Effects of Ridogrel, a Thromboxane Synthase Inhibitor and Receptor Antagonist, on Blood Pressure in the Spontaneously Hypertensive Rat

Ridogrel is a dual acting thromboxane synthase inhibitor/TP receptor antagonist. We examined the effects of single and multiple doses on systolic blood pressure in stroke-prone spontaneously hypertensive rats. Single doses of ridogrel (5 to 125 mg/kg) did not affect systolic blood pressure or furosemide-stimulated excretion rates of thromboxane B2 or 6-keto-prostaglandin F1alpha, although ex vivo serum thromboxane B2 was dose-dependently reduced up to 95%. In contrast, repeated dosing (7 days) with ridogrel (3 to 25 mg/kg/day), had an antihypertensive effect in 12-week-old stroke-prone spontaneously hypertensive rats. At 25 mg/kg/day, ridogrel reduced systolic blood pressure from 200+/-6.1 to 173+/-6.7 mmHg (n=12, P<0.01). Ridogrel dose-dependently reduced serum thromboxane B2 and increased plasma renin activity. Unlike single doses, repeated dosing reduced urinary thromboxane B2 excretion (from 103+/-7 ng/day to 49+/-10 ng/day, P<0.01) while preserving 6-keto-prostaglandin F1alpha excretion. Ketoprofen, a cyclo-oxygenase inhibitor, (10 mg/kg/day for 7 days), depressed urine 6-keto-prostaglandin F1alpha in addition to attenuating serum and urine thromboxane B2. Ketoprofen prevented the antihypertensive effects of ridogrel. Ridogrel did not lower systolic blood pressure in Sprague-Dawley rats. We conclude that the antihypertensive effect of ridogrel involves preserving renal prostaglandin synthesis during thromboxane attenuation.