T3-release from autonomously functioning thyroid nodules in vitro

Toxic thyroid nodules have been shown to be of clonal origin. In a portion of them, point mutations affecting either the gene of the TSH receptor (TSH r) or the alpha-subunit of stimulating G-protein, consecutively leading to enhanced cAMP levels which may enhance growth or functional activity of the thyrocyte or both, were recently found. To complement these studies, we ev aluated hormone response (i.e. T3 release) in vitro from tissues derived fr om toxic thyroid nodules as compared directly to the surrounding paranodula r tissues as well as tissues derived from euthyroid goiter and from patient s with Graves' disease. Experiments were conducted in the presence and abse nce of bTSH or Graves' immunoglobulines. Tissues obtained during surgery we re incubated over 5 h, followed by equilibrium dialysis for 24 h, and deter mination of free T3 in an aliquot by RIA. Basal T3 release in nodular tissu es (n = 10) was significantly higher (median: 7.3 ng/l) compared to paranod ular tissues (3.2 ng/l; P < 0.01), tissues derived from euthyroid goiter (1 .3 ng/l; n = 12; P < 0.001) and thyroid tissues derived from patients with Graves' disease (2.5 ng/l; n = 6; P < 0.001). Upon stimulation with bTSH (1 IU/l), median T3 concentrations markedly increased to 11.5 ng/l (P < 0.05) , 7.3 ng/l (P < 0.05), 4.2 ng/l (P < 0.01) and 3.2 ng/l (P = N.S.), respect ively. Stimulation over basal values was 1.6-fold in nodular tissues, 2.3-f old in paranodular tissues, 3.2-fold in euthyroid goiter and 1.3-fold in Gr aves' disease. In toxic thyroid nodules basal hormone-releasing activities were stimulated by fifteen out of twenty (75%) Graves' sera tested. For com parison, stimulation in other tissues occurred in 45% (paranodular), 80% (e uthyroid goiter) and 35% (Graves' disease), respectively. In conclusion, tissue derived from toxic thyroid nodules exhibits enhanced basal hormone release as compared to both, the surrounding paranodular tiss ues and tissues from euthyroid goiter in vitro, which may reflect constitut ional activation of TSHr, alpha-subunit of stimulating G-protein or other s o far unknown intermediate by point mutations affecting the respective gene s. Hyperactivities in toxic thyroid nodules may be even further enhanced by external stimulators such as TSH or TSH receptor antibodies. The first sti mulator may have clinical relevance in patients with toxic thyroid nodules and not yet suppressed TSH; the latter could play a role in the rare Marine Lenhart syndrome.