Effects of ridogrel on the prostacyclin-thromboxane ratio in nulliparous third trimester-pregnant rhesus monkeys

Placental transfer of the thromboxane synthetase inhibitor ridogrel in the late-pregnant ewe

OBJECTIVES

To assess the occurrence of placental transfer of the thromboxane synthetase inhibitor ridogrel in the pregnant ewe and to determine its effect on prostanoid levels in the ewe and fetal lamb, on uterine contractility and on maternal and fetal hemodynamics.

STUDY DESIGN

Five chronically instrumented pregnant ewes at 122 days of gestation received intravenous infusions of 5 mg/kg/3 h ridogrel and solvent. Maternal and fetal arterial samples were obtained at predetermined intervals to determine concentrations of ridogrel and prostaglandin metabolites TXB2, 6-keto-PGF1alpha, PGF2alpha, and PGE2. Maternal and fetal responses of blood flow and pressures were determined.

RESULTS

Fetal ridogrel levels were 25% of maternal concentrations. Ridogrel showed rapid and marked thromboxane synthetase inhibition and augmentation of levels of prostaglandin metabolites. There was no evidence of change in amniotic pressure, uterine blood flow, maternal and fetal blood pressure and heart rate.

CONCLUSION

Ridogrel is a potent thromboxane synthetase inhibitor which passes the sheep placenta, does not influence maternal and fetal hemodynamics and uterine contractility, and shows similar antiplatelet activity in the ewe and the fetal lamb.

The effect of indomethacin and prostacyclin agonists on blood pressure in a rat model of preeclampsia

OBJECTIVE

This study was designed to determine the effects of cyclooxygenase inhibition and prostacyclin agonists on the hypertension induced by nitric oxide synthase blockade in a previously characterized rat model of preeclampsia.

STUDY DESIGN

A condition similar to preeclampsia was induced by infusing pregnant rats with the nitric oxide synthase inhibitor N G -nitro- L -arginine methyl ester through subcutaneously implanted osmotic minipumps. Blood pressure was measured with the tail cuff method. In the first experiment the rats received either vehicle alone (control group), N G -nitro- L -arginine methyl ester (50 mg/d), indomethacin (0.1 mg/d), or N G -nitro- L -arginine methyl ester plus indomethacin beginning on day 17 of pregnancy. In the second experiment the rats received vehicle alone (control group), N G -nitro- L -arginine methyl ester (50 mg/d), or N G -nitro- L -arginine methyl ester plus iloprost (31 microgram/d). In a third experiment cicaprost (15 microgram/d) was substituted for iloprost.

RESULTS

Except for an increase on the day after insertion of the pump indomethacin had no significant effect on the hypertension induced by N G -nitro- L -arginine methyl ester. Both prostacyclin agonists (iloprost and cicaprost), however, attenuated the rise in blood pressure usually seen after N G -nitro- L -arginine methyl ester administration.

CONCLUSIONS

Nonselective inhibition of the cyclooxygenase enzymatic system does not influence the hypertension seen in the rat preeclampsia model induced by chronic nitric oxide deficiency. The hypertension in this model can be partially reversed with prostacyclin analogs.

Comparative efficacy of nonsteroidal anti-inflammatory drugs and anti-thromboxane agents in a rabbit adhesion-prevention model

A variety of nonsteroidal anti-inflammatory drugs (NSAIDs) has been found to inhibit postsurgical peritoneal adhesion formation in a number of animal models. A rabbit uterine horn adhesion model was used to directly compare several commonly used NSAIDs of different chemical classes in a single animal study to evaluate their ability to prevent adhesion formation. The effect of thromboxane inhibitors on adhesion prevention was also evaluated. Each of the NSAIDs tested (tolmetin, ibuprofen, aspirin, and indomethacin) showed significant and comparable efficacy. In this same study, imidazole, a thromboxane synthetase inhibitor, also showed significant efficacy. In a second study, ridogrel, an inhibitor of thromboxane synthetase as well as a thromboxane A2 receptor blocker, also showed significant efficacy in reducing peritoneal adhesion severity. These results further support the view that NSAIDs act to prevent adhesions through a common mechanism. In addition, thromboxane A2 inhibitors were also shown to be efficacious in adhesion prevention, suggesting that platelets may play a substantial role in adhesion formation.

Ridogrel improves maternal/fetal homeostasis in an ovine model of pregnancy-induced hypertension

The effects of ridogrel (a thromboxane synthetase inhibitor/endoperoxide receptor antagonist) were assessed in an ovine model of pregnancy-induced hypertension. Maternal serum prostacyclin and thromboxane levels were quanitiated using RIA, and maternal and neonatal coagulation status was assessed. Pregnancy and neonatal outcome were recorded. Ridogrel, (E)-5-[[[3-pyridinyl)[3-(trifluoromethyl)phenyl]methylen]amin++ +] oxy]pentanoic acid, was administered in one bolus dose at 0.1 or 1.0 mg/kg IV, three hours following the onset of a 27 hour magnesium sulfate infusion given hypertensive ewes to prevent maternal seizures. At both doses, ridogrel improved neonatal outcome (0% neonatal mortality in each ridogrel group versus 67% neonatal mortality in the magnesium sulfate group), and ridogrel at 0.1 mg/kg IV normalized birth weights. Abnormalities of maternal platelet function (abnormal or no response to collagen), occurring during the ovine syndrome, resolved following ridogrel treatment. Ridogrel's effects on maternal and neonatal coagulation were more dramatic at the 0.1 mg/kg IV dose. Ridogrel appeared to be beneficial in this model of pregnancy-induced hypertension.