Ta. Brown et Td. Braden, Expression of insulin-like growth factor binding protein (IGFBP)-3, and the effects of IGFBP-2 and-3 in the bovine corpus luteum, DOM ANIM EN, 20(3), 2001, pp. 203-216
The present study was conducted to gain insight into the insulin-like growt
h factor (IGF) system in the bovine corpus luteum (CL). Specific aims were
to measure the levels of IGF binding protein-3 (ICFBP-3) and RNA encoding I
GFBP-3 in the CL throughout diestrus, and to investigate the effects of IGF
BP-2 and -3 on ICF-I-stimulated progesterone (P l) production and IGF-I-rec
eptor binding. Bovine CL were collected from a local abattoir and classifie
d according to stage of diestrus based on anatomical characteristics. Corpo
ra lutea from early, mid and late diestrus were each analyzed for the prese
nce of IGFBP-3 by ligand blot analysis, and for RNA encoding IGFBP-3 by Nor
thern blot analysis. Dissociated cells from mid-cycle CL were treated with
IGF-I, IGFBP-2 or -3, or a combination of IGF-I and IGFBP-2 or -3. The effe
ct of IGFBP-2 and IGFBP-3 on [I-125] IGF-I binding to its receptor on CL pl
asma membranes also was investigated. IGFBP-3 protein and RNA expression we
re higher in early CL, compared to mid or late CL (p < 0.05). IGF-I stimula
ted P4 production in a dose-dependant manner (I, < 0.05). IGFBP-2 and -3 bl
ocked the stimulatory effect of IGF-I on P4 production (p <less than> 0.05)
, Both IGFBP-2 and -3 inhibited [I-125]-IGF-I binding to its receptor in a
dose-dependant manner. These results demonstrate that IGFBP-3 protein and R
NA are expressed predominantly during early diestrus in the bovine CL. More
over, both IGFBP-2 and -3 can modulate IGF-I actions in the CL by interferi
ng with binding of IGF-I to its receptor. (C) 2001 Elsevier Science Inc. Al
l rights reserved.