Possible interference of synthetic estroprogestins with thyroid hormone production

The mechanism of action of oral contraceptives (OCs) can be exercised at different levels; at the hypothalamic level by inhibition of the production of gonadotropin-releasing hormones at the ovarian level at the tubal level by interfering with motility at the endometrial level by modification of the endometrial structure at the cervical level by modification of the consistency of the cervical mucus and directly on spermatozoa by inhibiting their motility. The effects of OCs on thyroid functions are still the subject of considerable debate. The authors studied 15 women aged 15-42 observed for thyroid pathology and who had been treated either for contraceptive or therapeutic reasons with estroprogestational agents. 5 patients had presented signs of thyroid malfunction prior to OC treatment; of the 10 remaining patients 7 had developed primary goiter 2 had developed goiter together with reduced production of thyroid hormones and 1 had developed acute thyroiditis. These findings indicated that administration of OCs especially for a period over 5 months may favor the onset or the recurrence of thyroid pathology through the inhibition of intraglandular hormone production; at the same time hypothalamic thyroid-releasing hormone (TRH) and thyroid-stimulating hormone production are increased with resulting thyroid hyperplasia. In vitro experiments as yet unconfirmed in man provide evidence of a direct action of estrogens on the pituitary response to TRH as a result of an increased concentration of TRH receptors in the pituitary. The problem is not yet solved but the presence of goiter must be considred an absolute contraindication to the use of OCs. (summary in ENG)