Effects of rilmenidine and hydrochlorothiazide on human platelet α2-adrenoceptors

This study was designed to better characterise in humans the mechanism of action of rilmenidine, a new antihypertensive oxazoline derivative. The functional relationship between hypotensive response, adrenergic nerve activity and platelet α2-adrenoceptor number and function was evaluated in hypertensive subjects, both before and after prolonged treatment with this drug. The effect of rilmenidine were compared with those induced by a diuretic drug (hydrochlorothiazide). After 1 month of placebo, 24 patients with essential hypertension were randomly allocated to either rilmenidine 1 mg once daily or hydrochlorothiazide 25 mg once daily. At the end of the first month of treatment, the 2 drugs were combined in the patients whose diastolic blood pressure was higher than 90 mmHg. On days, 0, 30, and 60, the number and affinity of blood platelet α2-adrenoceptors were measured by 3H-yohimbine labelling, and plasma catecholamines were determined. On days 0 and 30, platelet aggregation was also ossessed. The results show that the administration of rilmenidine exerts significant and lasting antihypertensive activity. This effect, however, is not associated with a modification in platelet α2-adrenoceptor density and function, nor does it seem to affect catecholamine plasma levels, thus suggesting a negligible role for α2-adrenoceptor stimulation in the antihypertensive action of rilmenidine.