Insulin-like growth factor I (IGF-I) receptors on Sertoli cells from immature rats and age-dependent testicular binding of IGF-I and insulin.
Insulin-like growth factor I (IGF-I) binding to cultured Sertoli cells from immature rats was quantitatively evaluated. The binding of 125I-IGF-I to the Sertoli cells was specific, time- and pH-dependent and reversible. Scatchard analysis yielded a Kd of 3.5 X 10(-9) M and a binding capacity of 2080 fmol/mg protein. Competition with IGF-I resulted in a half-maximal displacement by 2 nM IGF-I, whereas insulin up to a concentration of 100 nM gave virtually no displacement of IGF-I binding. Similarly, the gonadotropic hormones follitropin and lutropin did not compete with 125I-IGF-I binding. In previous studies, it was shown that cultured Sertoli cells from immature rats bind insulin with a Kd of 1.8 X 10(-9) M and a binding capacity of 8.5 fmol/mg protein. The binding of IGF-I and insulin to a total testis membrane fraction was studied using testes from immature and adult rats. In testis from 21-day-old rats, the maximal specific binding was relatively high for IGF-I (871 +/- 50 fmol/g wet weight) and relatively low for insulin (118 +/- 11 fmol/g wet weight). In adult testis, the maximal specific binding of IGF-I was 324 +/- 40 fmol/g wet weight and that of insulin was 330 +/- 17 fmol/g wet weight. The binding of IGF-I and insulin expressed as fmol bound per testis was increased 6-fold and 45-fold, respectively, between the age of 21 days and adult age. It is discussed that the numbers of receptors for IGF-I and insulin in testis may be developmentally regulated, and that IGF-I may be more important than insulin with respect to testis development and Sertoli cell maturation in the immature rat.
Oonk
R B
RB
Department of Biochemistry, Medical Faculty, Erasmus University Rotterdam, The Netherlands.
Grootegoed
J A
JA
D000375:Aging; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007668:Kidney / Q000254:growth & development / Q000378:metabolism; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000378:metabolism*; D017451:Receptors, Somatomedin; D012708:Sertoli Cells / Q000378:metabolism*; D012741:Sexual Maturation; D013002:Somatomedins / Q000378:metabolism*; D013737:Testis / Q000254:growth & development* / Q000378:metabolism
D007328:Insulin; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin