Prostatic inflammation induces urinary frequency in adult mice

Abstract

Lower urinary tract symptoms (LUTS) including urinary frequency and nocturia are common in aging men. Recent studies have revealed a strong association of prostatic inflammation with LUTS. We developed an animal model of bacterial induced, isolated prostatic inflammation and examined the effect of prostatic inflammation on voiding behavior in adult C57BL/6J mice. Prostatic inflammation was induced by transurethral inoculation of uropathogenic E. coli-1677. Bacterial cystitis was prevented by continuous administration of nitrofurantoin. Hematoxylin and eosin (H&E) staining and bacterial culture were preformed to validate our animal model. Voiding behavior was examined by metabolic cage testing on post-instillation day 1 (PID 1), PID 4, PID 7 and PID 14 and both voiding frequency and volume per void were determined. Mice with prostatic inflammation showed significantly increased voiding frequency at PID 1, 7 and 14, and decreased volume per void at all time points, as compared to mice instilled with saline and receiving nitrofurantoin (NTF). Linked analysis of voiding frequency and voided volumes revealed an overwhelming preponderance of high frequency, low volume voiding in mice with prostatic inflammation. These observations suggest that prostatic inflammation may be causal for symptoms of urinary frequency and nocturia.

Fig 1. Experimental design to study the effects of isolated prostatic inflammation on voiding behavior.

For mice receiving NTF, NTF was injected sc, twice daily, beginning one day prior to transurethral instillation and continuing until the end of the experiment. Either saline or uropathogenic E.coli 1677 (2 x 10⁶ per ml), 200 µl per mouse, was instilled transurethral. (A) Histologic analysis and tissue culture was performed at the time points indicated for mice in the Naïve + NTF, Saline + NTF, E.coli + NTF and E.coli only groups. (B) Voiding behavior of mice in Saline + NTF and E.coli + NTF groups was determined by metabolic cage tests at PID 1, 4, 7 and 14.

Fig 2. E.coli 1677-induced prostatic inflammation.

Representative H&E stained sections of the DLP (A, C, E, G) and bladder (B, D, F, H) of mice in the Saline + NTF and E.coli + NTF groups at PID 2 and PID 14, respectively.

Fig 3. Voiding behavior of mice in the Saline + NTF and E.coli + NTF groups.

(A) Voiding frequency (number) at PID 1, 4, 7 and 14. (B) Volume per void (μl) at PID 1, 4, 7 and 14 (B). n = 13 of Saline + NTF (gray bar), n = 12 of E.coli + NTF (black bar).

Fig 4. 2D plot of voiding frequency and volume per void.

Distribution of voiding frequency (number) and average volume per void (μl) for each mouse mice in the Saline + NTF (gray circle) and E.coli + NTF (black square) groups at (A) PID 1, (B) PID 4, (C) PID 7 and (D) PID 14. P-values were calculated by Multivariate Analysis (MANOVA). * statistically significant.

Fig 5. Combined analysis of voiding frequency and average voided volumes.

(A) When average voided volume and voiding frequency are plotted together, the upper left hand corner is the domain of low frequency high volume (LVHF) voiding. The limits of this domain can be defined by percentile cut-points. (B) Plot of voiding frequency and average volume per void (μl) for each mouse mice in the Saline + NTF (gray circle) and E.coli + NTF (black square) groups at PID 14 with the LVHF domain defined by the 50^th percentile of frequency and volume.