Disparity in the response of sex steroid-binding protein and corticosteroid-binding globulin to thyroxine in the primate.
There is uncertainty regarding the differential effects of thyroid hormone on the circulating levels of sex steroid-binding protein (SBP) and corticosteroid-binding globulin (CBG). Therefore, we studied the effects of elevated thyroxine (T4) on SBP and CBG concentrations in serum in 4 baboon (Papio anubis) infants between 6 and 7 mo of age. The infants were given levothyroxine in increasing doses (25 to 600 micrograms) over a 1-mo period until the peripheral T4 levels were 3-4 times higher than baseline values. Each animal served as its own control. Blood samples were obtained at 2- to 3-day intervals prior to and during treatment. Serum T4 was measured by RIA. SBP and CBG were measured by diethylaminoethyl cellulose filter paper assays. Elevations in serum T4 resulted in a dose-response increase in circulating SBP concentrations with a maximal increase at the 600-micrograms dose of T4 (p less than 0.001). In contrast, significant elevations in peripheral CBG levels occurred with 50 and 100 micrograms of T4 (p less than 0.025 and p less than 0.01, respectively), but decreased thereafter with higher doses of T4. At the 600-micrograms dose of T4, CBG concentrations returned to baseline values. We conclude that in the baboon, T4 increases the circulating levels of SBP in a graded fashion, while the effect on CBG is biphasic.
Stanczyk
F Z
FZ
Division of Reproductive Biology and Behavior, Oregon Regional Primate Research Center, Beaverton 97006.
Nakamura
R M
RM
Novy
M J
MJ
D000818:Animals; D002352:Carrier Proteins / Q000097:blood / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D010215:Papio / Q000502:physiology*; D012738:Sex Hormone-Binding Globulin; D013974:Thyroxine / Q000494:pharmacology*; D014156:Transcortin / Q000502:physiology*
D002352:Carrier Proteins; D012738:Sex Hormone-Binding Globulin; D014156:Transcortin; D013974:Thyroxine