Gas Chromatography-Mass Spectrometry of Androgens in Equine Ovarian Follicles at Ultrastructurally Defined Stages of Development. Identification of 19-Nortestosterone in Follicular Fluid

Follicular fluid was obtained from equine follicles at different stages of development as determined by ultrastructural study. Gas chromatography-mass spectrometry associated with stable isotope dilution permitted the demonstration of high levels of 4-estrene-3,7-dione and 17 beta-hydroxy-4-estren-3-one, 17 beta-hydroxy-4-estren-3-one levels often being about 10 times higher than those of testosterone. These findings suggest that in the mare ovary, an aromatizing pathway may proceed using these 19-norsteroids as intermediates. As a consequence of this high level of 19-norsteroids, testosterone content may be most often overestimated by RIA. RIA of steroids in follicular fluid should be validated by a reference technique based on gas chromatography-mass spectrometry, associated with stable isotope dilution.