Oxybutynin decreases renal pelvic pressures in normal and infected rat urinary tract

Since abnormally elevated renal pelvic pressures may contribute to renal damage, we examined whether an anticholinergic agent could decrease elevated renal pelvic pressures. We have previously demonstrated in a rat model that renal pelvic pressures rise physiologically during normal bladder filling and high urinary flows; these pressures rise to abnormal levels during acute urinary tract infection (UTI). In these studies we investigated the effects of oxybutynin on the in vivo rat urinary tract. Simultaneous bladder and renal pelvic pressures were measured with and without oxybutynin at low (<2 ml./kg./hr.), moderate (2-10), high (10-20), and very high (>20) urinary flows while the rat bladder filled and emptied spontaneously. Although minimal differences were found between bladder filling pressures with and without oxybutynin, at higher urinary flows the renal pelvic pressure in oxybutynin treated rats was significantly lower than in nontreated animals. Indeed, when rats with urinary tract infection were treated with oxybutynin, their renal pelvic pressures were lower than those in uninfected rats. We conclude that oxybutynin affects rat upper urinary collecting system pressures, and is capable of decreasing abnormally elevated renal pelvic pressures due to urinary tract infection to normal or subnormal levels.