title: The role of estrogen as a parahormone in brain and pituitary.
abstract: Where aromatase and estrogen receptors are co-localized in brain and pituitary, estrogen functions as a parahormone, and estrogen levels which determine the occurrence or magnitude of a response are those in close proximity to targets. Teleost fish, a vertebrate group characterized by exceptionally high aromatase in neuroendocrine tissues, are technically advantageous animal models for studying the cellular location of aromatase, natural changes correlated with seasonal reproductive cycles, substrate-dependence of the reaction, steroid induction of enzyme activity, and possible non-genomic actions of estrogen on cultured neurons. In addition, characterization of steroid receptors reveals that the androgen receptor, like aromatase, is present in unusually high concentrations (10- to 100-fold higher than in mammalian brain). Since androgen receptors and aromatase both utilize testosterone as a ligand, their high abundance in teleost brain may be the consequence of a functional interdependence during evolution, although the primary causal factor is unknown. These studies illustrate the usefulness of unconventional species and a comparative approach for obtaining new insights into brain-steroid interactions.
authors.affiliation: Department of Biology, Boston University, MA 02215.
authors.forename: G V
authors.initials: GV
authors.lastname: Callard
authors.forename: M
authors.initials: M
authors.lastname: Pasmanik
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology*; D004967:Estrogens / Q000502:physiology*; D010902:Pituitary Gland / Q000502:physiology*
chemical_list: D004967:Estrogens