Glomerular capillary pressure and hypertension

Questioning the renoprotective role of L-type calcium channel blockers in chronic kidney disease using physiological modeling

Chronic kidney disease (CKD) is characterized by the progressive functional loss of nephrons and hypertension (HTN). Some antihypertensive regimens attenuate the progression of CKD (blockers of the renin-angiotensin system). Although studies have suggested that calcium channel blocker (CCB) therapy mitigates the decline in renal function in humans with essential HTN, there are few long-term clinical studies that have determined the impact of CCBs in patients with hypertensive CKD. Dihydropyridine (DHP) or L-type CCBs preferentially vasodilate the afferent arteriole and have been associated with glomerular HTN and increases in proteinuria in animal models with low renal function. Small clinical studies in vulnerable populations with renal disease such as African Americans, children, and diabetics have also suggested that DHP CCBs exacerbate glomerular injury, which questions the renoprotective effect of this class of antihypertensive drug. We used an established integrative mathematical model of human physiology, HumMod, to test the hypothesis that DHP CCB therapy exacerbates pressure-induced glomerular injury in hypertensive CKD. Over a simulation of 3 yr, CCB therapy reduced mean blood pressure by 14-16 mmHg in HTN both with and without CKD. Both impaired tubuloglomerular feedback and low baseline renal function exacerbated glomerular pressure, glomerulosclerosis, and the decline in renal function during L-type CCB treatment. However, simulating CCB therapy that inhibited both L- and T-type calcium channels increased efferent arteriolar vasodilation and alleviated glomerular damage. These simulations support the evidence that DHP (L-type) CCBs potentiate glomerular HTN during CKD and suggest that T/L-type CCBs are valuable in proteinuric renal disease treatment.NEW & NOTEWORTHY Our physiological model replicates clinical trial results and provides unique insights into possible mechanisms that play a role in glomerular injury and hypertensive kidney disease progression during chronic CCB therapy. Specifically, these simulations predict the temporal changes in renal function with CCB treatment and demonstrate important roles for tubuloglomerular feedback and efferent arteriolar conductance in the control of chronic kidney disease progression.

Estimation of the relationship between the polymorphisms of selected genes: ACE, AGTR1, TGFβ1 and GNB3 with the occurrence of primary vesicoureteral reflux

PURPOSE

Etiopathogenesis of VUR is composite and not fully understood. Many data indicate the importance of genetic predisposition. The aim of this study was to establish the relationship of selected polymorphisms: 14094 polymorphism of the ACE, polymorphism rs1800469 of TGFβ-1, rs5443 gene polymorphism of the GNB3 and receptor gene polymorphism rs5186 type 1 AGTR1 with the occurrence of the primary vesicoureteral reflux.

MATERIAL

The study included 190 children: 90 with the primary VUR confirmed with the voiding cystourethrogram and excluded secondary VUR and a control group of 100 children without a history of the diseases of the genitourinary tract.

METHODS

The study was planned in the scheme: "tested case versus control." Genomic DNA was isolated from the leukocytes of peripheral blood samples. The results were statistically analyzed in the Statistica 10 using χ ² test and analysis of the variance Anova.

RESULTS

Any of the four studied polymorphisms showed no difference in the distribution of genotypes between patients with primary vesicoureteral reflux and the control group. In patients with VUR and TT genotype polymorphism rs5443 GNB3 gene, the glomerular filtration rate was significantly higher than in patients with genotype CC or CT.

CONCLUSIONS

(1) No relationship was found between the studied polymorphisms (14094 ACE gene, rs1800469 gene TGFβ1, GNB3 gene rs5443, rs5186 AGTR1 gene) and the occurrence of primary vesicoureteral reflux. (2) TT genotype polymorphism rs5443 GNB3 gene may be a protective factor for the improved renal function in patients with primary vesicoureteral reflux in patients with genotype CC or CT.

Renal resistance index and progression of renal disease

The progression of renal disease depends on various clinical parameters such as hypertension and proteinuria. We recently showed that an increased renal resistance index measured by duplex ultrasound is associated with a poor prognosis in patients with renal artery stenosis. We now prospectively tested the hypothesis that a high renal resistance index (greater-than-or-equal 80) predicts progression of renal disease in patients without renal artery stenosis. In 162 patients newly diagnosed with renal disease, the resistance index (1-[end diastolic velocity/maximum systolic velocity]*100) was measured in segmental arteries of both kidneys. Creatinine clearance was measured at baseline, at 3, 6, and 12 months, and then at yearly intervals thereafter (mean follow-up 3 +/- 1.4 years). The combined endpoint was a decrease of creatinine clearance by greater-than-or-equal 50%, end-stage renal disease with replacement therapy, or death. Twenty-five patients (15%) had a renal resistance index value greater-than-or-equal 80 at baseline. Nineteen (76%) had a decline in renal function; 16 (64%) progressed to dialysis, and 6 (24%) died. In comparison, in patients with renal resistance index values <80, 13 (9%) had a decline in renal function, only 7 (5%) became dialysis-dependent, and 2 (1%) died (P<0.001). In a multivariate regression analysis, only proteinuria and resistance index were independent predictors of declining renal function. A renal resistance index value of greater-than-or-equal to 80 reliably identifies patients at risk for progressive renal disease.

Long-term renal and cardiovascular effects of antihypertensive treatment regimens based upon isradipine, perindopril and thiazide

The aim of this study was to describe the renal function (renal hemodynamics, water and sodium handling) and its relation to cardiovascular structural changes in a population of essential hypertensive patients before and after antihypertensive treatment. Glomerular filtration rate and renal plasma flow were measured by a constant infusion technique. The reference substances used were [131I]iodohippurate (Hippuran) and [125I]iothalamate. The lithium clearance method was used for measuring renal water and sodium handling. Microalbuminuria was measured. A subcutaneous gluteal biopsy was taken and the media thickness to lumen diameter ratio of small resistance vessels was determined. Left ventricular mass index was determined by echocardiography. Thirty-seven patients with newly diagnosed or poorly controlled essential hypertension were randomized to treatment with regimens based upon either isradipine, perindopril or hydrochlorothiazide-amiloride. Atenolol and hydralazine were added as secondary and tertiary drugs, respectively, when needed for normalization of diastolic blood pressure. Investigations were performed before and after 9 months of normalization of blood pressure. Renal function in untreated hypertensive patients was characterized by increased renal vascular resistance, decreased renal blood flow, normal glomerular filtration fraction and normal serum creatinine. No association was found between peripheral resistance vessel structure in subcutaneous vessels and renal hemodynamic parameters. Patients with severe left ventricular hypertrophy (left ventricular mass >360 g) had lower glomerular filtration fraction, greater renal vascular resistance, lower renal blood flow and increased microalbuminuria in comparison with patients with less pronounced cardiac changes. After 1 year of treatment, which had a profound effect on heart and vessel structure, renal hemodynamics were unchanged in patients receiving antihypertensive treatment regimens based on the ACE inhibitor perindopril or the Ca-antagonist isradipine, whereas renal plasma flow was reduced, glomerular filtration rate preserved and filtration fraction significantly increased in those treated with a regimen based on diuretics. The serum creatinine concentration was decreased in the former group, whereas it was unchanged in the latter two. Significantly detrimental effect on uric acid homeostasis was only found in patients treated with a regimen based on diuretics.

Effects of cilazapril on renal haemodynamics and function in hypertensive patients: a randomised controlled study versus hydrochlorothiazide

In this study the efficacy and safety of short-term cilazapril administration on renal haemodynamics were evaluated in mild to moderate hypertensive subjects. Our final goal was to evaluate whether the reduction in blood pressure achieved by treatment was associated with maintained renal function. After a run-in period with placebo, 40 hypertensive subjects without renal or cardiac diseases were randomly allocated to a double-blind 4 week controlled trial with cilazapril 5 mg once a day (20 patients) or hydrochlorothiazide 25 mg once a day (20 patients). Renal haemodynamics measurements included effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) by radionuclide study using 131I-hippuran and 99mTc, according to the methods described by Schlegel and Gates, respectively. Effective renal blood flow [ERBF = ERPF/(1-Ht)], filtration fraction (FF = GFR/ERPF) and renal vascular resistance (RVR = MBP x 80/ERBF) were calculated. At the end of cilazapril and hydrochlorothiazide administration significant decreases (p < 0.001) in SBP, DBP and MBP vs baseline values were observed. In the cilazapril group a significant decrease (p < 0.001) in RVR and FF and a significant increase (p < 0.001) in ERPF and ERBF were also found. In the hydrochlorothiazide group a significant decrease (p < 0.001) in RVR was found. No important side effects were observed with either treatment. In conclusion our data indicate that both cilazapril and hydrochlorothiazide reduced blood pressure equally well but only cilazapril improved renal blood flow and reduced filtration fraction.

Are renal hemodynamics a key factor in the development and maintenance of arterial hypertension in humans?

The kidney plays a key role in the control of body fluids and blood pressure. Evidence has shown that impairment of renal function can lead to the development of arterial hypertension. The regulation of renal blood flow appears to be a key element in the pathophysiology of the hypertensive process, because multiple evidence suggests the existence of a functional enhancement of renal vascular tone in this disorder. The existence of renal vasoconstriction and of an inherited defect in the regulation of renal blood flow has been proposed in the prehypertensive stage. The mechanisms responsible for this alteration include a lack of modulation of the renal vasculature to angiotensin II, increased sympathetic activity, or suppressed renal dopaminergic activity. Established hypertension is characterized by elevated renal vascular resistance, decreased renal blood flow, sustained glomerular filtration rate, and increased filtration fraction. The increase in renal vascular resistance is initially due to elevations in renal vascular tone and is reversible, whereas later it becomes irreversible because of structural changes involved in nephrosclerosis. Antihypertensive drugs are able to decrease blood pressure and to prevent the development of further renal vascular damage independently of variable effects on renal hemodynamics.