Insulin-like growth factor I in the anterior pituitary of the clawed frog Xenopus laevis: immunocytochemical and autoradiographic indication for a paracrine action and corelease with prolactin.
Insulin-like growth factor I (IGF-I) and its receptor are present in human and rat anterior pituitary. However, few data exist on the potential presence of IGF-I or its receptor in the non-mammalian pituitary and the cellular sites of IGF-I production have not been identified in any species. Thus, we investigated the anterior pituitary of the clawed frog Xenopus laevis which is widely used to study growth and differentiation. The study was performed with antisera against mammalian insulin-like growth factor I (IGF-I), prolactin (PRL) and growth hormone (GH) using immunohistochemical and immunocytochemical techniques. IGF-I binding was determined by in-vitro receptor autoradiography. The PRL-and GH-immunoreactive cells exhibited distinct distribution patterns. Neither at the light nor the electron microscopical level any colocalization of PRL-and GH-immunoreactivities was apparent. The PRL-immunoreactive cells exhibited round granules of medium electron density (mean diameter: 312 nm) and the GH-immunoreactive cells spherical granules of medium electron density (mean diameter: 165 nm). By the use of serial semithin sections IGF-I-immunoreactivity was exclusively located in PRL-immunoreactive cells. At the ultrastructural level, IGF-I-immunoreactivity was confined to the secretory granules in coexistence with PRL-immunoreactivity using the double labelling immunogold technique. Specific IGF-I binding sites were localized throughout the pituitary. The results provide evidence for a concomitant release of PRL and IGF-I and suggest autocrine/paracrine actions of IGF-I in the anterior pituitary.
David
I
I
Division of Neuroendocrinology, Institute of Anatomy, University of Zürich, Zürich, Switzerland.
Bosshard
R
R
Kloas
W
W
Reinecke
M
M
D000818:Animals; D001345:Autoradiography; D003594:Cytoplasmic Granules / Q000737:chemistry; D013006:Growth Hormone / Q000032:analysis; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000378:metabolism; D007457:Iodine Radioisotopes; D008854:Microscopy, Electron; D010902:Pituitary Gland / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D011388:Prolactin / Q000032:analysis / Q000378:metabolism*; D014982:Xenopus laevis
D007457:Iodine Radioisotopes; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D013006:Growth Hormone