Peristaltic flow of urine in the renal capillary collecting ducts of hamsters.

Urine movements in the papillary collecting ducts were studied visually, in vivo, through the intact renal pelvic wall in anesthetized (Inactin 150 mg/kg) hamsters having a normal range of urine flow rates (0.5 to 3.8 microliters.min(-1).100 g of body wt-1). Urine was given a contrasting color by a continuous i.v. infusion of lissamine green (0.5 to 2%) in saline. The lower renal pelvis with about 1.3 mm of the renal papilla was illuminated with a fiber optic light, and the movements of urine in the medullary collecting ducts were observed and filmed through a dissecting microscope. Urine flow was determined indirectly by measuring changes in the urinary bladder diameter, and the rate of urine formation was manipulated by changing the rate of lissamine green-saline infusion. Urine, propelled by pelvic peristaltic waves, moved as discreet boluses in a pulsatile fashion through the papillary collecting ducts. The length of the urine boluses and the percent of time the papillary collecting ducts were in contact with urine increased in direct proportion to urine flow. At the lowest urine flow rate, the papillary collecting ducts (at 1.0 mm from the tip) were empty 94% of the time. The velocity (1.6 +/- 0.1 mm.sec-1) and frequency (12.6 +/- 0.5 contractions.min-1) of the pelvic peristaltic waves were not related to urine flow rate. The renal pelvic contractions were also observed to cause discontinuous blood flow in the vasa recta. In the context of Stephenson's mass balance equation for the concentration ratio of the kidney, the discontinuous fluid movements imposed by the renal pelvis may resulted in an increased urine concentrating ability.