Identification of insulin-like growth factor-I and its receptors in the rat testis.
As part of a study of the testicular production and action of insulin-like growth factor-I (IGF-I), adult rat testes were extracted with acidified methanol, yielding an immunoreactive IGF-I fraction corresponding in size to human IGF-I. The mean IGF-I content (+/- SEM) of testes weighing approximately 1.1 g was 51.5 +/- 5.6 ng/testis, and was not due to serum contamination. After a 3-day fast testicular IGF-I decreased by 80%, whereas serum IGF-I levels declined by 90%. Testicular homogenates and isolated Leydig cells were shown to contain specific IGF-I receptors, Ka = 2 X 10(9) M-1, with 10% IGF-II cross-reactivity. The concentration of these receptors was 2 pmol binding sites per testis, or 3.3 fmol per 10(6) Leydig cells. However IGF-I at 250 ng/ml had no effect on basal or hCG-stimulated testosterone production by isolated Leydig cells, measured over 3 h. Although an effect of IGF-I over longer incubation periods cannot be excluded, it is also possible that testicular IGF-I has a mitogenic role, rather than acting on differentiated testicular functions.
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D007328:Insulin / Q000032:analysis* / Q000494:pharmacology; D007985:Leydig Cells / Q000378:metabolism; D008297:Male; D010455:Peptides / Q000032:analysis* / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000032:analysis*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000032:analysis* / Q000494:pharmacology; D013737:Testis / Q000378:metabolism*; D013739:Testosterone / Q000096:biosynthesis
D007328:Insulin; D010455:Peptides; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D013739:Testosterone