Simultaneous Measurement of Secretory Rates of Aldosterone and 18-Hydroxycorticosterone

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Abstract
Secretory rates of aldosterone and 18-hydroxycorticosterone were estimated simultaneously by the single injection isotope dilution technique from the specific activities of their respective major unique urinary metabolites, tetrahydroaldosterone and 18-hydroxytetrahydro A. Both metabolites were measured in the form of their etiolactone monoacetate derivatives using 1 of 2 alternative methods of isolation. In one method, urinary metabolite glucuronides were hydrolyzed enzymatically, the α-ketol forms isolated chromatographically, and converted to etiolactones with periodic acid. In the second method, periodic acid, added directly to urine, accomplished both steps simultaneously. A comparison of the specific activities of 18-hydroxytetrahydro A and free 18-hydroxycorticosterone in urine, following the injection of labeled 18-hydroxycorticosterone, indicated that urinary 18-hydroxytetrahydro A was derived largely or entirely from secreted 18-hydroxycorticosterone and that the specific activity of the urinary metabolite was a valid index of the adrenal secretion of 18-hydroxycorticosterone. 18-Hydroxycorticosterone was a normal secretory product. A series of normal values ranged from 145 to 460 μg/day and were on the average 2.26 times greater than the simultaneously determined aldosterone secretory rates which ranged from 70 to 210 μg/day.