A randomized double-blind trial of 3 aspirin regimens to optimize antiplatelet therapy in essential thrombocythemia

Essential thrombocythemia (ET) is characterized by abnormal megakaryopoiesis and enhanced thrombotic risk. Once-daily low-dose aspirin is the recommended antithrombotic regimen, but accelerated platelet generation may reduce the duration of platelet cyclooxygenase-1 (COX-1) inhibition. We performed a multicenter double-blind trial to investigate the efficacy of 3 aspirin regimens in optimizing platelet COX-1 inhibition while preserving COX-2-dependent vascular thromboresistance. Patients on chronic once-daily low-dose aspirin (n = 245) were randomized (1:1:1) to receive 100 mg of aspirin 1, 2, or 3 times daily for 2 weeks. Serum thromboxane B2 (sTXB2), a validated biomarker of platelet COX-1 activity, and urinary prostacyclin metabolite (PGIM) excretion were measured at randomization and after 2 weeks, as primary surrogate end points of efficacy and safety, respectively. Urinary TX metabolite (TXM) excretion, gastrointestinal tolerance, and ET-related symptoms were also investigated. Evaluable patients assigned to the twice-daily and thrice-daily regimens showed substantially reduced interindividual variability and lower median (interquartile range) values for sTXB2 (ng/mL) compared with the once-daily arm: 4 (2.1-6.7; n = 79), 2.5 (1.4-5.65, n = 79), and 19.3 (9.7-40; n = 85), respectively. Urinary PGIM was comparable in the 3 arms. Urinary TXM was reduced by 35% in both experimental arms. Patients in the thrice-daily arm reported a higher abdominal discomfort score. In conclusion, the currently recommended aspirin regimen of 75 to 100 once daily for cardiovascular prophylaxis appears to be largely inadequate in reducing platelet activation in the vast majority of patients with ET. The antiplatelet response to low-dose aspirin can be markedly improved by shortening the dosing interval to 12 hours, with no improvement with further reductions (EudraCT 2016-002885-30).

Lumiracoxib Does Not Affect the Ex Vivo Antiplatelet Aggregation Activity of Low-Dose Aspirin in Healthy Subjects

This randomized, double-blind, placebo-controlled study evaluated the pharmacodynamic effects of concomitant low-dose aspirin and lumiracoxib in healthy subjects. Participants received lumiracoxib 400 mg once daily (n = 14) or placebo (n = 14) for 11 days, with concomitant low-dose aspirin (75 mg once daily) from days 5 to 11. Ex vivo pharmacodynamic assessments included assays of platelet aggregation and urinary thromboxane and prostacyclin metabolite profile. Arachidonic acid-stimulated platelet aggregation was reduced from 76.3% on day 4 to 4.8% on day 11 in the placebo group and from 75.8% on day 4 to 5.1% on day 11 in the lumiracoxib group. Collagen-induced platelet aggregation was reduced from 77.5% on day 4 to 52.8% on day 11 in the placebo group and from 79.5% on day 4 to 55.9% on day 11 in the lumiracoxib group. Urinary thromboxane and prostacyclin were unaffected by lumiracoxib. In conclusion, concomitant lumiracoxib did not interfere with the cyclooxygenase-1-mediated antiplatelet effects of low-dose aspirin.

Prostaglandin I2 release following mesenteric traction during abdominal surgery is mediated by cyclooxygenase-1

Our study aimed to determine the role of cyclooxygenase-2 in the release of prostaglandin-(PG)-I2 following mesenteric traction during abdominal surgery. In a prospective double-blind, randomized, placebo-controlled study, 40 patients electively scheduled for non-laparoscopic abdominal surgery, were pretreated with the cyclooxygenase-2 inhibitor parecoxib (n=20) or placebo (n=20). Heart rate, arterial blood pressure, oxygenation ratio and plasma concentrations of the stable PGI2-metabolite 6-keto-PGF1alpha were compared between groups before injection of parecoxib (-40 min), immediately before mesenteric traction (0 min), and 5, 10, and 30 min thereafter. In addition, plasma concentrations of valdecoxib, the active metabolite of the prodrug parecoxib, were determined. Plasma concentrations of 6-keto-PGF1alpha and heart rate increased in both groups after mesenteric traction. There were no significant differences between groups at individual times in heart rate, arterial blood pressure and plasma concentrations of 6-keto-PGF1alpha. Oxygenation ratio decreased after 10 and 30 min following mesenteric traction in the parecoxib group with a significant difference between treatment groups at 10 and 30 min. Plasma concentrations of valdecoxib revealed therapeutic values. Our data indicate that PGI2 release following mesenteric traction is mediated by cyclooxygenase-1.

Prostacyclin, thromboxane A and the effect of low-dose ASA in pregnancies at high risk for hypertensive disorders

BACKGROUND

The aim of this study was to investigate the prostanoid production in pregnancies at high risk for hypertensive disorders, and the effect of low-dose acetylsalicylic acid (ASA) on prostanoids.

MATERIAL AND METHODS

Ninety women with a bilateral notching in uterine arteries screened by Doppler ultrasound at 12-14 gestational weeks were randomized to the ASA (0.5 mg/kg/day) or placebo group. Forty-three women in both groups were followed up throughout the pregnancy. Urine samples were taken at baseline, and at 24-26 and 32-34 weeks of gestation to determine the urinary 11-dehydrothromboxane B(2) (u-11-dehydro-TxB(2)) and 2,3-dinor-6-keto-prostaglandin F(1alpha) (u-2,3-dinor-6-keto-PGF(1alpha)), the metabolites of thromboxane A(2) and prostacyclin, respectively.

RESULTS

In the pregnancies with pregnancy-induced hypertension (PIH) before 37 gestational weeks, the 2,3-dinor-6-keto-PGF(1alpha)/11-dehydro-TxB(2) ratio did not increase as much as in other pregnancies (P = 0.028). In the placebo group pregnancies with preeclampsia had significantly lower 2,3-dinor-6-keto-PGF(1alpha) (P = 0.019) at 12-14 weeks of gestation compared to other pregnancies. In the placebo group the 2,3-dinor-6-keto-PGF(1alpha)/11-dehydroTxB(2) ratio remained unchanged throughout the pregnancy, with no significant difference between pregnancies with a normal or an adverse outcome. In the ASA group the 2,3-dinor-6-keto-PGF(1alpha)/11-dehydro-TxB(2) ratio increased (P < 0.001, early vs. midpregnancy). Again, the changes were similar in pregnancies with a normal or an adverse outcome.

CONCLUSION

The balance of prostacyclin and thromboxane A(2) shifted in an unfavorable direction in pregnancies complicated by PIH. ASA had a favorable effect on the prostanoids.

Pharmacokinetic and pharmacodynamic differences between two low dosages of aspirin may affect therapeutic outcomes

BACKGROUND

Meta-analyses of the prevention of major vascular events by aspirin suggest therapeutic equivalence of all dosages. However, the optimal dosage still remains problematic, and a recent trial found aspirin 160 mg/day to be more effective than 80 mg/day for secondary prevention of ischaemic stroke.

OBJECTIVE

To evaluate two low dosages of aspirin in terms of pharmacokinetics and pharmacodynamics (inhibition of platelet thromboxane generation and urinary excretion of thromboxane and prostacyclin metabolites).

DESIGN AND PARTICIPANTS

A randomised cross-over study was performed in 16 healthy volunteers (9 women and 7 men, 33.8 +/- 5.1 years old) given enteric-coated aspirin 80 or 160 mg/day for 7 days.

METHODS

Plasma concentrations of salicylate and aspirin were measured by high-performance liquid chromatography (HPLC) after both the first and the last dose (days 1 and 7). The usual pharmacokinetic parameters were then derived. Serum thromboxane B2 (TxB2) was measured by radioimmunoassay. The urinary excretion of 11-dehydro-TxB2 and 2,3-dinor-6-keto-prostaglandin F1alpha were measured on 8-hour urine samples by immunoassay after extraction and HPLC separation, both before and after 7 days of drug administration.

RESULTS

With the 160 mg dosage, but not with the 80 mg dosage, higher concentrations of aspirin were found at day 7 compared with day 1. For aspirin 80 mg/day, 24-hour area under the concentration-time curve (AUC24) was similar on days 1 and 7 (569 +/- 339 vs 605 +/- 377 microg. h/L), but increased from 904 +/- 356 microg. h/L on day 1 to 1355 +/- 883 microg. h/L on day 7 with the higher dosage. Similarly, the AUC24 for salicylate was similar on days 1 and 7 with the lower dosage, but significantly increased from day 1 to day 7 after the higher dosage. This paralleled inhibition of serum TxB2 levels (99% vs 95% average inhibition by 160 and 80 mg/day) and of urinary excretion of thromboxane metabolite (77% vs 61% average inhibition by 160 and 80 mg/day), without altering the excretion of prostacyclin metabolite.

CONCLUSIONS

Inhibition of serum TxB2 generation and of thromboxane metabolite urinary excretion by the lower dosage of aspirin, although substantial, still appeared incomplete. The small but significant further increase of serum TxB2 inhibition by the higher dosage was accompanied by an even greater inhibition of urinary excretion. We suggest that in some instances this difference would translate into a greater clinical benefit with the higher aspirin dosage. Our findings may also contribute to better definition of the recent concept of 'aspirin resistance'.

Cocaine decreases urinary prostacyclin release in pregnancy: correlation with uterine and umbilical Doppler velocimetry

OBJECTIVE

The purpose of this study was to determine maternal urinary prostacyclin and thromboxane excretion in patients with recent cocaine use, compared to cocaine-free controls, and correlate the findings with Doppler velocimetry.

STUDY DESIGN

Seventeen patients admitted with premature rupture of membranes between the gestational ages of 24 and 34 weeks were tested for urinary cocaine metabolites. Eleven patients had positive screening and six patients were negative and served as controls. After initial stabilization, 24-h urine collections were obtained and were assayed for the prostacyclin metabolite 2,3-dinor-6-keto-PGF(1alpha), and the thromboxane metabolite 2,3-dinor TXB2. These patients underwent uterine and umbilical arterial Doppler velocimetry expressed as the pulsatility index. Statistical analysis was performed by the SPSS statistical package using the non-paired Student t test, and Spearman correlation coefficient with p < 0.05 being considered significant.

RESULTS

Compared with controls, urinary excretion of prostacyclin in pregnant women with recent cocaine use was significantly lower. The pulsatility index of the uterine arteries of the cocaine-positive individuals was higher than in controls and had a significant inverse correlation with prostacyclin metabolite excretion. Umbilical arterial velocimetry was similar in the two groups.

CONCLUSION

Recent cocaine ingestion in pregnant women decreases production of prostacyclin and negatively affects the pulsatility index of the uterine artery.

Effect of two oral contraceptives with different ethinyl estradiol and levonorgestrel concentrations on the urinary excretion of biochemical vasoactive markers

In the present study the effect on the urinary excretion of vasoactive markers of two oral contraceptives (OCs), i.e., Leios, containing 0.02 mg ethinyl estradiol and 0.1 mg levonorgestrel, and Stediril 30, containing 0.03 mg ethinyl estradiol and 0.15 mg levonorgestrel, was investigated. cGMP, prostacyclin and its antagonist thromboxane, serotonin, and urodilatin, a natriuretic and diuretic peptide formed in the kidney, were measured as markers. In a comparative, double-blind, randomized, parallel group study, 34 women received Leios and 33 women Stediril 30. Nocturnal urine was collected before treatment and during cyclic treatment after 3 and 12 cycles. Both contraceptives significantly enhanced cGMP excretion after 12 cycles. The prostacyclin metabolite remained unchanged for both formulations, but the excretion of the thromboxane metabolite was significantly decreased after 12 cycles. Thus, the ratio of prostacyclin to thromboxane, crucial for the resulting effect on vascular tone, increased significantly. For the serotonin metabolite, no changes were observed for both contraceptives. The excretion of urodilatin significantly increased for both preparations after 12 cycles compared to the pretreatment values. These results indicate that the low-dose OCs Leios and Stediril 30 may stimulate the production of some vasoactive markers, at least after 12 cycles of treatment. The positive influence of these contraceptives on the various markers investigated may improve vascular tone, impede development of atherosclerosis and arterial thrombosis, and improve water and electrolyte homeostasis. These effects most likely can be attributed to the estrogenic component. Levonorgestrel may elicit no impact on these estrogen-induced changes that, however, seem only to be manifested after a longer treatment period.

Relationship between thromboxane/prostacyclin ratio and diabetic vascular complications

To elucidate the relationship between the thromboxane A2/prostacyclin (TXA2/PGI2) ratio and diabetic complications, the levels of 11-dehydro-thromboxane B2 and 2,3-dinor-6-keto-prostaglandin F1alpha, the urinary metabolites of thromboxane A2 and prostacyclin, were measured in diabetics by gas chromatography/selected ion monitoring. We compared the TXA2/PGI2 ratio in healthy volunteers and diabetics. The TXA2/PGI2 ratio of diabetics was significantly higher than that of healthy volunteers and we could reconfirm the hypercoagulable condition in diabetics. We also investigated the difference of TXA2/PGI2 levels in diabetics with retinopathy and neuropathy. The TXA2/PGI2 ratio of diabetics with retinopathy showed significantly higher level than without retinopathy. However, the TXA2/PGI2 ratio of diabetics with neuropathy was the same as without neuropathy. These results suggest that the TXA2/PGI2 ratio reflects the pathological conditions of diabetes, especially the change of vasculature. The monitoring and improvement of TXA2/PGI2 ratio could be useful for the prevention of diabetic vascular complications.

Analysis of urinary prostacyclin and thromboxane/prostacyclin ratio in patients with rheumatoid arthritis using gas chromatography/selected ion monitoring

We investigated production of prostacyclin and the urinary ratio of thromboxane and prostacyclin in patients with rheumatoid arthritis. The prostacyclin production level was assessed according to the level of urinary 2,3-dinor-6-keto-prostaglandin F(1 alpha)measuring by gas chromatography/selected ion monitoring. In patients receiving medication, the prostacyclin level was lower and the thromboxane/prostacyclin ratio was greater compare with that of healthy volunteers. The prostacyclin level in patients without medication was approximately 4-fold higher than that of healthy volunteers and 8-fold higher than those of medicated groups. Although the ratio of the group without medication was similar to that of healthy volunteers, the urinary levels of each prostanoid were higher than those of other groups. Then, the ratios of groups receiving steroids were higher than that of other groups owing to high TX level. The present findings demonstrated that endogenous prostacyclin and thromboxane production increased in patients without medication, and prostacyclin production decreased with medication.

[Effect of transdermal versus oral estradiol administration on the excretion of vasoactive markers in postmenopausal women]

OBJECTIVES

Can transdermal (n=20) and oral (n=20) estradiol substitution influence the urinary excretion of vasoactive substances in postmenopausal women?

METHOD

The vasoactive substances prostacyclin and thromboxane, cyclic guanosine monophosphate, which can reflect the systemic NO production, serotonin, relaxin, insulin and melatonin were measured in nocturnal 8-hour urine before and after 2 and 4 weeks' estradiol treatment.

RESULTS

The excretion ot prostacyclin and thromboxane, calculated as a prostacyclin/thromboxane quotient, was shifted towards higher prostacyclin production. Only minor changes could be registered for the cyclic guanosine monophosphate excretion. The production of serotonin, relaxin and insulin was increased only after transdermal treatment with estradiol. For melatonin no changes could be observed.

CONCLUSIONS

Hormone substitution therapy with estradiol in postmenopausal women is able to increase the urinary excretion of various vasoactive substances, both after transdermal and oral application, indicating a vasodilatory estrogenic action. Transdermal administration was more effective, although lower dosages were applied. An explanation may be that transdermal estradiol elicits continuous and constant effects on estrogenic target organs.

Volume-induced natriuresis in healthy women: renal metabolism of prostacyclin and thromboxane, and physiological role of prostanoids

In healthy women submitted to a short-term expansion in extracellular fluid volume we have evaluated the urinary excretory profile of the stable metabolites of prostaglandin(PG) I2 and thromboxane(TX) A2, 6-keto-PGF1 alpha(6KPGF) and TXB2 respectively, and assessed the physiological role played by the prostanoids in this experimental condition. Salt retention (SR group, n=9) was induced by repeated i.v. infusion of saline solution (0.9% NaCl). At the end of the treatment the body weight had increased by 0.7+/-0.2 kg (mean+/-SEM) (P<0.05). Renal functional exploration [clearance (cl.) method] was performed during hypotonic polyuria (induced by oral water load) and subsequent moderate antidiuresis (induced by low-dose infusion of an antidiuretic hormone analogue). Urinary 6KPGF and TXB2 concentrations were estimated by RIA method during polyuria (P cl. period), early and late antidiuresis (A1 and A2 cl. periods). Paired functional explorations were performed in absence (control study) and presence of indomethacin. Basal values of plasma sodium and potassium concentrations, plasma renin activity (PRA) and urinary aldosterone excretion were determined just before the control study. The results in salt retention were compared to those previously obtained in healthy women submitted to a moderate salt depletion (SD2 group, n=6), in absence and presence of the drug. Women in salt retention received 100 mg i.m. of the drug, whereas salt-depleted women received only a halved dose as in previous studies in salt depletion the full dose produced prolonged anuria. (I) Salt retention vs salt depletion. The basal values of PRA and urinary aldosterone excretion were significantly lower. During polyuria, urinary excretion of 6KPGF, 6KPGF/TXB2 ratio, urinary flow rate, creatinine cl. and absolute and fractional excretions of sodium and chloride were significantly higher. In salt retention during polyuria, significant positive correlations were found between 6KPGF excretion and functional excretory parameters. (II) Indomethacin in salt retention. The following effects were significant: (a) a reduction in prostanoid excretions in P and A1 cl. periods only; (b) during polyuria, an increase in arterial pressure, a reduction in urinary flow rate and creatinine cl. (saluresis showed not significant reduction). During polyuria significant positive correlations occurred between the absolute effects of indomethacin on 6KPGF excretion and those on functional excretory parameters. (III) Comparative effects of indomethacin in salt retention and salt depletion. Despite the double dosage of the drug, the significant reductions in urinary metabolite excretions were not significantly different during P cl. period and significantly lower in A1 cl. period compared to the corresponding significant reductions in salt depletion. During polyuria, the significant increase in arterial pressure was significantly different from the not significant effect in salt depletion; the not significant effect on saluresis was significantly different from the significant reduction in salt depletion. The results suggest the following conclusions: (1) The present model showed the functional pattern of the volume-natriuresis; (2) In salt retention, in contrast with salt depletion, indomethacin induced an increase in arterial pressure consistent with the inhibition of a PG-dependent vasodilator mechanism active at the systemic level; (3) In salt retention, in contrast with salt depletion, indomethacin failed to induce a significant reduction in saluresis. This failure can be attributed to the drug's blunted effectiveness in inhibiting the renal synthesis of saluretic PGs, and probably to the interference of the concurrent increase in arterial pressure in the renal treatment of sodium and chloride.

Urinary thromboxane, prostacyclin, cortisol, and 8-hydroxy-2'-deoxyguanosine in nonsmokers exposed and not exposed to environmental tobacco smoke

This study tested the hypotheses that (1) increased platelet aggregation, as measured by 2,3-dinor-thromboxane B(2) (Tx-M) and 2,3-dinor-6-keto-prostaglandin F(1alpha) (PGI-M), and (2) increased oxidative stress, as measured by 8-Hydroxy-2'-deoxyguanosine (8-OHdG), would occur in ETS-exposed nonsmokers as compared with non-ETS-exposed nonsmokers. The concentrations of the stable urinary metabolites of thromboxane (Tx-M) and prostacyclin (PGI-M), cortisol and 8-OHdG were measured in a 24-h urine sample from 3 groups of subjects: 21 nonsmokers with minimal (15 min or less per day) ETS exposure (termed non-ETS-exposed), 22 nonsmokers with at least 5 h per day of ETS exposure (termed ETS-exposed), and 20 cigarette smokers who served as a positive control group. The self-reported levels of ETS exposure were verified by personal air monitors. As compared with either group of nonsmokers, cigarette smokers excreted significantly more urinary Tx-M. Non-ETS-exposed nonsmokers showed a statistically significantly higher level of urinary Tx-M over that seen in nonsmokers with considerably more ETS exposure. Urinary concentrations of PGI-M were marginally higher in the smokers and did not differ between the nonsmoker groups. Nonsmokers exposed to at least five h of ETS per day did not have significantly higher excretion of 8-OHdG than non-ETS-exposed nonsmokers. The results from this study suggest that platelet aggregation, as measured by the thromboxane metabolite Tx-M and prostacyclin metabolite PGI-M, is not associated with ETS exposure. Therefore, platelet aggregation is not a plausible or quantitatively consistent mechanism to explain the nonlinear dose-response hypothesis of cardiovascular disease and ETS exposure.

Urinary prostaglandin excretion in pregnancy: the effect of dietary sodium restriction

INTRODUCTION

Dietary sodium restriction results in activation of the renin-angiotensin-aldosterone-system. In the non-pregnant situation renin release in response to a low sodium diet is mediated by prostaglandins. We studied the effect of dietary sodium restriction on urinary prostaglandin metabolism in pregnancy.

PATIENTS AND METHODS

In a randomized, longitudinal study the excretion of urinary metabolites of prostacyclin (6-keto-PGF(1 alpha)and 2,3-dinor-6-keto-PGF(1 alpha)) and thromboxane A(2)(TxB(2)and 2,3-dinor-TxB(2)) was determined throughout pregnancy and post partum in 12 women on a low sodium diet and in 12 controls.

RESULTS

In pregnancy the excretion of all urinary prostaglandins is increased. The 6-keto-PGF(1 alpha)/ TxB(2)-ratio as well as the 2, 3-dinor-6-keto-PGF(1 alpha)/ 2,3-dinor-TxB(2)-ratio did not significantly change in pregnancy. CONCLUISION Prostacyclin and thromboxane do not seem to play an important role in sodium balance during pregnancy.

Habitual smoking causes an abnormality in platelet thromboxane A2 metabolism and results in an altered susceptibility to aspirin effects

The present study investigates the effects of aspirin (100 mg every second day for 14 days) on platelet function in nine healthy non-smokers and in nine healthy habitual smokers. There was a significantly (P < 0.05) stronger inhibition of collagen (0.6 microgram/ml)- and ADP (2 microM)-induced platelet aggregation by aspirin in smokers as compared to non-smokers. This difference occurred in the presence of an almost complete (> 95%) inhibition of thromboxane A2 (TXA2) synthesis in both groups. The platelet capacity to generate TXA2 in vitro was significantly reduced in smokers, urinary excretion of TXA2, however, was significantly increased. Thus, the better susceptibility of smokers to anti-aggregatory effects of aspirin is very likely to be related to a chronic smoking-induced alteration of platelet TXA2 system. Cessation of smoking should, therefore, be encouraged.

Changes of the thromboxane A2/prostacyclin balance in the urine of patients with renal diseases analyzed by gas chromatography/selected ion monitoring

The thromboxane A2/prostacyclin (TX/PGI) ratios were measured in patients with renal diseases to elucidate the relationship between the ratios and the pathological changes of the diseases. Urinary stable metabolites of thromboxane A2 and prostacyclin, 11-dehydro-thromboxane B2 and 2,3-dinor-6-keto-prostaglandin F1alpha, respectively, were converted to 1-methyl ester-propylamide-9,12,15-tris-dimethylisopropylsilyl ether derivative and 1-methyl ester-6-methoxime-9,12,15-tris-dimethylisopropylsilyl ether derivative, respectively, and applied to a gas chromatography/selected ion monitoring. The TX/PGI ratios of 10 outpatients and 6 inpatients with chronic glomerulonephritis were higher than those of 13 healthy volunteers. In an inpatient with systemic lupus erythematoides, the TX/PGI ratios were gradually lowered to the normal level with the therapies. Furthermore, the ratios seemed to change in advance of the changes of the levels of urinary protein and hematuria. These observations suggested that the TX/PGI ratio was a useful index to assess the pathological condition of renal diseases and the effects of treatment.

Reduced prostacyclin to thromboxane A2 ratio is correlated with central apneas in preterm infants

Prostacyclin has a vasodilating effect on pulmonary vessels, whereas thromboxane A2 results in vasoconstriction. This study was designed to test the hypothesis that recurrent central apneas in preterm infants are correlated with a reduced prostacyclin to thromboxane A2 ratio. Twelve preterm infants with clinical events of apneas were matched with 12 control infants. Urinary concentration of 2,3-dinor-6-keto-PGF1alpha and 2,3-dinor-TxB2 was determined, and the ratio correlated with the number of central apneas (>20s) measured in overnight polygraphy. The number of central apneas >20s/12h was 97.4 (SE 7.8) in the study group, and 47.3 (SE 6.6) in the control group (p = 0.001). There was a significant correlation between the number of central apneas and the 2,3-dinor-6-keto-PGF1alpha/2,3-dinor-TxB2-ratio in all infants combined (r = -0.72, p < 0.0001) as well as in the two subject groups. Central apneas in premature infants are correlated with an decreased prostacyclin to thromboxane A2 ratio. The underlying pathomechanism may be increased intrapulmonary shunts with reflexive central apneas due to reduced pulmonary oxygenation.

Urinary thromboxane A2/prostacyclin balance reflects the pathological state of a diabetic

Levels of the stable urinary metabolites of thromboxane A2 and prostacyclin, 11-dehydro-thromboxane B2 (11-dehydro-TXB2) and 2,3-dinor-6-keto-prostaglandin F1alpha (2,3-dinor-6-keto-PGF1alpha) were measured in diabetics to elucidate the relation between the thromboxane A2/prostacyclin (TX/PGI) balance and pathological states of diabetes mellitus. 11-Dehydro-TXB2 and 2,3-dinor-6-keto-PGF1alpha were derivatized to methyl ester-propylamide-dimethylisopropylsilyl ether and methyl ester-methoxime-dimethylisopropylsilyl ether derivatives, respectively, and applied to a gas chromatography/selected ion monitoring. The TX/PGI ratios of diabetics were higher than those of healthy volunteers, suggesting the hypercoagulative states of this disease. The ratios showed positive correlations with the levels of blood glucose. The levels of hemoglobin A1c and triglyceride were correlated weakly with the ratio. Some of the patients who had relatively low levels of blood glucose also showed high TX/PGI ratios. Furthermore, the ratio increased in the order of the groups 1, 2, and 3; group 1 contained patients who did not take medicine for diabetes, group 2 contained those who took oral hypoglycemic agents, and group 3 contained those who received insulin therapy. These observations indicate that the TX/PGI ratio reflects the pathological conditions of diabetes and is a useful marker, having few different features from other markers that are presently used.

Monitoring of the thromboxane A2/prostacyclin ratio in the urine of patients with retinal vascular occlusion through the low-dose-aspirin therapy using the gas chromatography/selected ion monitoring method

We determined the levels of the stable urinary metabolites of thromboxane A2 and prostacyclin, 11-dehydro-thromboxane B2 (11-dehydro-TXB2) and 2,3-dinor-6-keto-prostaglandin F1alpha (2,3-dinor-6-keto-PGF1alpha) in patients with retinal vascular occlusion (RVO) to elucidate the change of the thromboxane A2/prostacyclin (TX/PGI) ratio with this disease and the effect of low-dose-aspirin therapy. 11-Dehydro-TXB2 and 2,3-dinor-6-keto-PGF1alpha were converted to 1-methyl ester-propylamide-9,12,15-tris-dimethylisopropylsilyl ether derivative and 1-methyl ester-6-methoxime-9,12,15-tris-dimethylisopropylsilyl ether derivative, respectively, and applied to a gas chromatography/selected ion monitoring. The average level of 11-dehydro-TXB2 in 30 patients with RVO was 1038 +/- 958 pg/mg creatinine. It was significantly higher than that of 27 healthy volunteers, which was 616 +/- 294 pg/mg creatinine (p < 0.05 with unpaired t-test). However, 2,3-dinor-6-keto-PGF1alpha levels were not significantly different between these two groups. The average ratio of TX/PGI in the RVO patients was 32 +/- 26 and it was significantly higher than that of healthy volunteers, 17 +/- 10 (p < 0.01). Patients with central retinal artery occlusion or branch retinal artery occlusion showed greatly high 11-dehydro-TXB2 levels and TX/PGI ratios, although the number of patients was limited in the current study. After the administration of low-dose aspirin (40 mg/day) for about 1 month, the TX/PGI ratio decreased to around the normal level. Following the levels for up to 10 months, they also remained at the normal level. These observations suggested that the 11-dehydro-TXB2 levels and the TX/PGI ratio reflect the pathological conditions of RVO and are useful markers of the treatment.

Effects of very low dose and enteric-coated acetylsalicylic acid on prostacyclin and thromboxane formation and on bleeding time in healthy subjects

OBJECTIVE

Low dose acetylsalicylic acid (ASA) is widely used as an anti-aggregatory agent in the primary and secondary prevention of cardiovascular diseases. In an effort to spare prostacyclin formation and to reduce gastrointestinal side-effects, both very low doses and enteric-coated formulations of ASA have been introduced. However, it still remains unclear whether these different formulations and dosages are equally effective with respect to inhibition of platelet aggregation and thromboxane A2 (TXA2) formation.

METHODS

In a randomized study, we therefore investigated the effects of 100 mg ASA plain (p), 100 mg ASA enteric-coated (ec) and 40 mg ASA (p) to 36 healthy male subjects given for 7 days on platelet aggregation and endogenous prostanoid formation rates. Platelet aggregation and platelet TXB2 release in platelet rich plasma (PRP) and serum TXB2 and 6-keto-PGF1alpha levels were determined at baseline and after 7 days of each medication. The urinary metabolites of TXA2 (2,3-dinor-TXB2) and prostacyclin (2,3-dinor-6-keto-PGF1alpha) were measured by gas chromatography/tandem mass spectrometry in 24-h-urines at baseline and on day 7 of each medication.

RESULTS

Collagen-induced platelet aggregation was 73.1+/-1.6% of maximal aggregation at baseline. It was inhibited by 68.9%, 58.6% and 24.0% by ASA 100 mg plain, 100 mg enteric-coated, and 40 mg plain on day 7, respectively. Platelet TXB2 release was 11592.0+/-367.5 pg x ml(-1) PRP. It was inhibited by 90.1%, 86.5%, and 55.2% by ASA 100 mg plain, 100 mg enteric-coated, and 40 mg plain, respectively. Serum TXB2 was almost completely reduced on day 7 by 100 mg ASA, but not by 40 mg ASA; serum 6-keto-PGF1alpha was slightly, but significantly reduced in all three groups. Urinary 2,3-dinor-TXB, excretion was 196.0+/-41.5 pg x mg(-1) creatinine at baseline. It was reduced by 80.3% and 79.1% by ASA 100 mg plain and enteric-coated, respectively (each P < 0.05 versus baseline), but only by 55.4% by ASA 40 mg plain (P < 0.05 versus both formulations of ASA 100 mg).

CONCLUSIONS

Our present data show that the plain and enteric-coated formulations of 100 mg ASA are equally effective in inhibiting platelet aggregation, platelet thromboxane production, and urinary 2,3-dinor-TXB2 excretion rates. In contrast, a very low dose of 40 mg ASA was significantly less effective in inhibiting these indices of platelet activation in healthy human subjects. ASA enteric-coated 100 mg may be a useful alternative to 100 mg ASA (p) in patients with gastrointestinal side-effects, whereas 40 mg ASA (p) may be too low to inhibit sufficiently platelet activity in patients with cardiovascular diseases in whom platelet activity is increased.

Ticlopidine increases nitric oxide generation in heart-transplant recipients: a possible novel property of ticlopidine

The objective of this study was to evaluate the effects of ticlopidine on the generation of eicosanoids and nitric oxide in heart-transplant recipients. In a randomized double-blind study, we studied the urinary excretion of the stable metabolites of thromboxane, prostacyclin, and nitric oxide before and after ticlopidine (250 mg/day). Platelet aggregation was significantly reduced in ticlopidine-treated patients [from 40.2 +/- 24.2% of maximal aggregation to 14.7 +/- 8.2% in response to adenosine diphosphate (ADP); p < 0.001] but not in the placebo group, confirming the efficacy of the drug with that dosage in these specific patients. The 24-h urinary excretion of prostacyclin metabolites was not modified by ticlopidine (1,865 +/- 833 ng/24 h at day 14 and 1,664 +/- 425 ng/24 h at day 0), whereas the excretion of thromboxane B2 tended to increase in the ticlopidine group (from 3,854 +/- 1,163 ng/24 h at day 0 to 5,014 +/- 2,914 ng/24 h at day 14), although not significantly. The excretion of nitric oxide metabolites (although not different from that of healthy nonimmunosuppressed subjects) was significantly (p < 0.005) increased in the ticlopidine group (from 3,082 +/- 1,683 micromol/24 h at day 0 to 4,133 +/- 2,262 micromol/24 h at day 14), but not in controls. Thus ticlopidine does not reduce prostacyclin but increases the systemic generation of nitric oxide, both substances having major antiplatelet and vasodilator properties. Further studies are warranted to examine whether ticlopidine could reduce the incidence of thromboembolic complications in these patients and whether this possible novel property of ticlopidine is restricted to immunosuppressed heart-transplant recipients.

Chronic dietary supplementation with L-arginine inhibits platelet aggregation and thromboxane A2 synthesis in hypercholesterolaemic rabbits in vivo

OBJECTIVES

L-arginine exerts anti-atherosclerotic effects in hypercholesterolaemic rabbits via modulating endogenous NO production. We investigated whether L-arginine inhibits thromboxane formation in vivo and platelet aggregation ex vivo in this animal model.

METHODS

The urinary excretion rates of 2,3-dinor-6-keto-PGF1 alpha (major urinary metabolite of PGI2) and 2,3-dinor-TXB2 (major urinary metabolite of thromboxane A2) were used as indicators of platelet-endothelial cell interactions in vivo. Rabbits were fed 1% cholesterol (Cholesterol group, N = 8), 1% cholesterol plus 2.25% L-arginine (Cholesterol + L-arginine, N = 8), or normal rabbit chow (Control, N = 4) for 12 weeks. Urine samples were collected in weekly intervals. At the end of the study period platelet aggregation ex vivo and endothelium-dependent and -independent vascular function of isolated aortic rings in vitro was assessed.

RESULTS

Urinary 2,3-dinor-TXB2 excretion significantly increased in the cholesterol group (p < 0.05), and endogenous NO formation (measured as urinary nitrate excretion) decreased (p < 0.05). Both parameters were significantly correlated with each other (R = 0.48, p < 0.01). L-arginine partly restored urinary nitrate excretion and significantly reduced TXA2 production to values even below those in the control group (p < 0.001). Urinary 2,3-dinor-6-keto-PGF1 alpha excretion increased in early hypercholesterolaemia and returned to control values in the second half of the study period. The early increase in urinary 2,3-dinor-6-keto-PGF1 alpha excretion was attenuated by L-arginine. Platelet aggregation was significantly enhanced in cholesterol-fed rabbits and attenuated by dietary L-arginine. L-arginine also improved the impaired endothelium-dependent relaxations to ADP, and normalized the vasoconstrictor effects of 5-HT in isolated aortic rings.

CONCLUSIONS

Cholesterol-feeding enhances platelet aggregation and TXA2 formation, and stimulates platelet-endothelial cell interaction in rabbits. These effects are probably due to impaired NO elaboration, as indicated by decreased urinary nitrate excretion. Chronic dietary supplementation with L-arginine elevates systemic NO elaboration and significantly increases the PGI2/TXA2 ratio. It thus beneficially influences the homeostasis between vasodilator and vasoconstrictor prostanoids in vivo.

Which prostanoid metabolites should be determined for the study of reproductive processes?

The non-enzymatic metabolites of prostacyclin (PGI2) and thromboxane A2 (TXA2), 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) and thromboxane B2 (TXB2), and their 2,3-dinor metabolites, 2,3-dinor-6-keto-PGF1alpha and 2,3-dinor-TXB2, were measured in early morning urine samples in 24 in vitro fertilization (IVF) cycles in 24 women and in 27 women who became pregnant after IVF and embryo transfer (ET). The sum of the non-enzymatic metabolites and their 2,3-dinor metabolites was considered to be a reflection of total PGI2 and total TXA2 production in vivo. Both the ratio of 'total' PGI2/'total' TXA2 and the ratio of the 2,3-dinor metabolites were calculated. TXB2 concentrations showed virtually no change and the ratios of the non-enzymatic metabolites of PGI2 and TXA2 versus their 2,3-dinor metabolites remained relatively constant. As a consequence, the ratio of 2,3-dinor-6-keto-PGF1alpha/2,3-dinor-TXB2 was a close reflection of the ratio of 'total' PGI2/'total' TXA2, although the latter ratio was significantly higher all the time. We conclude that for comparative studies on the balance between PGI2 and TXA2 in IVF cycles and during gestation, the determination of the 2,3-dinor metabolites alone can replace the measurement of all four metabolites.

The effect of short-term diets rich in fish, red meat, or white meat on thromboxane and prostacyclin synthesis in humans

Foods which increase tissue arachidonic acid levels have been proposed to increase thrombosis tendency, presumably through increased platelet aggregation. This study examined the effect of doubling the dietary arachidonic acid (20:4n-6) using meat- or fish-based diets on the systemic production of prostacyclin (PGI2) and thromboxane (TXA2) in 29 healthy, nonsmoking adults. There were three, 3-wk low-fat dietary periods (< 15% energy as fat) in which subjects consumed a vegetarian diet for 1 wk followed by 2 wk on diets containing meat or fish as sources of 20:4n-6. Between each diet period, there was a 3-wk washout period, during which subjects returned to their normal diets. The level of 20:4n-6 consumed during the last 2 wk of each study was approximately double the usual intake (mean 140 mg/d), while the mean eicosapentaenoic acid (20:5n-3) content of the diets varied from 1 mg/d on the white meat diet to 70 mg/d on the red meat diet and to 847 mg/d on the fish diet. The serum phospholipid (PL) 20:4n-6/20:5n-3 ratios were 11:1 on the vegetarian diet, 15:1 on the white meat diet, 8:1 on the red meat diet, and 2:1 on the fish diet (P < 0.001). Neither white nor red meat diets affected platelet 20:4n-6 levels, platelet aggregation, ex vivo platelet TXB2 production, or the systemic PGI2 or TXA2 production as measured by gas chromatography-mass spectrometry analysis of the excretion levels of the principal urinary metabolites 2,3-dinor-6-keto-PGF1 alpha (PGI2-M) and 11-dehydro-TXB2 (TXA2-M), respectively. The fish diet decreased the 20:4n-6/20:5n-3 ratio in platelet PL from the baseline level of 45:1 to 13:1 (P < 0.001), had no effects on platelet aggregation, but significantly decreased platelet TXB2 production (collagen-stimulated) and TXA2-M production, while PGI2-M levels were unaltered. These results indicate that short-term diets which double the usual 20:4n-6 intake using white meat (175-330 g/d) or red meat (275-530 g/d) are not associated with an increased TXA2 production, but this does not rule out the adverse effects of 20:4n-6 at higher levels in the diet, or for more prolonged periods. Short-term diets containing fish (100-200 g/d with 90-210 mg/d 20:4n-6 and approximately 650-1000 mg/d 20:5n-3) led to significant increases in platelet 20:5n-3 levels and a decrease in the ex vivo and systemic TXA2 production.

A human dietary arachidonic acid supplementation study conducted in a metabolic research unit: rationale and design

While there are many reports of studies that fed arachidonic acid (AA) to animals, there are very few reports of AA feeding to humans under controlled conditions. This 130-d study was conceived as a controlled, symmetrical crossover design with healthy, adult male volunteers. They lived in the metabolic research unit (MRU) of the Western Human Nutrition Research (WHNRC) for the entire study. All food was prepared by the WHNRC kitchen. The basal (low-AA) diet consisted of natural foods (30 en% fat, 15 en% protein, and 55 en% carbohydrate), containing 210 mg/d of AA, and met the recommended daily allowance for all nutrients. The high-AA (intervention) diet was similar except that 1.5 g/d of AA in the form of a triglyceride containing 50% AA replaced an equal amount of high-oleic safflower oil in the basal diet. The subjects (ages 20 to 39) were within -10 to +20% of ideal body weight, nonsmoking, and not allowed alcohol in the MRU. Their exercise level was constant, and their body weights were maintained within 2% of entry level. Subjects were initially fed the low-AA diet for 15 d. On day 16, half of the subjects (group A) wee placed on the high-AA diet, and the other group (B) remained on the low-AA diets. On day 65, the two groups switched diets. On day 115, group B returned to the low-AA diet. This design, assuming no carryover effect, allowed us to merge the data from the two groups, with the data comparison days being 65 (low-AA) and 115 (high-AA) for group B and 130 (low-AA) and 65 (high-AA) for group A. The main indices studied were the fatty acid composition of the plasma, red blood cells, platelets, and adipose tissue; in vitro platelet aggregation, bleeding times, clotting factors; immune response as measured by delayed hypersensitivity skin tests, cellular proliferation of peripheral blood mononuclear cells in response to various mitogens and antigens, natural killer cell activity, and response to measles/mumps/rubella and influenza vaccines; the metabolic conversion of deuterated linoleic acid to AA and the metabolic fate of deuterated AA in the subjects on and off the high-AA diet; and the production of eicosanoids as measured by excretion of 11-DTXB2 and PGI2-M in urine. The results of these studies will be presented in the next five papers from this symposium.

The effects of ibuprofen on the physiology and survival of patients with sepsis. The Ibuprofen in Sepsis Study Group

BACKGROUND

In patients with sepsis the production of arachidonic acid metabolites by cyclooxygenase increases, but the pathophysiologic role of these prostaglandins is unclear. In animal models, inhibition of cyclooxygenase by treatment with ibuprofen before the onset of sepsis reduces physiologic abnormalities and improves survival. In pilot studies of patients with sepsis, treatment with ibuprofen led to improvements in gas exchange and airway mechanics.

METHODS

From October 1989 to March 1995, we conducted a randomized, double-blind, placebo-controlled trial of intravenous ibuprofen (10 mg per kilogram of body weight [maximal dose, 800 mg], given every six hours for eight doses) in 455 patients who had sepsis, defined as fever, tachycardia, tachypnea, and acute failure of at least one organ system.

RESULTS

In the ibuprofen group, but not the placebo group, there were significant declines in urinary levels of prostacyclin and thromboxane, temperature, heart rate, oxygen consumption, and lactic acidosis. With ibuprofen therapy there was no increased incidence of renal dysfunction, gastrointestinal bleeding, or other adverse events. However, treatment with ibuprofen did not reduce the incidence or duration of shock or the acute respiratory distress syndrome and did not significantly improve the rate of survival at 30 days (mortality, 37 percent with ibuprofen vs 40 percent with placebo).

CONCLUSIONS

In patients with sepsis, treatment with ibuprofen reduces levels of prostacyclin and thromboxane and decreases fever, tachycardia, oxygen consumption, and lactic acidosis, but it does not prevent the development of shock or the acute respiratory distress syndrome and does not improve survival.

Different effects of oral and transdermal hormonal replacement on prostacyclin and thromboxane A2

OBJECTIVE

To elucidate the mechanism of cardiovascular protection of hormone replacement therapy (HRT) by comparing the effect of oral and transdermal HRTs on the production of antiaggregatory, vasodilatory prostacyclin, and its endogenous antagonist, thromboxane A2.

METHODS

Oral estradiol (2.0 mg/d) plus norethisterone acetate (1.0 mg/d) (n = 13) or transdermal estradiol (50 micrograms/d) plus medroxyprogesterone acetate (10 mg/d) as 12-day courses at 4-week intervals (n = 13) were given to postmenopausal women. Urinary excretion of the metabolites of prostacyclin, ie, 6-ketoprostaglandinF1 alpha and 2,3-dinor-6-ketoprostaglandinF1 alpha, as well as those of thromboxane A2, ie, thromboxane B2 and 2,3-dinor-thromboxane B2, were measured by radioimmunoassays, after purification by extraction and high performance liquid chromatography, before and during the sixth and the 12th treatment cycles.

RESULTS

Oral HRT stimulated excretion of thromboxane B2 from 3.4 +/- 0.7 ng/mmol creatinine to 4.5 +/- 1.5 (mean +/- standard deviation, P < .05) and that of 2,3-dinor-thromboxane B2 from 16.6 +/- 8.0 ng/mmol creatinine to 26.2 +/- 10.7 (P < .01), and thus led to the dominance of thromboxane A2. No changes in prostanoids occurred during transdermal HRT.

CONCLUSIONS

The effects of various HRTs on prostanoids may significantly differ.

Profound decrease of in vivo formation of thromboxane during oestrogen therapy

Oestrogen has been proposed to influence platelet activity and formation of the vasoactive eicosanoids thromboxane and prostacyclin. Previous studies have been based on ex vivo techniques with well-known artifacts during blood sampling and ex vivo conditions. The present study is the first to assess in vivo formation through gas chromatographic/mass spectrometric analysis of the major urinary metabolites 2,3-dinor-thromboxane B2 and 2,3-dinor-6-keto-PGF1 alpha. Ten consecutive male patients with prostatic carcinoma participating in a randomized study comparing the effects of parenteral oestrogen therapy (n = 5) with orchidectomy (n = 5) were included. Oestrogen was given as polyestradiol phosphate 240 mg i.m. every month, 2,3-dinor thromboxane B2 and 2,3-dinor-6-keto-PGF1 alpha were analysed with the help of tetradeuterated internal carriers/standards. We found a consistent decrease of in vivo formation of thromboxane by approximately 40% during parenteral oestrogen therapy (P = 0.008) and a doubling after surgical castration. The ratio of prostacyclin to thromboxane increased by approximately 50% (P = 0.023) during oestrogen therapy. In conclusion, oestrogen induced a marked decrease of in vivo formation of thromboxane and a marked increase in the ratio of prostacyclin to thromboxane formation in all patients. According to current knowledge this should be beneficial for the cardiovascular system. Furthermore, thromboxane formation increased after surgical castration. The latter fact should direct attention to the influence of androgens on thromboxane synthesis. Our findings discloses a marked sex-hormone sensitivity of the thromboxane-forming system.

Effect of captopril on prostacyclin and nitric oxide formation in healthy human subjects: interaction with low dose acetylsalicylic acid

1. Angiotensin converting enzyme inhibitors have been suggested to act in part by potentiating the stimulatory effect of bradykinin on endothelial prostacyclin and/or nitric oxide (NO) formation. This may give rise to interaction with cyclo-oxygenase inhibiting drugs like acetylsalicylic acid, which is most often used in low doses in patients with cardiovascular diseases. 2. We investigated the effects of captopril (2 x 25 mg day-1), or ASA (1 x 100 mg day-1), or the combination of both drugs for 7 days, on blood pressure, prostanoid and NO formation rates in a double-blind, double dummy, randomized crossover study in 13 healthy female subjects. The urinary metabolites of thromboxane A2 (2,3-dinor-TXB2) and prostacyclin (2,3-dinor-6-keto-PGF1 alpha), and PGE2 were measured by gas chromatography/tandem mass spectrometry in urine on days 1, 6 and 7 of each medication. NO formation was assessed using urinary NO3- and cyclic GMP as indicators. 3. Urinary 2,3-dinor-6-keto-PGF1 alpha excretion was not significantly changed by either captopril, ASA, or their combination. Urinary 2,3-dinor-TXB2 excretion was inhibited by > 80% by ASA alone or in combination with captopril (each P < 0.05), but was not affected by captopril alone. Urinary PGE2 excretion was not significantly changed by either of the treatments. Urinary NO3- and cyclic GMP excretion rates were not significantly changed by captopril, ASA, or their combination. 4. Blood pressure was slightly reduced by captopril. ASA had no effect on blood pressure when given alone, nor did it modulate the effect of captopril on blood pressure during co-administration. Angiotensin II/angiotensin I ratio (index of ACE activity) was significantly decreased by captopril alone or in combination with ASA, but was unaffected by ASA alone. 5. Captopril does not stimulate prostacyclin formation in healthy human subjects in a dose sufficient to substantially inhibit ACE activity. Co-administration of ASA significantly inhibits 2,3-dinor-TXB2 excretion, but does not interfere with the blood pressure lowering effect of captopril in healthy human subjects.

Biosynthesis of prostacyclin and thromboxane A2 during chronic hypoxaemia in children with cyanotic congenital heart disease

The high risk of vaso-occlusive events in children younger than 4 years with cyanotic congenital heart disease and polycythaemia has been attributed to increased thromboxane (Tx) A2 formation. In older children with cyanotic congenital heart disease, however, the risk of vaso-occlusive events is much lower. We therefore hypothesized that the formation of TxA2 and prostacyclin is not disturbed in this age group. We measured urinary excretion of stable index metabolites of in vivo TxA2 and prostacyclin formation by gas chromatography-mass spectrometry in nine children (age 5.9-14.4, median 8.7 years) with cyanotic congenital heart disease, and in nine healthy, age-matched control subjects. The patients excreted less 2,3-dinor-TxB2 (systemic TxA2 formation, P = 0.03), 2,3-dinor-6-keto-PGF1 alpha (systemic prostacyclin formation. P = 0.03) and TxB2 (renal TxA2 formation, P = 0.01) than the control subjects. We conclude that in children older than 5 years with cyanotic congenital heart disease, endogenous synthesis of TxA2 and prostacyclin is not stimulated. This result may explain the lower risk of vaso-occlusive events in this age group as compared with younger children. In addition, our results suggest that chronic hypoxaemia may affect the in vivo formation of TxA2 and prostacyclin and the metabolic disposition of TxB2.

Prostanoid biosynthesis in patients with cystic fibrosis

The urinary excretion rate (ng/h/1.73 m2) of prostanoids was determined with a capillary gas-liquid chromatographic mass spectrometric method in 19 patients with cystic fibrosis (CF) aged 1-29 years. Patients with CF showed an increased excretion of prostaglandin E2 metabolites (PGE-M) and thromboxane B2 and its metabolites at all ages. An imbalance in the excretion pattern of thromboxane B2 metabolites also suggested a relative impairment of beta-oxidation. There was no increased excretion of dinor-6-keto-PGF1 alpha, indicating normal prostacyclin biosynthesis. No correlation was found to genotype, clinical score, lung function or bacterial colonization but a significant negative relation was found between the main prostanoids in the urine and serum phospholipid levels of essential fatty acids. The results show that, contrary to the generally accepted decrease of prostanoid excretion in essential fatty acid deficiency, patients with CF increase their production parallel to the development of the deficiency. Since prostanoid synthesis is rate limited by arachidonic acid release, our data support a previously presented hypothesis about a pathological regulation of the release of arachidonic acid in CF.

Effect of antiestrogen regimen on prostacyclin and thromboxane A2 in postmenopausal patients with breast cancer: evidence of significance of hypertension, smoking or previous use of estrogen therapy

To explore the mechanism(s) by which antiestrogens may protect against the development of cardiovascular disorders, we measured the production of vasodilatory, antiaggregatory prostacyclin (PGI2) and that of vasoconstrictive, proaggregatory thromboxane A2 (TxA2) before and after 6 months' use of antiestrogens in postmenopausal patients after operation for stage II breast cancer (n = 38). Urine samples were assayed by high performance liquid chromatography and radio-immunoassays for 2,3-dinor-6-ketoprostaglandin F1 alpha (= metabolite of PGI2, dinor-6-keto) and for 2,3-dinor-thromboxane B2 (= metabolite of TxA2, dinor-TxB2). In addition, in 35 of these 38 patients we assayed the capacity of platelets to produce thromboxane A2 during standardized blood clotting. The 4 patients using low-dose aspirin had low thromboxane production, and were excluded from further analysis of the data. An antiestrogen regimen consisting either of tamoxifen (n = 15) or of toremifene (n = 19) caused no changes in production of PGI2 or TxA2, or in their ratio, and in this regard, these antiestrogens behaved similarly. Hypertensive patients (n = 7) using different anti-hypertensive agents were characterized by reduced urinary out-put of dinor-6-keto (18.5 +/- 6.1 vs 35.5 +/- 18.5 ng/mmol, mean +/- SD, p < 0.05) and reduced platelet capacity to produce TxA2 (62.6 +/- 67.8 vs 134.6 +/- 75.6 ng/mL, p < 0.05). The patients (n = 15) who had used estrogen replacement therapy (ERT) up until diagnosis of breast cancer showed reduced dinor-TxB2 excretion (15.5 +/- 12.7 vs 29.9 +/- 20.9 ng/mmol, p < 0.05) before initiation of antiestrogens, and elevated dinor-6-keto output during the antiestrogen regimen (32.4 +/- 21.2 vs 22.7 +/- 8.7 ng/mmol, p = 0.07). Smokers (n = 6) had elevated dinor-TxB2 output before and during antiestrogen use. Thus we conclude that the cardiovascular protection provided by an antiestrogen regimen is unlikely to be mediated through vaso- and platelet active PGI2 and TxA2.

Analysis of the thromboxane/prostacyclin balance in human urine by gas chromatography/selected ion monitoring: abnormalities in diabetics

We microanalyzed 2,3-dinor-6-keto-prostaglandin F1 alpha (2,3-dinor-6-keto-PGF1 alpha 1) and 11-dehydrothromboxane B2 (11-dehydro-TXB2, 2) in human urine. Samples containing a [2H4]-analogue as an internal standard were extracted by chromatography using Sep Pak tC18 and silica gel. The compounds were then analysed by means of the lactone ring opening reaction and dimethylisopropylsilylation. The conversion of 1 to 1-methyl ester (ME)-propylamide (PA)-9, 12, 15-dimethylisopropylsilyl (DMIPS) ether derivative and of 2 to 1-ME-6-methoxime (MO)-9, 12, 15-tris-DMIPS ether derivative was followed by gas chromatography/selected ion monitoring (GC/SIM). Interfering substances from the urine matrix were eliminated during GC/SIM analysis using a DB-5 column. We were able to detect 1 (222-1031 pg/mg creatinine) and 2 (18-155 pg/mg creatinine) in human urine. Furthermore, the thromboxane/prostacyclin (IX/PGI) ratio in the urine of diabetics was higher than that of healthy volunteers. This method can be used to determine the TX/PGI balance in human urine.

A 12-lipoxygenase product, 12-hydroxyeicosatetraenoic acid, is increased in diabetics with incipient and early renal disease

Earlier studies in diabetic animal models or ex vivo from diabetics suggest a deficiency in prostacyclin (PGI2) production and an increase in an alternate arachidonic acid metabolite, 12-hydroxyeicosatetraenoic acid (12-HETE), which stimulates angiogenesis, mitogenesis, and inhibits renin secretion. We studied the urinary excretion rate of 6-keto-PGF1 alpha (a stable metabolite of PGI2) and 12-HETE in controls and 42 noninsulin-dependent diabetes mellitus (NIDDM) patients with normal renal function and those with micro- or macroalbuminuria/hyporeninemic hypoaldosteronism (HH). The 2 eicosanoids were measured in urine using previously described high pressure liquid chromatography and RIA methods. Normal subjects and patients with NIDDM and microalbuminuria were infused with low dose calcium infusions that stimulate prostacyclin production in normal subjects. The PGI2 excretion rate of NIDDM patients with normal renal function was not different from that of controls (143 +/- 17 vs. 118 +/- 34 ng/g creatinine), but was reduced in those with microalbuminuria (75 +/- 10) and in macroalbuminuria patients (48 +/- 7; P < 0.01). In contrast, 12-HETE was increased in diabetics with normal renal function as well as in those with micro- or macroalbuminuria patients (69 +/- 18 vs. 250 +/- 62 vs. 226 +/- 60 and 404 +/- 131 ng/g creatinine; P < 0.01). Calcium did not stimulate PGI2, but increased 12-HETE in diabetics with microalbuminuria in contrast to levels in normal subjects. HH patients excreted less PGI2 (as previously reported), but had increased 12-HETE. HETE/PGI2 ratios further demonstrated these changes in the various groups. In a nondiabetic hypertensive microalbuminuria group, 12-HETE excretion was normal (73 +/- 28 ng/g creatinine). We conclude that the lipoxygenase product 12-HETE is increased early in the diabetic process, whereas PGI2 production is progressively impaired in NIDDM. These changes may play a role in the vascular disease of diabetes and partially explain the HH syndrome.

Dose-related effects of low dose aspirin on hemostasis parameters and prostacyclin/thromboxane ratios in late pregnancy

BACKGROUND

The purpose of this study was to determine which low dose of low dose aspirin (LDA) optimized the urinary prostacyclin (PGI2)/thromboxane (TXA2) ratio and minimized evidence of platelet aggregation during normal late pregnancy.

METHODS

Twelve women with uncomplicated singleton pregnancies between 28 and 34 weeks gestation participated in a randomized blinded study. Blood samples for salicylate levels were obtained pretreatment, 4 hours and 7 days after administration of placebo, 20mg, 40mg or 80mg of aspirin. Twenty-four hour urine specimens collected at the same intervals were assayed for PGI2 and TXA2 metabolites. In addition, bleeding time and platelet aggregation studies were performed prior to and after 7 days of LDA or placebo.

RESULTS

A dose-related increase in bleeding time occurred with 40 mg and 80 mg of LDA, but not with the 20 mg dose or placebo. Platelet aggregation studies changed progressively from a normal baseline to abnormal with an increasing dose of LDA. The PGI2/TXA2 ratio increased with aspirin doses as low as 20mg, with a decrease in TXA2 metabolites but not in PGI2 metabolites. Serum salicylate was not detectable in any sample from any patient.

CONCLUSION

There are dose-related changes in platelet aggregation and bleeding times with progressively increasing doses of LDA. A lower dose of LDA, such as 20-40 mg per day, may be as efficacious as higher doses in the prophylaxis of pre-eclampsia in high risk populations.

Eicosanoid modulation of the norepinephrine effect on blood pressure and renal hemodynamics in humans

The main objective of this study was to investigate the role of eicosanoids in modulating the effect of norepinephrine (NE) on blood pressure and renal hemodynamics during NE administration. Eight healthy volunteers were randomly assigned to three (1 week apart) infusion periods (180 min) with either dextrose 5% or NE, with or without indomethacin pretreatment. Pressor doses of NE induced marked alterations in renal hemodynamics and concomitant increases in eicosanoid excretion rates. The production of the vasodilatory prostacyclin (PGI2), as reflected in the excretion rate of the stable metabolites 6-keto-prostaglandin (PG)F1(alpha) and 2,3-dinor-6-keto-PGF1(alpha), was 2.7 times higher than that of the constrictor thromboxane (TX)A2, which was measured as the stable derivative TXB2. Indomethacin pretreatment blunted the NE-induced augmentation in eicosanoid excretion and resulted in further increases in arterial pressure and in renal vascular resistance. These results demonstrate that PGI2 attenuates the systemic and the renal hemodynamic vasoconstrictor effect of NE in normotensive control normal subjects.

Urinary excretion of prostacyclin in a rat model of uteroplacental vasculature occlusion: implications for fetal growth retardation

An experimental model was devised in the pregnant rat to study by a combined high pressure liquid chromatography and radioimmunoassay technique the accumulation of prostanoids (PNs) in the urine after transient-complete or permanent-partial interruption of the maternal-fetal blood flow. After 8 min of complete restriction of the blood flow in the pregnant rat at 18 days of gestation, the urinary concentration of 6-keto-prostaglandin F1 alpha (6k-PGF1 alpha, the stable prostacyclin metabolite) increased from 4.97 +/- 1.27 ng mg-1 creatinine to 8.09 +/- 2.47 ng mg-1 creatinine and 13.02 +/- 4.5 ng mg-1 creatinine after the second and third post-operative day respectively. The urinary concentration of the 2,3-dinor derivative of prostacyclin reached 12.35 +/- 5.44 ng mg-1 creatinine after the second post-operative day and was reduced to 4.71 +/- 1.94 ng mg-1 creatinine after the third post-operative day. The concentration of thromboxane B2 (TxB2, the stable thromboxane A2 metabolite) increased approximately 7-fold and 13-fold over that of the control after the second and third post-operative day respectively. The urinary concentration of the 2,3-dinor derivative of TxB2 (d-TxB2) increased from about 1.42 +/- 0.3 ng mg-1 creatinine to 4.49 +/- 0.9 ng mg-1 creatinine and 7.76 +/- 2.63 ng mg-1 creatinine under the same experimental conditions. Increases in the urinary concentrations of 6k-PGF1 alpha and d-TxB2 to 94 +/- 27.76 ng mg-1 creatinine and 12.05 +/- 2.26 ng mg-1 creatinine, respectively, were observed on the second post-operative day, after the restriction time was increased to 30 min. Permanent-partial occlusion of the maternal fetal circulation resulted in excretion of PNs in the urine to similar levels produced after transient-complete restriction. High concentrations of prostacyclin (range, 0.8 ng min-1 mg-1 wet weight) were produced in vitro by uterine preparations from restricted animals after the second post-operative day. Placenta preparations from restricted animals generally exhibited a lower ability to synthesize PNS (up to 0.006 ng min-1 mg-1 wet weight) compared with uterine tissue but produced more thromboxane than their sham counterparts. The data suggest that the uterus constitutes the main source for urinary PN excretion following short episodes of maternal-fetal blood flow interruption.

Prostanoid excretion before in vitro fertilization relates to the likelihood of pregnancy

The objective of this study was to determine the urinary excretion of prostacyclin (PGI2) and thromboxane A2 (TXA2) metabolites during in vitro fertilization (IVF) in relation to the clinical outcome of IVF. Urine was obtained overnight every 3 to 4 days from 24 women during IVF cycles. TXB2, 6-keto-PGF1 alpha and their 2,3-dinor derivatives were measured by high-pressure liquid chromatography with radioimmunoassay. The patients were women with (n = 16, 119 samples) and without (n = 8, 53 samples) a clinical IVF pregnancy. Concentrations of 2,3-dinor-TXB2 and 2,3-dinor-6-keto-PGF1 alpha were lower before embryo transfer in women who achieved a pregnancy than in those who did not conceive (p < 0.05). Contrary to women who did not conceive, women who achieved pregnancy had an increase in 6-keto-PGF1 alpha excretion after embryo transfer (p = 0.04). In women who did not conceive, levels of 2,3-dinor-TXB2 were higher before embryo transfer than after transfer (p = 0.04) and than levels in women who did conceive (p = 0.01). We concluded that differences in urinary prostanoid metabolite excretion before embryo transfer appear to relate to the likelihood of pregnancy, but the nature of this relationship remains elusive.

Urinary prostaglandin and prostaglandin metabolite excretion in patients with essential hypertension or hypertension with renal artery stenosis

BACKGROUND

Recent studies have reported elevated prostaglandin levels in patients with renal artery stenosis and hypertension. To investigate whether a distinction between essential hypertension and hypertension with renal artery stenosis is possible by measuring eicosanoid excretion, we studied the excretion of these compounds in patients with essential hypertension and in hypertensives with concomitant renal artery stenosis.

METHODS

The 24-h urinary excretion of metabolites of prostaglandin I2, prostaglandin E2 and metabolites of thromboxane A2 was sampled under standardised conditions, in 15 patients with essential hypertension and in 15 patients with unilateral renal artery stenosis with hypertension. Also clinical and biochemical characteristics of the subjects were analysed.

RESULTS

The patients with renal artery stenosis had significantly lower excretion of prostaglandin I2 than did the essential hypertensive patients. However, the overlap in the values was large, thus not allowing a diagnostic differentiation according to urinary prostaglandin I2 levels. The excretion of prostaglandin E2 and of metabolites of thromboxane A2 showed no significant differences among the groups.

CONCLUSIONS

Measurement of urinary prostaglandin or prostaglandin metabolite excretion did not contribute to the non-invasive detection of the presence of a renal artery stenosis in the patients in this study.

Implications of the prognostic importance of exercise-induced thromboxane formation in survivors of an acute myocardial infarction

Thirty-two patients with acute myocardial infarction performed an exercise stress test one month after hospital discharge. The in vivo formation of thromboxane and prostacyclin formation before and during the exercise stress test was analyzed with gas chromatography-mass spectrometry of the in vivo formed metabolites 2,3-dinor-TxB2 and 2,3-dinor-6-keto-PGF1 alpha. Patients with a significant increase in thromboxane formation (> 30%) during exercise (P < 0.0001) had a worse prognosis, with a 60% incidence of coronary events during the three years following the index infarction as compared to only 8% in the group without such an increase in thromboxane formation during exercise (P = 0.008). The group with coronary events and increased thromboxane formation included patients not detected by classical risk factors. Our findings suggest that exercise-induced thromboxane formation in survivors of an acute myocardial infarction may include prognostic information not defined by other risk indicators.

Serum lipoproteins, insulin, and urinary prostanoid metabolites in normal and hypertensive pregnant women

OBJECTIVE

To determine if hyperinsulinemia, hypertension, hypertriglyceridemia, and low levels of high-density lipoprotein (HDL) cholesterol are present in women with pregnancy-induced hypertension or preeclampsia.

METHODS

Serum concentrations of insulin, uric acid, total and lipoprotein cholesterol, triglyceride, and apolipoproteins A-I and B were measured in 31 women with pregnancy-induced hypertension (eight with proteinuria) and in 21 healthy, pregnant, weight-matched controls at 30-39 weeks' gestation. The urinary excretion of the stable metabolites of prostacyclin (PGI2) (6-keto-prostaglandin [PG] F1 alpha and 2,3-dinor-6-keto-PGF1 alpha) and thromboxane A2 (TxA2) (thromboxane B2 and 2,3-dinor-thromboxane B2) was assessed in 17 women with pregnancy-induced hypertension and in eight controls.

RESULTS

Women with pregnancy-induced hypertension exhibited 18% lower mean serum HDL2 cholesterol levels (0.9 versus 1.1 mmol/L, P < .05) and 65% higher mean triglyceride levels (3.3 versus 2.0 mmol/L, P < .05) compared to controls, whereas other serum lipid and apolipoprotein values did not differ significantly in the two groups. Mean serum insulin levels (13.3 versus 6.5 mU/L, P < .01) and uric acid levels (339.7 versus 231.2 mumol/L, P < .01) in patients with pregnancy-induced hypertension were significantly higher than those in the controls. Urinary output of PGI2 metabolites was reduced by 35-45% in patients with pregnancy-induced hypertension, whereas no differences were seen in the excretion of TxA2 metabolites. Serum HDL2 cholesterol concentrations correlated positively with 2,3-dinor-6-keto-PGF1 alpha excretion, and serum triglyceride concentrations correlated positively with 2,3-dinor-thromboxane B2 excretion. In addition, insulin levels correlated positively with triglyceride levels but negatively with HDL2 cholesterol concentrations.

CONCLUSION

The metabolic characteristics (hypertriglyceridemia, hyperinsulinemia, hyperuricemia, low HDL2 cholesterol) in pregnancy-induced hypertension resemble the main features of the "insulin resistance syndrome." This may result in endothelial cell dysfunction as evidenced by PGI2 suppression.

Resolution of posttransplant hypertension after liver transplantation despite impaired glomerular filtration

Hypertension developing after transplantation is characterized by widespread vasoconstriction including the kidney. Late resolution (mean, 29 +/- 4 months) of posttransplant hypertension has been observed in 15 (Group I) of 278 subjects monitored after liver transplantation. These studies were undertaken to define the systemic and renal changes associated with resolution, as compared with a group matched for age, sex, and time after transplant who remained hypertensive (Group II; N = 15) or a group who never developed hypertension (Group III; N = 23). Blood pressure during resolution paralleled changes in the systemic resistance index, which fell from 3,052 +/- 548 to 1,872 +/- 205 dyne/s.cm5/m2 (P < 0.01). GFR and RBF remained low, despite the resolution of hypertension, and renal vascular resistance did not change. Circulating endothelin levels remained above normal in all transplant recipients (Group I, 11.9 +/- 3.0 versus normal subjects, 7.0 +/- 1.1 pg/mL; P < 0.05), and urinary prostacyclin excretion was suppressed (880 +/- 120 versus 2,247 +/- 187 ng/day; P < 0.01). No hormonal differences were apparent between transplant groups. These results demonstrate the capacity for systemic vasodilation to occur after transplantation, independent of vascular tone in the kidney. They further suggest that renal vasoconstriction and impaired GFR alone are not sufficient to explain de novo hypertension after transplantation.

Effect of intracardiac repair on biosynthesis of thromboxane A2 and prostacyclin in children with a left to right shunt

OBJECTIVE

To investigate the effect of intracardiac repair on the abnormal biosynthesis of prostacyclin (PGI2) and thromboxane A2 (TXA2) in children with congenital heart disease and increased pulmonary blood flow.

DESIGN

A prospective study with immunoaffinity chromatography and gas chromatography-mass spectrometry to measure the urinary excretion products of PGI2 (2,3-dinor-6-oxo-prostaglandin (PG) F1 alpha (2,3-dinor-6-oxo-PGF1 alpha)) and TXA2 (2,3-dinor-TXB2) before operation, in the first 12-24 h after operation, and at discharge from hospital.

SETTING

A supraregional referral centre for patients with congenital heart disease.

PATIENTS

15 patients aged 2 to 60 months (median 7 months) with a left to right shunt who underwent intracardiac repair.

RESULTS

The preoperative 2,3-dinor-TXB2 excretion rate was greater than that found previously in a control group of 16 healthy children with a median (range) age of 24 (6-36) months (1159(201) v 592(122) ng/g creatinine in controls, P = 0.006). The excretion rate rose after operation to 9600(3832) ng/g creatinine (P = 0.01) and decreased before discharge to 1071(191) ng/g creatinine (NS), but remained greater than that of the control group (P = 0.014). Before operation 2,3-dinor-6-oxo-PGF1 alpha excretion rates were similar to those of the healthy children (482(68) v 589(95) ng/g creatinine in controls) but increased after operation to 19,668(11,162) ng/creatinine (P = 0.002) and fell at discharge to 1621(245) ng/g creatinine although this was higher than both preoperative and control rates (P = 0.005 and P = 0.0002 respectively). The preoperative ratio of 2,3-dinor-TXB2 to 2,3-dinor-6-oxo-PGF1 alpha excretion was greater than that of the control group (3.2(0.8) v 1.3(0.22) in controls, (P = 0.005)), decreased significantly after operation to 0.9(0.13) (P = 0.016), and changed little, to 0.7(0.12), before discharge. The last two ratios were similar to those in normal children and significantly lower than those before operation (P = 0.004).

CONCLUSION

In children with a left to right shunt the ratio of the excretion rates of the metabolites of TXA2 and PGI2 was abnormal before operation, which favoured vasoconstriction and platelet aggregation, but had decreased at discharge from hospital. The increase in excretion of PGI2 metabolites over TXA2 metabolite after intracardiac repair augurs well for pulmonary vascular recovery.

Inter-species extrapolation of pharmacokinetic data of three prostacyclin-mimetics

Cica-, eptalo- and iloprost are chemically and metabolically stabilized derivatives of prostacyclin which maintain the pharmacodynamic profile of the endogenous precursor. While iloprost is still subject to beta-oxidative degradation of the upper side chain, cicaprost is highly metabolically stable. Eptaloprost was synthesized to realize the pro-drug concept in PGI2-mimetics and was designed to be activated to cicaprost by single beta-oxidation. All three prostacyclin-mimetics were studied in various animal species (mouse, rat, rabbit, monkey, dog and pig) and in man to determine their pharmacokinetic profiles. Based upon this data, it was of interest whether an inter-species extrapolation of pharmacokinetic parameters can be performed to show the predictive value of animal experimentation. Allometric inter-species extrapolation is performed by modelling pharmacokinetic data (Y) as exponential functions (x) of species characteristics (e.g. body weight, W) as: Y = .aWx. For total clearance and volumes of distribution at steady state, a clear-cut correlation with x-values of 0.6-0.8 and 1.0-1.1 could be shown for all three compounds. For cicaprost, which was excreted unchanged in several species, renal and non-renal clearance was also mathematically scalable. Due to the use of different compartment models to describe plasma disposition, different sets of half-life data were obtained and could not be extrapolated reasonably. However, mean residence time showed a dependency on body weight with 0.25 as power function. In case of cicaprost, only the dog, which extensively metabolizes the compound, could not be enrolled in inter-species extrapolation. Excretion half-lives or residence times did not show a significant correlation to body weight or maximum life time potential. The present inter-species extrapolation showed a dependency from species body weight for model-independent pharmacokinetic data, e.g. clearance, volume of distribution at steady state and correspondingly mean residence time. The disposition profile of these compounds can therefore be predicted. Preliminary information on bio-degradation is an additional prerequisite for extrapolation. These data demonstrate that basic physiologically determined processes, which show some evolutionary allometric dependency, also influence the disposition of prostacyclin-mimetics. An extrapolation of data from animal to man could easily be realized giving additional justification for animal studies in pharmacology, toxicology and pharmacokinetics.

Adrenaline infusion increases systemic prostacyclin production in man

We have previously shown that adrenaline infusion induces an almost twofold increase in systemic thromboxane synthesis, measured as urinary 11-dehydrothromboxane B2. The purpose of the present study was to investigate whether high levels of adrenaline, found e.g. in heavy physical exercise and myocardial infarction are involved in the regulation of prostacyclin synthesis. To this end the effect of adrenaline infusion (0.1 microgram/kg/min for 45 min and thereafter 0.2 microgram/kg/min for 15 min) on prostacyclin synthesis in healthy male volunteers was investigated. Adrenaline infusion produced an over twofold increase in systemic prostacyclin synthesis, measured as urinary 2,3-dinor-6-keto-prostaglandin F1 alpha. Our study demonstrates that high circulating levels of adrenaline are associated with increased formation of prostacyclin.

Effects of dietary fat content, saturated fatty acids, and fish oil on eicosanoid production and hemostatic parameters in normal men

Populations that consume a diet rich in marine lipids have been reported to have a lower risk of coronary heart disease. However, some Western population groups with a high fish consumption continue to suffer elevated rates of coronary heart disease. Many of these individuals consume a diet rich in saturated fats in addition to the fish. To examine these possible dietary interactions we fed six healthy men diets that contained two levels of saturated fat (5% and 19% of energy). During 3-week periods the study subjects were given diets with a low-(25% of energy) and high-(39% of energy) fat content with and without inclusion of n-3 polyunsaturated or monounsaturated fatty acids (2% of energy). The effects of the n-3 fatty acids on the principal plasma lipid fractions were similar regardless of the saturated fat intake. Platelet function, as measured by the skin bleeding time, was inhibited when n-3 fatty acids were added to the low saturated-fat diet. In vivo thromboxane A2 production as assessed by urinary metabolites also declined (p < 0.01) during supplementation with n-3 fatty acids to a low-fat diet. Prostacyclin production were reduced on a low-fat diet compared to a high-fat diet regardless of supplementation with n-3 fatty acids. N-3 fatty acids stimulated the synthesis of modest amounts of thromboxane A3 and prostacyclin I3, on both the low and high saturated-fat diets. These studies showed that the effects of eicosapentaenoic and docosahexaenoic acids on platelet and vascular function and eicosanoid production are modulated by the content of saturated fatty acids in the diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dopamine2 blockade on renal function under varied sodium intake

This study explored the role of the dopamine-2 receptor (DA2) in the control of renal blood flow (RBF) and the influence of variations in sodium intake. These relationships have not been previously defined in man. Seven normotensive male subjects underwent a low dose dopamine (DA) infusion (1 microgram/kg.min) for 3 h, known to activate both DA1 and DA2 receptors. The effect of DA2 receptor on renal hemodynamics was studied using a relatively specific DA2 blocker [domperidone (DOM); 60 mg, orally] alone and with a DA infusion. Systemic and renal hemodynamics parameters were measured noninvasively. Urinary prostacyclin was measured in 3-h urine specimens, obtained during the DA infusion. The DA infusion increased RBF and prostacyclin during both normal and high salt diets, but this effect was attenuated on a low salt diet. DOM alone significantly reduced basal RBF during normal (1304 +/- 48 vs. 1175 +/- 45 mL/min.1.73 m2; P < 0.01) and low salt diets (1402 +/- 80 vs. 1220 +/- 101 mL/min.1.73 m2; P < 0.02), but was without effect during high sodium intake. DOM had no effect on prostacyclin excretion at any level of salt intake. These results suggest that both DA1 and DA2 are activated in renal vessels by DA, and that DA2 receptors play a role in the renal vasodilating action of DA. Changes in sodium balance alter the actions of the two receptors (DA1 and DA2) in a coordinated fashion in the regulation of RBF.

The effect of linoleic, arachidonic and eicosapentaenoic acid supplementation on prostacyclin production in rats

We examined the effect of dietary supplementation of linoleic acid (LA), arachidonic acid (AA) or eicosapentaenoic acid (EPA) to rats fed a diet low in linoleic acid on in vitro and in vivo production of prostacyclin. Male Sprague Dawley rats were fed a high-fat diet (50% energy as fat, 1.5% linoleic acid) for two weeks. Three of the groups were then supplemented orally with either 90 mg/d of LA, AA or EPA, all as the ethyl esters, for a further two weeks while remaining on the high-fat diet. Forty-eight hour urine samples were collected at the end of the second and fourth weeks. In vivo prostacyclin production was determined by a stable isotope dilution, gas chromatography/mass spectrometry assay for the major urinary metabolite of prostacyclins (2,3-dinor-6-keto-PGF1 alpha or PGI2-M and delta 17-2,3-dinor-6-keto-PGF1 alpha or PGI3-M). In vitro prostacyclin production was determined by radioimmunoassay of the stable metabolite (6-keto-PGF 1 alpha) following incubation of arterial tissue. Oral supplementation with AA resulted in a rise in plasma and aorta 20:4n-6, and increased in vitro prostacyclin and urinary PGI2-M production. EPA supplementation resulted in a rise in plasma and aorta 20:5n-3 and 22:5n-3, and a decline in plasma 20:4n-6, but not in the aorta. In the EPA-supplemented group, the in vitro prostacyclin and the urinary PGI3-M increased, but urinary PGI2-M decreased. The increase in in vitro prostacyclin production in the EPA-supplemented rats was unexpected and without obvious explanation.(ABSTRACT TRUNCATED AT 250 WORDS)