IMMUNOCYTOCHEMICAL STUDY OF THE ULTIMOBRANCHIAL TUBULE IN WISTAR RATS

A systematic immunohistochemical study of the ultimobranchial tubule ( UBT) has been carried out in 45 Wistar rats of different ages (0, 5, 1 0, 15, 20, 25, 30, 60 and 120 days). The existence of calcitonin immun oreactive cells in the UBT wall has been demonstrated in a 5-days old rat. In addition, immunohistochemical studies for thyroglobulin reveal ed positive staining in follicular cells connected to the UBT and, occ asionally, in isolated cells lying within solid clusters from the UBT. These last results together with the continued and repeated existence of numerous mitosis and PAS (+) microfollicles, apparently rising fro m the UBT, support the hypothesis that the ultimobranchial body (UBB) may contribute partially to the formation of a part of the follicular component.