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  • Title: Sex hormone binding globulin: effect of synthetic steroids on the assay and effect of oral contraceptives.
    Author: Bowles SM, Mills RJ.
    Journal: Ann Clin Biochem; 1981 Jul; 18(Pt 4):226-31. PubMed ID: 7197136.
    Abstract:
    The effect that synthetic steroid components of different oral contraceptives have on the assay system for measurement of sex hormones binding globulin (SHBG)-binding capacity, has been examined. Interference with the assay was not demonstrable at therapeutic levels of the drugs. d-Norgestrel was the only steroid studied which bound to SHBG with an affinity comparable to the endogenous sex hormones; it also tended to decrease SHBG-finding capacity, whereas preparations containing low levels of norethisterone increased the binding capacity. We suggest that measurement of changes in SHBG-binding capacity in subjects taking oral contraceptives may prove useful in indicating changes in sex hormone balance, particularly in view of the well-recognised side-effect of these drugs. This study examines the effect of synthetic steroid components of 7 commonly prescribed oral contraceptives on the assay of sex hormone binding globulin (SHBG). The 7 oral contraceptives and the number of patients taking each preparation are: 1) Minovlar (n=10); 2) Ortho-Novum 1/50 (n=2); 3) Gynovlar 21 (n=8); 4) Minilyn (n=5); 5) Eugynon-50 (n=2); 6) Eugynon-30 (n=10) and 7) Microgynon (n=3). The blood SHBG-binding capacity of these 40 women was measured. The method of Rosner was used in the SHBG-binding capacity assay. Serum samples from each woman were treated with charcoal to remove the endogenous and exogenous steroids; the samples were assayed for SHBG-binding capacity before and after the charcoal treatment. Binding studies were also done. The results show that the synthetic compounds do not cause significant interference with the assay system when used at therapeutic levels. Of the synthetic steroids studied, d-Norgestrel was the only 1 which bound to SHBG with an affinity comparable to the endogenous sex hormones. D-Norgestrel also tended to decrease SHBG-binding capacity. This finding supports the observation that d-Norgestrel has androgenic activity due to its structure, as there is an apparent relation between the in vivo androgenic activity of steroids and their ability to bind to SHBG; the more potent the androgen, the greater its binding to SHBG. It is probable that d-Norgestrel exerts a direct inhibiting effect on SHBG synthesis, as do endogenous androgens. The ideal oral contraceptive preparation is one which maintains the existing sex hormone balance, avoiding the undesirable effects of excess estrogen administration on the one hand and excess androgenicity on the other. Measurement of SHBG-binding capacity would be a useful tool for determining changes in sex hormone balance. As women vary in their requirement, measurement of SHBG-binding capacity before and during contraceptive therapy may be a better indicator of hormonal balance in an individual woman.
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