Effects of Papaverine on Cell Separation in the Mammalian Kidney Papilla.

The low red cell content of the renal papilla can be explained by the plasma skimming hypothesis of Pappenheimer and Kinter. However, previous studies raise serious doubt as to the existence of this mechanism in the mammalian kidney. An alternate explanation is here offered. It is proposed that the descending limbs of the vasa recta contain myogenic sphincters which impede the passage of red cells into the papilla under normal conditions. The cell rich blood proximal to the sphincters is shunted back toward the outer medulla. Papaverine was administered intravenously in order to relax these sphincters. A rise in red cell content in the papilla and no change in the outer medulla and cortex was observed. These findings are compatible with the proposed hypothesis.