Prolactin receptor expression in rat spermatogenic cells.

To identify target cells of prolactin (PRL) in the male gonad, the expression of prolactin receptor (PRL-R) mRNA in adult rat testes was investigated by in situ hybridization using a digoxigenin-labeled cRNA probe. We also investigated PRL binding to testicular cells in vitro. Signals for PRL-R mRNA were detected not only in interstitial cells but also in spermatogenic cells. Although the reaction was positive in all phases of spermatogonia and spermatocytes, it disappeared in early round spermatids. No signals were detected in elongated spermatids or spermatozoa. The signal intensity varied among each phase of spermatogenic cells. PRL-R mRNA was expressed in all stages of the cycle of the seminiferous epithelium. PRL-R were detected on the surface of Leydig cells, Sertoli cells, all phases of spermatogonia and spermatocytes, elongated spermatids, and spermatozoa. Ovine PRL. did not bind to round spermatids. In Leydig cells, pachytene spermatocytes, and spermatozoa, PRL-R were observed in relatively large numbers. There were fewer receptors in other phases of spermatogenic cells. These results indicate that PRL-R mRNA expression is almost consistent with PRL binding sites except for elongated spermatids and spermatozoa, and suggest that PRL may have direct effects on spermatogenic cells.