Changes in fluid compartments in hamster renal papilla due to peristalsis in the pelvic wall

The pelvic peristalsis "milks" the renal papilla in rodents. This study investigates the effect of the pelvic contractions upon the fluid in papillary loops of Henle (LH) and capillaries (cap) and on the volume of collecting duct (CD) cells, papillary epithelial (PE) cells and interstitium. In the anesthetized antidiuretic hamsters the urine was made green by an intravenous infusion of lissamine green. A snare was placed loosely around the papilla. The peristalsis was recorded on a Grass recorder using a fiberoptic light signal which changed intensity with the events in the pelvis and papilla. In one group of hamsters the snare was tightened during the contraction and in another group at the beginning of the relaxation. The papilla within the pelvis was then fixed immediately. It was epon-embedded for light and electron microscopy. In the group with contracted pelvis CD, LH, and cap were all closed and empty; the papilla was elongated. In the group with relaxed pelves these structures were full and open spaces were seen between the cells of CD and PE. Morphometric measurements showed that the intercollecting duct volume was larger in the papillae with relaxed pelvis, but that cell volume of PE was larger in the papillae with contracted pelvis. It is suggested that fluid moves into the cells during contraction when urine flows through the CD and into the interstitium during relaxation.