Renin-angiotensin blockade improves renal cGMP production via non-AT(2)-receptor mediated mechanisms in hypertension-induced by chronic NOS inhibition in rat

Prevention of salt-induced hypertension and fibrosis by AT1-receptor blockers in Dahl S rats

In Dahl S rats, high salt intake causes hypertension and cardiovascular hypertrophy and fibrosis, associated with an apparent increase in activity of tissue RAAS. In the current study, we assessed the effects of two AT1-receptor blockers (ARB) on AT1- and AT2-receptors and ACE densities and salt-induced cardiovascular changes. The hydrophilic ARB losartan (30 or 100 mg.kg.d) and the lipophilic ARB telmisartan (10 or 30 mg.kg.d) were administered once daily, and a high-salt diet was provided from 5 to 9 weeks. In Dahl S but not R rats, the high-salt diet caused marked hypertension, cardiac and kidney hypertrophy, and fibrosis. Both ARBs dose-dependently inhibited binding of Ang II to AT1-receptors and reversed the salt-induced increases in AT2-receptor densities in the CNS. Both ARBs at regular doses attenuated the salt-induced hypertension and, at high doses, prevented the increase in BP during the day but not during the night. Both ARBs similarly prevented high-salt-induced interstitial and perivascular fibrosis in the LV and RV as well as fibrosis in the aorta and renal tubules. RV hypertrophy was also prevented, but LV hypertrophy only partially, and kidney hypertrophy not at all. In Dahl S rats, AT1-receptor stimulation seems to play a critical role in salt-induced hypertension and fibrosis, but a lesser role in tissue hypertrophy.

Synthetic Human α-Atrial Natriuretic Peptide Improves the Management of Postoperative Hypertension and Renal Dysfunction after the Repair of Abdominal Aortic Aneurysm

OBJECTIVE

Delayed hypertension (HT) and renal dysfunction (RD) are observed after aortic operations accompanied by infra-renal aortic cross-clamping (AXC). Atrial natriuretic peptide (ANP) has effects on vasodilation and renal protection, and we examined the hypothesis that synthetic human alpha-ANP (hANP) improves the postoperative management for abdominal aortic aneurysm (AAA).

METHODS

Fifty patients undergoing elective aneurysmectomy for infrarenal-AAA between 1998 and 2001 (M:F = 43:7, mean age 70.5 +/- 7.7 years) were randomly allocated to one of 2 groups; Group H (n = 24) received hANP immediately after operation (initial dose: 0.025 microg/kg/min), and Group C (n = 26) served as a control group.

RESULTS

All patients in Group C required nicardipine hydrochloride (4.41 +/- 1.68 mg/h) for prevention of postoperative HT, whereas only 6 patients in Group H required the increase in hANP dose due to HT (P < 0.0001). Maximum hANP dose was 0.035 +/- 0.019 microg/kg/min. Group H showed significantly smaller furosemide dosage in the initial 3 days (H vs. C; 9.2 +/- 11.0 vs. 58.8 +/- 41.5 mg, P < 0.0001), significantly lower peak-Crn (H vs. C; 1.16 +/- 0.53 vs. 2.58 +/- 1.42 mg/dL, P < 0.0001), and significantly lower plasma renin-activity (7.09 +/- 2.38 vs. 11.52 +/- 4.89 ng/mL/h, P = 0.0002) and aldosterone (51.6 +/- 12.7 vs. 81.2 +/- 34.2 pg/mL, P = 0.0002) on the first postoperative day than Group C did.

CONCLUSIONS

These results imply that renin-angiotensin system may play a role in the incidence of postoperative HT and RD, and suggest that hANP infusion is a simple, reliable, and effective method for management during the immediate period after AAA operations.

Angiotensin II and nitric oxide interaction

Nitric oxide degradation linked to endothelial dysfunction plays a central role in cardiovascular diseases. Superoxide producing enzymes such as NADPH oxidase and xanthine oxidase are responsible for NO degradation as they generate a variety of reactive oxygen species (ROS). Moreover, superoxide is rapidly degraded by superoxide dismutase to produce hydrogen peroxide leading to the uncoupling of NO synthase and production of increased amount of superoxide. Angiotensin II is an important stimulus of NADPH oxidase. Through its AT(1) receptor, Ang II stimulates the long-term increase of several membrane component of NADPH oxidase such as P(22) phox or nox-1 and causes an increased activity of NADPH oxidase with inactivation of NO leading to impaired endothelium-dependent vasorelaxation, vascular smooth muscle cell hypertrophy, proliferation and migration, extracellular matrix formation, thrombosis, cellular infiltration and inflammatory reaction. Several preclinical and clinical studies have now confirmed the involvement of the AT(1) receptor in endothelial dysfunction. It is proposed that the AT(2) receptor counterbalances the deleterious effect of the Ang II-induced AT(1) receptor stimulation through bradykinin and NOS stimulation. This mechanism could be especially relevant in pathological cases when the NADPH oxidase activity is blocked with an AT(1) receptor antagonist.