Implantation, Pregnancy and Parturition
(M589) STEROIDOGENIC ENZYME EXPRESSION IN VASCULAR TISSUE OF MARINE MAMMALS MAY CONTRIBUTE TO FETAL PROFUSION.
Browne, Patience 1, Conley, Alan1, 1 University of California Davis, Davis, CA
ABSTRACT- Physiology of diving mammals has been of interest for over half a century. Pinnipeds experience a relatively long gestation following obligate delayed implantation, and gestation proceeds in an environment of severe hypoxia. Though studies of dive physiology have elucidated mechanisms of oxygen conservation, pregnant females have been largely overlooked. Our initial objective was to examine the contribution of maternal, placental, and fetal tissue to the endocrinology of pinniped pregnancy, but in doing so, a potential method of selectively maintaining fetal tissue perfusion emerged. Sex steroid concentrations (progesterone, estrone, estradiol, dihydroepiandrosterone, androstenediol, androstenedione, and testosterone) were determined by radioimmunoassay of serum collected from adult female northern fur seals (Callorhinus ursinus) on rookeries (and therefore, likely pregnant). Tissues were also collected opportunistically from adult females and fetuses. Distribution of steroidogenic enzymes (cytochromes P450 c17, aromatase, b5, oxidoreductase, and 3-HSD) in reproductive tissue was determined by immunohistochemistry and expression was confirmed by Western immunoblot. Steroidogenic interstitial tissue of the fur seal ovary suggested a high capacity for androgen synthesis, while aromatase expression was limited to granulosa cells of tertiary follicles and corpora lutea. Hypothesized steroid synthesis was supported by substantial levels of androgens and relative paucity of estrogens in peripheral circulation of adult females. While the gonad of the term-fetus was apparently steroidogenically active, enzyme expression was generally absent from placental trophoblast. Most interesting was the expression of both aromatase and 3-HSD in vascular tissue of the adult and fetal gonad and the placenta. These findings suggest that circulating androgens originating from the fetal and/or maternal gonad can be locally converted to estrogens in vascular tissue. Estrogen has been shown to induce a rapid vasorelaxive response in vitro and in vivo and though distribution of steroidogenic enzymes in vascular tissue is not unique to diving mammals, vascular estrogen synthesis in an otherwise estrogen-poor environment may promote fetal perfusion during dives.
KEY WORDS: estrogen, vasoactive, pregnancy, placenta