Changes in physiologically free circulating estradiol and testosterone during exposure to levonorgestrel.
J Clin Endocrinol Metab
; 52(1): 138-43, 1981 Jan.
Article
em En
| MEDLINE
| ID: mdl-6778889
ABSTRACT
PIP The biological activity of circulating sex steroids is dependent upon the relative binding to (SHBG) sex hormone-binding globulin. Only that fraction which is not specifically bound to the high affinity binding protein is available to the receptors or for metabolism. (D-Ng) Levonorgestrel, a synthetic gestagen used for contraception decreases the hepatic production of SHBG. Volunteers wearing contraceptive vaginal rings containing (E2) estradiol and d-Ng were studied to determine the changes in sex steroid binding which occur when d-Ng is administered in a sustained release fashion. The % of steroids not specifically bound to SHBG was measured by fractionating the serum proteins with ammonium sulfate precipitation. A binding capacity assay was used to quantitate SHBG. During the normal menstrual cycle in control subjects, the unbound fractions of both E2 and (T) testosterone remained constant at about 25% of total E2 and 10% of total T. During treatment with d-Ng, however, the % of unbound E2 increased to about 80% of the total, and that of T increased to about 55% of the total, significantly greater than that in the control cycles (p 0.01). SHBG was constant during the normal menstrual cycle, averaging 85.9 + or - 1.92 nM but was suppressed during the administration of d-Ng to 10.0 + or - 2.6 nM. When SHBG concentration was greater than 50 nM, the % binding of both E2 and T were independent of the concentration of this binding protein. When SHBG was suppressed below 50 nM, the % binding of E2 and T was directly related to the concentration of the binding protein. The affinity of SHBG for d-Ng allows competition with E2 and T for SHBG-binding sites at concentrations of SHBG below 50 nM. The increase in physiologically free E2 and T, therefore, may be a result of both the suppression of SHBG concentration by d-Ng as well as the competition between d-Ng and endogenous sex steroids for the decreased number of available binding sites on SHBG.^ieng
Palavras-chave
Androgens; Biology; Contraception; Contraceptive Agents; Contraceptive Agents, Female; Contraceptive Agents, Progestin; Endocrine System; Estradiol--analysis; Estrogens; Family Planning; Hormones; Laboratory Procedures; Levonorgestrel; Menstrual Cycle; Menstruation; Physiology; Reproduction; Silastic Ring; Testosterone--analysis
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Testosterona
/
Estradiol
/
Norgestrel
Limite:
Adult
/
Female
/
Humans
Idioma:
En
Revista:
J Clin Endocrinol Metab
Ano de publicação:
1981
Tipo de documento:
Article