Renin inhibition mitigates anti-angiogenesis in spontaneously hypertensive rats

BACKGROUND: Spontaneously hypertensive rats (SHRs) are characterized by capillary rarefaction, which may contribute to blood pressure elevation. We hypothesized that capillary rarefaction involves a suppressed angiogenesis; renin inhibition influences anti-angiogenesis homeostasis by acting on angiopoietins; transient renin blockade reduces anti-angiogenesis thereby ameliorating long-lasting blood pressure and cardiac hypertrophy in SHRs. METHODS: First, serum angiopoietin-1 and angiopoietin-2 were measured in 2-month old normotensive Wistar-Kyoto rats (WKYs) and SHRs after renin inhibition (aliskiren: 1 and 10 mg/kg per day) or placebo. Second, 4-week old SHRs were prehypertensively treated with aliskiren (1 and 10 mg/kg per day) or placebo for 4 weeks. After 4 weeks of 'drug holiday' 12-week old SHRs were given L-nitro-arginine methyl ester (L-NAME) (25 mg/kg per day) for a 4-week interval to promote capillary rarefaction. Thereafter, mean arterial pressure (MAP), cardiac remodeling, capillary density, pAkt/Akt as marker for cellular survival, pro-angiogenic genes and systemic angiopoietins were investigated. RESULTS: Baseline angiopoietin levels were similar between WKYs and SHRs. Renin inhibition increased angiopoietin-1 in SHR and reduced angiopoietin-2 in both WKY and SHR blood pressure independently. Prehypertensive renin inhibition reduced MAP and cardiac hypertrophy in adult SHRs. This was associated with higher cardiac capillary density, pAkt/Akt, pro-angiogenic expression pattern and serum angiopoietin-1, whereas angiopoietin-2 was lower as compared to vehicle-pretreated SHRs. These results were independent of prehypertensive blood pressure lowering by aliskiren. CONCLUSION: We conclude that renin inhibition modulates anti-angiogenesis signaling independently of blood pressure by increasing angiopoietin-1/angiopoietin-2 ratio. This promotes in SHR stabilization of endothelial cells, favors pro-angiogenic action and consequently results in higher capillary density.