Abstract
A method for the determination of 17-hydroxycorticosteroids employing periodate oxidation was studied for reliability, and the secretion rate of cortisol was then compared with urinary steroid excretion in a number of subjects. The urinary assay was found to be satisfactory in terms of precision and accuracy. The correlation between urinary steroid excretion and secretion rate was acceptable in the normal range, but became poor as the secretion rate increased. Two patients with Cushing's syndrome showed elevated cortisol secretion rates as compared to the control subjects, but urinary steroid excretion was within the normal range. Examination of the percentage conversion of cortisol to urinary 17-hydroxycorticosteroids suggests there is a progressive decrease in the proportion converted as the secretion rate rises. It is concluded that a progressive alteration in steroid metabolism occurs as the secretion rate of cortisol rises, with the formation of metabolites which are not included in the urinary assay. This finding may impose some limitation on the interpretation of urinary steroid excretion values as an index of cortisol secretion rates.
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