Differential effects of antihypertensive drugs on renal and glomerular hemodynamics and injury in the chronic nitric-oxide-suppressed rat

Antihypertensive and renoprotective actions of soluble epoxide hydrolase inhibition in ANG II-dependent malignant hypertension are abolished by pretreatment with L-NAME

OBJECTIVE

The present study was performed to investigate in a model of malignant hypertension if the antihypertensive actions of soluble epoxide hydrolase (sEH) inhibition are nitric oxide (NO)-dependent.

METHODS

ANG II-dependent malignant hypertension was induced through dietary administration for 3 days of the natural xenobiotic indole-3-carbinol (I3C) in Cyp1a1-Ren-2 transgenic rats. Blood pressure (BP) was monitored by radiotelemetry and treatment with the sEH inhibitor [cis-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyl-oxy]-benzoic acid (c-AUCB)] was started 48 h before administration of the diet containing I3C. In separate groups of rats, combined administration of the sEH inhibitor and the nonspecific NO synthase inhibitor [Nω-nitro-L-arginine methyl ester (L-NAME)] on the course of BP in I3C-induced and noninduced rats were evaluated. In addition, combined blockade of renin-angiotensin system (RAS) was superimposed on L-NAME administration in separate groups of rats. After 3 days of experimental protocols, the rats were prepared for renal functional studies and renal concentrations of epoxyeicosatrienoic acids (EETs) and their inactive metabolites dihydroxyeicosatrienoic acids (DHETEs) were measured.

RESULTS

Treatment with c-AUCB increased the renal EETs/DHETEs ratio, attenuated the increases in BP, and prevented the decreases in renal function and the development of renal damage in I3C-induced Cyp1a1-Ren-2 rats. The BP lowering and renoprotective actions of the treatment with the sEH inhibitor c-AUCB were completely abolished by concomitant administration of L-NAME and not fully rescued by double RAS blockade without altering the increased EETs/DHETEs ratio.

CONCLUSION

Our current findings indicate that the antihypertensive actions of sEH inhibition in this ANG II-dependent malignant form of hypertension are dependent on the interactions of endogenous bioavailability of EETs and NO.

Partial adherence to antihypertensive therapy fails to achieve full cardiovascular benefits in hypertensive rats

BACKGROUND

Partial adherence to antihypertensive therapy remains a public health challenge and may be associated with increased cardiovascular risk. We quantitatively evaluated cardiovascular risk inherent in partial therapy adherence in spontaneously hypertensive rats with accelerated hypertension.

METHODS

Adult spontaneously hypertensive rats were divided into 5 groups; Group 1 (controls) did not receive any treatment, whereas all other rats (Groups 2-5) were given nitric oxide synthase inhibitor N-nitro-l-arginine methyl ester (L-NAME) to exacerbate hypertension. Group 2 (untreated/nonadherers) was given L-NAME but not antihypertensive medication; Group 3 (Perfect Adherers) was treated daily with candesartan (10 mg/kg); Group 4 was given candesartan 3 times a week, whereas Group 5 received candesartan only during the last 6 days of the 3-week experiment (Partial Adherers). At the end, indices of systemic and regional (kidneys, brain, and heart) hemodynamics, and indices of left ventricular function were determined.

RESULTS

Treatment with L-NAME aggravated hypertension, adversely affected target organ blood flows and resistances, and grossly impaired ventricular function. Perfect adherence with candesartan completely reversed the adverse cardiovascular effects of L-NAME intervention. In partial adherers (Groups 4 and 5), arterial pressure decreased and reached control values. However, target organ hemodynamics and heart function showed only slight improvements, if any.

CONCLUSIONS

The results demonstrate that partial adherence to therapy reduces arterial pressure, but may not prevent target organ damage. If replicated in humans, these results may have important clinical implications in hypertensive patients.

Uric acid: Its relationship to renal hemodynamics and the renal renin-angiotensin system

Reports relating hyperuricemia and hypertension have been filed for many decades. Nevertheless, controversy remains concerning serum uric acid concentration as an independent risk factor underlying coronary heart disease (CHD) and essential hypertension or as an indirect marker of renovascular involvement. Earlier studies in normotensive subjects and hypertensive patients demonstrated that serum uric acid concentration was closely related to intrarenal hemodynamic alterations, suggesting that it is an excellent marker of vascular involvement. Our data from clinical studies and in an animal model of severe hypertensive nephrosclerosis have strengthened this concept. Conversely, other reports have suggested that uric acid may be a pathogenetic factor. Supporting arguments for this theory maintain that experimental hyperuricemia induces hypertension and renal damage. Epidemiologically, hyperuricemia is associated with hypertension, CHD, renal disease, toxemia of pregnancy, and other outcomes, although mechanisms remain unclear. Additionally, there are no available data on the effects of lowering uric acid on pressure control and organ protection.

Superiority of combination of thiazide with angiotensin-converting enzyme inhibitor or AT1-receptor blocker over thiazide alone on renoprotection inl-NAME/SHR

The renal and glomerular dynamic effects of combining thiazide and angiotensin antagonists have not been reported. The present study was designed to examine the effects of hydrochlorothiazide (HCTZ) alone or in combination with an angiotensin-converting enzyme inhibitor or ANG II type 1-receptor blocker on renal hemodynamics, glomerular dynamics, renal function, and renal histopathology in the Nω-nitro-l-arginine methyl ester-treated spontaneously hypertensive rat (l-NAME/SHR) model. HCTZ (80 mg·kg−1·day−1) alone or in combination with enalapril (30 mg·kg−1·day−1) or losartan (30 mg·kg−1·day−1) or enalapril (15 mg·kg−1·day−1) plus losartan (15 mg·kg−1·day−1) was administered to l-NAME/SHR (5.0 ± 0.10 mg·kg−1·day−1) for 3 wk. Mean arterial pressure, total peripheral resistance, renal plasma flow, glomerular filtration rate, glomerular hydrostatic pressure, afferent and efferent glomerular arteriolar resistances, single nephron plasma flow, single nephron glomerular filtration rate, serum creatinine concentration, 24-h urinary protein excretion, and glomerular and arteriolar injury scores were determined. HCTZ reduced mean arterial pressure, total peripheral resistance, glomerular hydrostatic pressure, and afferent and efferent glomerular arteriolar resistances ( P < 0.05, at least) but slightly increased renal plasma flow and single nephron plasma flow associated with reduced serum creatinine concentration, urinary protein excretion, and arteriolar injury score compared with l-NAME/SHR control. However, the combination of enalapril and/or losartan with HCTZ markedly improved each of these functions. These results demonstrated minor benefits of HCTZ monotherapy and a marked superiority of its combination with enalapril and/or losartan over HCTZ monotherapy on renoprotection in l-NAME/SHR, thereby providing strong evidence of their clinical benefits for hypertensive patients with renal functional impairment.