Immunohistochemical localization of rK9, an enzyme of the kallikrein gene family, in the rat ventral prostate.

The rat kallikrein family consists of multiple closely related proteins. Most of these proteins have been purified from rat submandibular gland (SMG), among them rK9, an enzyme that has a direct vasoconstrictory effect on isolated aortic rings. Recently, two members of the kallikrein family, rK8 and rK9, were also purified from rat prostate, whereas other family members were not detected in this organ. In the present study, the immunohistochemical localization of rK9 was determined in rat prostate by the indirect immunofluorescence technique with polyclonal antisera against rat SMG rK9 in the first layer. The crossreactivity pattern of the antiserum against rat prostate tissue extract was established by flat-bed isoelectrofocusing and immunoblotting. The antiserum reacted with prostate rK9 but not with prostate rK8. Specificity of the immunofluorescent staining reaction was verified by staining with the primary antiserum after addition of purified SMG or prostate rK9, or other members of the kallikrein family including prostate rK8. rK9-specific immunofluorescence was detected in the prostate ductal structures. In the distal (acinar) segments, rK9 was found in the cytoplasm as granular staining in the middle third of the cell, in the luminal cell wall, and in the secretion within the lumen. In the intermediate segments, strong rK9-specific staining was observed adhering to the luminal wall as well as abundantly within the ductal lumen.