Biological characteristics of adenomatous nodules, adenomas, and hyperfunctioning nodules as defined by adenylate cyclase activity and TSH receptors

This study was designed to examine the functional characteristics of thyroid adenomas, adenomatous (colloid) nodules, hyperfunctioning nodules, and normal thyroid parenchyma with respect to the presence of TSH receptors, levels of adenylate cyclase, and the responsiveness of adenylate cyclase to specific stimuli, e.g., NaF (sodium fluoride), GTP_γS [guanosine 5′-0-(3-thiotriphosphatate)], PGE₁, and TSH. Aliquots of specimens from patients undergoing thyroidectomy [11 normal thyroids, 7 adenomas, 8 adenomatous (colloid) nodules, 5 hyperfunctioning nodules] were immersed in liquid nitrogen and stored at 90°C. Studies were performed on partially purified plasma membranes. Receptor binding of¹²⁵I-TSH was quantitated and analyzed according to Scatchard. Adenylate cyclase activity was assayed in the same tissue fraction by conversion of (α-³²P) ATP to cAMP. High- and low-affinity TSH receptors were present in adenomatous (colloid) nodules, hyperfunctioning nodules, and normal thyroid parenchyma. The thyroid adenomas had high-affinity receptors in normal quantities; low-affinity receptors were present at normal or decreased levels. The basal adenylate cyclase activity was slightly increased in thyroid adenomas. All groups had adenylate cyclase response to NaF with the thyroid adenomas being 60% more responsive than normal thyroid parenchyma (p <0.005). All tissues responded to PGE₁, with normal thyroid parenchyma being twice as responsive as thyroid adenomas. The adenylate cyclase response of adenomatous (colloid) nodules and hyperfunctioning nodules was distinct from that of adenomas and comparable to that of normal thyroid parenchyma. The adenylate cyclase response to TSH was fourfold in thyroid adenomas and twofold in adenomatous (colloid) nodules compared to normal thyroid parenchyma.