Free myo-Inositol in Canine Kidneys: Selective Concentration in the Renal Medulla (41361)

The concentration of free and lipid-bound myo-inositol (MI) was measured in outer and inner cortical zones and in outer and inner medullary zones of the dog kidney. Lipid-bound MI was highest in the outer cortex (0.86 μ mole/g wet wt) and decreased progressively to the inner medulla (0.28 μ mole/g). In contrast free MI was highest in the outer medulla (18.4 ± 2.2 μ mole/g wet wt) as compared to the cortical zones (3.45 ± 0.19 and 5.30 ± 0.33 μ mole/g in outer and inner zones, respectively). The concentration ratio of free MI in outer medullary zone cellular water to plasma water was in excess of 1000. We cannot attribute this high MI concentration to tubular transport because this transport system is present in cortical zone proximal tubules. Water diuresis did not deplete outer medullary MI significantly which suggests that the high medullary MI is independent of the medullary countercurrent mechanism.