Objective: 

NADPH oxidase (Nox) and Rho kinase (Rock) contribute to the development of hypertension. We tested whether angiotensin II-induced activation of Nox depends on Rock in isolated rat vascular smooth muscle cells (VSMC) and whether Nox-dependent superoxide formation and Rock activity are increased in renal resistance arteries from rats with angiotensin II-dependent hypertension.

Methods: 

VSMC were stimulated with angiotensin II in the absence or presence of Rock inhibition. Nox-dependent superoxide formation was measured by lucigenin-enhanced chemiluminescence. Renal resistance arteries were isolated from cyp1a1ren-2 transgenic rats without or with angiotensin II-dependent hypertension (i.e. without or with induction of the renin transgene). Nox activity, mRNA expression and myosin phosphatase target subunit 1 (MYPT1) phosphorylation were measured and myography was performed.

Results: 

In VSMC angiotensin II caused a 2.5-fold increase in Nox activity that was abolished by Rock inhibition. In renal resistance arteries from cyp1a1ren-2 transgenic rats Nox activity as well as Nox1 and Nox2 mRNA expression were increased in the initial phase of hypertension. These effects disappeared within 14 days. Rock activity remained unchanged and agonist-induced constriction did not show enhanced sensitivity to superoxide scavenging and Rock inhibition, in the initial phase (3 days) of angiotensin II-dependent hypertension.

Conclusion: 

In isolated VSMC angiotensin II-induced stimulation of Nox activity is Rock-dependent while in renal resistance arteries from rats with developing angiotensin II-dependent hypertension Nox activation is not accompanied by Rock activation. This suggests that Nox is activated by different mechanisms in isolated VSMC and in renal resistance arteries in vivo.