Subcellular Localization of the Receptor for Gonadotropin-Releasing Hormone in Pituitary and Ovarian Tissue*

Abstract

The subcellular localization of GnRH receptors in weanling rat anterior pituitary and ovarian tissue was determined by radioligand binding in biochemically defined fractions prepared by differential and density centrifugation. Morphological identification of membrane organelles or fragments, visualized by electron microscopy, confirmed the biochemical characterization. The greatest amount of specific ligand binding in both tissues was measured in the crude membrane fraction, while small amounts were detected in other fractions. The distribution of pituitary binding sites in sucrose gradient subfractionation of crude membranes correlated with the distribution of plasma membrane (assessed by 5′-nucleotidase activity and electron microscopy), but not that of secretory granules (identified by immunoreactive LH) or lysosomes (acid phosphatase activity). These data suggest that the GnRH-binding sites detected by radioligand binding assay in pituitaries of rats not previously exposed to GnRH are localized almost exclusively in the plasma membrane fraction.