Acute salt loading induces sympathetic nervous system overdrive in mice lacking salt-inducible kinase 1 (SIK1)

Loss of salt-inducible kinase 1 (SIK1) triggers an increase in blood pressure (BP) upon a chronic high-salt intake in mice. Here, we further addressed the possible early mechanisms that may relate to the observed rise in BP in mice lacking SIK1. SIK1 knockout (sik1^-/-) and wild-type (sik1^+/+) littermate mice were challenged with either a high-salt (8% NaCl) or control (0.3% NaCl) diet for 7 days. Systolic BP was significantly increased in sik1^-/- mice after 7 days of high-salt diet as compared with sik1^+/+ mice and to sik1^-/- counterparts on a control diet. The renin-angiotensin-aldosterone system and the sympathetic nervous system were assayed to investigate possible causes for the increase in BP in sik1^-/- mice fed a 7-day high-salt diet. Although no differences in serum renin and angiotensin II levels were observed, a reduction in aldosterone serum levels was observed in mice fed a high-salt diet. Urinary L-DOPA and noradrenaline levels were significantly increased in sik1^-/- mice fed a high-salt diet as compared with sik1^-/- mice on a control diet. Similarly, the activity of dopamine β-hydroxylase (DβH), the enzyme that converts dopamine to noradrenaline, was significantly increased in the adrenal glands of sik1^-/- mice on a high-salt intake compared with sik1^+/+ and sik1^-/- mice on a control diet. Treatment with etamicastat (50 mg/kg/day), a peripheral reversible DβH inhibitor, administered prior to high-salt diet, completely prevented the systolic BP increase in sik1^-/- mice. In conclusion, SIK1 activity is necessary to prevent the development of salt-induced high blood pressure and associated SNS overactivity.