Sertoli cells in culture secrete paracrine factor(s) that inhibit peritubular myoid cell proliferation: Identification of heparinoids as likely candidates

Conditioned medium from Sertoli cells, prepared from testes of 20‐day‐old rats, contains component(s) that inhibit the incorporation of [ 3 H]‐thymidine into DNA of peritubular myoid cells (PMC) and inhibit the proliferation of PMC. These components are trypsin‐resistant, heat‐stable compounds having a molecular weight less than 30,000. The active inhibitory components in Sertoli cell conditioned medium are inactivated by treatment with heparinase, but not by treatment with hyaluronidase or chondroitin sulfate lyases. Addition of heparin or heparan sulfate results in inhibition of DNA synthesis by PMC in a dose‐dependent manner, whereas other glycosaminoglycans (GAGs) examined (hyaluronic acid, keratan sulfate, and chondroitin sulfate) have no detectable effects. Heparin and heparan sulfate are unique among GAGs tested in inhibiting the characteristic multilayer growth pattern of PMC following the attainment of confluence in serum‐rich medium. On the basis of these and other data presented, it is concluded that heparin and other heparin‐like GAGs synthesized by Sertoli cells are implicated in the modulation of growth of PMC in vitro during co‐culture. It is postulated that heparin may play a similar role in maintaining the quiescent peritubular myoid cell phenotype in vivo.