Cannulation in situ of equine umbilicus. Identification by gas chromatography-mass spectrometry (GC-MS) of differences in steroid content between arterial and venous supplies to and from the placental surface

Abstract

Equine umbilicus was cannulated in utero and a series of cord plasma samples removed for analysis. After steroid extraction and derivatisation, gas chromatographic-mass spectrometric (GC-MS) analysis demonstrated large differences in steroid content between the plasma samples obtained from the umbilical artery and vein, the blood supplies leading to and from the placental surface, respectively. 3 β-Hydroxy-5,7-androstadien-17-one, dehydroepiandrosterone, pregnenolone, 3 β-hydroxy-5 α-pregnan-20-one, 5-pregnene-3 β,20 β-diol and 5 β-pregnane-3 β,20 β-diol were identified as major constituents in extracts from umbilical arterial plasma samples, mostly as unconjugated steroids. Together with 5 α-pregnane-3,20-dione, these steroids were identified in extracts from umbilical venous plasma samples but at significantly reduced levels to those determined in arterial plasma samples. Oestradiol-17 α, dihydroequilin-17 α and dihydroequilenin-17 α were identified in extracts (mostly sulphate-conjugated) from both umbilical arterial and venous plasma samples, much larger amounts being detected in the plasma sampled from, rather than to, the placental surface. Equilin, equilenin, oestrone, oestradiol-17 β, dihydroequilin-17 β and dihydroequilenin-17 β were not detected in the present studies. Isomers of 5(10)-oestrene-3,17 β-diol together with 5(10),7-oestradiene-3,17 β-diol and its possible oxidative artifact, 5(10),7,9-oestratriene-3,17 β-diol, were tentatively identified only in sulphate-conjugated extracts from umbilical venous plasma samples. No glucuronic acid-conjugated steroids could be detected. The implications of this work in the elucidation of the biosynthetic pathways leading to both the formation of oestrogens and C 18 neutral steroids at the placental surface are discussed.