Characterization of pituitary IGF-I receptors: modulation of prolactin and growth hormone.
There have been no studies in any vertebrate that have localized insulin-like growth factor (IGF)-I receptors in prolactin (PRL) cells or that have correlated pituitary binding to the potency of IGF-I in regulating both PRL and growth hormone (GH) secretion. We show that IGF-I binds with high affinity and specificity to the pituitary gland of hybrid striped bass (Morone saxatilis x M. chrysops). IGF-I and IGF-II were equipotent in inhibiting saturable (125)I-IGF-I binding, whereas insulin was ineffective. IGF-I binds with similar affinity to the rostral pars distalis (>95% PRL cells) as the whole pituitary gland and immunohistochemistry colocalizes IGF-I receptors and PRL in this same region. Des(1-3)IGF-I, a truncated analog of IGF-I that binds with high affinity to IGF-I receptors but weakly to IGF-I binding proteins (IGFBPs), showed a similar inhibition of saturable (125)I-IGF-I binding, but it was more potent than IGF-I in stimulating PRL and inhibiting GH release. These results are the first to localize IGF-I receptors to PRL cells, correlate IGF-I binding to its efficacy in regulating GH and PRL secretion, as well as demonstrate that IGFBPs may play a significant role in modulating the disparate actions of IGF-I on PRL and GH secretion.
Fruchtman
Shira
S
Department of Zoology, North Carolina State University, Raleigh 27695-7617, USA.
McVey
Douglas C
DC
Borski
Russell J
RJ
D000818:Animals; D001492:Bass; D001667:Binding, Competitive / Q000187:drug effects; D003433:Crosses, Genetic; D004305:Dose-Response Relationship, Drug; D013006:Growth Hormone / Q000032:analysis / Q000096:biosynthesis*; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007328:Insulin / Q000493:pharmacokinetics; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000493:pharmacokinetics; D007335:Insulin-Like Growth Factor II / Q000493:pharmacokinetics; D010446:Peptide Fragments / Q000493:pharmacokinetics; D010902:Pituitary Gland / Q000737:chemistry / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000032:analysis / Q000096:biosynthesis*; D011869:Radioligand Assay; D017526:Receptor, IGF Type 1 / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity
D007328:Insulin; D018969:Insulin-Like Growth Factor Binding Proteins; D010446:Peptide Fragments; C058957:insulin-like growth factor 1, des-(1-3)-; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D011388:Prolactin; D013006:Growth Hormone; D017526:Receptor, IGF Type 1