Effects of Different Types of Oral Contraceptives on the Protein-Bound Iodine and the ¹²⁵-Triiodothyronine Uptake on Sephadex

Abstract

The protein-bound iodine (PBI) and the uptake of ¹²⁵I-triiodothyronine on Sephadex (T₃S) were determined in 47 control subjects and in 277 women taking oral contraceptives. Mean PBI was increased and mean T₃S was decreased in women taking combined or sequential drugs, while the mean ‘free thyroxine index’ was unchanged in all groups. PBI was increased in 41–43%, and T₃S decreased in 85–88% of the women taking combined or sequential drags, while 96% of the PBI-determinations and 91% of the T₃S-determinations were normal in those taking low doses of gestagens. Norethindrone (1–2 mg) counteracted the depressing effect of oestrogens on the T₃S while chlormadinone acetate (3 mg) had no effect.

Key Words:

• Free thyroxine index
• gestagen
• oestrogen
• oral contraceptives
• progestogen
• protein-bound iodine
• thyroid function tests
• triiodothyronine uptake