The whole situation on the news caused me to read up on related articles. Apparently all mammals urinate through their penis, none of them have a separate urethra except monotremes.
It is the urine that must effect the prostate gland. Perhaps if there is a lot of alcohol and sugar in your urine, it could cause your prostate gland to become swollen.
Urine is made up of nitrate compounds and excess water that is released into the blood by our tissues.