prostacyclin production was found in pulmonary vascular smooth muscle cells exposed to hypoxia. These data suggest that the increased prostacyclin production reported in lungs exposed to hypoxia is not due to a direct effect of hypoxia on the main prostacyclin producing cells of the pulmonary circulation.     

Comparison of umbilical vein models for measurement of relative prostacyclin and thromboxane production

There is growing evidence that blood vessels generate TXA2 in addition to PGI2. We examined effluents from continuously perfused human umbilical vein and supernatants from umbilical vein rings for TXB2 and 6-keto-PGF1 alpha measurements (stable metabolites of TXA2 and PGI2, respectively). TXB2 and 6-keto-PGF1 alpha were identified in all samples. 6-keto-PGF1 alpha to TXB2 ratio was higher in intact vein effluents than in the venous ring supernatants (112:1 and 28:1, respectively, P less than 0.01). Arachidonate stimulation increased 6-keto-PGF1 alpha and TXB2 levels similarly in the intact vein effluent. In contrast, stimulation of the venous rings resulted in a relatively larger increase in TXB2 than in 6-keto-PGF1 alpha. This caused 6-keto-PGF1 alpha to TXB2 ratio to decline (p less than 0.01). The identity of TXB2 was confirmed in several different ways. These data suggest that 1) human umbilical veins produce TXA2 in addition to PGI2, 2) TXA2 release is more by venous rings than by the intact vein probably reflecting contribution from non-endothelial layers, and 3) arachidonate stimulation causes relatively greater release of TXA2 than of PGI2 from the venous rings, whereas release of PGI2 and TXA2 is similar from the intact vein.     

Docosahexaenoic acid metabolism and effect on prostacyclin production in endothelial cells

Bovine aortic endothelial cultures readily take up docosahexaenoic acid (DHA). Most of the DHA was incorporated into phospholipids, primarily in ethanolamine and choline phosphoglycerides, and plasmalogens accounted for 34% of the DHA contained in the ethanolamine fraction after a 24-h incubation. The retention of DHA in endothelial phospholipids was not greater than other polyunsaturated fatty acids and unlike arachidonic and eicosapentaenoic acids, DHA did not continue to accumulate in the ethanolamine phosphoglycerides after the initial incorporation. About 15% of the [14C(U)]DHA uptake was retroconverted to docosapentaenoic and eicosapentaenoic acids in 24 h. Some of the newly incorporated [14C(U)]DHA was released when the cells were incubated subsequently in a medium containing serum and albumin. The released radioactivity was in the form of free fatty acid and phospholipids and after 24 h, 11% was retroconverted to docosapentaenoic and eicosapentaenoic acids. Total DHA uptake was decreased only 10% by the presence of a 100 microM mixture of physiologic fatty acids, but as little as 10 microM docosatetraenoic acid reduced DHA incorporation into phospholipids by 25%. DHA was not converted to prostaglandins or lipoxygenase products by the endothelial cultures. When DHA was available, however, less arachidonic acid was incorporated into endothelial phospholipids, and less was converted to prostacyclin (PGI2). Enrichment of the endothelial cells with DHA also reduced their capacity to subsequently produce PGI2. These findings indicate that endothelial cells can play a role in DHA metabolism and like eicosapentaenoic acid, DHA can inhibit endothelial PGI2 production when it is available in elevated amounts.     

Regulation of prostacyclin and thromboxane production by human umbilical vessels: The effect of estradiol and progesterone in a superfusion model

To study the production of the vasodilatory prostacyclin (PGI₂) and vasoconstrictory thromboxane A₂ (TxA₂) by the human umbilical vessels, vascular segments collected from the cords of healthy newborns (n=15) after normal pregnancies were superfused with Eagle's medium at 37°C under continuous oxygenation. The stable metabolites of PGI₂ and TxA₂, 6-keto-prostaglandin F_1α and thromboxane B₂ (TxB₂) respectively, were measured from the superfusates with radioimmunoassays. All vascular segments studied produced 6-keto-PGF_1α and TxB₂ without any significant difference between the arteries and veins. 6-keto-PGF_1α was produced some 10–15 times more than TxB₂. 17-β-est-radiol at concentrations of 10, 100 and 1000 ng/ml dose-dependently stimulated the 6-keto-PGF_1α formation, but had no effect on TxB₂ generation. Progesterone 50, 500 and 5000 ng/ml caused no changes in 6-keto-PGF_1α or TxB₂ generations but even the smallest concentration of progesterone abolished the stimulating effect of estradiol. These results thus suggest that the high circulating levels of 17-β-estradiol and progesterone in the umbilical vessels may be important in the regulation of PGI₂ synthesis in the umbilical vessels in vivo.     

The effect of magnesium sulfate infusion on systemic and renal prostacyclin production

Recent in vitro studies have suggested that magnesium sulfate (MgSO4) infusions may increase prostacyclin production. We studied the effect of MgSO4 infusion on prostacyclin (PGI2) metabolite excretion in women with either pregnancy induced hypertension or preterm labor. Excretion of renal and systemic metabolites of PGI2 was measured prior to and following the start of MgSO4 infusion in the two groups. An increased in renal PGI2 metabolite preterm labor excretion was noted in the hypertension group but no change was noted in systemic PGI2 excretion in either group. These data fail to support a generalized, short term increase in endothelial cell PGI2 production as the basis for the beneficial effect of MgSO4.     

17 alpha-ethinylestradiol decreases production and release of prostacyclin in cultured human umbilical vein endothelial cells

Human umbilical vein endothelial cells (HUVEC) were incubated with the estrogen 17 alpha-Ethinylestradiol (30 ng/ml) in order to examine its regulating influence on synthesis and release of prostacyclin (PGI2). ATP (1 mg/ml) was used to stimulate PGI2-production through the purine receptors. We demonstrated that this level of estrogen decreases PGI2-synthesis by 11% and PGI2-release by 32% within 300 sec. Longer incubation times (48 hrs) resulted in the same inhibitory effect. Intracellular ATP content and methyl-3H-thymidine uptake demonstrated that the decrease of prostacyclin-concentration is not caused by reduced viability of the cells but by a direct inhibitory effect on prostacyclin synthesis and release.     

Inhibitory effect of insulin on prostacyclin production by isolated rat adipocytes

Physiologic concentrations of insulin completely inhibited the norepinephrine-induced increment in the production of 6-keto-prostaglandin (PG) F_1α, the stable derivative of prostacyclin (PGI₂), by isolated rat adipocytes. The inhibition of PGI₂ production by insulin in isolated rat adipocytes supports the view that the elevated plasma level of 6-keto-PGF_1α in rats with non-ketotic diabetes mellitus and diabetic ketoacidosis is derived at least in part from production of PGI₂ by the adipocyte cell mass.     

Lack of effect of ischemia and dipyridamole on prostacyclin production in arteriosclerosis obliterans

Six patients with advanced arteriosclerosis obliterans in the lower extremities were subjected to an exercise test on a tread mill with and without dipyridamole treatment. Prostacyclin (PGI2) release was measured by the concentration of its stable metabolite, 6-keto-prostaglandin F1 alpha in plasma. All the patients suffered from ischemic pain during both tests, but no changes were seen in plasma 6-keto-PGF1 alpha. Dipyridamole did not affect the physical performance. Our results suggest that atherosclerotic vessels do not increase PGI2 production in response to ischemia and that a single dose of dipyridamole does not change PGI2 production.     

Lack of effect of ischemia and dipyridamole on prostacyclin production in arteriosclerosis obliterans

Six patients with advanced arteriosclerosis obliterans in the lower extremities were subjected to an exercise test on a tread mill with and without dipyridamole treatment. Prostacyclin (PGI₂) release was measured by the concentration of its stable metabolite, 6-keto prostaglandin F_1α in plasma. All the patients suffered from ischemic pain during both tests, but no changes were seen in plasma 6-keto-PGF_1α. Dipyridamole did not affect the physical performance. Our results suggest that atherosclerotic vessels do not increase PGI₂ production in response to ischemia and that a single dose of dipyridamole does not change PGI₂ production.     

The effect of exercise on bleeding time and local production of prostacyclin and thromboxane

Exercise at a heart rate corresponding to 30% VO2max for 15 min was associated with an increase in the volume of bleeding time blood from a mean of 133 microliters before exercise to a mean of 218 microliters during and immediately after the exercise. There was similarly an increase in thromboxane B2 production from 6.40 nmol.l-1 before to 11.50 nmol.l-1. Most subjects also showed an increase in the length of the bleeding time and in the production of bleeding time 6-keto-PGF1 alpha. The extent of increase in the bleeding time and in production of 6-keto-PGF1 alpha was quite variable, with subjects showing the largest increases in bleeding time also demonstrating the greatest increases in 6-keto-PGF1 alpha (r = 0.76, P = 0.004). The ingestion of aspirin before exercise markedly inhibited basal bleeding time thromboxane B2 production and blocked the exercise-associated increments in thromboxane B2 and 6-keto-PGF1 alpha production. While the aspirin itself increased the length of the bleeding time, there was not any further increase associated with exercise. In contrast to the effects of acute short-term exercise, long-distance running was associated with a significant decrease in bleeding time, but no change in bleeding time blood volume, bleeding time thromboxane B2, or bleeding time 6-keto-PGF1 alpha. The results show that acute low-level exercise can be associated with significant changes in the volume of blood oozing from a bleeding time incision and in the amount of thromboxane production stimulated at the incisional site. Following exhaustive exercise of long duration, the above changes are no longer seen.