Measurement of a specific circulating hormone or its excreted metabolite often confirms a suspected cause of secondary hypertension. Excess of plasma cortisol, aldosterone, or catecholamines may pinpoint, respectively, a case of Cushing's disease, Conn's syndrome or pheochromocytoma where clinical and laboratory findings are otherwise inconclusive. Similar confirmatory value is now being sought for the diagnosis of renovascular hypertension in bilateral estimations of renal vein renin.
Though itself not a hormone but an enzyme stored in juxtaglomerular cells, renin can be estimated only by a bioassay of the hormone angiotensin II, which, as an end product of enzymatic action initiated by renin, reflects the latter's activity. This activity has been studied in normal and hypertensive subjects by a number of investigators. Using an original method of bioassay which involves determination of vasoconstricting effects of dialyzed plasma on strips of rabbit aorta, Helmer1 demonstrated elevated renin levels in renal and, to