1. The effect of the intravenous administration of aldosterone on the colonic potential difference has been studied in eight normal young males and compared with effects on renal function.

2. Under control conditions the colonic potential was remarkably stable over a period of 10 h of recumbency whereas with infusions of aldosterone ranging from 5·6 to 89·6 pmol min−1 kg−1 (2 to 32 ng min−1 kg−1), the colonic potential difference increased in a quantitatively reproducible fashion. The correlation between change in plasma aldosterone and in colonic potential was highly significant.

3. The delay between the end of the infusion and the maximum change in colonic potential was 4 h. The shortest latent period before any change in colonic potential occurred was 70 min after the start at infusion rates of 11·2 pmol min−1 kg−1 or more. The effect, although still present at 10 h, had returned to control values at 20 h after the start.

4. The main renal effect of aldosterone was on sodium excretion, which was reduced at infusion rates of 11·2 pmol min−1 kg−1 and more, but the relation to dose of aldosterone was not very quantitative and the effect was more like a threshold response.

5. The conclusion is that the colonic potential difference may be used as a quantitative indicator of the actions of aldosterone and is more sensitive and dose-dependent than the renal effects.

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