Progesterone is conjugated in human urine

Abstract

The discovery of two previously unknown progesterone conjugates in human urine is presented. Urine from near-term pregnant women was applied to an anion exchange column and then eluted with an increasing concentration gradient of sodium chloride. Aliquots of collected fractions were subjected to four different treatments: (1) immediate extraction, (2) incubation at 37°C, (3) β-glucuronidase hydrolysis and (4) acid hydrolysis. All eluent aliquots were then further purified on a thin layer chromatographic system and measured for progesterone content by radioimmunoassay. The results suggest that progesterone, a non-hydroxylated Δ 4-3 ketosteroid, occurs in at least two negatively charged conjugated forms in human urine. Comparison with elution patterns of known testosterone conjugates shows that these conjugates of progesterone travel on an anion exchange column similarly to testosterone glucuronide and testosterone sulphate. Although the exact structure of these progesterone conjugates remains to be elucidated, the property of physiological conjugation of progesterone has not previously been described. Quantitatively each of these conjugates appears to exist in amounts equal to or greater than the levels of free (unconjugated) urinary progesterone.