Water imbibition in the rat prostate during castration‐induced regression

The present study was conducted to examine changes in water concentration in the ventral prostate of adult rats at different intervals following castration. The prostatic dry weight was obtained by drying the fresh prostate at 70°C for at least 110 hr and the prostatic water content was calculated from its wet and dry weight. Under normal conditions, the prostatic water concentration ranges from 81.9 to 82.7% in uncastrated rats. The prostatic water concentration started to increase at 8 hr postcastration (83.1%) but this increase was not statistically significant. By 16 hr postcastration, the prostatic water concentration (83.8%) became significantly higher than that of the uncastrated animals. In rats of day 1 to day 10 postcastration, the prostate contained significantly more water (84.4%‐84.7%) than those in uncastrated animals. By day 21 postcastration, the prostatic water concentration (81.5%) was not significantly different from that of uncastrated rats. Unlike the prostate, the skeletal muscle did not significantly change the water concentration following castration. The ⁵¹Cr‐EDTA space in the prostate was not significantly different in rats before and after castration. These results indicate that water imbibition in the rat prostate is associated with an active period of prostatic regression and that the change in the ⁵¹Cr‐EDTA space during prostatic regression is not the major cause of water imbibition in the tissue. Therefore, the present findings suggest that castration‐induced water imbibition in the rat prostate is caused by an increase in the intracellular water space.