[Rectal electrical potential difference and plasma aldosterone in hyperaldosteronism and low-, normal- and high-renin...

Rectal electrical potential difference (P.D.), plasma aldosterone and plasma renin activity were measured in 25 normal subjects, 80 patients with untreated essential hypertension, 4 patients with primary and 9 patients with secondary hyperaldosteronism. In normal subjects the rectal P.D. was 26 +/- 10 mV (+/- S.D.); in patients with hyperaldosteronism it was 51 +/- 7 mV. Plasma aldosterone and rectal P.D. were correlated significantly (r = 0.84, p less than 0.001) in these two groups combined. In 29% of patients with low-renin hypertension, in 9% of patients with normal-renin hypertension and in 3 out of 8 patients with high-renin hypertension, rectal P.D. was found to be elevated in the presence of normal plasma and urinary aldosterone and no correlation was observed between plasma aldosterone and rectal P.D. (r = --0.09, n.s.). In 3 out of 7 patients with low-renin hypertension and high rectal P.D., plasma and urinary aldosterone were consistently suppressed. Since patients with low renin and high rectal P.D. responded favourably to spironolactone therapy it is suggested that mineralocorticoids other than aldosterone may contribute to the pathogenesis of the hypertension in these cases. The aetiology of raised rectal P.D. in normal and high-renin hypertension is not clear, but both catecholamines and angiotensin II may be involved. The measurement of rectal P.D. alone is of limited value as a screening test for primary hyperaldosteronism in hypertensive patients, but combined with renin measurements it is a valuable tool for further investigation of patients with suspected mineralocorticoid excess syndromes, as well as for adjusting therapy with competitive aldosterone antagonists in patients with proven primary or secondary hyperaldosteronism.