[Comparison of the effect of TSH and fluoride on the adenylate cyclase activity of cold thyroid nodules (author's transl)]

Abstract

Using a simple and reliable assay technique in which the actuel amount of cyclic AMP generated during incubation is determined by competitive protein binding assay, adenylate cyclase activity was measured in 7 cold nodules and 3 samples of normal thyroid tissue. Mitochondrial fraction prepared from surgically obtained tissues was used as the source of the enzyme. We observed an increased adenylate cyclase activity in cold nodules as compared to normal. More importantly, this activity was much more responsive to TSH in cold nodules than in normal (maximal stimulation: 1050+/-200% vs 320+/-120%). Also, maximal TSH stimulation was similar to that elucited by fluoride in the cold nodules but only one-third in normal tissue. These results suggest that higher efficiency of TSH in cold nodules may be related to increased TSH binding or coupling of TSH receptors with the caralytic subunit of adenylate cyclase.