The protocol of the study was approved by the local ethics committee, and all subjects gave informed consent to participate in the study. We studied 20 patients with essential hypertension (untreated or after 2-week pharmacological washout) and 26 healthy controls. Secondary causes of hypertension were excluded on the basis of negative history and absence of clinical signs, normal renal function, normal serum electrolytes, and normal aldosterone and renin plasma levels. We excluded from the study subjects drinking >60 g of ethanol per day or consuming licorice, smokers, and women taking oral contraceptives. We avoided testing women during menstrual and premenstrual