Dynamics of upper urinary tract. II. An electrophysiologic in vivo study of renal pelvis in pigs: analysis of the modality of pelvic activity during normal hydration and diuresis.

Renal pelvic function of Danish Landrace pigs under anesthesia was analyzed during "normal" and forced diuresis. Measurements were made of intrapelvic pressures, electromyogram recordings were taken from the pelvis and ureter, and bolus formation was followed. During constant diuresis, pelvic activity displayed a dominant frequency which varied between individuals. When pressure rose or fell, pelvic activity increased or decreased in proportion to the speed rather than the extent of the pressure change. Thus, after furosemide administration urine flow increased and pelvic pressure rose; and in association with the pressure rise, pelvic activity increased significantly when mean pelvic activity in the phase of steep pressure rise was compared with the mean activity over the last 5 min of the observation period before induction of diuresis. Thereafter, pelvic activity decreased despite maintenance of a higher pressure plateau than that in the initial low diuresis observation period. This mode of function can be explained by reference to the characteristics of smooth muscle. Postulation of a specific pacemaker is unnecessary.