The properties of adenyl-cyclase and of cAMP phosphodiesterase of normal thyroid and of a transplantable thyroid tumor of the rat have been compared. The adenyl-cyclase of the tumor and the normal thyroid were both stimulated by sodium fluoride. TSH significantly stimulates adenyl-cyclase of normal thyroid, but fails to stimulate the tumor enzyme. cAMP-phosphodiesterase was found in the 22,000 g supernatant of both tissues. In the presence of 5 × 10-3M theophylline the enzyme of both tissues was inhibited by 40%. TSH also fails to stimulate 1-14C glucose oxidation and phospholipid metabolism in tumor slices, whereas, DBcAMP significantly stimulates the metabolism of both. The inability of the tumor adenyl-cyclase to respond to TSH may be due to a structural alteration of the receptor site for TSH in the neoplastic cell. (Endocrinology90: 1483, 1972)
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Macchia et al. (1972) studied this question.