Clonidine in unilateral renal artery stenosis and unilateral renal parenchymal disease--similar antihypertensive but different renin suppressive effects.

The effects of 300 micrograms oral clonidine were studied in 15 hypertensive patients with unilateral renal involvement -nine had renal artery stenosis and six renal parenchymal disease. After clonidine blood pressure fell substantially in both groups, with the maximum fall in the fourth hour and effects persisting after 6 h. Levels of plasma renin activity were considerably higher in the renal artery stenosis patients and remained unchanged during the study; there was a progressive fall in levels in each of the patients with renal parenchymal disease. Plasma noradrenaline levels fell in both groups. Clonidine therefore lowers blood pressure in patients with unilateral renal artery stenosis and renal parenchymal disease. The known pharmacological effects of clonidine would thus favour either an increase or an inappropriate maintenance of central pressor activity as a contributory factor to the hypertension in both groups. The central mechanisms raising blood pressure may result not only from high angiotensin II levels but to other less well defined effects, from an ischaemic or diseased kidney. The lack of fall of plasma renin activity in the renal artery stenosis patients probably indicates the greater influence of ischaemia and renal baroreceptor stimulation over sympathetically mediated renin release.