Ultrastructural and Cytochemical Studies on the Thyroid Gland of Normal Metamorphosing Frogs (Rana japonica Guenther)

II. Peroxidase Activity

Abstract

The peroxidase activity in the thyroid gland of developing frogs, Rana japonica Guenther, has been observed in the course of metamorphosis. The enzyme first appears in the vesicles near the Golgi complex or near the plasma membrane and sometimes in the cisternae of the inner parts of Golgi lamellae in the early premetamorphosis. As cytoplasmic organelles develop, the density of the reaction product and the number of positively reacted vesicles increase gradually. During climax metamorphosis, the peroxidase activity reaches its maximum. The reaction product is found in the numerous vesicles and multivesicular bodies at the apical cytoplasm, and many vesicles and the cisternae of a few inner lamellae of the Golgi complex. Figures showing reverse pinocytosis of the apical peroxidase positive vesicles into the follicular lumen are often seen.
Four tadpoles at stage XX and XXI were kept in water containing ¹²⁵I for 2 or 50hrs, and sacrificed. After the technique for the cytochemical demonstration of endogeneous peroxidase activity, autoradiographic procedures were performed for simultaneous demonstration of peroxidase reaction and silver grains of ¹²⁵I were mostly localized on the colloid lumen and few were found on the peroxidase positive vesicles in the cytoplasm. It is suggested that the apical cell membrane region and peripheral colloid lumen are the major sites of iodination of thyroglobulin.