Rapid blood pressure increase after renal denervation in anaesthetized rats: interaction of oxidative stress and neuronal nitric oxide synthase

We showed previously that in anaesthetized rats acute noninvasive renal denervation (DNX) induced an increase in arterial blood pressure (MABP), unlike the usual hypotensive effect. Here we aimed to establish the background of such unusual response, especially the role of oxidative stress as suggested by an earlier study. The contribution of oxidative stress was explored by studying the effects on DNX-induced MABP increase of pretreatment with 4-hydroxy-3-methoxyacetophenone (apocynin, APO), a powerful antioxidant and antihypertensive agent, and N(omega)-propyl-L-arginine (L-NPA), a blocker of neuronal nitric oxide synthase (nNOS). In anaesthetized Wistar rats maintained on standard (STD) or high-salt (HS) diet sequential right- and left-side DNX was performed. MABP responses were examined without pretreatment and after APO (20 mg/day on two preceding days) and L-NPA (1 mg/kg/h throughout experiment), given alone or combined. In untreated rats, bilateral DNX increased MABP by 6% on STD and 15% on HS diet (P < 0.01 or less); the difference between MABP responses was highly significant (P = 0.002). In STD rats APO or APO + L-NPA treatment failed to alter post-DNX MABP increases whereas L-NPA alone reversed the response and a significant 7% decrease occurred. In HS rats APO and L-NPA given alone reversed the MABP response and significant decreases of 14% (P = 0.001) and 8% (P = 0.01), were seen. Surprisingly, with L-NPA + APO pretreatment only abolishment (not reversal) of post-DNX pressure increase occurred. The results suggest that both systemic, intrarenal and brain oxidative stress, and excessive nNOS activity, mostly in the brain, determine the unexpected post-DNX pressure increase.

End-organ damage in hypertensive transgenic Ren-2 rats: influence of early and late endothelin receptor blockade

The rat strain transgenic for the murine Ren-2 renin gene (TGR) is defined as a monogenic model of angiotensin II-dependent hypertension with endogenous activation of the renin-angiotensin system. Homozygous males TGR develop malignant hypertension with a strong salt-sensitive component. These animals show severe hypertension, proteinuria and high mortality. Morphological changes of renal parenchyma correspond to chronic ischemic glomerular changes. Heterozygous TGR develop only mild hypertension and thus provide a more suitable model of hypertension regarding to clinical studies. Within the renal parenchyma, secondary focal segmental glomerulosclerosis (FSGS) predominates. High-salt diet in heterozygous animals induces transition from benign to malignant phase of hypertension. In this case, ischemic glomerular changes are superimposed on preexisting secondary FSGS. In the regression model of hypertension (late-onset treatment) the effect of salt intake is attenuated. In homozygous TGR, early selective ET(A) receptor blockade decreased blood pressure and ameliorated end-organ damage. Late selective ET(A) receptor blockade reduced podocyte injury despite final severe hypertension. Survival rate was markedly improved in both regimens with ET(A) selective blockade, while there was only partial improvement with early non-selective blockade. Both bosentan and atrasentan decreased ET-1 levels in both regimens. In heterozygous TGR, early and late ET(A) treatment substantially while ET(A)/ET(B) treatment partially improved survival rate. Significant effect on BP was found with early and late ET(A) blockade, while ET(A)/ET(B) blockade had no effect. Bosentan and atrasentan similarly decreased ET-1 levels on both regimens. In conclusion, selective ET(A) receptor blockade is superior to nonselective ET(A)/ET(B) receptor blockade in attenuating hypertension and end-organ damage. Its effect is more pronounced when applied early in the life.