The AQP2-positive area was measured semi-quantitatively (Figure 3M–O), and the mean ± SEM values in the PAN group relative to the control group were 149.8 ± 8.7% (n = 3, p < 0.01) in the cortex, 163.7 ± 12.5% (p < 0.01) in the outer medulla (OM), and 145.4 ± 13.1% (p < 0.05) in the IM on day 2, 55.2 ± 4.1% (p < 0.01) in the cortex, 63.9 ± 7.7% (p < 0.01) in the OM, and 81.5 ± 8.7% in the IM on day 5, and 73.8 ± 8.6% (p < 0.05) in the cortex, 53.7 ± 6.0% (p < 0.01) in the OM, and 35.3 ± 2.7% (p < 0.01) in the IM on day 8. Here, AQP2 is linked to polyarteritis nodosa.