B2 bradykinin receptor mediates the stimulatory effect of bradykinin on rat germ cell proliferation in vitro.

The contribution of B1 and B2 bradykinin receptors to germ cell proliferation was studied by using in vitro organ cultures of testicular fragments of 3.5-day-old rats in the presence of 3H thymidine. Different combinations of agonists and antagonists of B1 and B2 receptors exerted differential mitogenic effect on pro-spermatogonial cells. Application of bradykinin (B2 receptor agonist) alone induced a threefold increase in germ cell labelling index compared with the control, whereas des-Arg9-bradykinin (B1 receptor agonist) caused weak stimulation (24%) on spermatogonial mitotic activity. The bradykinin-induced germ cell proliferation was significantly affected by B2 receptor antagonist (HOE-140) but not by B1 receptor antagonist. When B1 or B2 receptor antagonists were applied with des-Arg9-bradykinin, the germ cell labelling indices were nonsignificantly different compared with those of B1 receptor agonist only. The present findings suggest that B2 receptor is involved in mediating the stimulatory effect of bradykinin on germ cell proliferation and therefore bradykinin might be an important local testicular factor in the regulation of spermatogonial division and germ cell number.

Stage-specific nuclear antigen is expressed in rat male germ cells during early meiotic prophase.

A germ cell nuclear antigen with approximately 44-kDa molecular weight was identified by a novel monoclonal antibody designated as Mab 2F2 from the library we have accumulated against rat testicular cells. In immature 20-day-old and adult rat testis the recognized antigen was expressed in the nuclei of early meiotic cells from preleptotene to early pachytene spermatocytes exhibiting a stage-specific appearance in the cycle of the seminiferous epithelium. The immunoreactivity was clearly associated with the meiotic chromosomes. The antigen was not detected in the late pachytene spermatocytes and more advanced stages of spermatogenesis. No labeling was observed in spermatogonia and somatic Sertoli and Leydig cells. The pattern of expression of the recognized antigen during early meiotic stages of spermatogenesis but not in mitotically dividing spermatogonia could strengthen its possible role in meiotic division.

A monoclonal antibody raised against rat ovarian antigen recognizes Leydig cell surface: an immunocytochemical study.

Using a monoclonal antibody (Mab) against constituents of rat ovarian granulosa cells, we found a 59-kDa protein located on the plasma membrane of a number of granulosa cells in follicles at different stages of development. This Mab (5G5) was found to bind to Leydig cells in rat male gonads. The localization of the antigen, recognized by Mab 5G5 in rat testis, was studied by light and electron microscopic immunocytochemistry (ABC method and IGS technique). Even though Sertoli cells in male gonads are regarded as the counterpart of granulosa cells in ovaries, the results of the experiments described here do not allow such an interpretation because staining with this antibody was restricted to the Leydig cell surface. The immunoreactivity in testicular sections from immature rats was similar to that found in adult testicular tissue. Our immunocytochemical results indicate that the plasma membrane of Leydig cells in rat male gonads shares certain biochemical and molecular properties with rat ovarian granulosa cells. On the basis of the immunocytochemical studies reported here, we suggest that the antigen recognized by Mab 5G5 may be common to all rat steroidogenic organs. Further studies are needed to establish the identity of the antigen in Leydig cells as well as its site of synthesis and its site of action. Thus, Mab 5G5 appears to hold significant potential as a powerful tool for future investigations.