We have recently reported on the isolation and characterization of the predominant protein of canine prostatic fluid and the subsequent identification of this protein as a proteolytic enzyme. In this report, we described the preparation and characterization of a rabbit antiserum against this secretory protease which was purified from canine prostatic fluid by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Specificity of the antiserum has been established by immunoblot analysis and immunoprecipitation of the secretory protease present in canine prostatic fluid and tissue homogenates. The antiserum was used to localize (by immunofluorescence) and quantitate (by single radial immunodiffusion) the secretory protease in prostatic tissue obtained from intact and castrated dogs. These analyses can be summarized as follows: 1) the secretory protease is strictly localized in the apical portions of the columnar epithelial cells in prostates of intact dogs, where it comprises almost 60% of the total Triton X-100-soluble protein; and 2) the level of secretory protease decreases at least 500-fold in prostates of castrated dogs, demonstrating the androgendependent nature of this enzyme. Proteins immunologically related to the secretory protease were detected at low levels in the pancreas and salivary glands of the dog. Such proteins were not detectable in canine liver, kidney, vas deferens, testis, epididymis, lung, spleen, skin, small intestine, or sartorius muscle, suggesting a high degree of prostatic specificity for the secretory protease. These results demonstrate that the canine prostate is highly specialized with respect to its androgen-dependent synthesis and secretion of this secretory protease and that the antiserum specific for this protein can be used to assess canine prostatic function under varying hormonal conditions.
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