Characterization of insulin-like growth factor i receptors in the median eminence of the brain and their modulation by food restriction

Nancy J. Bohannon, Eric S. Corp, Barbara J. Wilcox, Dianne P. Figlewicz, Daniel M. Dorsa, Denis G. Baskin

Research output: Contribution to journalArticle

37 Scopus citations

Abstract

High affinity binding sites for 125I-labeled [Thr59]insulin-like growth factor I (IGF-I) were measured in rat median eminence by in vitro autoradiography with slidemounted sections of frozen rat brain. Specific binding of 0.1 nM iodo-[Thr59]IGF-I to brain slices reached maximum by 12 h at 4 C and was unchanged at 24 h. Densitometry by computer digital image analysis of autoradiographic images indicated that specific binding of iodo-[Thr59]IGF-I to the median eminence was reversible. The specificity of binding was evaluated with competition of iodo-[Thr59]IGF-I with unlabeled [Thr59]IGF-I, ratlGFII (multiplication-stimulating activity), and porcine insulin. All were recognized by the binding site, but the rank order of potency was [Thr59]IGF-I < IGF-II < insulin. Somatostatin was completely ineffective. Further, an antibody against the rat IGF-II receptor did not block binding of iodo-[Thr59]IGF-I to the median eminence. Fourteen days of food restriction (75% of food intake of controls) resulted in significant weight loss and reduction of plasma immunoreactive IGF-I in six food-restricted rats (0.9 ±0.1 U/ml) compared with values in six controls (2.6 ± 0.5 U/ml; P < 0.001). Binding of 125I-labeled [Thr59]IGF-I in the median eminence was significantly increased in the food-restricted rats, primarily due to an increase in the concentration of iodo-[ThrS9]IGF-I-binding sites in the median eminence; the affinity (Kd) of binding was unchanged. The results indicate that the median eminence has type I IGF-I receptors, which become more numerous under metabolic conditions associated with decreased caloric intake and lowered plasma IGF-I levels.

Original languageEnglish (US)
Pages (from-to)1940-1947
Number of pages8
JournalEndocrinology
Volume122
Issue number5
DOIs
StatePublished - May 1 1988

ASJC Scopus subject areas

  • Endocrinology

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