Antinatriuretic and Kaliuretic Activities of the Reduced Derivatives of Aldosterone*

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Abstract
The mineralocorticoid activities of the two dihydro- and the four tetrahydroisomers of the ring A-reduced derivatives of aldosterone were tested in adrenalectomized male rats. Potency was assessed by three criteria. Overall mineralocorticoid activity is expressed as the ability to reduce the urinary Na+/K+ ratio; antinatriuretic activity is represented by decreases in urinary Na+/creatinine; kaliuretic activity is shown by increases in K+/creatinine. All measurements were made on urine collected in the period 1–3 h postinjection. Measurements of overall activity indicate that the potency of aldosterone is greater than 5α-dihydroaldosterone (DHA) greater than 3α,5α-tetrahydroaldosterone (THA) greater than 3α,5β-THA greater than 3β,5α-THA greater than 5β-DHA greater than 3β,5β-THA. Measurements of individual cation effects indicated that reduced derivatives generally, and the 5α-reduced derivatives in particular, have greater antinatriuretic than kaliuretic activity. For example 5α-DHA possesses between 7% and 17% of the antinatriuretic activity of aldosterone but only 0.7–2.7% of the kaliuretic activity. 5α-DHA and 3α,5β-THA at concentrations of 10-7 M were also shown to have mineralocorticoid activity in the isolated toad bladder; both caused an increase in the short circuit current across this epithelium although not to the level shown by a similar concentration of aldosterone. 5β-DHA appeared to be inactive at this dose.