Urinary analysis of 16(5α)-androsten-3α-ol by gas chromatography/combustion/isotope ratio mass spectrometry: implications in anti-doping analysis

We present a method for the analysis of urinary 16(5α)-androsten-3α-ol together with 5β-pregnane-3α,20α-diol and four testosterone metabolites: androsterone (Andro), etiocholanolone (Etio), 5α-androstane-3α,17β-diol (5αA), 5β-androstane-3α,17β-diol (5βA) by means of gas chromatography/combustion/isotopic ratio mass spectrometry (GC/C/IRMS). The within-assay and between-assay precision S.D.s of the investigated steroids were lower than 0.3 and 0.6‰, respectively. A comparative study on a population composed of 20 subjects has shown that the differences of the intra-individual δ13C-values for 16(5α)-androsten-3α-ol and 5β-pregnane-3α,20α-diol are less than 0.9‰. Thereafter, the method has been applied in the frame of an excretion study following oral ingestion of 50 mg DHEA initially and oral ingestion of 50 mg pregnenolone 48 h later. Our findings show that administration of DHEA does not affect the isotopic ratio values of 16(5α)-androsten-3α-ol and 5β-pregnane-3α,20α-diol, whereas the isotopic ratio values of 5β-pregnane-3α,20α-diol vary by more 5‰ upon ingestion of pregnenolone. We have observed δ13C-value changes lower than 1‰ for 16(5α)-androsten-3α-ol, though pregnenolone is a precursor of the 16-ene steroids. In contrast to 5β-pregnane-3α,20α-diol, the 16-ene steroid may be used as an endogenous reference compound when pregnenolone is administered.