Changes in cyclic nucleotides of rat thyroid by chronic administration of LATS and TSH

The effects of LATS and TSH on the cyclic nucleotide content and enzymatic activity in rat thyroid was observed during the continuous administration of LATS or TSH for 6 days. Serum T4 and T3 levels were increased significantly compared with the saline controls. The cyclic nucleotide (cAMP and cGMP) levels and enzyme activities per wet weight of tissue were determined. The thyroid weight in both the LATS and TSH groups increased approximately two-fold, but cAMP and cGMP content per wet weight did not significantly change. Neither cyclic nucleotide showed any significant change in plasma. The cAMP-PDE activity in the thyroid significantly increased in both the LATS and TSH groups, but the cGMP-PDE activity was unchanged. Neither was cyclic nucleotide-PDE activity changed in the plasma. The ATPase activity in the thyroid increased markedly in both the LATS and TSH groups, while 5'-nucleotidase activity did not change. These data suggest that LATS and TSH appear to have a stimulatory effect on the metabolism of cAMP, but do not affect the metabolism of cGMP.