Prostacyclin and human foetal circulation

Developmental Differences in Platelet Inhibition Response to Prostaglandin E1

BACKGROUND

The mechanisms underlying neonatal platelets hyporesponsiveness are not fully understood. While previous studies have demonstrated developmental impairment of agonist-induced platelet activation, differences in inhibitory signaling pathways have been scarcely investigated.

OBJECTIVE

To compare neonatal and adult platelets with regard to inhibition of platelet reactivity by prostaglandin E1 (PGE1).

METHODS

Platelet-rich plasma from umbilical cord (CB) or adult blood was incubated with PGE1 (0-1 μM). We assessed aggregation in response to adenosine diphosphate (ADP), collagen, and thrombin receptor activating peptide as well as cyclic adenosine 3'5'-monophosphate (cAMP) levels (ELISA). Gαs, Gαi2, and total- and phospho-protein kinase A (PKA) were evaluated in adult and CB ultrapure and washed platelets, respectively, by immunoblotting.

RESULTS

Neonatal (vs. adult) platelets display hypersensitivity to inhibition by PGE1 of platelet aggregation induced by ADP and collagen (PGE1 IC50: 14 and 117 nM for ADP and collagen, respectively, vs. 149 and 491 nM in adults). They also show increased basal and PGE1-induced cAMP levels. Mechanistically, PGE1 acts by binding to the prostanoid receptor IP (prostacyclin receptor), which couples to the Gαs protein-adenylate cyclase axis and increases intracellular levels of cAMP. cAMP activates PKA, which phosphorylates different target inhibitor proteins. Neonatal platelets showed higher basal and PGE1-induced cAMP levels, higher Gαs protein expression, and a trend to increased PKA-dependent protein phosphorylation compared to adult platelets.

CONCLUSION

Neonatal platelets have a functionally increased PGE1-cAMP-PKA axis. This finding supports a downregulation of inhibitory when going from neonate to adult contributing to neonatal platelet hyporesponsiveness.

Preeclampsia activates 15-lipoxygenase and its metabolite 15-hydroxyeicosatetraenoic acid enhances constriction in umbilical arteries

OBJECTIVE

To compare the differential expression of 15-lipoxygenase (15-LO) isoenzymes, 15-LO-1 and 15-LO-2 in preeclampsia (PE), and normal pregnancy and its metabolite 15-hydroxyeicosatetraenoic acid (15-HETE) on the vasoconstriction of human umbilical artery (HUA) rings.

STUDY DESIGN

We performed western blotting and isometric tension studies and t-test analysis on data from 6 women with normal pregnancy and 8 women with PE.

RESULTS

Expressions of 15-LO-1 and 15-LO-2 in placentas and HUA rings in PE increased more than that in normal groups (P<0.01). 15-HETE increased HUA rings tension in a dose-dependence manner, which were significantly greater in PE than in normal pregnant controls (P<0.01). However, the constriction of HUA rings was completely eliminated by 2-aminoethoxydiphenyl borate (2-APB) in both normal pregnancy and PE (P<0.01) and attenuated partly by nifedipine in dose-dependence in normal pregnancy (10(-8)mol/L P>0.05; 10(-7), 10(-6)mol/L P<0.05) and in PE (P<0.01).

CONCLUSION

PE upregulates 15-LO pathway via 15-HETE, which increased intercellular calcium level to cause constriction of HUA rings.

The biological investigation of prostacyclin in preeclamptic women seen reduced endothelial function

OBJECTIVE

Our aim was to determine the biological investigation of prostacyclin in preeclamptic women seen reduced endothelial vasodilatation by non-invasive technique in vivo.

METHODS

Using a high resolution ultrasound transducer, diameters of brachial arteries were determined after reactive hyperemia in 15 non-pregnant, 20 normotensive pregnant and 20 preeclamptic women. The concentrations of 6-keto-prostaglandin F 1alpha (6keto-PGF 1alpha) in plasma and the concentrations of adenosine-3', 5'-cyclic monophosphate (cyclic AMP) in platelets and serum were measured among the groups.

RESULTS

Flow-mediated vasodilatation at 1 min after reactive hyperemia was higher in normotensive pregnant than in the non-pregnant or preeclamptic women. The plasma concentration of 6 keto-PGF 1alpha as well as the serum concentration of cyclic AMP were lower in preeclamptic than those in normotensive pregnant women. The increase in cyclic AMP in the presence of a prostacyclin analogue in platelets was seen at similar levels in all three groups.

CONCLUSION

From these results, the concentrations of prostacyclin in plasma and cyclic AMP in serum might be low possibly due to reduced production of prostacyclin in preeclamptic women seen reduced endothelial function.

Effects of arecoline in relaxing human umbilical vessels and inhibiting endothelial cell growth

This study investigated the effects of arecoline, an active ingredient of the areca nut, on the tone of human umbilical arteries and veins and on the eNOS expression and cell proliferation of human umbilical vein endothelial cells (HUVECs). We found that arecoline relaxes the human umbilical artery and vein rings in a concentration-dependent manner; the higher the concentration of arecoline, the greater the relaxation of the rings. However, the relaxation decreases after the endothelium was removed or pretreated with L-NAME, a nitric oxide synthase inhibitor. Moreover, arecoline increases in a dose-dependent way the cGMP levels of human umbilical arteries and veins. In HUVECs, arecoline also increases the eNOS expression. Therefore, the relaxant effects of arecoline on the umbilical artery and vein rings were endothelium-dependent through the NO-cGMP systems. In addition, arecoline at higher doses (100-1000 microM) inhibits endothelial cell proliferation; the exposure toarecoline (100-1000 microM) for 24 and 48 h induces G2/M cell cycle arrest of HUVECs. Our results indicate that arecoline would decrease vascular tone, in part mediated by NO. Higher doses of arecoline inhibit endothelial cell growth, which suggest that long-term use or high doses of areca nut might induce endothelial dysfunction and associated diseases.

Reduced function of endothelial prostacyclin in human omental resistance arteries in pre-eclampsia

It remains unclear in pre-eclampsia whether or not a functional change occurs in the role played by prostacyclin in endothelium-dependent relaxation in resistance arteries. We examined this using human omental resistance arteries (obtained from pre-eclamptic or normotensive pregnant women) in the presence of N(G)-nitro-L-arginine (L-NNA, an inhibitor of nitric oxide synthase). In endothelium-intact strips from both groups, 9,11-epithio-11,12-methano-thromboxane A(2) (STA(2), a thromboxane A(2) mimetic) produced a contraction. Diclofenac (an inhibitor of cyclooxygenase) enhanced the STA(2) contraction only in the normotensive pregnant group (1.4 times control, P < 0.01). In the presence of STA(2), bradykinin (0.1 microM) produced an endothelium-dependent relaxation in both groups, the relaxation being significantly smaller for the pre-eclamptic group (P < 0.002). Diclofenac significantly attenuated the bradykinin-induced relaxation only for the normotensive pregnant group (31 % inhibition, P < 0.001). The bradykinin-induced membrane hyperpolarization consisted of diclofenac-sensitive and -insensitive components. The former, but not the latter, was significantly smaller in pre-eclampsia (-4.3 vs. -2.6 mV, P < 0.05). The concentrations of 6-keto-PGF(1alpha) (a stable metabolite of prostacyclin) in these arteries were significantly lower in pre-eclampsia in both the absence and presence of bradykinin (about 0.2-0.4 times the normotensive pregnant value in each case, P < 0.01). By contrast, both the relaxation and the membrane hyperpolarization in response to beraprost (10 nM, a stable analogue of prostacyclin) were similar between the two groups. We conclude that, in pre-eclampsia, a reduced part is played by prostaglandins in the endothelium-dependent relaxation seen in resistance arteries and that this may be due to a reduced production of prostacyclin by the endothelium.

Vasoactive mediator release by fetal endothelial cells in intrauterine growth restriction and preeclampsia

OBJECTIVE

Preeclampsia and fetal growth restriction are associated with poor placental perfusion, which may be accompanied by a compensatory release of vasoactive substances in the fetoplacental circuit. This study examines the effects of preeclampsia and fetal growth restriction on nitric oxide and prostacyclin signaling pathways in fetal endothelial cells.

STUDY DESIGN

Human umbilical vein endothelial cells from 30 control pregnancies, 18 pregnancies with preeclampsia, and 9 pregnancies with intrauterine growth restriction were cultured. Intracellular cyclic guanosine monophosphate accumulation and 6-keto-prostaglandin F1alpha production were determined.

RESULTS

Intracellular accumulation of cyclic guanosine monophosphate was significantly higher in the preeclampsia group and lower in the growth restriction group than in the control group (9.8, 1.8, and 3.9 pmol/microg protein for 5 minutes, respectively), whereas 6-keto-prostaglandin F1alpha production was not significantly different in the 3 groups.

CONCLUSION

The data suggest that the fetoplacental vascular response to preeclampsia is to increase production of cyclic guanosine monophosphate, perhaps to maintain vessel dilatation and maximum flow through placental villi. In fetal growth restriction the umbilical vein endothelial cells do not or cannot respond to chronic hypoxia by increasing cyclic guanosine monophosphate, which may lead to fetoplacental vasoconstriction.

Any physiological role for prostacyclin in regulation of fetal vessel tone?

This study investigates the contribution of endogenous prostacyclin and nitric oxide (NO) for maintenance of umbilical artery tone in vitro. Treatment with indomethacin as well as removal of the endothelium was followed by contractions of umbilical arteries and a reduced formation of prostacyclin. In contrast, vessel tone was not affected by inhibition of NO synthesis, using nitro-L-arginine. Thus, prostacyclin rather than nitric oxide appears to be the endogenous endothelium-derived factor in the umbilical circulation that is involved in regulation of vessel tone.

Transfer of aspirin across the perfused human placental cotyledon

Pregnancy-induced hypertension is associated with a reduction in prostacyclin synthesis that is relative to normotensive pregnancy, whereas thromboxane A2 synthesis is unchanged or increased. The net effect is a decreased prostacyclin/thromboxane ratio that may result in the reduced fetal-placental blood flow seen in pregnancy-induced hypertension because thromboxane is known to constrict this circulation. Low-dose aspirin (acetylsalicylic acid), which is used to treat pregnancy-induced hypertension, selectively inhibits thromboxane synthesis and therefore may alter fetal-placental blood flow. We have investigated the transfer of acetylsalicylic acid in the perfused human placental cotyledon and its effects on fetal-placental perfusion pressure. Human placental cotyledons were perfused with tissue culture medium 199 plus 5% polyvinylpyrrolidone that was gassed with 95% oxygen/5% carbon dioxide at flow rates of 10 ml/min (maternal) and 4 ml/min (fetal). Acetylsalicylic acid (10(-5) mol/L) was added to the maternal circuit, and cotyledons were perfused for 1 hour with aliquots taken from a closed fetal circuit every 5 minutes. Acetylsalicylic acid was assayed by spectrofluorometry at 306/412 nm. Our data indicate an initial rapid transfer of acetylsalicylic acid during the first 5 minutes into the fetal-placental circulation, the concentration then decreased to a steady state at 0.4 x 10(-5) mol/L. Resting perfusion pressure of both maternal and fetal circulation did not change after the addition of acetylsalicylic acid to maternal perfusate and transfer to the fetal circulation.

Synergistic inhibitory effects of adrenoceptor antagonists and prostacyclin, and umbilical artery-derived prostacyclin-like activity on platelet aggregation

Adrenoceptor antagonists are being used increasingly for the treatment of pregnancy-induced hypertension (PIH). Previous studies have shown that these drugs can inhibit platelet aggregation and thromboxane production. The aims of this study were to determine (i) whether adrenoceptor antagonists had any effect on vascular prostacyclin (PGI2) production and (ii) whether these drugs acted synergistically with PGI2 and the PGI2-like activity derived from umbilical artery to inhibit platelet aggregation in vitro. The adrenoceptor antagonists labetalol, pindolol and propranolol were found to have no effect on PGI2 production from the umbilical artery at low drug concentrations. These agents were also found to act synergistically with both pure PGI2 and PGI2-like activity derived from umbilical artery to inhibit platelet aggregation. This synergistic effect may be beneficial in the treatment of disorders which are associated with reduced PGI2 production, such as PIH where such synergy may help compensate for PGI2 deficiency.

Effect of low-dose aspirin on fetal and maternal generation of thromboxane by platelets in women at risk for pregnancy-induced hypertension

There is evidence that aspirin in low doses favorably influences the course of pregnancy-induced hypertension, but the mechanism, although assumed to involve suppression of the production of thromboxane by platelets, has not been established. We performed a randomized study of the effect of the long-term daily administration of 60 mg of aspirin (n = 17) or placebo (n = 16) on platelet thromboxane A2 and vascular prostacyclin in women at risk for pregnancy-induced hypertension. Low doses of aspirin were associated with a longer pregnancy and increased weight of newborns. Serum levels of thromboxane B2, a stable product of thromboxane A2, were almost completely (greater than 90 percent) inhibited by low doses of aspirin. The urinary excretion of immunoreactive thromboxane B2 was significantly reduced without changes in the level of 6-keto-prostaglandin F1 alpha, a product of prostacyclin. Mass spectrometric analysis showed that aspirin reduced the excretion of the 2,3-dinor-thromboxane B2 metabolite--mainly of platelet origin--by 81 percent and of thromboxane B2, probably chiefly of renal origin, by 59 percent. The urinary excretion of 6-keto-prostaglandin F1 alpha and of its metabolite 2,3-dinor-6-keto-prostaglandin F1 alpha was not affected. Low doses of aspirin only partially (63 percent) reduced neonatal serum thromboxane B2. No hemorrhagic complications were observed in the newborns. Thus, in women at risk for pregnancy-induced hypertension, low doses of aspirin selectively suppressed maternal platelet thromboxane B2 while sparing vascular prostacyclin, but only partially suppressed neonatal platelet thromboxane B2, allowing hemostatic competence in the fetus and newborn.

Comparison of the vasoactive effects of leukotrienes with thromboxane mimic in the perfused human placenta

Vasoactive effects of leukotrienes and thromboxane mimic were tested in the perfused human placental cotyledon. Tissue viability was demonstrated by oxygen consumption and by carbon dioxide and lactate production. Vasoconstrictive effects of leukotrienes B4, C4, and D4 were compared with those of a known potent vasoconstrictor, thromboxane mimic (U 46619). The leukotrienes and thromboxane mimic were administered as bolus injections into a chorionic plate artery in doses ranging from 10(-6) to 25 micrograms. In each placenta only one leukotriene was compared with thromboxane mimic. Vasoconstrictive effects were determined by maximum increases in resistance occurring after each injection. Thromboxane mimic caused significantly greater increases in resistance than any of the leukotrienes (p less than 0.001). Thromboxane mimic and leukotriene D4 had significantly lower threshold doses than leukotriene B4 or C4 (p less than 0.001). We concluded: (1) Thromboxane mimic is a potent vasoconstrictor in the human placental vasculature; (2) leukotrienes also cause vasoconstriction but are much less potent than thromboxane; (3) thromboxane mimic and leukotriene D4 have vasoconstrictor effects at significantly lower (p less than 0.001) concentrations than leukotriene B4 or C4.

Connective tissue disease associated with sclerodermoid features, early abortion, and circulating anticoagulant

An 18-year-old white woman admitted for an incomplete septic abortion was found to have thrombocytopenia, anemia, and increased activated partial thromboplastin time (PTT). Additionally, results of nontreponemal serologic tests for syphilis were positive, and the fluorescent antinuclear antibody was weakly positive. A mixture of the patient's plasma with normal control plasma showed that the elevation in activated PTT was the result of a circulating anticoagulant, not an inherent clotting defect. Sclerodermoid features were present and consisted of bound-down, hairless skin and scattered subcutaneous indurated plaques. A faint pattern consistent with livedo reticularis was recognized on all extremities. Biopsy specimens of sclerodermoid lesions showed increased and thickened dermal collagen consistent with morphea. We believe that this patient's condition represents an unusual connective tissue disease syndrome consisting of abortion, livedo reticularis, thrombocytopenia, circulating "anticoagulant," negative or slightly positive antinuclear antibodies, and false positive results on nontreponemal serologic tests for syphilis. Sclerodermoid lesions were also a unique feature in our patient.

In vitro activity of nicotinamide adenine dinucleotide- and nicotinamide adenine dinucleotide phosphate-linked 15-hydroxyprostaglandin dehydrogenases in placentas from normotensive and preeclamptic/eclamptic pregnancies

Concentrations of prostaglandins E2 and I2 may be decreased in preeclamptic and eclamptic pregnancies. Because these prostaglandins produce vasodilation and inhibit platelet aggregation it has been suggested that a reduction in their biosynthesis might play an important role in the pathogenesis of the hypertension and coagulation abnormalities associated with preeclampsia. Placental tissue is an extremely rich source of several enzymes that catalyze the catabolism of prostaglandins. The present study was initiated to determine whether one of these catabolic enzymes might be increased in preeclamptic/eclamptic pregnancies. The activities of the NAD- and the NADP-linked 15-hydroxyprostaglandin dehydrogenases were measured in 16 preeclamptics (mean diastolic pressure, 108 +/- 13 mmHg) and compared with 16 normotensive controls matched for age (20.8 +/- 5.43 vs. 20.6 +/- 5.16) and gestational week of delivery (34.6 +/- 5.40 vs. 35.0 +/- 5.06). These results indicate that the activity of the placental NAD-linked 15-hydroxyprostaglandin dehydrogenase is elevated in preeclampsia (40.1 +/- 31.3 vs. 14.9 +/- 8.30 mU/g tissue, P less than 0.01). If this increase were also expressed in vivo, its effect on prostaglandin metabolism could be mistaken for impaired prostacyclin biosynthesis unless both the 6-keto- and 6,15-diketo-metabolites of prostacyclin were measured.

Effect of prostacyclin on the perfusion pressure and on the vasoconstrictor response of angiotensin II in the human isolated foetal placental circulation

The effect of prostacyclin infusion on the perfusion pressure and on the vasoconstrictor response to three doses of angiotensin II was investigated in six full-term human placentas. The placentas were perfused with a modified Krebs-Henseleit solution and placenta perfusion pressure was recorded. Prostacyclin 5 X 10(-8) M, infused through the foetal placental circulation, produced a significant decrease in placental vascular resistance. The vasodepressor effect of prostacyclin persisted throughout the perfusion period and promptly disappeared when the infusion was stopped. The pressor response of angiotensin II was significantly reduced by prostacyclin infusion. These data suggest an interaction between the vascular effects of prostacyclin and angiotensin II on the placental circulation that might be important in the control of foetal placental blood flow.

Prostaglandin metabolism in umbilical vessels of smoking and non-smoking mothers

Arachidonic acid (AA) and its metabolites are responsible for the regulation of the umbilical blood flow. We investigated the prostaglandin (PG) synthesis in umbilical arteries and veins of 16 smoking and 17 non-smoking mothers. AA and PGs were analyzed after extraction of samples by means of thin layer chromatography (TLC). Of all the AA metabolites in umbilical arteries and veins, prostacyclin reached the highest concentration. In non-smoking mothers the conversion rate of AA in arteries and veins was similar. The only exception was PGE2 which showed a significantly lower concentration in umbilical veins of smoking mothers. However, the influence of PGE2 on the blood flow of umbilical arteries and veins seems to be of minor importance compared to other vessels.

The structural specificity of anti-phospholipid antibodies in autoimmune disease

Antibodies to phospholipids represent a unique set of incompletely characterized antibodies prevalent in patients with systemic lupus erythematosus and related autoimmune disorders. Little is known concerning their induction and pathogenesis. Here we provide an overview of what is currently known about these antibodies and explore the possibility that they interact with and are perhaps specific for unusual lipid structures. Particular attention is given to the physical chemical nature and phase behaviour of associated putative lipid antigens. This analysis suggests that alterations in the phospholipid architecture of cell membranes may play an important role in the immunoregulation of autoimmunity.

Thrombosis, recurrent abortions and intrauterine foetal death in a patient with lupus anticoagulant

The authors describe a case report of a patient suffering from thrombosis and recurrent abortions. Routine coagulation screening was abnormal and investigation showed the presence of a circulating anticoagulant. High titres of anticardiolipin antibodies were demonstrated. Antinuclear antibodies were slightly positive and antinative DNA antibodies were present. Lupus anticoagulant activity and anticardiolipin antibodies seem to be strong markers of a thrombotic tendency.

Inhibition by aspirin of human arterial and venous prostacyclin synthesis

Prostacyclin (PGI2) synthesis by human mesenteric arteries and veins was measured ex vivo in 62 patients who received either no medication or a single oral dose of aspirin 40 mg, 75 mg or 300 mg approximately 24 hrs pre-operatively. Each dose of aspirin caused a significant reduction in both arterial and venous PGI2 synthesis compared with the untreated group. Arterial PGI2 synthesis did not differ significantly from venous PGI2 synthesis whether assessed by sample weight or sample area.

Digoxin inhibition of relaxation induced by prostacyclin and vasoactive intestinal polypeptide in small human placental arteries

Small chorionic plate arteries were obtained from human placentae following normal vaginal delivery. Tubal vascular preparations were dissected, mounted in organ baths, and their isometric tension was recorded. Digoxin (10(-6) M) caused a rise in basic tension, reaching a maximum of 17 per cent of contractions induced by potassium (124 mM) depolarization. Pretreatment with digoxin did not significantly influence the concentration-dependent contractile responses to 5-hydroxytryptamine and prostaglandin F2 alpha (PGF2 alpha). In preparations contracted with PGF2 alpha, cumulative addition of prostacyclin (PGI2) and vasoactive intestinal polypeptide (VIP) produced concentration dependent relaxations. Digoxin (10(-8) to 10(-6) M) inhibited and finally abolished these relaxant effects of PGI2 and VIP in a concentration-dependent fashion. Pretreatment by digoxin (10(-8) to 10(-6) M) diminished the relaxant effect of sodium nitroprusside, but the effect was less pronounced than that on PGI2- and VIP-induced relaxation. As PGI2 and VIP may be of importance for the maintenance of a low resistance of the fetal placental vascular bed, the finding that digoxin decreases the vasodilating effects of these agents might imply effects on placental resistance of cardiac glycosides when used in late human pregnancy.

Prostacyclin and thromboxane in gynecology and obstetrics

The gynecologic and obstetric implications of the smooth muscle-relaxing, antiaggregatory prostacyclin and its endogenous antagonist, thromboxane A2, are reviewed. In addition to the vascular wall and circulating platelets, which are primary sources for prostacyclin and thromboxane A2, respectively, reproductive tissues produce great amounts of these prostanoids, evidently for the regulation of the vascular tone and/or vascular platelet interaction. Several gynecologic and obstetric disorders are characterized by abnormalities in prostacyclin and/or thromboxane A2. In primary menorrhagia the uterine release of prostacyclin is increased, and consequently menstrual blood loss can be reduced with various prostaglandin synthesis inhibitors. Prostacyclin relaxes the nonpregnant myometrium in vitro and may also do so in vivo, although intravenous infusion of prostacyclin has no effect upon the uterine contractility in nonpregnant or pregnant subjects. Patients with pelvic endometriosis may have increased levels of prostacyclin and thromboxane A2 metabolites in the peritoneal fluid. The prostacyclin/thromboxane A2 balance shifts to thromboxane A2 dominance in patients with gynecologic cancer. During pregnancy the production of prostacyclin and thromboxane A2 increases in the mother and fetoplacental tissue. Preeclampsia and other chronic placental insufficiency syndromes are accompanied by prostacyclin deficiency in the mother and in fetomaternal tissues and by an overproduction of thromboxane A2, at least in the placenta. These changes may account for the vasoconstriction and platelet hyperactivity, which are pathognomonic for hypertensive pregnancies. By directing the prostacyclin/thromboxane A2 balance to prostacyclin dominance (by dietary manipulation, administration of prostacyclin and/or its analogues, drugs with prostacyclin-stimulating and/or thromboxane A2-inhibiting action), it may be possible to prevent and/or treat hypertensive pregnancy complications in the future.

6-Keto prostaglandin F1 alpha, thromboxane B2, and 13,14-dihydro-15-keto prostaglandin F concentrations of normotensive and preeclamptic patients during pregnancy, delivery, and the postpartum period

Plasma 6-keto prostaglandin F1 alpha, 13,14-dihydro-15-keto prostaglandin F, and thromboxane B2 levels were measured in normotensive and preeclamptic patients during pregnancy and the postpartum period. From 30 to 40 weeks of gestation, 6-keto prostaglandin F1 alpha levels of preeclamptic patients were significantly lower than those of normotensive women; 13,14-dihydro-15-keto prostaglandin F and thromboxane B2 concentrations in preeclamptic patients did not significantly differ from those of the normotensive group. At delivery, 6-keto prostaglandin F1 alpha levels of maternal and umbilical venous plasma of preeclamptic women were also significantly lower than those of normotensive women. In the postpartum period these three prostanoids were not significantly different in normotensive women compared to preeclamptic women, with clinical preeclamptic symptoms soon disappearing in most of our patients. From the results, it seems that prostacyclin plays an important role in preeclampsia.

6-Keto prostaglandin F1 alpha, thromboxane B2 and 13,14-dihydro-15-keto prostaglandin F levels in maternal and fetal plasma

In order to investigate the physiological roles of prostaglandins during pregnancy, delivery and the postpartum period, the plasma concentration of 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha), a stable metabolite of prostacyclin, thromboxane B2 (TXB2), a stable metabolite of thromboxane A2, and 13,14-dihydro-15-keto prostaglandin F(PGFM) were measured by specific radioimmunoassay. In addition, at delivery, plasma 6-keto PGF1 alpha and PGFM concentration were measured in maternal, umbilical arterial and venous plasma. 6-Keto PGF1 alpha, TXB2 and PGFM levels did not change during pregnancy. 6-Keto PGF1 alpha level at delivery was somewhat higher than during pregnancy but not significantly so. PGFM level was significantly higher than during pregnancy. Umbilical arterial 6-keto PGF1 alpha concentration was significantly higher than umbilical venous or maternal plasma at delivery. Umbilical venous 6-keto PGF1 alpha level was somewhat higher than that of maternal plasma but the increase was not significant. There was no significant difference between umbilical arterial and venous concentrations of PGFM, but maternal PGFM level was significantly higher than that of fetal plasma. In the postpartum period, PGFM and TXB2 concentrations were significantly higher than before delivery. However 6-keto PGF1 alpha level in the postpartum period did not significantly differ from before delivery. The results of this study may indicate high prostacyclin production by the fetus and that PGF and TXA2 concentration change in the postpartum period.

Production of prostacyclin, 6-keto-PGF1 alpha and thromboxane B2 by incubated samples of umbilical vessels: a comparison of methods for expressing the results on dry weight, wet weight, protein or DNA bases

The production of PGI2 (determined by bioassay), and of 6-keto-PGF1 alpha and TXB2 (determined by radioimmunoassay) by samples of human umbilical vessels have been measured. The results have been calculated on four bases: dry weight, wet weight, protein and DNA. There was a higher production of PGI2 and 6-keto-PGF1 alpha by umbilical veins than by umbilical arteries; no significant difference in TXB2 production was observed between umbilical veins and arteries. The ratio of 6-keto-PGF1 alpha: TXB2 production was about 100 for the samples of veins and about 40 for the samples of arteries. The best methods of expressing the results were on the bases of protein and DNA, the latter basis being marginally the best. The least satisfactory method for expressing the results was that based on dry weight. The physiological and practical implications of the results are discussed.

Correlation of prostacyclin synthesis by human umbilical artery with status of essential fatty acid

Prostacyclin production by human umbilical artery rings was measured in a variety of incubation media and related to gestational age, mode of delivery, and birth weight. Prostacyclin production was directly correlated with the status of essential free fatty acid in the tissue as assessed by the ratio of tissue concentrations of arachidonic acid and Mead's acid. The results indicate a possible association of the essential fatty acid status both with intrauterine growth retardation and with fetal vascular prostacyclin production.

Recent aspects of hemostasis, hematology and hemorheology in preeclampsia-eclampsia

Because intravascular fibrin deposition is found in the glomerular capillaries of patients who have died of eclampsia, it was long assumed that a chronic form of intravascular clotting represents the decisive cause of the condition. Fibrin deposition is also typically observed in the uteroplacental bloodstream. The occurrence of high levels of soluble fibrin and fibrin(ogen) degradation products, which in severe cases can also include fibrin oligomers, in combination with thrombocytopenia and factor VIII consumption were interpreted as additional evidence for the significance of intravascular clotting in the pathogenesis of EPH gestosis. The hemolysis of the microangiopathologic type, which occurs in severe cases, was attributed to the resulting impairment in microcirculation. Doubts regarding this theory arose when it was noted that the course of EPH gestosis is not altered by the use of heparin, and that even in severe cases of eclampsia with hemolysis and thrombocytopenia the plasmatic clotting system is involved only to a small extent and probably only secondarily. More recent investigations have yielded the first evidence of reduced prostacyclin synthesis in maternal and fetal vessels in patients with EPH gestosis. Since prostacyclins lower arterial resistance yet at the same time are strong inhibitors of thrombocyte aggregation, this prostacyclin deficiency could account for the hypertension and the occurrence of platelet thrombi in the placental bloodstream associated with EPH gestosis. The observation of a reduction in the number of thrombocytes as a consequence of increased platelet breakdown, which precedes a rise in the level of fibrin(ogen) degradation products, also points to the significance of an abnormal interrelation between platelets and endothelium. In addition to the plasmatic and thrombocytic hypercoagulability and impaired prostacyclin synthesis, hemoconcentration with increased microvascular permeability is also observed. Early detection of disturbances of the vessel wall and vessel contents may provide a means of prophylaxis.

Maternal smoking and prostacyclin production by cultured endothelial cells from umbilical arteries

A study was made of the production of prostacyclin (PGI2) by cultured endothelial cells from the umbilical veins of mothers who smoked and of matched mothers who did not smoke. Cells were obtained from 58 umbilical cords from 22 apparently healthy women, 11 mild smokers (less than 15 cigarettes per day), and 25 heavy smokers (more than 15 cigarettes per day). Production of PGI2 by the cells was calculated by measuring the amount of 6-keto-prostaglandin F1 alpha released in the culture medium after the addition of arachidonic acid, by means of a specific radioimmunoassay. Endotheliai cells from mild and heavy smokers were significantly less able to grow and to reach confluency than cells from nonsmokers. Smoking also resulted in a marked reduction in the capacity of cultured cells to produce PGI2. This was particularly apparent for the cells from heavy smokers. Smoking during pregnancy appears to induce some modifications in the enzymes of the prostacyclin pathway which persist in endothelial cells undergoing replication in primary culture even in the absence of the pathogenic factor.

Platelet sensitivity to a prostacyclin analogue in normal and pathological pregnancy

Platelet sensitivity to a prostacyclin analogue (PSP) was investigated at different stages of normal and pathological pregnancies. During uncomplicated pregnancy PSP decreased progressively by about 30% and returned to almost normal values in the puerperium. In pre-eclamptic women PSP was reduced by 49% and in pregnant diabetics by 50% compared with normal pregnant individuals of corresponding gestational age. Reduced PSP in normal and pathological pregnancy seems to be another aspect of increased coagulability and platelet aggregation found in these patients.

Low prostacyclin synthetase activity of fetal rat aorta. Progressive increase after birth

Aortae from fetal or 3 weeks old rats produced very small amounts of PGI2, prostacyclin. This production increased from 4 weeks on, reaching adult values at about ten weeks. This maturation seemed to be predominantly determined by a change in the PGI2 synthetase system, rather than in arachidonic acid availability, phospholipase or cyclo-oxygenase activity. The anti-oxidant ascorbic acid stimulated prostacyclin production more strongly in adult than in young rat aortae. This finding suggests that the lower production of PGI2 by young tissues is not due to an enhanced inhibition of prostacyclin synthetase by lipid peroxides.

Prostacyclin producing activity of human umbilical, placental and uterine vessels

Prostacyclin-like material producing activity of umbilical, placental and uterine vessels was studied. Umbilical arteries and veins were separated at sites 10-15cm and 1-2cm from insertion of the umbilical cord to the placenta. Placental arteries and veins were prepared from the first, second and third branches on the chorionic plate. Uterine vessels were obtained at abdominal hysterectomy. After incubation of each specimen in Tris buffer 1 ml (pH8.5, 0.5M) for 30 min at room temperature, the inhibitory effect of the medium on ADP induced platelet aggregation was measured and the prostacyclin-like material was quantified. These procedures were repeated consecutively four times in total for each specimen. Prostacyclin-like material production rate and its total production were calculated. In total prostacyclin-like material production, umbilical arteries and veins were much higher than placental arteries and veins respectively (p less than 0.001), but there was no significant difference between placental and uterine vessels. These results showed that prostacyclin-like material producing activity of blood vessels declined remarkably at the transitive region from umbilical to placental vessels. It seems that this distribution of vascular prostacyclin-like material producibility in the fetoplacental vascular system correlates with that of vascular reactivity to prostacyclin.

Thrombosis of the right umbilical artery, presumably related to the shortness of the umbilical cord: an unusual cause of fetal distress

This case report concerns a late pregnancy complication, clinically apparent as severe variable decelerations in the first stage of labor. Emergency cesarean section delivered a mildly asphyxiated full-term newborn infant. Examination of the umbilical cord revealed a thrombus of the right umbilical artery, near the fetal side, confirmed by histological examination. The total length of the umbilical cord, only 30 cm, was below the limit necessary for uncomplicated delivery of the fetus near term. Transient stretching during fetal descent is thought to be responsible for constriction of the umbilical arteries, blood flow sludging and thrombosis. Although only a few cases have been reported, thrombosis of the umbilical vessels has to be considered whenever the fetal heart rate pattern shows unexplained variable decelerations.

Prostacyclin metabolism in adults and neonates. Urinary profiles of 6-ketoprostaglandin F1 alpha and 2,3-dinor-6-ketoprostaglandin F1 alpha studied by gas chromatography-mass spectrometry

Metabolism of endogenous prostacyclin was studied in adults and neonates by measuring urinary levels of 6-ketoprostaglandin F1 alpha (spontaneous hydrolysis product) and 2,3-dinor-6-ketoprostaglandin F1 alpha (enzymatically formed by beta-oxidation). Quantification of prostanoids was achieved by capillary gas chromatography-mass spectrometry using the stable isotope dilution technique. Purification of the urinary lipid extract included silicic acid column chromatography and reverse- and straight-phase high-pressure liquid chromatographies. Accuracy of the method was proven by recovery experiments for both metabolites. Partial mass spectra of endogenous 6-ketoprostaglandin F1 alpha and 2,3-dinor-6-ketoprostaglandin F1 alpha were obtained from urine samples. In neonates (third day of life, n - 5 pooled urines) levels of 2,3-dinor-6-ketoprostaglandin F1 alpha (0.28 +/- 0.18 ng/ml) were much lower than those of 6-ketoprostaglandin F1 alpha (2.13 +/- 1.10 ng/ml), indicating low beta-oxidation activity at high prostacyclin formation. In adults (n = 7), levels of 2,3-dinor-6-ketoprostaglandin F1 alpha (0.27 +/- 0.21 ng/ml) and levels of 6-ketoprostaglandin F1 alpha (0.20 +/- 0.11 ng/ml) were about the same, indicating relatively high beta-oxidation at low prostacyclin formation. Values are expressed as mean +/- S.D.

Preeclampsia -- a state of prostaglandin deficiency? Urinary prostaglandin excretion, the renin-aldosterone system, and circulating catecholamines in preeclampsia

Urinary excretion of prostaglandin E2 (PGE2) and F2 alpha (PGF2 alpha), plasma concentrations of renin, aldosterone, norepinephrine (NE) and epinephrine (E) were determined during pregnancy, 5 days, 3, and 6 months after delivery in preeclampsia, normotensive pregnant, and nonpregnant control subjects. The PGE2 was higher in normotensive pregnant control subjects than in nonpregnant subjects. In preeclampsia, PGE2 was reduced to nonpregnant level. PGF2 alpha was the same in preeclampsia and in normotensive pregnancy, but elevated when compared to the normotensive nonpregnant control group. Plasma concentrations of renin and aldosterone were increased during pregnancy, but considerably less in preeclampsia than during normotensive pregnancy. NE and E were the same as in nonpregnant subjects during both hypertensive and normotensive pregnancy. All parameters were normal 3 months after delivery. There were no correlations between PGE2, PGF2 alpha, plasma concentrations of renin, aldosterone, NE, or E and blood pressure level in third trimester either in preeclampsia or in normotensive pregnancy. PGE2 was positively correlated to plasma concentrations of renin. It is suggested that the lack of renal PGE2 in preeclampsia might be responsible for the decrease in renal blood flow and sodium excretion. It is hypothesized that preeclampsia is a state of prostaglandin deficiency. The changes in the renin-aldosterone system may be secondary to changes in prostaglandin concentration both in preeclampsia and normotensive pregnancy.

Prostacyclin production in whole blood throughout normal pregnancy

In a longitudinal study of twelve normal pregnant women the base-line plasma values of 6-keto prostaglandin (PG)F1 alpha, the stable degradation product of prostacyclin, were determined. At the same time the capacity of their blood to produce prostacyclin was assessed using a stimulation test. When collagen is added to citrated whole blood there is a prompt rise in plasma 6-keto PGF1 alpha, which results from the synthesis of prostacyclin by leukocytes. These cells use cyclic endoperoxides in part coming from activated platelets and in part derived from endogenous substrate to produce prostacyclin. Both the base-line values and the capacity to produce prostacyclin fell significantly after 33 weeks of pregnancy. The decreased capacity to produce prostacyclin in the later stages of pregnancy may help account for the relatively diminished refractoriness to angiotensin II, characterizing the last two months of normal pregnancies.

Lipoxygenase activity in human uterine and intrauterine tissues: new prospects for control of prostacyclin production in pre-eclampsia

The formation of lipoxygenase metabolites by human uterine and intrauterine tissues was evaluated using [1-14C]arachidonic acid (AA) as substrate. The major lipoxygenase product synthesized by human amnion, decidua vera and placenta was identified as 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE); smaller amounts of 5-HETE and 5-HETE (lactone form) were also formed. In chorion laeve only a trace amount of 12-HETE was detected. Human myometrium and cervical tissue converted [1-14C]AA to 5-HETE and 12-HETE in almost equal amounts. The formation of lipoxygenase products in all tissues was markedly inhibited by nordihydroguaiaretic acid (NDGA) an inhibitor of lipoxygenase activity and slightly stimulated or inhibited by indomethacin, an inhibitor of cyclooxygenase activity. These results are indicative that uterine and intrauterine tissues are probably potential sources of lipoxygenase products during pregnancy and parturition. Since 12-hydroperoxy-eicosatetraenoic acid (12-HPETE), the labile precursor of 12-HETE potently inhibits prostacyclin biosynthesis, our findings are suggestive of the possibility that aberrant lipoxygenase activities may contribute to the complications of pre-eclampsia.

Prostanoid synthesis by human umbilical artery

A discrepancy between published values of PGI2 production by human umbilical artery in vitro measured by platelet bioassay, compared with values of 6-oxo-PGF1 alpha by radioimmunoassay, raised the possibility that another anti-aggregatory prostanoid was produced by this tissue. To test this hypothesis, umbilical artery rings were incubated in buffer and PGI2 determined by platelet bioassay and by a more specific radioimmunoassay based on comparison of 6-oxo-PGF1 alpha in hydrolysed and non-hydrolysed samples. 6-oxo-PGF1 alpha, PGF2 alpha and TXB2 were also measured by gas chromatography negative ion chemical ionisation mass spectrometry. PGI2 concentrations by radioimmunoassay and bioassay were significantly correlated (r = 0.92, p less than 0.01). There was no difference between them, disproving the presence of an additional antiaggregatory substance. PGI2 production determined by bioassay (mean 1.21 ng/mg wet weight/h, range 0.59-1.53 ng/mg/h) differed from previously reported values (range 70-325 ng/mg/h). 6-oxo-PGF1 alpha concentrations were confirmed by gas chromatography negative ion chemical ionisation mass spectrometry. Previous determinations of PGI2 production by this tissue overestimated it by approximately 100 times.

Reduced umbilical artery prostacyclin formation in complicated pregnancies

Prostacyclin synthesis is severely depressed in the umbilical arteries of neonates of mothers with gestational diabetes mellitus, juvenile-onset diabetes mellitus, or preeclamptic symptoms, and of mothers who smoke during pregnancy and diabetic mothers who smoke. The reduced production of prostacyclin might be responsible for an increased abortion rate and a higher rate of intrauterine fetal death because of a decrease in placental perfusion and umbilical blood flow.

Plasma prostacyclin from birth to adolescence

The plasma concentration of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), the stable hydration product of prostacyclin, was measured by radioimmunoassay in 111 healthy children aged between 1 day and 16 years and in 21 healthy adults aged between 21 and 72 years. The 6-keto-PGF1 alpha levels in children up to age 16 years were higher than those in adults. During the first 4 days of life the plasma concentrations of 6-keto-PGF1 alpha in term infants were higher (P less than 0.05) than the respective levels in preterm infants. There was no difference between the 6-keto-PGF1 alpha levels measured simultaneously in umbilical arterial and peripheral venous plasma in 7 newborn infants. Maternal pre-eclampsia or epidural analgesia during labour, mode of delivery, birthweight, or sex of the infants were not related to the plasma 6-keto-PGF1 alpha levels on the first day of life. High levels of vasodilatory and anti-aggregatory prostacyclin during the first days of life may play a role in the postnatal adaptation of the circulation and platelet function.

Prostacyclin production during pregnancy: comparison of production during normal pregnancy and pregnancy complicated by hypertension

We investigated prostacyclin (PGI2) biosynthesis during pregnancy by measuring urinary excretion of 2,3-dinor-6-keto-prostaglandin F1 alpha (dinor) and 15-keto-13,14-dihydro-2,3-dinor-6-keto-prostaglandin F1 alpha (15 kd dinor) with the use of specific gas chromatography-mass spectrometry assays. Nine normotensive nonpregnant women, five normotensive women in the mid-trimester of pregnancy, eight normotensive women in the third trimester of pregnancy, and six women who developed hypertension during the third trimester provided 24-hour samples of urine. Normal pregnant women had a fivefold increase in urinary excretion of dinor in comparison to nonpregnant women (253 +/- 21 ng dinor/gm creatinine for controls vs. 1,224 +/- 110 and 1,127 +/- 152 for second and third trimesters) (mean +/- SEM). Pregnant subjects with hypertension had a significant (50%) reduction in urinary dinor excretion in comparison to normotensive pregnant subjects (561 +/- 105 ng dinor/gm creatinine). In subjects selected from each group, the ratio of dinor to 15 kd dinor remained constant. We conclude that PGI2 biosynthesis is increased during normal pregnancy, and that this increase is less in pregnancy-induced hypertension. This raises the possibility that PGI2 helps mediate hemodynamic changes during normal pregnancy, and that a relative decrease in production might be related to the pathogenesis of pregnancy-induced hypertension.