An improved receptor assay for TSH receptor antibodies is described in which detergent-solubilized TSH receptors and 125I-labelled TSH are used. Normal human serum and immunoglobulin concentrates from normal serum showed little effect on the interaction between labelled TSH and detergent-solubilized receptors whereas immunoglobulin concentrates from some Graves sera caused marked inhibition of TSH binding. Precipitation with polyethylene glycol was the most convenient way of preparing immunoglobulin concentrates and using this technique the assay could be completed in a few hours. The coefficient of inter assay variation at 51% inhibition of labelled TSH binding was 3.7% and analysis of serum samples from patients with Graves' disease (n = 42), Hashimoto's disease (n = 26), multinodular goitre (n = 9), rheumatoid arthritis (n = 10) and normal donors (n = 35) suggested that the assay could detect TSH receptor antibodies in about 80% of patients (treated and untreated) with Graves' disease.

No abstract

An investigation of the ability of TSH receptor antibodies to bind to the TSH receptor and stimulate thyroid function is described. Binding studies were carried out using 125I-labelled TSH and detergent solubilised porcine TSH receptors, and the parameter of thyroid stimulation employed was 125I-organification in isolated porcine thyroid cells. Different Graves' sera were found to show different dose-response relationships and three types of antibody activity were evident in the six samples studied. In two samples receptor binding and thyroid stimulating activities were approximately parallel. In two receptor binding was detectable at lower doses than stimulation while in the last two stimulation was detectable at lower doses than binding. It is proposed that these characteristics are due to different populations of receptor antibodies which exhibit different degrees of TSH agonism. Furthermore one of the reasons for the relatively poor correlation between TSH receptor binding and thyroid stimulation observed in series of individual Graves' sera may be the presence of different populations of antibodies showing different dose-response relationships with regard to binding and stimulation.

No abstract

The effect of conditioned vs. fresh culture medium on the dopaminergic inhibition of TSH and PRL secretion by primary cultures of male rat anterior pituitary cells has been studied. In the presence of conditioned medium (that had been in contact with the cells over the 3-day culture period) 10(-6) M dopamine (DA) inhibited PRL secretion by 50% and TSH secretion by 30%. After 4 h of incubation with fresh medium 10(-6) M DA still inhibited PRL secretion by 50% but increased TSH release by 20%. TSH release was rapid and could be prevented by 10(-6) M prazosin, an alpha 1 adrenoreceptor antagonist. Fresh medium did not alter TRH induced TSH release. In parallel cultures and under identical conditions fresh medium reduced [3H]dihydroergocryptine (DHE) binding to DA receptors from 2.5 +/- 0.4 fmol/10(5) cells to 0.95 +/- 0.3 fmol/10(5) cells (means +/- SEM, n = 5, P less than 0.001). The effect of fresh medium was dose dependent against the dopaminergic inhibition of TSH secretion and against DA receptor binding. If 1 mU TSH was included, in fresh medium, the dopaminergic inhibition of TSH secretion remained unchanged and [3H]DHE binding to DA receptors did not fall. The rank order of potency of thyroid stimulators was bovine TSH (21 U/mg) greater than semipurified bovine TSH (Thytropar, 1.4 U/mg) greater than endogenous rat TSH (0.03 U/mg expressed as NIADDK-rat TSH-RP2) greater than Graves' immunoglobulin G (0.01 U/mg) when either DA or bromocriptine was used as the dopaminergic agonist. When anterior pituitary cells from hypothyroid rats were examined, the effects of culture medium on the dopaminergic inhibition of TSH and on DA receptor binding were approximately twice those observed in normal cells, but the inclusion of 1 mU TSH in the fresh medium completely prevented the loss of DA function and binding. PRL, human CG, ACTH, insulin, glucagon, and heat-inactivated TSH were unable to prevent the effect of medium replacement on dopaminergic inhibition of TSH and DA receptor binding. The data suggest a mechanism whereby TSH may control its own secretion via DA.