Studies related to the metabolism of anabolic steroids in the horse: the metabolism of 1-dehydrotestosterone and the use of fast atom bombardment mass spectrometry in the identification of steroid conjugates.

The metabolism and urinary excretion of 1,2(n)-3H-1-dehydrotestosterone were studied in cross-bred gelded horses. Approximately 40% of the dose was excreted in 24 h. The steroid metabolites were extracted by Amberlite XAD-2 resin and fractionated into glucuronides and sulphoconjugates. Unchanged 1-dehydrotestosterone was the only component identified by gas chromatography mass spectrometry after solvolysis of the sulphoconjugates. Positive and negative ion fast atom bombardment mass spectra were obtained on the purified 1-dehydrotestosterone sulphoconjugate isolated from horse urine and on the alkali metal salts of three standard steroid conjugates. Spectra obtained in the different modes were of comparable intensity. Positive ion spectra were generally more complex due to the formation of alkali metal adduct ions containing several sodium cations. The most abundant ion in the negative ion spectra corresponded to the loss of the alkali metal cation to give [M]-. Thus, the structure of a conjugate can be defined from the combination of mass spectrometric techniques.