Does antihypertensive therapy protect the kidney in essential hypertension?

The renal antifibrotic effects of angiotensin-converting enzyme inhibition involve bradykinin B2 receptor activation in angiotensin II-dependent hypertension

OBJECTIVE

The renoprotective action of angiotensin I-converting enzyme inhibitors (ACE-Is) is well established, but the role played by bradykinin (BK) remains unclear. We therefore investigated whether an enhanced BK effect on B2 receptor subtype mediated the antifibrotic effect of ACE-Is and whether neutral endopeptidase (NEP) inhibition, which can blunt BK degradation more effectively than ACE inhibition, provided further renoprotection in a rat model of angiotensin (Ang) II-dependent renal damage.

METHODS

Five-week-old Ren-2 transgenic rats (TGRen2) received, for 8 weeks, a placebo, ramipril (5 mg/kg body weight) or the dual ACE + NEP inhibitor MDL 100,240 (MDL) (40 mg/kg body weight). After 4 weeks, the B2 receptor antagonist icatibant (0.5 mg/kg body weight) was administered on top of active treatment for 4 weeks to 50% of the TGRen2 rats. Blood pressure was measured weekly by a tail-cuff method and, after sacrifice, kidney weight, glomerular volume, density of glomerular profiles were measured; tubulo-interstitial fibrosis, glomerular and perivascular fibrosis were quantified by histomorphometry.

RESULTS

The development of hypertension and tubulo-interstitial fibrosis was prevented by both ramipril and MDL (P = 0.0001 versus placebo); icatibant annulled the latter effect. Glomerular and perivascular fibrosis were unaffected by either ramipril or MDL alone; however, combined treatment with icatibant enhanced glomerular fibrosis (P = 0.0001 versus placebo).

CONCLUSION

Enhanced BK effect on B2 subtype receptors is essential for the prevention of tubulo-interstitial fibrosis with ACE or dual ACE + NEP inhibition in TGRen2 rats.

Quantitative Evaluation of Urinalysis Test Strips

Background: Urine test strip results are generally reported in categories (i.e., ordinal scaled), but automated strip readers are now available that can report quantitative data. We investigated the possible use of these meters to complement flow cytometry of urine and compared reflectance readings with quantitative determinations of urinary glucose and microalbumin.

Methods: We compared URISYS 2400 (Roche) quantitative reflectance data with data from the UF-100 (Sysmex) and biochemical data for 436 nonpathologic and pathologic urine samples.

Results: Reproducibility of the reflectance signal was good for high- and low-concentration urine pools for protein (0.8% and 0.9% and 1.5% and 2.2% within and between runs, respectively), leukocyte esterase (1.1% and 1.0%; 5.1% and 1.2%), hemoglobin (1.7% and 1.1%; 8.9% and 1.1%) and glucose (2.1% and 0.5%; 6.5% and 2.3%). Fair agreement was obtained between UF-100 and test strip reflectance data for erythrocytes and hemoglobin (r = −0.680) and leukocytes and leukocyte esterase (r = −0.688). Higher correlations were observed for biochemical and test strip data comparing protein and albumin (r = −0.825) and glucose data (r = −0.851). The lower limits of detection for erythrocytes and leukocytes were 8 × 106/L and 19 × 106/L, respectively. The protein test (n = 220) detected 86% (95% confidence interval, 78–92%) of samples with <30 mg/L albumin with a specificity of 84% (95% confidence interval, 76–91%).

Conclusions: In urine test strip analysis, quantitative hemoglobin and leukocyte esterase reflectance data are complementary with flow cytometric results and glucose and albumin results.

Anesthesia for kidney transplant surgery

Organ viability associated with renal transplantation is a product of the managing of the donor patient, the allograft, and the recipient patient. Short- and long-term outcome is influenced by perioperative fluid and drug treatment, and the function and viability of the transplanted kidney seem to be optimized if graft perfusion is maximized through mild hypervolemia. At the same time, careful balancing of intraoperative fluids is necessary against cardiovascular problems frequently encountered in patients with uremia. Close intraoperative monitoring, optimization of intravascular fluid volume status to maximize kidney perfusion, and prompt correction of electrolyte disturbances (especially potassium) are key to short- and long-term success of renal transplants.

Hypertension

The current JNC-VI criteria for diagnosis and classification of hypertension are discussed. The laboratory evaluation of both essential and secondary hypertension is examined, and recommendations are made in this regard. Finally, the complications and treatment of essential hypertension and the causes and management of resistant hypertension are discussed.

Heme oxygenase-1 is upregulated in the kidney of angiotensin II-induced hypertensive rats : possible role in renoprotection

In this study, we investigated the regulation and physiological role of heme oxygenase-1 (HO-1) in the kidney of rats with hypertension. Rats were continuously administered either angiotensin II (Ang II) or norepinephrine with an osmotic minipump for up to 7 days. Ang II infusion decreased the glomerular filtration rate (GFR) as determined through creatinine clearance (3.2+/-0.2 versus 1.2+/-0.2 mL/min with Ang II infusion, P<0.01) and increased proteinuria (9. 7+/-1.3 versus 28.1+/-7.2 mg/d with Ang II infusion, P<0.01). In contrast, norepinephrine did not alter these laboratory values. Ang II infusion significantly increased HO-1 expression in mRNA (442+/-98% of control at day 5, P<0.01) and protein levels (314+/-49% of control at day 5, P<0.01). Immunohistochemistry showed that in the kidney of normotensive rats, HO-1 was expressed mainly in the basal side in the renal tubules. After Ang II infusion, HO-1 staining was more extensively dispersed in the tubular epithelial cells. The intraperitoneal administration of zinc protoporphyrin, an HO inhibitor, to Ang II-infused rats further decreased GFR (0.8+/-0. 1 mL/min) and increased proteinuria (52.5+/-13.0 mg/d). In contrast, the administration of hemin, an HO inducer, ameliorated the Ang II-induced decrease in GFR (2.4+/-0.2 mL/min) and increase in proteinuria (9.3+/-4.5 mg/d). These data suggest that HO-1 upregulation in the kidney of Ang II-induced hypertensive rats may exert a renoprotective effect against Ang II-induced renal injury.

Cardiovascular disease and the kidney: an epidemiologic overview

Essential hypertension and congestive heart failure (CHF) are examples of cardiovascular disorders that may cause renal failure, although sometimes a primary kidney defect may lead to hypertension. Renal damage in malignant and severe hypertension is dramatic, extensive, and rapidly progressive, although nephrosclerotic damage, which develops slowly and appears late in hypertension, is a rare cause of morbidity because mild to moderate hypertension is now the most common form. However, the incidence of end-stage renal failure associated with hypertension is markedly increasing, perhaps because of underdiagnosis of renal damage in hypertension, insufficient lowering of blood pressure in clinical practice, or inability of antihypertensive drugs to lower blood pressure sufficiently to preserve the kidney, a goal that may need specific drugs that act, for example, on the renin-angiotensin system (RAS). Renal vasoconstriction and reduction of renal blood flow are early companions of cardiac insufficiency and may be involved in the development of sodium and water retention. Profound reduction of cardiac output and arterial hypotension in severe CHF may lead to acute renal failure. Chronic renal insufficiency is associated with elevated cardiovascular morbidity and mortality. Renal impairment is often caused by a disease process, such as diabetes mellitus, that involves both the cardiovascular system and the kidney. When the primary disease is renal, possible reasons for an association include renal-dependent increase in blood pressure, activation of the RAS, overproduction of other vasoactive substances of renal origin, and electrolyte imbalances leading to fatal arrhythmias.

Angiotensin converting enzyme gene I/D polymorphism in essential hypertension and nephroangiosclerosis

An insertion/deletion (I/D) polymorphism of the angiotensin converting enzyme (ACE) gene significantly influences circulating ACE levels and plays a role in the development of target organ damage, that is, left ventricular hypertrophy in essential hypertension (EH), and microalbuminuria in diabetes mellitus. We have examined the role of the I/D polymorphism in essential hypertensive patients with renal involvement. The study was divided in two independent protocols. In protocol 1, we retrospectively analyzed the ACE genotypes in 37 essential hypertensive patients with a clinical and histopathological diagnosis of nephroangiosclerosis. In protocol 2, ACE genotypes as well as microalbuminuria and renal hemodynamic parameters were investigated in 75 patients with EH with normal renal function and a strong family history of hypertension. As control group, 75 healthy subjects with BP < 130/85 mm Hg and no family history of cardiovascular diseases were studied. The ACE variants were determined by PCR and the genotypes were classified as DD, DI and II. In protocol 1, patients with nephroangiosclerosis displayed a significant difference in the genotype distribution (57% DD, 27% DI, 16% II) when compared to the control population (25% DD, 64% DI, 11% II; P < 0.001). There was no significant difference in genotype distribution between hypertensive patients with normal renal function (protocol 2; 33% DD, 59% DI, 8% II) and the control group. There were no differences in age, blood pressure, microalbuminuria and duration of the disease among the three genotypes in the EH group from protocol 2. Taken together, these findings suggest that the DD genotype of ACE is associated with histopathologic-proven kidney involvement in patients with EH and that this polymorphism could be a potential genetic marker in hypertensives at risk of renal complications.

Arthus C. Corcoran Memorial Lecture. Influence of nitric oxide and angiotensin II on renal involvement in hypertension

Remarkable advances have been made with prolonged antihypertensive therapy in reversing cardiovascular morbidity and mortality. Deaths from stroke have been reduced by 70% and from coronary heart disease by 35%. In contrast, endstage renal disease resulting from hypertension continues to increase. The explanations for this seeming paradox remain unresolved even though experimental models have demonstrated that certain antihypertensive agents may have beneficial renal and intrarenal hemodynamic effects; but reversal of the intrarenal pathological lesions have not been shown to improve. This discussion summarizes recent studies from our laboratory in aged (73- and 85-week-old) spontaneously hypertensive rats (SHR) with naturally occurring end-stage renal disease and in a model of aged SHR employing nitric oxide inhibition in younger, adult (20-week-old) SHR. Our findings demonstrated that the systemic and whole renal hemodynamics, intrarenal glomerular dynamics, proteinuria, and renal pathological lesions can be prevented or reversed with angiotensin-converting enzyme inhibition therapy but not with hydrochlorothiazide (at similar levels of arterial pressure reduction). The implications and possible mechanisms involved in the development of both naturally occurring and nitric oxide-exacerbated SHR are multifactorial, involving the endothelial nitric oxide system and its interaction with angiotensin II (and possibly bradykinin) among other factors. Moreover, these pathophysiological cellular mechanisms may be shared by the aging process as well as in naturally occurring spontaneous hypertension in the rat and, perhaps, in humans with essential hypertension. Thus, antihypertensive therapy seems to be specific in its ability to prevent and even reverse the pathophysiological derangements of renal involvement in hypertension. Thus, prevention and reversal of end-stage renal disease do not seem to require greater reduction of arterial pressure than with other target-organ involvement. However, they do require specific inhibition of the arteriolar and glomerular lesions produced by the disease.