Effect of clonidine on blood pressure in chronic one-kidney, one-clip and two-kidney, one-clip hypertensive rats.

Oral administration of clonidine lowered the high blood pressure in two-kidney, one-clip hypertensive rats in chronic stage (three to four months), but not in one-kidney, one-clip hypertensive rats. This reduction of blood pressure was well correlated with decrease in plasma renin concentration, but not with decrease in urinary noradrenaline excretion. These results suggest that the reduction of blood pressure in two-kidney, one-clip hypertensive rats may be due to reduced renin release through the action of clonidine, while in one-kidney, one-clip hypertensive rats the sympathetic nervous activity may play little or no role in the maintenance of high blood pressure.