Pituitary responsiveness to gonadotropin-releasing hormone (GnRH) and thyrotropin-releasing hormone (TRH) during different phases of the same cycle of oral contraceptive steroid therapy.

To study the pituitary luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), and thyroid-stimulating hormone (TSH) secretory capacity and to determine whether the gonadotropes, lactotropes, and thyrotropes have a circatrigintan cycle of variation under hormonal contraception, women under combined oral contraceptive steroid treatment were challenged with a combination of 100 micrograms of gonadotropin-releasing hormone (GnRH) and 200 micrograms of thyrotropin-releasing hormone (TRH) given intravenously at weekly intervals. Significant releases of LH (P less than 0.001), FSH (P less than 0.05), PRL (P less than 0.001) and TSH (P less than 0.001) occurred in response to GnRH-TRH. The LH integrated change score (ICS), calculated as the difference between post-GnRH-TRH hormonal release and the average baseline levels, was higher (P less than 0.001) after ingestion of tablet 7 than after the 7th day after ending the previous cycle of treatment and after ingestion of tablet 21. The FSH ICS decreased as the cycle of treatment advanced in comparison with the ICS of the 7th day after the end of the previous cycle of treatment. The PRL and TSH ICS were not influenced by oral contraceptives. The LH, FSH, PRL, and TSH releases were not influenced by the dose of estrogens given daily.