“In Vitro” Study on Release of Cyclic AMP and Thyroid Hormone in Autonomously Functioning Thyroid Nodules

Summary The TSH effect on slice and the incubation medium cyclic AMP levels and T 3 and T 4 released from 8 autonomously functioning thyroid nodules (AFTN) and their respective perinodular (PN) tissues were examined. The thyroid slices were incubated in Eagle's Medium containing TSH (5 to 100 mU/ml) for 60 min and 300 min for tissue cyclic AMP generation and for cyclic AMP, T 3 and T 4 release, respectively. Basal cyclic AMP levels were not different either in AFTN and in PN slices or into the incubation medium. In both tissues TSH produced a similar cyclic AMP generation. In contrast, cyclic AMP released into the incubation medium was significantly higher in AFTN than in PN tissues, after TSH stimulation. Basal T 3 values and TSH-stimulated T 3 release in AFTN were not different from PN tissue. However, basal T 4 levels were significantly higher in AFTN than in PN tissue as well as T 4 released in response to TSH. In addition, T 3 /T 4 ratio was lower in AFTN than in PN tissues. The cyclic AMP released into the incubation medium correlated with both T 3 and T 4 release in PN tissue but in the AFTN tissue no correlations were found. These findings suggest that the adenylate cyclase-cyclic AMP system is more sensitive to TSH-stimulation in AFTN when compared with PN tissue and that AFTN tissue has a preferential T 4 secretion.