Surgical reversal of two-kidney one clip hypertension during inhibition of the renin-angiotensin system.

Conscious rats with two-kidney one clip Goldblatt hypertension had the constricting clip removed during continuous infusion of either dextrose, saralasin, or captopril. Other dextrose-infused animals underwent removal of the ischemic kidney or a sham procedure. Direct arterial blood pressure (BP) was recorded throughout the 15-hour preoperative and subsequent 24-hour postoperative period. Rats were studied in the "early" phase (1-3 weeks duration) or "chronic" phase (greater than 4 months) of hypertension. Animals subjected to a sham procedure returned to preoperative BP values. The BP of animals unclipped or nephrectomized did not return to previous hypertensive levels. Instead, a biphasic response was seen where BP partially recovered from an operative fall and then slowly declined to normal at 24 hours; this effect occurred in both stages of hypertension. At 24 hours, removal of the ischemic kidney was as effective as removal of the constricting clip in the correction of both early and chronic phase hypertension. Rats infused with saralasin or captopril demonstrated an acute (within 2 hours) and sustained fall in BP, but not to normotensive levels. This fall was significant in all animals (p less than 0.01) apart from chronic phase rats infused with saralasin where no significant fall was seen. Although animals infused with saralasin or captopril commenced at a lower preoperative BP, the biphasic pattern of response to unclipping was identical to that of dextrose-infused unclipped rats. Thus, sustained inhibition of the renin-angiotensin system did not modify the correction of hypertension produced by removal of the constricting clip, and the response to surgical correction did not appear to be entirely mediated by changes in the activity of the renin-angiotensin system, particularly in the chronic stage. Equally, the rapidity of correction is not consistent with a role of vascular hypertrophy.