Platelet vasopressin receptor in essential hypertension

The specific vasopressin receptor of V1 vascular subtype, which mediates platelet aggregation, has been found on human platelets. We investigated the binding characteristics using tritiated arginine vasopressin [3H]-AVP and platelet aggregation with AVP turbidometrically in normal subjects, patients with WHO class II essential hypertension and patients with malignant-phase hypertension. In essential hypertensives Bmax was significantly higher than that in normal subjects, but there were no differences in affinity and the maximal percentage aggregation between them. In malignant-phase hypertensives Bmax and maximal percentage aggregation were significantly lower than those in normals and essential hypertensives, although there was no difference in the affinity between them. With radio-immunoassay, the mean platelet-free plasma AVP level was significantly higher in malignant-phase hypertensives than those in normals and essential hypertensives, whereas there was no difference in mean platelet AVP levels between them. In essential hypertensives Bmax and maximal percentage aggregation did not change, but in malignant-phase hypertensives Bmax increased significantly and maximal percentage aggregation tended to normalize after treatment.