Interaction of testosterone, corticosterone and corticosterone binding globulin in the white-throated sparrow (Zonotrichia albicollis)

M. B. Swett, C. W. Breuner

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Plasma binding globulins bind steroid hormones and are thought to regulate hormone access to tissues. Mammals have both sex steroid binding globulin (SSBG) and corticosteroid binding globulin (CBG). Birds, however, have no detectable SSBG, leading to the early conclusion that birds have no plasma regulation of sex steroids. CBG, however, can bind androgens with relatively high affinity. In birds, therefore, the control of androgenic effects may be tightly regulated by glucocorticoid physiology because glucocorticoids compete with androgens for CBG binding sites. We report levels of total testosterone (T), total corticosterone, CBG, and estimated free T in the males, the more aggressive morph had higher levels of total T; female morphs did not differ. Approximately 96% of T was bound to CBG, but a lack of morph or sex-specific differences in corticosterone titers or CBG capacity caused patterns of free T to mirror those of total T. While CBG has the potential to greatly influence T availability to tissues, in this species interactions between T, CBG and corticosterone do not appear to alter general patterns of T availability to tissues.

    Original languageEnglish
    Pages (from-to)226-231
    Number of pages6
    JournalComparative Biochemistry and Physiology - A Molecular and Integrative Physiology
    Volume151
    Issue number2
    DOIs
    StatePublished - Oct 2008

    Keywords

    • Behavioral polymorphism
    • Corticosterone
    • Corticosterone binding globulin
    • Free-hormone hypothesis
    • Testosterone
    • White-throated sparrow

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