Angiotensin II utilizes Janus kinase 2 in hypertension, but not in the physiological control of blood pressure, during low-salt intake

Abstract

Janus kinase (JAK) 2 is activated by ANG II in vitro and in vivo, and chronic blockade of JAK2 by the JAK2 inhibitor AG-490 has been shown recently to attenuate ANG II hypertension in mice. In this study, AG-490 was infused intravenously in chronically instrumented rats to determine if the blunted hypertension was linked to attenuation of the renal actions of ANG II. In male Sprague-Dawley rats, after a control period, ANG II at 10 ng·kg(-1)·min(-1) was infused intravenously with or without AG-490 at 10 ng·kg(-1)·min(-1) iv for 11 days. ANG II infusion (18 h/day) increased mean arterial pressure from 91 ± 3 to 168 ± 7 mmHg by day 11. That response was attenuated significantly in the ANG II + AG-490 group, with mean arterial pressure increasing only from 92 ± 5 to 127 ± 3 mmHg. ANG II infusion markedly decreased urinary sodium excretion, caused a rapid and sustained decrease in glomerular filtration rate to ∼60% of control, and increased renal JAK2 phosphorylation; all these responses were blocked by AG-490. However, chronic AG-490 treatment had no effect on the ability of a separate group of normal rats to maintain normal blood pressure when they were switched rapidly to a low-sodium diet, whereas blood pressure fell dramatically in losartan-treated rats on a low-sodium diet. These data suggest that activation of the JAK/STAT pathway is critical for the development of ANG II-induced hypertension by mediating its effects on renal sodium excretory capability, but the physiological control of blood pressure by ANG II with a low-salt diet does not require JAK2 activation.

Fig. 1.

Mean arterial pressure (MAP) of chronically catheterized rats treated with vehicle (control) or ANG II at 10 ng·kg⁻¹·min⁻¹ with or without the JAK2 inhibitor AG-490 at 10 ng·kg⁻¹·min⁻¹ and a subset of the ANG-II + AG-490 group in which AG-490 was removed on day 13 (AG-490 removed). *P ≤ 0.05 compared with ANG II + AG-490. +P ≤ 0.05, ANG II + AG-490 vs. control + AG-490.

Fig. 2.

A: glomerular filtration rate (GFR) of chronically catheterized rats treated with vehicle (control) or ANG II at 10 ng·kg⁻¹·min⁻¹ with or without AG-490 at 10 ng·kg⁻¹·min⁻¹ and a subset of the ANG II + AG-490 group in which AG-490 was removed on day 13. *P ≤ 0.05 compared with ANG II + AG-490. B: 24-h urinary sodium excretion of chronically catheterized rats treated with vehicle (control) or ANG II at 10 ng·kg⁻¹·min⁻¹ with or without AG-490 at 10 ng·kg⁻¹·min⁻¹ and a subset of the ANG II + AG-490 group in which AG-490 was removed on day 13. *P ≤ 0.05 compared with ANG II + AG-490.

Fig. 3.

A: JAK2 phosphorylation in kidney cortex homogenates from chronically catheterized rats treated with vehicle (control) or ANG II at 10 ng·kg⁻¹·min⁻¹ with or without AG-490 at 10 ng·kg⁻¹·min⁻¹: control (n = 4), control + AG-490 (n = 5), ANG II (n = 6), and ANG II + AG-490 (n = 5). pJAK2, phosphorylated JAK2. *P ≤ 0.05 compared with ANG II + AG-490. B: STAT3 phosphorylation in kidney cortex from chronically catheterized rats treated with vehicle or ANG II at 10 ng·kg⁻¹·min⁻¹ with or without AG-490 at 10 ng·kg⁻¹·min⁻¹: control (n = 4), control + AG-490 (n = 5), ANG II (n = 6), and ANG II + AG-490 (n = 5). pSTAT3, phosphorylated STAT3. *P ≤ 0.05 compared with ANG II + AG-490.

Fig. 4.

JAK1 phosphorylation in kidney cortex from chronically catheterized rats treated with vehicle (control) or ANG II at 10 ng·kg⁻¹·min⁻¹ with or without AG-490 at 10 ng·kg⁻¹·min⁻¹: control (n = 4), control + AG-490 (n = 5), ANG II (n = 6), and ANG II + AG-490 (n = 5). pJAK1, phosphorylated JAK1. *P ≤ 0.05 compared with control.

Fig. 5.

A: contractile response of thoracic aorta to 1 nM–1 μM ANG II in the presence or absence of 1 μM AG-490 (n = 6 for both groups). *P ≤ 0.05 compared with vehicle (DMSO). B: maximal contractile response of thoracic aorta to 65 mM KCl in the presence or absence of 1 μM AG-490 (n = 4 for both groups).

Fig. 6.

Contractile responses of thoracic aorta to a 5-HT concentration-response curve in the presence or absence of 1 μM AG-490.

Fig. 7.

A: MAP in chronically catheterized rats treated with normal-salt diet (♦, n = 4), sodium-deficient diet (■, n = 5), sodium-deficient diet with AG-490 at 10 ng·kg⁻¹·min⁻¹ (▴, n = 6), and sodium-deficient diet with losartan at 10 ng·kg⁻¹·min⁻¹ (▾, n = 6). *P ≤ 0.05 compared with sodium-deficient control. B: JAK2 phosphorylation in kidney cortex homogenates from chronically catheterized rats treated with normal-salt diet, sodium-deficient diet, sodium-deficient diet with AG-490 at 10 ng·kg⁻¹·min⁻¹, and sodium-deficient diet with losartan at 10 ng·kg⁻¹·min⁻¹.

Fig. 8.

A: MAP in chronically catheterized rats treated with vehicle (control) and ANG II at 1.0, 2.5, 5.0, and 10 ng·kg⁻¹·min⁻¹. *P ≤ 0.05 compared with control. B: JAK2 phosphorylation in kidney cortex homogenates from chronically catheterized rats treated vehicle (control, n = 6) or ANG II at 1.0, 2.5, 5.0, and 10 ng·kg⁻¹·min⁻¹ (n = 6 each). *P ≤ 0.05 compared with control.