Autoradiographical evidence for increased thyrotropin binding to autonomously functioning thyroid gland tissue.

The aim of this study was to quantify thyrotropin (TSH) binding to individual cells from autonomously functioning thyroid gland tissue (AFTT) in comparison with the corresponding non-autonomous cells. Cryostatic tissue sections from ten thyroid glands with autonomously functioning adenomas were incubated in 125I-labeled TSH. TSH-binding density (TBD) was visualized by means of autoradiography and quantified by means of reflection photometry. Eight out of ten specimens showed a significant (p less than 0.001), up to tenfold increase in TBD of AFTT cells. All ten specimens had a significantly increased number of TSH molecules bound per thyrocyte in comparison both with the corresponding non-autonomous cells and also with tissues from non-functioning thyroid neoplasms (n = 6). The increased TBD of AFTT persisted after transplantation onto nude mice. The paranodular tissue from thyroid glands with scintigraphically compensated adenomas showed in four out of six cases an increased TBD when compared with normal thyroid tissue. It can be concluded that AFTT possesses distinct cytoplasm membrane characteristics as evinced by TSH binding analysis. Increased TSH binding should be considered as a possible cause of metabolic hyperactivity of AFTT cells. The concomitant existence of functional autonomy in the paranodular tissue might lead to a false supposition of a compensated autonomous adenoma as revealed by scintigraphical evidence.