Thyrotrophin and prostaglandin E2 increase calmodulin levels and cyclic AMP phosphodiesterase activity in cultured porcine thyroid cells.

Thyrotrophin (TSH) and prostaglandin E2 (PGE2) increased cellular cyclic AMP (cAMP), calmodulin levels and cAMP phosphodiesterase activity in cultured porcine thyroid cells. Dibutyryl cAMP (dbcAMP), a stable analogue of cAMP, increased calmodulin levels and cAMP phosphodiesterase activity. These results indicate that TSH- and PGE2-stimulated increases in calmodulin are mediated by cAMP. This increased concentration of calmodulin in turn stimulates cAMP phosphodiesterase. Double reciprocal plots of cAMP hydrolysis yielded two apparent Michaelis constants (Km); the lower in the 1 mumol/l and the higher in the 10 mumol/l range. Thyrotrophin, PGE2 and dbcAMP increased the values of maximal velocity without changing the Km values.