Immunohistochemical Localization of Insulin-Like Growth Factor-I in the Eustachian Tube of the Rat

Yoon, Yong Joo; Park, Byung Am; Kim, Young Ki

Abstract

Insulin-like growth factor-I(IGF-I) is a peptide hormone of approximately 7.5 kilodaltons which has been shown to be involved in cellular growth and differentiation. Because the IGF-I is synthesized in a variety of tissues, it is thought to act both locally in a paracrine/autocrine manner, as well as a true endocrine hormone after entering the circulation. It may be considered that IGF-I is very important for differentiation of bone, cartilage, and muscle. The eustachian tube has the function of ventilation, clearance, and protection of the middle ear, contributing to the maintenance of normal hearing. After the opening of eustachian tube, it may return to its original position by elasticity resulting from the recoil of elastic fiber, muscle itself, and other deformed soft tissues surrounding the tube. Previously we have studied the distribution of elastic fibers in the rat eustachian tube and ascertained enormous elastin in the cartilage of the eustachian tube. The maintenance of elasticity in the tubal cartilage, related to closing of the eustachian tube, has been suspected as one of important factors in the pathogenesis of otitis media. Rich13) previously described that IGF-I acts as a modulator of the elastogenesis, essential for stretch and recoil actions. However, the examination of the presence of IGF-I in the eustachian tube, especially cartilage may very important as one of factors for well functioning of the eustachian tube. This immunohistochemical study, the tubal cartilage has a considerable content of IGF-I in the capsule around the chondrocytes. The submucosal connective tissue layer of the eustachian tube contained some immunostained cells, considered to be fibroblasts. These findings suggest that IGF-I may be important for normal chondrocyte growth of rat eustachian tube.