Characterization of insulin-like growth factor I receptors in the median eminence of the brain and their modulation by food restriction
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 slide-mounted 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, rat IGF-II (multiplication-stimulating activity), and porcine insulin. All were recognized by the binding site, but the rank order of potency was (Thr59)IGF-I greater than IGF-II greater than 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 less than 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-(Thr59)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.
- Research Organization:
- Veterans Administration Medical Center, Seattle, WA (USA)
- OSTI ID:
- 7196270
- Journal Information:
- Endocrinology; (United States), Journal Name: Endocrinology; (United States) Vol. 122:5; ISSN ENDOA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
ANIMALS
AUTORADIOGRAPHY
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BODY
BRAIN
CENTRAL NERVOUS SYSTEM
CHEMICAL COMPOSITION
DAYS LIVING RADIOISOTOPES
DOMESTIC ANIMALS
ELECTRON CAPTURE RADIOISOTOPES
FOOD
GROWTH FACTORS
HORMONES
INSULIN
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPES
KINETICS
MAMMALS
MEMBRANE PROTEINS
MITOGENS
NERVOUS SYSTEM
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANS
PEPTIDE HORMONES
PROTEINS
RADIOISOTOPES
RATS
REACTION KINETICS
RECEPTORS
RODENTS
SOMATOSTATIN
SPECIFICITY
SWINE
VERTEBRATES