Effects of Angiotensin II on Erythropoietin Production in the Kidney and Liver

Figure 1. Epo mRNA expression. (a) Plasma Epo concentration in control and ATII-injected rats. ATII significantly increased the plasma Epo concentration from 1.4 ± 0.2 to 2.9 ± 0.3 mIU/mL (* p < 0.05). (b,c) ATII significantly increased Epo mRNA expression in the renal cortex (13.2 ± 4.7 and 11.4 ± 0.6 times increase by A1 and A10, respectively) (b), and HIF2α mRNA expression was also stimulated by ATII (9.6 ± 3.7 and 8.6 ± 2.6 times increase by A1 and A10, respectively) (c). (d–f) In microdissected nephron segments, ATII increased Epo mRNA expression in PCT (d) and MAL (f). HIF1α mRNA was also increased by ATII in PCT (e). C, control; A1, ATII 1 mg/kg; A10, ATII 10 mg/kg; ATII9, AT2 10−9 M; ATII6, ATII 10−6 M. * p < 0.05, ** p < 0.01 by the t-test or a non-parametric analysis using the Kruskal–Wallis test and multiple comparisons by the Dunnett or Shirley–Williams’ test.

Figure 2. Effects of ATII on Epo mRNA expression evaluated by ISH. In situ hybridization was used to analyze the effects of ATII on Epo, HIF2α, and PHD2 mRNA expression in mouse kidneys. Epo mRNA expression was observed in cortical nephrons under basal conditions (1-a,d). ATII stimulated Epo mRNA expression in PCT, MAL, CCD, and OMCD at 2–6 h (2~4-a,d) and HIF2α mRNA expression in most nephron segments and peritubular cells of both the cortex and the medulla at 2–6 h (2~4-b,e). In contrast, ATII stimulated PHD2 mRNA expression in MAL, CCD, and OMCD at 4–6 h (3~4-c,f). (a–c) Renal cortex and (d–f) renal outer medulla. The numbers 1, 2, 3, and 4 show 0, 2, 4, and 6 h after the injection of ATII, respectively.

Figure 3. Effects of fludrocortisone and ATII on Epo protein expression in the kidney and liver. (a) Effects of fludrocortisone on Epo production in the kidney. Fludrocortisone increased deglycosylated Epo protein expression at 2 and 4 h after the injection. The levels returned to basal values after 6 h. (b) ATII dose-dependently increased deglycosylated Epo protein expression in the renal cortex and outer medulla. The effects were larger in the renal cortex than in the renal outer medulla. (c) ATII increased deglycosylated Epo production in the renal cortex by 1.6- and 3.4-fold by 1 and 10 mg/kg, respectively. (d) In contrast, deglycosylated Epo production was not observed in control and ATII-injected livers. Recombinant rat Epo is shown as the control in Figure 3c. Glycosylated Epo and deglycosylated rat Epo were used in lane 1. Glycosylated Epo and deglycosylated Epo were used in lanes 11 and 12, respectively. * p < 0.05, ** p < 0.01 by a non-parametric analysis using the Kruskal–Wallis test and multiple comparisons by the Shirley–Williams’ test.

Figure 4. Immunohistochemical study of the effects of ATII on Epo production by the kidney. Under basal conditions, Epo staining was found from the proximal tubules to the collecting ducts (proximal tubules < thick ascending limbs < collecting ducts) (1-a–c). ATII increased Epo production in MAL, CCD, and OMCD (3~4-a–c), particularly in the type A intercalated cells, after 4–6 h (brown cells in 3~4-a–c). The renal outer medulla is shown at a different magnification. The numbers 1, 2, 3, and 4 show 0, 2, 4, and 6 h after the injection of ATII, respectively.