Immunohistochemical localization of insulin-like growth factor-II in the perinatal rat gonad

To clarify the participation of insulin-like growth factor type-II (IGF-II) in rat gonadal differentiation, immunohistochemical localization of IGF-II was chronologically studied in Sprague-Dawley rat gonads from gestational day (GD) 13 to postnatal day (PD) 21 by using avidin-biotin complex technique. In male gonads, most cells were negative to IGF-II immunostaining during the perinatal period. Only Leydig/interstitial cells expressed positive reactivity from GD 21 to PD 11: the intensity of staining and the number of positive cells were gradually increased until PD 11. In female gonads, almost all cells showed negative immunoreactivity. Mesonephric tubules in both sexes exhibited slight or moderate reactivity on GD 13. These results indicate that IGF-II is likely to participate in the regression of fetal-type Leydig cells and/or the proliferation of adult-type Leydig cells around birth, and in the development of mesonephric tubules in the initial stage of gonadal differentiation.