Browsing by Author "Petkam, R."
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- In vitro metabolism of pregnenolone to 7 alpha-hydroxypregnenolone by rainbow trout embryosPublication . Petkam, R.; Renaud, R. L.; Freitas, A. M. M. S.; Canario, Adelino V. M.; Raeside, J. I.; Kime, D. E.; Leatherland, J. F.Tissues taken from rainbow trout embryos at several developmental stages, were incubated in the presence of radioactively-labelled pregnenolone in order to determine the capability of salmonid embryos to metabolize steroids, such as pregnenolone, that are incorporated into the oocyte during gonadal growth and maturation. High performance liquid chromatography was used to separate the steroid products, and gas chromatography–mass spectrometry was applied for the chemical identification of the product. 7α-Hydroxypregnenolone, previously known to be produced only by ovarian tissues, was found to be the sole metabolite of pregnenolone metabolism by rainbow trout embryos. Sulfate and glucuronide conjugated forms of 7α-hydroxypregnenolone were also produced. We hypothesize that this metabolite provides a pathway for excretion of pregnenolone, enabling the embryo to maintain its own steroid milieu, although the possibility of 7α-hydroxypregnenolone also playing a physiological role cannot be excluded.
- In vitro metabolism of progesterone, androgens and estrogens by rainbow trout embryosPublication . Petkam, R.; Renaud, R. L.; Freitas, A. M. M. S.; Canario, Adelino V. M.; Leatherland, J. F.The purpose of the study was to determine the steroid metabolic pathways used by rainbow trout (Oncorhynchus mykiss) embryos. Whole embryo preparations at 42, 53 and 65 days post fertilization (dpf) were incubated, in vitro, with the tritium-labelled steroids, progesterone (P4), testosterone (T), androstenedione (A4), 17β-estradiol (E2), and estrone (E1), and the metabolites formed were separated and identified by reverse phase high performance liquid chromatography (HPLC). The degree of metabolism for each of the substrates was dependent on the age of the embryos, and was always higher in older embryos. P4 yielded three metabolites, one of them identified by gas chromatography-mass spectroscopy as 3β,7α-dihydroxy-5α-pregnan-20-one. Several unknown metabolites of a similar profile on HPLC were produced for T and A4, in addition to A4 and T as metabolites of T and A 4 metabolism, respectively. Likewise, E2 and E1 yielded each other and an unknown polar metabolite. These observations argue for the presence of 5α-reductase, 7α-hydroxylase and 17β-hydroxysteroid dehydrogenase activity in embryo tissues which, by their conversion of biologically active yolk steroids of maternal origin, may provide a protective environment for the embryo during early development