The Binding of Androsterone Sulfate, Etiocholanolone Sul- fate, and Dehydroisoandrosterone Sulfate by Human Plasma Protein *

The 17-ketosteroids appearing in largest quan-tity in the urine of human subjects are dehydro-isoandrosterone, androsterone, and etiocholano-lone.1 These steroids are not excreted to any ap-preciable extent in unconjugated form, but are conjugated as sulfates and glucuronides (1, 2). Dehydroisoandrosterone is excreted mainly as its sulfate congener, whereas androsterone and etio-cholanolone appear in the urine mainly as glucuro-nides. Nevertheless, the latter two compounds are also excreted as sulfates, and the concentration of these sulfates in urine may equal or exceed that of dehydroisoandrosterone sulfate (1, 2). It has been established that dehydroisoandrosterone sul-fate (D-S) is the main 17-ketosteroid in human peripheral plasma (3-5). Androsterone sulfate (A-S) has been identified in smaller quantity in plasma (4-6), and etiocholanolone sulfate (E-S) is present in the smallest concentration of the three conjugates (7). Since the urinary concentration of these steroid sulfates does not appear to be a simple reflection of their usual plasma levels and there is present evidence that A-S is cleared by the kidney at a more rapid rate than D-S (8), it became pertinent to study the excretion of these compounds by the kidney. The glomerular fil-trate presented to the kidney tubules may be ideally considered as a protein-free ultrafiltrate of plasma containing only that fraction of the con-jugates not bound to plasma proteins. As the * Submitted for publication January 18, 1965; ac