Endogenous angiotensin II modulates nNOS expression in renovascular hypertension

Nitric oxide (NO) influences renal blood flow mainly as a result of neuronal nitric oxide synthase (nNOS). Nevertheless, it is unclear how nNOS expression is modulated by endogenous angiotensin II, an inhibitor of NO function. We tested the hypothesis that the angiotensin II AT1 receptor and oxidative stress mediated by NADPH oxidase contribute to the modulation of renal nNOS expression in two-kidney, one-clip (2K1C) hypertensive rats. Experiments were performed on male Wistar rats (150 to 170 g body weight) divided into 2K1C (N = 19) and sham-operated (N = 19) groups. nNOS expression in kidneys of 2K1C hypertensive rats (N = 9) was compared by Western blotting to that of 2K1C rats treated with low doses of the AT1 antagonist losartan (10 mg·kg-1·day-1; N = 5) or the superoxide scavenger tempol (0.2 mmol·kg-1·day-1; N = 5), which still remain hypertensive. After 28 days, nNOS expression was significantly increased by 1.7-fold in the clipped kidneys of 2K1C rats and by 3-fold in the non-clipped kidneys of 2K1C rats compared with sham rats, but was normalized by losartan. With tempol treatment, nNOS expression increased 2-fold in the clipped kidneys and 1.4-fold in the non-clipped kidneys compared with sham rats. The changes in nNOS expression were not followed by changes in the enzyme activity, as measured indirectly by the cGMP method. In conclusion, AT1 receptors and oxidative stress seem to be primary stimuli for increased nNOS expression, but this up-regulation does not result in higher enzyme activity.

Niveles de angiotensina (1-7) en ratas con distinto genotipo de enzima convertidora de angiotensina I y efecto de la hipertensión renovascular / Levels of angiotensin (1-7) in rats with different ace genotypes and effect of renovascular hypertension

La mayor actividad de la enzima convertidora de angiotensina I (ECA) determina mayores niveles de angiotensina (Ang) II y menores de Ang-(1-7). Hemos observado mayores niveles de Ang II en ratas normotensas con mayor actividad de ECA y simultáneamente mayor hipertensión renovascular. Planteamos que en esta situación los niveles de Ang (1-7) podrían modificarse por la HTA y además ser inversamente proporcionales a la actividad de ECA y a los niveles de Ang II. Métodos: se determinó angiotensina II y (1-7) plasmáticas en ratas normotensas e hipertensas renovasculares (modelo Goldblatt 2 riñones, 1 clip) en cepas F2 homocigotas Brown Norway (BN, con ECA elevada) o Lewis (con ECA baja). Resultados: Promedio (ES). Los niveles de hipertensión arterial e HVI fueron similares en ambas cepas en los grupos Goldblatt. Los niveles plasmáticos de Ang II fueron 509 (37) U/ml en ratas BN normotensas y 173 (25) U/mL en ratas Lewis normotensas (p <0,05). Los niveles plasmáticos de Ang (1-7) fueron 4 veces mayores en ratas Lewis normotensas que las normotensas BN (p <0,05) y se elevaron significativamente con la hipertensión (p <0,05). Conclusión: Estos resultados podrían explicar la diferencia en la magnitud de la HTA observada previamente entre ambos genotipos de ECA y la mayor tendencia a presentar hipertensión arterial en hombres que presentan el alelo D del polimorfismo ECA I/D.

Heart prolyl endopeptidase activity in one-kidney, one clip hypertensive rats

1. Heart mass, prolyl endopeptidase activity and fractionated proteins from heart tissue were studied in one-kidney, one clip hypertensive rats (N=6) and compared to sham-operated rats (N=6). 2. Body weigh, arterial pressure and tissue mass were measured 4 weeks after artery clipping Z-Gly-Pro-p-nitroaniline hydrolysis was used to measure tissue prolyl endopeptidase activity in the homogenate. Protein was fractionated into the soluble and myofibrillar fractions. 3. In the normotensive rats, prolyl endopeptidase activity expressed in terms of protein specific activity (µM substrate hydrolyzed h-1 mg supernatant protein-1) occurred in atria and was 2.5-fold higher than in the ventricles (3.79 ñ 0.20 vs 1.44 ñ 0.02, P<0.05). In the one-kidney, one clip hypertensive rats, the left ventricle tissue increased 1.7-fold (2.27 ñ 0.11 vs 3.72 ñ 0.11 mg wet weight tissue/g body weight, P<0.001), the soluble protein fraction (54.86 ñ 3.60 vs 57.38 ñ 6.64 mg/g wet weight tissue) was unchanged, while the myofibrillar fraction increased 1.9-fold (118.9 ñ 9.09 vs 229.8 ñ 8.47 mg/g wet weight tissue, P<0.001). 4 The specific activity of the atrial and ventricular prolyl endopeptidase decreased in atria and increased in ventricles as the result of hypertension (3.79 ñ 0.2 vs 2.84 ñ 0.13 and 1.44 ñ 0.02 vs 1.87 ñ 0.13; respectively). These regional differences in prolyl endopeptidase enxyme content caused by one-kidney, one clip hypertension in neurosecretory and non-neurosecretory heart areas suggest that this enzyme plays a local role in the turnover of specific polypeptides