Alterations in type I and type II protein kinases in the thyroid and adenohypophysis in response to a dietary goitrogen

The goitrogen, propylthiouracil (PTU), when administered in the diet of white leghorn chickens resulted in a marked increase in weight of the thyroid gland within 7 days which was maximal (160% of control) within 14 days. This system was used to determine the alterations in cyclic AMP-dependent protein kinase activity ratios and to assess the amounts of type I and type II cyclic AMP-dependent protein kinases present in the thyroid as well as any changes related to hypertrophy and hyperplasia of the thyroid. There was a marked elevation in the cyclic AMP-dependent protein kinase activity ratio ( −cAMP +cAMP ) 7 days after initiation of treatment as well as an increase in the total amount of supernatant cyclic AMP-dependent protein kinase activity (+cAMP) which doubled within 14 days of dietary PTU. Both type I and type II cyclic AMP-dependent protein kinase activities were detectable in the thyroid and adenohypophysis. Type I comprised 10% and type II 90% of the total cyclic AMP-dependent protein kinase activity in both tissues. The total amount of type I protein kinase activity increased significantly by 7 days. By 14 days, both type I and II protein kinases were increased twofold. The amount of type I returned to a control value by 21 days whereas type II remained elevated. Adenohypophysial type II protein kinase activity decreased to 70% of control by 14 days. Cyclic AMP is known to exert its effect on trophic responses through the activation of cyclic AMP-dependent protein kinase. These data implicate both activation of the enzymes as well as increased amounts of types I and II protein kinase activity in the thyroid in response to goitrogen-induced hypertrophy and hyperplasia.