PERITUBULAR MYOID CELLS FROM IMMATURE RAT TESTES SECRETE ACTIVIN-A AND EXPRESS ACTIVIN RECEPTOR-TYPE-II IN-VITRO

The expression of activin type II and IIB receptors and inhibin alpha- , beta(A)-, and beta(B)-subunit messenger RNAs (mRNAs), and the secret ion of immunoreactive and bioactive activin during culture of testicul ar peritubular myoid cells and peritubular myoid cell lines were studi ed. Cultured peritubular myoid cells and cell lines expressed high lev els of inhibin beta(A)-subunit mRNA and some inhibin alpha- and beta(B )-subunit mRNA. Activin receptor type II mRNA was also detected, where as activin receptor type IIB mRNA expression was not found. Expression of the beta(A)-subunit mRNA was present immediately after isolation o f the cells and increased during culture in Eagle's Minimum Essential Medium containing 10% fetal calf serum. beta(A)-Subunit mRNA expressio n was not regulated by the synthetic androgen R1881. Western blotting of peritubular myoid cell- and peritubular cell line-conditioned media with a polyclonal antiserum against recombinant activin-ii revealed t he presence of 25-kilodalton activin-A, whereas activin bioactivity wa s detected using the animal cap assay. Because of the secretion of act ivin-A by peritubular myoid cells, the effects of recombinant activin- A on Sertoli cell inhibin and transferrin secretion were examined. Act ivin-A stimulated both basal and FSH-stimulated inhibin and transferri n production by Sertoli cells after 72 h of culture. These effects res emble the effects of the testicular para crine factor PmodS on Sertoli cell function. It is concluded that activin-A is secreted by peritubu lar cells in vitro and that activin-A shares a number of effects on Se rtoli cell function with PmodS.