EFFECT OF TSH ON ACID PHOSPHATASE AND THYROGLOBULIN HYDROLYZING ACTIVITIES IN GUINEA PIG THYROID

Acid phosphatase and thyroglobulin hydrolyzing activities were assayed in the thyroids from three groups of guinea pigs. The treatments of the animals were: thyroxine only for 4 days; thyroxine for 4 days + TSH 1 h before sacrifice; thyroxine for 4 days + TSH 24 h before sacrifice. It was found that 1 h action of TSH did not measurably change the enzyme activities. Twenty-four hours of TSH-stimulation resulted in a statistically significant increase of both enzyme activities when calculated as total glandular activity or on DNA basis. Parallel cytochemical studies in the electron microscope revealed that acid phosphatase activity was localized, in all three groups, to the lysosomes and, in the animals stimulated by TSH for 1 h, also to the colloid droplets. It is concluded that these findings, combined with earlier data demonstrating a rapid action of TSH on the thyroxine release, indicate that the mechanism for the increase of hormone release by TSH is not accelerated biosynthesis of thyroglobulin hydrolyzing enzymes but induction of endocytosis. © 1968.