The bovine placenta: a specific radioreceptor assay for both insulin-like growth factor I and insulin-like growth factor II.
Binding of labelled IGF-I and IGF-II was studied to bovine, ovine and human placental cell membranes. The data show a preponderance of type I receptors in human placental membranes, and of type II receptors in ovine placental membranes, confirming reported data. In contrast, bovine placental membranes are rich in both type I and type II receptors. Therefore, the bovine placenta offers a good model for measuring specifically IGF-I (cross-reactivity with IGF-II 7%) and IGF-II (cross-reactivity with IGF-I 4%). By Scatchard analysis the apparent Kd (1-1.36 nmol/l) for the high affinity binding sites of the type I receptor is similar in all three preparations. Total binding capacity in ovine placental membranes is, however, 4 times lower. The affinity for the type II receptor is lower than for type I, whereas total binding capacity is higher. Affinity cross-linking confirms the competition experiments, showing binding of IGF-I to typical type I and of IGF-II to type II receptors.
van Buul-Offers
S
S
University Hospital for Children and Youth, Het Wilhelmina Kinderziekenhuis, State University of Utrecht, The Netherlands.
Hoogerbrugge
C M
CM
de Poorter
T L
TL
D000818:Animals; D001345:Autoradiography; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D011869:Radioligand Assay / Q000379:methods*; D011972:Receptor, Insulin / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013045:Species Specificity
D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D011972:Receptor, Insulin