Cardiovascular and hormonal effects of clonidine in patients with essential hypertension and renal hypertension.

The putative role of the central nervous system in the maintenance of elevated blood pressure in patients with essential hypertension (EH) and renal hypertension [unilateral renal parenchymal disease (RPD) and unilateral renal artery stenosis (RAS)] was studied by investigating the cardiovascular and hormonal effects of the predominantly centrally acting sympatholytic agent, clonidine. Oral clonidine lowered blood pressure substantially in all three groups. Levels of plasma renin activity were unchanged in EH and RAS but progressively fell in RPD. Plasma noradrenaline levels fell in all three groups. Clonidine therefore reduced blood pressure to the same extent in three distinct groups of hypertensives, in two of which the initiating cause was undoubtedly renal. This indicates that, although the primary cause differed, a prominent factor sustaining hypertension may have been an increase or an inappropriate maintenance of central pressor mechanisms.