Thyroid function and thyrotropin levels in rabbits immunized to produce antibodies against thyroid hormones

Abstract

Various parameters of thyroid function were studied in 27 rabbits, out of which 10 were immunized to produce antibodies against triiodothyronine (T 3), 9 against thyroxine (T 4) and 8 were normals. Estimations of T 3, T 4, Free T 4 (FT 4) and thyrotropin (TSH) in blood, qualitative and quantitative analysis of iodoamino acids in serum, protein bound iodine-131 (PB 131I), butanol extractable iodine-125 (BE 125I) and measurement of the disappearance rates of 125I-labelled T 3 and T 4 from plasma were done. In addition, glandular changes were also studied by measurement of 131I uptake, thyroid scanning and chromatographic analysis of hydrolysate of soluble iodoproteins. In T 3 immunized animals, levels of T 3 in serum increased by 38 to 125 times, levels of TSH also showed a significant rise (7.4 ± 1.2 vs 28 ± 9 ng/mL). Chromatographic analysis of iodoamino acids in serum as well as in the hydrolysate of the thyroid gland demonstrated a selective increase in synthesis of T 3. Rate of disappearance of T 3 from blood showed a significant decline. Thyroid glands in the immunized rabbits showed signs of hypertrophy and hyperplasia. Identical studies done in rabbits immunized to produce antibodies against T 4 showed a similar pattern though of variable degree. Our studies indicate that the thyroid glands of the immunized rabbits undergo marked alterations resulting in selective increase in the synthesis and secretion of the particular thyroid hormone against which they were immunized. They do so under the influence of increased levels of TSH.