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Summary
Norethisterone (NET) levels in women taking oral contraceptives were studied. While total NET and SHBG-bound NET increased, the biologically active unbound fraction rose less, suggesting total levels don't fully represent efficacy.
Area of Science:
- Endocrinology
- Pharmacology
- Reproductive Biology
Background:
- Norethisterone (NET) is a progestin found in oral contraceptives.
- Hormone transport in blood involves binding to plasma proteins like albumin and sex hormone-binding globulin (SHBG).
- Only unbound hormones are generally considered biologically active.
Purpose of the Study:
- To investigate the binding of Norethisterone (NET) to SHBG.
- To assess how NET and SHBG concentrations change during oral contraceptive treatment.
- To determine the relationship between total NET levels and the biologically active fraction.
Main Methods:
- Studied five women over a 21-day treatment cycle with an oral contraceptive containing Norethisterone acetate and ethinylestradiol.
- Measured total and SHBG-bound Norethisterone (NET) concentrations.
- Monitored changes in SHBG levels.
Main Results:
- Total and SHBG-bound Norethisterone (NET) concentrations increased during treatment.
- SHBG levels also increased in parallel with NET concentrations.
- The unbound and free fractions of NET increased proportionally less than total NET.
Conclusions:
- Oral contraceptive treatment affects Norethisterone (NET) binding to SHBG.
- Increased SHBG during treatment influences NET distribution.
- Total Norethisterone (NET) levels measured by radioimmunoassay may not fully reflect the biologically active steroid fraction.
Keywords:
ContraceptionContraceptive Agents, EstrogenContraceptive Agents, FemaleContraceptive Agents, ProgestinContraceptive Agents--administraction and dosageContraceptive Agents--analysisEthinyl Estradiol--administraction and dosageExaminations And DiagnosesFamily PlanningLaboratory Examinations And DiagnosesLaboratory ProceduresNorethindrone Acetate--administraction and dosageNorethindrone--analysis