A blood-prostate barrier restricts cell and molecular movement across the rat ventral prostate epithelium

Blood-epithelial barriers have been described in the testis and epididymis, but the possibility of such barriers in other regions of the male genitourinary tract has received little investigation. The purpose of this study was to use in vivo micro-puncture to determine if the blood-epithelial barrier exists in the rat ventral prostate. In addition, using a model of prostatic inflammation, we sought to examine the effect of inflammation on the passage of blood borne molecules and leukocytes into the prostatic ductal lumen.

Adult Sprague-Dawley rats were divided into two groups, control and 24-hour lipopolysaccharide (LPS)-induced inflammation. Both groups were subjected to vascular infusion of radiolabeled 3H dextran, 14C urea, and 3H water. Contemporaneous in vivo micropuncture sampling of prostatic ductal fluid (DF) and arterial blood occurred at multiple time points over 120 minutes. Transepithelial movement of radiolabeled compounds at each sampling time point was quantified by the expression of DF isotope concentrations as a percentage of serum isotope concentrations at that time point. Histology of representative specimens of control and inflamed prostates was used to confirm the inflammatory response and to examine for the presence of leukocytes into the ductal lumen.

The transepithelial movement of radiolabeled compounds from blood to prostatic lumen varied in direct relationship to the compound's molecular weight. 3H-water (MW = 18) movement into the ductal lumina was relatively rapid plateauing at 70-80% of serum values. 14C urea (MW = 60) achieved intermediate penetration into ductal fluid (50-60% of serum values) and 3H dextran (MW = 2 x 106) was essentially excluded from entry (<2% of serum). These results were not altered by LPS-induced inflammation. Histology revealed a diffuse leukocyte infiltrate in the inflamed prostatic interstitium, but penetration of inflammatory cells into the ductal lumen was very restricted.

Our findings demonstrate a blood-prostate barrier in the rat ventral prostate with characteristics similar to the blood-testis barrier. This blood-prostate barrier is not affected by LPS-induced acute inflammation. Further, this persistent barrier apparently restricts the passage of leukocytes into prostate DF even in the presence of pronounced interstitial inflammation. This observation may help to explain the observation that expressed prostatic secretions in human males are often free of leukocytes in clinical prostatitis.