The effect of pregnancy on rat urinary tract dynamics.

We investigated the urodynamics of the renal pelvis and bladder during spontaneous bladder filling and emptying in 13 pregnant and 19 nonpregnant Sprague-Dawley rats to examine the characteristics of the dilated urinary tract in pregnancy. For each group renal pelvic and bladder pressures were measured continuously and simultaneously during various urinary flows, while the bladder was filled and emptied. In pregnant rats the ureter was wider and the renal pelvis was longer and wider than in nonpregnant rats. At urinary flows of 10 to 30 ml/kg. per hour pregnant rats had significantly lower renal pelvic pressures than nonpregnant rats during bladder filling. In addition, pregnant rats had higher bladder compliance and capacity than nonpregnant rats (compliance 0.09 +/- 0.12 ml./cm. water versus 0.05 +/- 0.05 ml./cm. water, p < 0.01 and bladder capacity 0.669 +/- 0.61 ml. versus 0.490 +/- 0.38 ml., p < 0.05). These findings imply that much of the hydroureteronephrosis during pregnancy may relate to increased urinary tract compliance rather than obstruction.