The medium of cultured Sertoli cells from immature rat testes contains 29 and 32 kDa proteins, which are recognized by an antiserum against the 22 N-terminal amino acids of the inhibin α-subunit. These proteins were detected by immunoprecipitation of labelled proteins after incubation of Sertoli cells with [35S]methionine, and by Western blotting. The amount of the 32 kDa protein was not affected by the addition of follicle-stimulating hormone (FSH) to the culture medium of the Sertoli cells, whereas FSH induced a large increase of the amount of the 29 kDa protein. Finally, the 29 and 32 kDa proteins in the medium from control and FSH-stimulated Sertoli cells were separated by sodium dodecyl sulfate-polyacrylamide electrophoresis, and inhibin bio- and immunoactivity were determined in eluates of the slices of the gel. Equal amounts of bioactivity were found in control and FSH-stimulated samples at 32 kDa, while the amount of immunoactivity at 29 kDa was increased; no bioactivity was detected in the eluates of these slices. It is concluded that FSH stimulates the secretion of a 29 kDa inhibin-like protein, which does not contain inhibin bioactivity. This indicates that results of experiments, in which antibodies against N-terminal peptides of the inhibin α-subunit are used to detect inhibin, do not necessarily reflect the amount of bioactive inhibin produced.

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Molecular and Cellular Endocrinology
Department of Biochemistry

Grootenhuis, A.J, van Beurden-Lamers, W.M.O, Timmerman, M.A, & de Jong, F.H. (1990). Follicle-stimulating hormone-stimulated secretion of an immunoreactive 29 kDa inhibin α-subunit complex, but not of 32 kDa bioactive inhibin, from cultured immature rat Sertoli cells. Molecular and Cellular Endocrinology, 74(2), 125–132. doi:10.1016/0303-7207(90)90114-N