Endocytosis of Thyreoglobulin and the Release of Thyroid Hormone

Abstract

Selected data from the literature on endocytosis and thyroid hormone release, as well as some unpublished results are presented. The morphologic changes following TSH stimulation are described, as well as some biochemical findings related to endocytosis. An attempt is made to explain the stimulation of endocytosis by TSH in terms of activation of adenyl cyclase, liberation of Ca⁺⁺ from membranes with subsequent effects on enzyme systems, and acceleration of the hexose-monophosphate shunt. Possible mechanisms of action of different drugs known to be active in inhibiting or promoting hormone release, as well as cellular factors limiting the rate of TSH-induced endocytosis under different conditions are discussed.

Key Words:

• Actinomycin
• colloid droplets
• Ca⁺⁺
• cyclic adenosine monophosphate
• cytosomes
• endocytosis
• hexose monophosphate
• iodide
• lysosomes
• pathway
• theophylline
• thyroglobulin
• thyroid follicle cells