Endocrine status affects bladder size and postvoid residual urinary volume in mice.

Urine is one of the major media for intraspecific chemical communication in mice. The urination pattern is dependent both on the mice's hormonal and social status. The urination pattern and the morphology of the urinary tract were examined in mice following hormonal manipulations. In the first experiment, we compared pairs of intact and castrated males: intact males urinated earlier when exposed to a new environment, with a greater number of drops that were smaller than those of castrated males. In the second experiment, groups of intact males, castrated, testosterone-supplemented castrated, and isolated intact males were compared. The micturition pattern of isolated intact males consisted of numerous small droplets of urine, with a high volume of urine retained in the bladder after voiding. This also applied to grouped intact males and testosterone-treated castrated mice, while castrated mice voided a larger fraction of bladder content. Bladder weight was higher in intact males and testosterone-treated castrated males, as compared to castrated males. In the third experiment, ovary-intact and testosterone-treated intact females were compared. Testosterone-treated ovary-intact females retained a larger quantity of urine in the bladder and also had a larger bladder compared to ovary-intact females. Testosterone thus induces the morphological modifications of the urinary tract necessary for the dominant male urination pattern, which is an increase in postvoid urinary residual volume and bladder weight. As evidenced from the comparison of histological sections from intact, castrated, and testosterone-treated castrated males, the increase in bladder weight was mainly due to the bladder muscular mass.