Effect of thyroxine on the inactivation of thyrotrophin-releasing hormone by rat and human plasma.
The inactivation of synthetic [3H]thyrotrophin-releasing hormone (TRH) by plasma was studied in rats treated with propylthiouracil (PTU) alone or with PTU and thyroxine. 48 h after the onset of treatment with thyroxine, the capacity of rat plasma to inactivate [3H]TRH was significantly increased. The percentage of deamidation of TRH to TRH-free acid was increased 2-fold after 4 days of administration of thyroid hormone. The inactivation of TRH by plasma from hypothyroid patients was compared to that obtained from hyperthyroid patients. Extraction of human plasma incubated with [3H]TRH, followed by thin-layer electrophoresis, showed that transformation of [3H[TRH into TRH-free acid was 44% higher in plasma from hyperthyroid than from hypothyroid patients (P less than 0-05). These data suggest that the inactivation process of TRH by blood proteins could be an important factor in the regulation of the hypothalamo-hypophyseal-thyroid axis in rat and man.
D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D004588:Electrophoresis, Cellulose Acetate; D006801:Humans; D006980:Hyperthyroidism / Q000378:metabolism; D007037:Hypothyroidism / Q000378:metabolism; D008297:Male; D011441:Propylthiouracil / Q000494:pharmacology; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000097:blood / Q000378:metabolism*; D013974:Thyroxine / Q000494:pharmacology*
D001798:Blood Proteins; D013973:Thyrotropin-Releasing Hormone; D011441:Propylthiouracil; D013974:Thyroxine