A radioimmunoassay for serum rat thyroglobulin. Physiologic and pharmacological studies.

Abstract

A B S T R A C T A double antibody radioimmunoassay has been developed to measure thyroglobulin in rat (RTg) serum. The lowest detectable quantity measurable was 5.0 ng/ml. Specificity was documented by: (a) fall in serum RTg to undetectable levels after thyroid ablation; (b) the fact that L-thyroxine, D-thyroxine, Ltriiodothyronine, D-triiodothyronine, triiodothyroacetic acid, tetraiodothyroacetic acid, triiodothyropropionic acid, monoiodotyrosine, diiodotyrosine, and human thyroglobulin (HTg) in concentrations up to 40,000 ng per tube did not cross-react in the assay; (c) the demonstration that constant levels of serum RTg were observed while varying amounts of serum (criterion of parallelism) were introduced in the assay. The mean RTg concentration in tail vein blood of adult SpragueDawley rats was 101.5±+13.0 ng/ml (SEM) (n=21); values ranged from 12.0 to 258.0 ng/ml. Chronic administration of a high-iodine diet (HID) did not affect serum thyroglobulin levels. Chronic administration of a low-iodine diet (LID) and propylthiouracil (PTU) led to a statistically significant increase in serum RTg that was accompanied by a significant rise in serum thyrotropin (rTSH). Serum thyroxine (T4) administered to normal rats for 14 days (20 Ag/day subcutaneously) depressed serum RTg concentration from a mean level of 119.4±17.5 ng/ml (n = 19) to a mean of 35.0± 0.27 ng/ml (n = 19) (P < 0.001). While rats were on continuous T4 suppression, bovine thyroid-stimulating hormone (bTSH) given intravenously (2 IU) resulted in a mean maximal increment of RTg of 332.0±81.5 ng/ml (n = 6) at 24 h. IgG-(LATS) long-acting thyroid stimulator injected intravenously resulted in a mean maximal increment of RTg concentration at 96 h of 87.2±14.3 ng/ml (n = 5). Normal IgG had no staPresented at the annual meeting of the American Federation for Clinical Research (Western Section), February 1975, Carmel, Calif.

Serum Tg—A Sensitive Marker of Thyroid Abnormalities and Iodine Deficiency in Epidemiological Studies

“…Thus, only little further reduction could be obtained with iodine supplementation. This was parallel to experimental data, where no effect of iodine supplementation to iodine-replete rats was seen, whereas iodine deficient rats had increased serum Tg (43). The different impact on serum Tg of iodine supplementation Data are from 3719 participants without known thyroid disease and with Tg antibodies Ͻ 20 kU/liter.…”

Thyroid Hormone Regulates the Hypotriglyceridemic Gene APOA5

“…Under these conditions, plasma T 4 levels fall significantly by 75-90%, and there is also an ϳ60% reduction of plasma T 3 (49 -51), whereas plasma thyroid-stimulating hormone concentrations rise (52). As shown in Fig.…”

Serum Thyroglobulin and Thyroglobulin Autoantibodies in Thyroid Diseases

“…This remains to be confirmed. In summary, the regulation may be multifactorial with involvement of the TSH-TRH system, thyroglobulin in itself inhibiting the TSH stimulatory effect (9, 54) (section 7), but degree of iodination (84,118), ratio between T3 and T4 (84), or ingestion of goitrogens seem to contribute (1 18). The Tg antigenic material measured in serum is probably the aminoacid sequence of the molecule, independent of the' incorporation of iodine.…”