Biology of Reproduction

In all mammalian females, follicular growth and maturation are essentially dependent on the pituitary gonadotropins, FSH and LH. These glycoprotein hormones have many similarities, but their actions, based on high affinity binding to specific membrane receptors, are quite different. The purpose of this study was to perform a sensitive localization of FSH and LII in secretory granules of gonadotrophs using highly specific antisera. This morphological study included light microscopy (PAP) and electron microscopy (immunogold single and double labeling) procedures. Histologically, approximatively 11.5% of cells were positive for LII, whereas only 54% of cells were positive for FSH. With the electron microscope, single labeling allowed identification of morphologically distinct UI-containing cells and FSH-containing cells. Double immunostaining confirmed that no cells contained both hormones. The finding that FSH and LII are produced in separate pituitary cells is in agreement with recent studies that have suggested a specific role and regulatory process for gonadotropins in the bovine species.