A comparison of some extra-renal effects of spironolactone and canrenone.

1 Measurement of changes in trans-mural rectal potential difference (t.m.r.p.d.) and plasma aldosterone levels have been used in a comparison of the extra-renal activities of spironolactone and its major metabolite canrenone. 2 A characteristic pressure artifact was observed during measurement of t.m.r.p.d. When pressure artifacts were eliminated, there was a log-linear relationship between increasing doses of intravenous aldosterone and maximum increase in t.m.r.p.d. 3 Pre-treatment for 5 days with spironolactone or canrenone produced a similar attenuation of the increase in t.m.r.p.d. produced by infused aldosterone, suggesting that canrenone is the active metabolite of spironolactone in the rectum. This is in contrast to the significantly greater renal activity of spironolactone that has been demonstrated after a similar treatment period. Neither antagonist treatment produced significant changes in pre-infusion plasma aldosterone concentrations. 4 The need for assay of the extra-renal activities of aldosterone antagonists in the assessment of their therapeutic potential is discussed.