K-Ras4A deficiency is associated to increased endothelial-dependent vasodilation in mice.

MJ Montero1, MA Sevilla1, MT Grande1, M Clemente1, JM López-Novoa1,2. 1Universidad de Salamanca, Fisiología y Farmacología, Spain, 2Instituto Reina Sofía de Investigación Nefrológica, Fundación Renal Iñigo Álvarez de Toledo, Spain

Ras GTPases superfamily (H-Ras, N-Ras, and K-Ras4B) regulate an astonishing diversity of cellular functions and current research relate them with cardiovascular diseases, such as cardiac hypertrophy, heart failure and endothelial dysfunction. In order to assess a possible role for Kras4A in regulating cardiovascular function, we studied blood pressure, heart function and vascular reactivity in K-Ras4A knockout (K-Ras4A-/-) and wild type (WT) mice. Data are expressed as mean±standard error of the mean. Statistically significant values were considered when p<0.05.

Systolic blood pressure measured in awake animals by the tail-cuff method revealed a lower arterial pressure in K-Ras4A-/- mice (93±2 mmHg vs 120±3 mmHg, p<0.05). Direct intra-arterial measurement in anaesthetized mice showed similar results. Echocardiographic data revealed no differences in cardiac output thus suggesting that hypotension was based on changes in peripheral vascular resistances. We assessed the changes in mean arterial pressure in response to the acute i.v. administration of the vasodilators as acetylcholine (ACh) and sodium nitroprusside (SNP). Whereas ACh produced a slightly greater reduction in blood pressure in K-Ras4A-/- (27.9±0.5 vs 33.1±0.6 mmHg, p<0.05), both kinds of animals had similar hypotensive responses to SNP. Measurement of plasma concentration of nitrite, a nitric oxide metabolite, (Griess method) showed greater levels in K-Ras4A-/- than in WT animals (21.85±4.65 nM vs 11.29±1.02 nM, p<0.05). Urinary Excretion of nitrites was also higher in K-Ras4A-/- than in WT mice. The underlying mechanisms of arterial hypotension were studied in resistance vessel using isolated perfused hindlimb model. The abdominal aorta was cannulated in a caudal direction near the aortic bifurcation; the cannula was connected to a pressure transducer and to a peristaltic pump. Hindlimbs were continuously perfused with warmed Krebs solution at a constant flow of 1 mL/min. Concentration response curves to ACh and SNP were made in phenylephrine precontracted preparations. As in the experiment carried out “in vivo” we observed again significant differences in vasorelaxation response to ACh. But not to SNP.

These data suggest a relationship between increased endothelium-dependent vasodilation and hypotension in K-Ras4A knockout mice.