Ultrastructure of thyroid follicular cells following hypophysial portal vascular infusion of thyrotropin‐releasing hormone

Abstract

AbstractUltrastructural changes in thyroid follicular cell morphology were studied following the infusion of thyrotropin‐releasing hormone (TRH) for 1 min into a hypophysial stalk portal vessel of adult male rats. At 1, 5, 15 and 30 min following infusion, thyroid glands were removed and prepared for electron microscopic examination. Thyroid follicular cells in unoperated, sham‐operated non‐infused, and saline‐infused control rats were cuboidal, generally lacked intracellular colloid droplets and contained variable numbers of electron‐dense lysosome‐like bodies distributed throughout the cytoplasm. In experimental animals, marked intracellular colloid droplet accumulation was observed 5 min after TRH infusion and remained a constant finding throughout the time‐periods studied. Numerous lysosome‐like dense bodies accumulated in the apical cytoplasm of thyroid follicular cells at 30 min. Fusion of colloid droplets and lysosome‐like bodies had apparently occurred by 30 min. At this time the colloid droplets were smaller, more electron‐dense and were often located more basally within the follicular cell cytoplasm. This study suggests that the morphological response of thyroid follicular cells to hypophysial portal vascular infusion of TRH occurs rapidly and mimics, both temporally and morphologically, the response observed following systemic administration of exogenous TSH.