Evaluation of pelvic contractility in ureteropelvic junction obstruction: an experimental study

Ureteropelvic junction (UPJ) obstruction causes adaptive and/or compensatory alterations in renal pelvic contractility. As these alterations directly affect the outcome after renal damage, definition of these alterations is of the utmost importance from a clinical point of view. Thus, an experimental study was designed to determine the alterations of renal pelvic contractility in response to partial and complete UPJ obstruction.

Fifteen adult female New Zealand white rabbits were randomly assigned into three groups (each containing 5 rabbits) according to the degree of unilateral UPJ obstruction. Group I: sham operation was performed and served as the control group; group II: partial UPJ obstruction was made; group III: complete UPJ obstruction was made. The animals in groups I and II were sacrificed after three weeks and the rabbits in group III were sacrificed after two weeks. Muscle strips from the renal pelvis were prepared. Spontaneous mechanical activity and contractile responses to phenylephrine (PE), serotonin (5-HT), and KCl were recorded isometrically and compared in all groups.

Both the frequency and amplitude of spontaneous mechanical contractions were significantly (p < 0.05) increased in partial (group II) and complete UPJ obstruction (group III) groups. PE and 5-HT-induced tonic contractions, which were more prominent in the complete and partial obstruction groups when compared with the control group (p < 0.05). PE and 5-HT also increased the frequency of spontaneous contractions in both partial and complete obstruction groups. KCl induced long lasting tonic contractions in the control muscles. The duration of contraction to reach the maximum amplitude was shortened in the obstruction groups and the amplitudes of the contractions were significantly augmented when compared to control preparations.

UPJ obstruction alters the contractile properties of renal pelvis smooth muscle. Increased frequency of spontaneous mechanical activity suggests that pacemaker cells of the renal pelvis change their activities in response to UPJ obstruction. Increase in tonic contraction amplitudes in response to PE and 5-HT suggests an increased sensitivity of smooth muscle cells to these agents. Potentiation of the contractile response to KCl suggests that adaptive changes take place at the level of excitation-contraction coupling in the smooth muscle of the renal pelvis following UPJ obstruction.