Comparative Studies of the Desert Rodent Dipodomys Merriami and Munich Wistar Rat Urine Concentrating Mechanisms

Abstract

Comparative studies of the mammalian renal medulla suggest that variations in the architecture of the thin limb of Henle’s loop contribute to variations in ability to produce concentrated urine. For this study, tubules and blood vessels of the renal inner medulla were identified by indirect immunofluorescence using antibodies and lectins that recognize segmentspecific proteins. Variations in axial expression of the water channel aquaporin 1 and the Cl channel ClC-K1 in the descending thin limb, suggest that equilibration of luminal fluid by water reabsorption occurs along a greater proportion of each loop length, and Cl reabsorption occurs along a shorter proportion of each prebend loop length in Dipodomys than in the Munich-Wistar rat. Interstitial nodal spaces adjacent to CDs exist in both species and preferential solute diffusion into these spaces may play a significant role in driving fluid reabsorption from CDs. In the terminal papilla, the ATL-to-CD surface area ratio is markedly greater in the Munich-Wistar rat, suggesting that NaCl reabsorption may have less of an impact on water reabsorption from terminal CDs in Dipodomys.