Studies on thyroid function in rats with experimentally induced thyroiditis.

Function of pituitary-thyroid axis was studied in rats with experimentally induced thyroiditisWistar strain female rats were immunized with homologous thyroid extract in Freund's complete adjuvant and with simultaneous intradermal injection of pertussis vaccine concentrate. They received booster shots at the first and third week after the initial immunization. Serum thyroid hormones and TSH were measured just before, and at weekly intervals after, the initial immunization. Histological examination of the thyroid gland at the second week after immunization showed slight infiltration of macrophages in the thyroid follicles. From the third to the fourth week, massive lymphoid cell infiltration and destruction of follicular architecture developed in all immunized rats. Serum R3 levels slightly decreased during the second week, increased transiently during the third week, then decreased again thereafter. Serum T4 levels decreased slightly durinf the fourth week. Serum TSH levels were not elevated significantly during the third week, but the response to TRH was significantly increased at this time. Basal TSH levels were increased during the fourth week. The TRH test was a sensitive method capable of detecting minimal failure of thyroid function undetected by other routine measuremens of thyroid hormones and TSH.