Differential evolution of blood pressure and renal lesions after RAS blockade in Lyon hypertensive rats

Renal and metabolic disorders depend on the renin-angiotensin system in Lyon hypertensive rats associated with diabetes

BACKGROUND

In Lyon genetically hypertensive (LH) rats with diabetes, the effects of angiotensin converting enzyme (ACE) inhibition with perindopril on the prevention of dyslipidemia and proteinuria were evaluated by comparison with a nonspecific antihypertensive treatment.

METHODS

Diabetes was induced in 2-day-old male LH rats by intraperitoneal injection of streptozotocin (75 mg/kg). Glucose tolerance (glucose 2 g/kg by gavage), blood pressure (BP), plasma lipids, and urinary protein excretion were studied in: (i) untreated diabetic LH rats, (ii) diabetic LH rats treated from 8 to 16 weeks of age with oral perindopril at a low dose (0.01 mg/kg/day), (iii) similar rats treated with oral perindopril for the same duration at a high dose (1 mg/kg/day), and (iv) similar rats treated for the same duration with a triple therapy regimen consisting of hydralazine, hydrochlorothiazide, and reserpine (75, 15, and 0.75 mg/kg/day, respectively).

RESULTS

The neonatal administration of streptozotocin in LH rats increased nonfasting glycemia and induced a marked glucose intolerance which was accompanied by further increases in BP, plasma cholesterol, and urinary protein excretion. None of the treatments was able to modify glucose tolerance in diabetic LH rats. The low dose of perindopril was ineffective in the prevention of hypertension, dyslipidemia, and proteinuria in diabetic LH rats, while the high dose of perindopril normalized the BP, reduced the plasma lipids, and lowered the proteinuria. However, in spite of significant reduction in BP, the triple therapy failed to improve dyslipidemia and proteinuria; on the contrary, the therapy worsened these two conditions.

CONCLUSIONS

In diabetic LH rats, only ACE inhibition is of benefit to the kidney and lipidemia, thereby demonstrating that antihypertensive regimens may differ in their capacity to protect the target organs and lipid metabolism in a diabetic setting.

Neonatal streptozotocin-induced glucose intolerance: different consequences in Lyon normotensive and hypertensive rats

BACKGROUND

Lyon hypertensive (LH) rats exhibit a mild hypertension associated with excessive body weight, spontaneous hyperlipidemia, elevated insulin/glucose ratio and exaggerated urinary protein excretion.

AIMS

We aimed to develop, in LH rats and their normotensive control (LL) rats, a moderate non-insulin-dependent diabetic model to study the different consequences on metabolic and renal functions.

METHODS

Non-insulin-dependent diabetes was induced by intraperitoneal injection of streptozotocin (STZ) at 2 days of age (50, 75 or 100 mg/kg for LH and 75, 100 or 125 mg/kg for LL rats). The evolution, with age, of glycemia, glucose tolerance (glucose 2 g/kg by gavage), blood pressure, plasma lipids and urinary protein and albumin excretions were studied in control and STZ-treated LH and LL rats.

RESULTS

Although fasting glycemia was not significantly changed, the neonatal administration of STZ increased non-fasting glycemia and induced a marked glucose intolerance that were comparable between LH rats receiving 75 mg/kg and LL rats receiving 100 mg/kg of STZ. Interestingly, in treated LH rats only, the impaired glucose tolerance was accompanied by further metabolic and renal dysfunctions characterized by additional increases in plasma cholesterol (+28%) and triglycerides (+105%) and accelerated progression of proteinuria (+36%) and albuminuria (+48%).

CONCLUSIONS

These observations indicate that susceptibility to diabetic metabolic disorders and renal diseases may be linked to the genetic predisposition to hypertension. This new model offers a reasonable reflection of the human situation, where hypertension and non-insulin-dependent diabetes often coincide, suitable for molecular, biochemical and pharmacological investigations.

Regulation of sodium-glucose cotransporter SGLT1 in the intestine of hypertensive rats

Experimental models of hypertension, such as spontaneously hypertensive rats (SHR), show alterations in cellular sodium transport that affects Na+-coupled cotransport processes and has been involved in the pathogenesis of this disease. The objective of the present study was to analyze the kinetic properties of the sodium-dependent glucose transport in the jejunum and ileum of SHR and its genetic control, Wistar-Kyoto (WKY) rats, as well as the regulation of the transporter, SGLT1. In hypertensive rats, the increased systolic blood pressure was accompanied by an enhancement of serum aldosterone levels compared with WKY rats, but no alterations were found in their body weight or serum glucose/insulin levels. The values for d-glucose maximal rate of transport (Vmax) were 42 and 60% lower, respectively, in the jejunum and ileum of SHR than those from WKY rats. On the other hand, the values for the Michaelis constant (Km) were similar in both animal groups, as was the diffusive component of transport (Kd). Immunoblotting and Northern blot analysis revealed the existence of a lower abundance of SGLT1 protein and mRNA in SHR. Moreover, hypertensive rats showed a decrease in the molecular mass of SGLT1 that could not be explained in terms of different glycosylation and/or phosphorylation levels or an alternative splicing in the expression of the protein. These findings demonstrate that SGLT1 is regulated at a transcriptional level in the intestine of hypertensive rats, and suggest that this transporter might participate in the dysregulation of sodium transport observed in hypertension.

Development of hypertension and kidney hypertrophy in transgenic mice overexpressing ARAP1 gene in the kidney

Angiotensin II regulates blood pressure via activation of the type 1 receptor. We previously identified a novel angiotensin II type 1 receptor-associated protein and demonstrated that it promotes receptor recycling to the plasma membrane. To delineate the pathophysiological function of the ARAP1 in the kidneys, we generated transgenic mice that overexpress rat ARAP1 cDNA specifically in proximal tubules and tested the hypothesis that proximal tubule-specific overexpression of ARAP1 causes hypertension. Two lines of male transgenic mice, 650 and 670, displayed kidney-specific transgene expression. Systolic blood pressure was significantly elevated by &20 to 25 mm Hg in these lines of mice at 20 weeks of age compared with their nontransgenic litter mates. Urine volume, but not water intake, was significantly decreased in both lines compared with nontransgenic controls. The kidney/body weight ratio was significantly increased in both lines compared with their nontransgenic litter mates at 12 and 20 weeks of age. In contrast, no difference was observed in the ratio of brain, spleen, heart, and testis to body weight between male transgenic and nontransgenic animals. Inhibitions of the renin-angiotensin system completely normalized the systolic blood pressure of transgenic mice. Moreover, low salt intake prevented the development of hypertension, whereas high salt intake exacerbated the increase in blood pressure in transgenic mice. Therefore, our data show that proximal tubule-specific overexpression of ARAP1 leads to hypertension, suggesting that renal ARAP1 plays an important role in the regulation of blood pressure and renal function via activation of the intrarenal renin-angiotensin system.

RAS blockade decreases blood pressure and proteinuria in transgenic mice overexpressing rat angiotensinogen gene in the kidney

Angiotensinogen (ANG) is the sole substrate of the renin-angiotensin system (RAS). Clinical studies have shown that RAS activation may lead to hypertension, a major cardiovascular and renal risk factor. To delineate the underlying mechanisms of hypertension-induced nephropathy, we generated transgenic mice that overexpress rat ANG (rANG) in the kidney to establish whether intrarenal RAS activation alone can evoke hypertension and kidney damage and whether RAS blockade can reverse these effects. Transgenic mice overexpressing renal rANG were generated by employing the kidney-specific, androgen-regulated protein promoter linked to rANG cDNA. This promoter targets rANG cDNA to renal proximal tubules and responds to androgen stimulation. Transgenic mice displayed kidney-specific expression of rANG, significantly increased blood pressure (BP) and albuminuria in comparison to non-transgenic littermates. Administration of losartan (an angiotensin II (type 1)-receptor antagonist) or perindopril (an angiotensin-converting enzyme inhibitor) reversed these abnormalities in transgenic animals. Renal injury was evident on examination of the kidneys in transgenic mice, and attenuated by losartan and perindopril treatment. We conclude that the overproduction of ANG alone in the kidney induces an increase in systemic BP, proteinuria, and renal injury. RAS blockers prevent these abnormalities. These data support the role of the intrarenal RAS in the development of hypertension and renal injury.

Regulation of D-fructose transporter GLUT5 in the ileum of spontaneously hypertensive rats

Abnormalities in carbohydrate metabolism and the insulin resistance status have been associated with hypertension. We have previously described alterations in the sodium-coupled sugar absorption in an experimental model of hypertension; in the present work, we studied the regulation of the sodium-independent, GLUT5-facilitated D-fructose intestinal transport in this pathology. Spontaneously hypertensive rats (SHR) and their normotensive, genetic control Wistar-Kyoto (WKY) rats, were used. Kinetic studies, carried out in ileal brush-border membrane vesicles (BBMVs), revealed a significant reduction (P < 0.05) in the maximal rate of transport (Vmax) for D-fructose in SHR, which, on the other hand, showed unaltered values for the Michaelis constant (Km) and the diffusion constant (Kd). Immunoblotting analysis revealed the existence of lower (P< 0.05) levels of GLUT5 in apical membranes from SHR, this reduction being similar to that of Vmax. Similarly, Northern blot studies on the abundance of GLUT5 mRNA from ileal enterocytes showed a decrease (P< 0.05) in hypertensive rats, following the same pattern mentioned above. Therefore, the impaired D-fructose intestinal absorption is another feature of SHR, and this decrease in D-fructose uptake correlates with a reduction in the abundance of the apical GLUT5 transporter, which is controlled at a transcriptional level.

Reduced cardiac expression of plasminogen activator inhibitor 1 and transforming growth factor beta1 in obese Zucker rats by perindopril

OBJECTIVE

To determine whether angiotensin converting enzyme inhibition by perindopril can reduce cardiac transforming growth factor beta1 (TGFbeta1) and plasminogen activator inhibitor 1 (PAI-1) and therefore control collagen accumulation in an animal model with the metabolic syndrome such as the obese Zucker rat (OZR).

ANIMALS

Male OZR (group 1, n = 10); OZR treated with perindopril (group 2, n = 10); and lean Zucker rats (group 3, n = 10).

METHODS

During six months, group 2 received 3 mg/kg/day of perindopril orally and group 1 and group 3 were given a vehicle. Hearts were processed for pathology studies including immunohistochemical analysis with antibodies to PAI-1, TGFbeta1, collagen type I, and collagen type III.

RESULTS

Group 2 had lower blood pressure (126.7 (2) v 148.6 (2.7) mm Hg, p < 0.01) than untreated OZR and had decreased cardiac PAI-1 (3.6 (0.4) v 13.5 (1.7)% of positive area/field, p < 0.01), TGFbeta1 in myocytes (0.13 (0.1) v 9.14 (4.7)%/area, p < 0.01) and in interstitium (19.8 (6.8) v 178.9 (27.4) positive cells/area, p < 0.01), collagen I (3 (0.8) v 13.3 (1)%/area, p < 0.01), collagen III (5 (0.6) v 9.5 (0.9)%/area, p < 0.01), and collagen I to collagen III ratio (0.59 (0.13) v 1.40 (0.15) p < 0.01) compared with untreated OZR.

CONCLUSION

These results suggest that perindopril reduces cardiac PAI-1 and TGFbeta1 and ameliorates cardiac fibrosis in a rat model with multiple cardiovascular risk factors.

Estrogen or the AT1 antagonist olmesartan reverses the development of profound hypertension in the congenic mRen2. Lewis rat

The influence of estrogen on the regulation of cardiovascular function remains a controversial and complex area of investigation. We assessed the effects of estrogen depletion in the congenic mRen(2). Lewis rat, established from the back-cross of the original (mRen2)-27 transgenic onto the Lewis inbred strain. Ovariectomy of heterozygous mRen(2). Lewis at 4 to 5 weeks resulted in a progressive increase in blood pressure compared with the sham surgery congenics at weeks 6 to 11. At 11 weeks, the ovariectomized mRen(2). Lewis (OVX) systolic blood pressure averaged 195+/-3.7 mm Hg versus 141+/-4.0 mm Hg for sham. Plasma Angiotensin (Ang) II, serum ACE activity, plasma renin concentration, as well as urinary excretion of Ang II, 8-isoprostane F2alpha, and endothelin-1 were elevated; however, renal mRNA levels of eNOS were suppressed after ovariectomy. Estrogen replacement reduced blood pressure below both the sham and OVX by 11 weeks (125+/-2.9 mm Hg, n=7, P<0.01 versus OVX and sham). Moreover, the AT1 receptor antagonist olmesartan (CS866; week 12 to 16) essentially normalized blood pressure to 113+/-5.4 mm Hg (n=6, P<0.01 versus OVX and sham). The attenuation of the hypertension was still evident 7 weeks after complete withdrawal of treatment (124+/-4.1 mm Hg at week 23). In summary, the OVX mRen.2. Lewis exhibited a rapid and sustained increase in blood pressure. Estrogen or olmesartan lowered pressure by a similar extent. We conclude that the ovary exerts considerable influence on the regulation of the blood pressure in the mRen2. Lewis strain, possibly by limiting activation of the renin-angiotensin system.