Mechanism of enhanced blood pressure rise after reclipping following removal of a renal artery clip in rats.

The effect of removing a renal artery clip 14 to 18 days after its application was studied in two-kidney, one clip hypertensive rats. Blood pressure decreased to a normotensive level within 24 hours after the removal of the clip. The cardiovascular effects of reapplication of the clip and infusion of renin, angiotensin II, and norepinephrine were assessed at that time. Reapplication of the clip to the unclipped renal artery was followed in 1 hour by an increase in blood pressure to the level of sham-operated renal hypertensive rats. After reapplication of the clip, plasma renin activity increased to the same level as after the initial application. Application of the clip to the contralateral renal artery did not affect blood pressure and failed to increase plasma renin activity. It appears that renin release is a prerequisite for the rapid rise of blood pressure after reapplication of the clip. The infusion of renin, angiotensin II, and norepinephrine for 90 minutes caused an enhanced blood pressure response similar to that observed following reapplication of the clip. The increase in blood pressure in control rats was associated with bradycardia, which was absent in unclipped rats. The enhanced response of unclipped rats to an infusion of renin was abolished by pithing. It is concluded that removal of a renal artery clip unmasks a hyperreactivity of the cardiovascular system to reapplication of the clip.