title: TeBG- and CBG-bound steroid hormones in rabbits are available for influx into uterus in vivo.
abstract: The metabolic clearance rate (MCR) of gonadal or adrenal steroid hormones in rabbits often does not bear the expected inverse relationship with hormone binding to testosterone-binding globulin (TeBG) or corticosteroid-binding globulin (CBG). This suggests TeBG or CBG may not impede steroid hormone delivery to tissues. The effects of rabbit plasma proteins on the influxes of 3H-labeled steroids from the circulation into the rabbit uterus were measured in vivo using a tissue sampling single-injection technique. In the absence of plasma proteins, estradiol (E2) and testosterone (T) were freely diffusible through the uterine microvasculature (i.e., extraction greater than 80%). The extractions of dihydrotestosterone (DHT) and corticosterone (B) ranged from 60 to 72%, while that of cortisol (F) was reduced at 40%. Rabbit serum exerted no inhibition of the influxes of the steroids tested. The influxes of T and B greatly exceeded the rates that would be expected if only the free and albumin-bound fractions estimated in vitro were diffusible in vivo. However, the extraction of [3H]corticosteroid-binding globulin or bovine [3H]albumin were low, consistent with little, if any, extravascular uptake of the plasma proteins. The results indicate both albumin-bound and globulin-bound steroid hormone are available for transport into the uterus in the rabbit in vivo without significant exodus of the plasma protein, per se.
authors.affiliation: Department of Obstetrics and Gynecology, School of Medicine, University of California, Los Angeles 90024.
authors.forename: G
authors.initials: G
authors.lastname: Chaudhuri
authors.forename: K A
authors.initials: KA
authors.lastname: Steingold
authors.forename: W M
authors.initials: WM
authors.lastname: Pardridge
authors.forename: H L
authors.initials: HL
authors.lastname: Judd
mesh_terms: D000818:Animals; D001682:Biological Availability; D003345:Corticosterone / Q000493:pharmacokinetics; D013196:Dihydrotestosterone / Q000097:blood / Q000493:pharmacokinetics; D004958:Estradiol / Q000097:blood / Q000493:pharmacokinetics; D005260:Female; D006854:Hydrocortisone / Q000493:pharmacokinetics; D008833:Microcirculation; D011817:Rabbits; D012709:Serum Albumin / Q000378:metabolism; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013739:Testosterone / Q000097:blood / Q000493:pharmacokinetics; D014156:Transcortin / Q000378:metabolism*; D014599:Uterus / Q000098:blood supply / Q000378:metabolism*
chemical_list: D012709:Serum Albumin; D012738:Sex Hormone-Binding Globulin; D013196:Dihydrotestosterone; D013739:Testosterone; D004958:Estradiol; D014156:Transcortin; D003345:Corticosterone; D006854:Hydrocortisone