No difference in renin between normotensive and hypertensive patients with renal fibromuscular dysplasia

Objective: Fibromuscular dysplasia (FMD) of the renal arteries is considered to be a cause of renovascular hypertension. However, a substantial portion of patients with renal FMD remains normotensive. We hypothesized that hypertensive patients with renal FMD secrete more renin than their normotensive counterparts. Design and method: In patients scheduled for renal angiography, we simultaneously collected blood samples for renin determination from the renal artery (A) and renal vein (V) of both kidneys. Renin was measured by a direct immunoradiometric assay. In each patient, we calculated the arterial-venous concentration increment in renin as (V-A)/A for both kidneys separately. In addition, we determined renin secretion rate as (V-A) times flow in those patients in whom we could measure renal blood flow by the xenon-washout technique. Results: A total of 132 FMD patients were studied of whom 62 (47%) were normotensive. There were no differences between the two groups in age (on average 54 years in both) and in the proportion of females (91%). Most patients had experienced a spontaneous coronary artery dissection earlier. Arterial renin levels were 24.4+6.3 mIU/L in the normotensive group and 27.2+5.1 mIU/L in the hypertensive group (difference not significant). Likewise, no differences in renal venous renin from either kidney were apparent between the groups. The renin concentration increments across the kidney varied from 13 to 64% but again without a difference between normotensives (13-62%) and hypertensives (15-64%). Finally, in the 53 patients in whom renal blood flow was measured, no difference in renin secretion rate between normotensives and hypertensives was found. Conclusions: Although blood pressure may vary substantially between patients with renal FMD, there is no difference in renin release between the normotensive and the hypertensive ones. Thus, other factors besides renin must contribute to the development of high blood pressure in such patients.