Up-regulation of pituitary [125I]insulin-like growth factor-I (IGF-I) binding and IGF binding protein-2 and IGF-I gene expression by estrogen.
To evaluate the effects of estrogen on the rat pituitary insulin-like growth factor (IGF) system, binding of [125I]IGF-I and in situ hybridization for IGF-I, the IGF-I receptor and IGF binding protein-2 (IGFBP-2) were coupled with quantitative autoradiography. The groups included intact cycling females, intact males, and gonadectomized males and females with or without estrogen pellet implants. Binding of [125I]IGF-I in the anterior lobe of the pituitary occurred in dense clusters over a diffuse lower density background. [125I]IGF-I binding was significantly increased in the estrogen-treated groups and was highest at proestrus compared to the rest of the estrous cycle. IGF-I receptor messenger RNA (mRNA) was distributed diffusely through the anterior pituitary and was not different between the respective gonadectomized and estrogen-treated groups. IGFBP-2 mRNA was clustered throughout the anterior pituitary and was significantly higher in the estrogen-treated groups as noted above for [125I]IGF-I binding. IGF-I mRNA was diffuse throughout the anterior pituitary and was also significantly higher in the estrogen-treated groups. In the neural lobe, [125I]IGF-I binding, IGFBP-2 mRNA, IGF-I receptor mRNA, and IGF-I mRNA were all uniformly distributed and did not differ between groups. The results show that circulating estrogen differentially regulates components of the pituitary IGF-I system in a region-specific manner and suggest that a portion of IGF binding in the anterior pituitary may be to IGFBP-2.
Michels
K M
KM
Laboratory of Clinical Science, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Lee
W H
WH
Seltzer
A
A
Saavedra
J M
JM
Bondy
C A
CA
D000818:Animals; D001345:Autoradiography; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D017403:In Situ Hybridization; D018971:Insulin-Like Growth Factor Binding Protein 2; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008297:Male; D009919:Orchiectomy; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000737:chemistry / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
D002352:Carrier Proteins; D018971:Insulin-Like Growth Factor Binding Protein 2; D007457:Iodine Radioisotopes; D012333:RNA, Messenger; D004958:Estradiol; D007334:Insulin-Like Growth Factor I