Changes in serum levels of SHBG, endogenous ligands and levonorgestrel induced by ethinylestradiol in Norplant users.
This work was done in search for a model to examine target organ response to fluctuations in serum levels of sex hormone-binding globulin (SHBG) and its ligands. The time course and magnitude of fluctuations of SHBG, levonorgestrel (L-Ng), estradiol (E2), testosterone (T) and dihydrotestosterone (DHT) in serum were examined during and after treatment with 50 ug of ethinylestradiol (EE2) daily for 10 days in 10 volunteer women using NORPLANT implants. Six of these volunteers were also treated with 20 ug of EE2 daily for 7 days and two additional volunteers using a copper-T IUD were treated with 50 ug of EE2 daily for 7 days. In all cases, SHBG and L-Ng levels increased in a close parallel manner several-fold above basal levels during treatment, reaching a maximum around two days after the last EE2 pill. In contrast, the levels of E2 and T increased in one subject, decreased in 5 and remained unchanged in 4, while changes of DHT were unrelated to those of the other ligands. Since the L-Ng "secretion rate" by NORPLANT implants is constant, it follows that the effect of EE2 on its levels is due to a decreased metabolic clearance rate, most likely secondary to the increased binding of L-Ng to SHBG in serum. This interpretation is in agreement with the close parallelism in the fluctuations of L-Ng and SHBG. It is concluded that in NORPLANT users, SHBG and L-Ng, but not the endogenous ligands, behave in a predictable manner in response to EE2. Thus, this model affords the possibility of exploring the influence of SHBG on tissue response to progestins.
Noé
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G
Unidad de Reproducción y Desarrollo, Facultad de Ciencias Biológicas, Universidad Católica de Chile, Santiago.
Pavez
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M
Croxatto
H B
HB
D013196:Dihydrotestosterone / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004343:Drug Implants; D004958:Estradiol / Q000097:blood; D004997:Ethinyl Estradiol / Q000493:pharmacokinetics / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007435:Intrauterine Devices, Copper; D016912:Levonorgestrel / Q000097:blood / Q000627:therapeutic use; D008657:Metabolic Clearance Rate; D012738:Sex Hormone-Binding Globulin / Q000032:analysis*; D013256:Steroids / Q000097:blood*; D013739:Testosterone / Q000097:blood
D004343:Drug Implants; D012738:Sex Hormone-Binding Globulin; D013256:Steroids; D013196:Dihydrotestosterone; D013739:Testosterone; D004997:Ethinyl Estradiol; D004958:Estradiol; D016912:Levonorgestrel