Testosterone, corticosterone, and photoperiod interact to regulate plasma levels of binding globulin and free steroid hormone in Dark-eyed Juncos, Junco hyemalis

Pierre Deviche, Creagh Breuner, Miles Orchinik

Research output: Contribution to journalArticlepeer-review

122 Scopus citations

Abstract

The pharmacology and regulation of corticosteroid binding globulins (CBG) in Dark-eyed Juncos, Junco hyemalis, was investigated. The equilibrium dissociation constant for [3H]corticosterone (CORT) binding to plasma was < 5 nM. This binding site had a similar high affinity for progesterone, approximately fivefold lower affinity for androgens, and negligible affinity for estradiol. The following data suggested that plasma CBG levels are regulated by both testosterone and day length: (1) CBG binding capacity in free-living adult males was greater in early than in late breeding season and greater in males than in females and (2) CBG levels were higher in testosterone-treated, castrated males than in castrated males receiving no testosterone and still higher in testosterone-treated males exposed to long days than in similar males exposed to short days. Birds apparently lack a sex steroid-specific binding globulin, but it was estimated that more than 90% of testosterone in junco plasma should bind to CBG. An increase in plasma CORT, such as occurs during a stress response, was judged to acutely increase free testosterone levels as much as fivefold. Corticosterone and testosterone may thus interact in a complex manner in species that lack sex hormone binding proteins.

Original languageEnglish
Pages (from-to)67-77
Number of pages11
JournalGeneral and Comparative Endocrinology
Volume122
Issue number1
DOIs
StatePublished - 2001

Keywords

  • Androgen
  • CBG
  • Castration
  • Dark-Eyed Junco
  • Seasonality
  • Sex hormones
  • Transcortin

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