Insulin-like growth factor I (IGF-I) and its receptor (IGF-1R) in the rat anterior pituitary.
Few and controversial results exist on the cellular sites of insulin-like growth factor (IGF)-I synthesis and the type 1 IGF receptor (IGF-1R) in mammalian anterior pituitary. Thus, the present study analysed IGF-I and the IGF-1R in rat pituitary. Reverse transcription-polymerase chain reaction revealed IGF-I and IGF-1R mRNA expression in pituitary. The sequences of both were identical to the corresponding sequences in other rat organs. In situ hybridization localized IGF-I mRNA in endocrine cells. The majority of the growth hormone (GH) cells and numerous adrenocorticotropic hormone (ACTH) cells exhibited IGF-1R-immunoreactivity at the cell membrane. At lower densities, IGF-1 receptors were also present at the other hormone-producing cell types, indicating a physiological impact of IGF-I for all endocrine cells. IGF-I-immunoreactivity was located constantly in almost all ACTH-immunoreactive cells. At the ultrastructural level, IGF-I-immunoreactivity was confined to secretory granules in co-existence with ACTH-immunoreactivity, indicating a concomitant release of both hormones. Occasionally, IGF-I-immunoreactivity was detected in an interindividually varying number of GH cells. In some individuals, weak IGF-I-immunoreactions were also detected also in follicle-stimulating hormone and luteinizing hormone cells. Thus, IGF-I seems to be produced as a constituent in ACTH cells, possibly indicating its particular importance in stress response. Generally, IGF-I from the endocrine cells may regulate synthesis and/or release of hormones in an autocrine/paracrine manner as well as prevent apoptosis and stimulate proliferation. Production of IGF-I in GH cells may depend on the physiological status, most likely the serum IGF-I level. IGF-I released from GH cells may suppress GH synthesis and/or release by an autocrine feedback mechanism in addition to the endocrine route.
Eppler
Elisabeth
E
Division of Neuroendocrinology, Institute of Anatomy, University of Zürich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland.
Jevdjovic
Tanja
T
Maake
Caroline
C
Reinecke
Manfred
M
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000818:Animals; D005260:Female; D015870:Gene Expression / Q000502:physiology; D007150:Immunohistochemistry / Q000379:methods; D017403:In Situ Hybridization / Q000379:methods; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D016253:Microscopy, Immunoelectron / Q000379:methods; D010903:Pituitary Gland, Anterior / Q000166:cytology* / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012737:Sex Factors
D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D000324:Adrenocorticotropic Hormone; D017526:Receptor, IGF Type 1