Tissue kallikrein and bradykinin B2 receptors in the reproductive tract of the male rat.

The setting of a local tissue kallikrein kinin system (tKKS) within the reproductive organs of the male rat was investigated by analysing bradykinin subtype 2 receptor (B2R) gene expression and cellular distribution of B2R protein and the kinin-liberating protease tissue kallikrein (tK). Reverse transcription-polymerase chain reaction showed B2R expression in testis, epididymis and prostate from prepubertal and sexually mature rats. In mature testis, in situ hybridization and immunohistochemistry localized B2R mRNA and protein besides endothelial cells of blood vessels exclusively on pachytene spermatocytes and round and elongated spermatids. B2R expression within the seminiferous tubules was found to be dependent on the stage of the spermatogenic cycle. In pre-pubertal rat testis, B2R mRNA and protein were additionally located in peritubular cells. In the testis, specific staining for tK occurred in addition to endothelial cells of blood vessels on the acrosomal cap of round and elongated spermatids. This immunostaining was also stage-dependent. In the epididymis, tK was detected on epithelial cells near the apical surface. The stage-dependent specific expression of tK and bradykinin B2Rs in developing germ cells and peritubular cells suggests a potential role of the tKKS in the local regulation of spermatogenesis and seminiferous tubule function.

Elements of the kallikrein-kinin system are present in rat seminiferous epithelium.

Peptide hormones are involved in the paracrine regulation of several physiological processes. A possible function of the kallikrein-kinin system (KKS) in mammalian reproduction has been discussed. To evaluate its putative role in spermatogenesis, we searched for components of the KKS (kallikrein, kininases, kinin receptor) in the rat testis. Specific immunostaining demonstrated that the kininogenase tissue kallikrein was present in round and elongated spermatids. Leydig cells, Sertoli cells, peritubular cells, spermatogonia and spermatocytes were not stained. Bradykinin in the supernatant of Sertoli cell cultures was effectively degraded. The resulting metabolites were analysed by high-performance liquid chromatography (HPLC). Specific protease inhibition in the degrading experiments confirmed the occurrence of several metalloproteases on Sertoli cell membranes, including neutral metalloendopeptidases (NEP 24.11 and NEP 24.15), kininase type II (angiotensin converting enzyme, ACE), and kininase type I (metallocarboxypeptidase). Northern blots hybridized with a bradykinin B2 receptor probe showed the presence of B2 receptor mRNA in testis homogenate and Sertoli cell extract. All components of the kallikrein-kinin system are present within the seminiferous epithelium of the rat. Therefore, this paracrine peptide system may play a role in the regulation of Sertoli cell function or in the Sertoli cell-germ cell crosstalk.