Tissue-localized angiotensin II enhances cardiac and renal disorders in Tsukuba hypertensive mice

Constitutive activation of the renin-angiotensin system reduces visceral fat and improves glucose tolerance in mice

INTRODUCTION

The renin-angiotensin system (RAS), and particularly angiotensin II, is involved in the control of energy balance, glucose homeostasis and kidney functions. The integrated impact of the RAS on glucose homeostasis is still a matter of debate.

MATERIALS AND METHODS

We used a model of constitutive RAS activation in double transgenic mice (dTGM) carrying both human angiotensinogen and human renin genes. We evaluated energy balance, measured renal functions, performed glucose and insulin tolerance tests, and used ramipril to inhibit the angiotensin-converting enzyme.

RESULTS

dTGM had a lower physical activity and an increased food intake without change in body weight. Renal impairment was characterized by low-grade albuminuria. High urinary output secondary to polydipsia was associated with proximal tubule dysfunction. Compared to controls, dTGM had a lower hyperglycemia induced by an intraperitoneal glucose administration. This decrease was not due to changes in insulin sensitivity and/or secretion. dTGM had an increased creatinine production and a lower epididymal fat mass. Acute inhibition of angiotensin-converting enzyme with ramipril did not suppress this improved glucose tolerance profile.

CONCLUSION

Chronic RAS activation is not sufficient to cause insulin resistance in mice. Moreover, adaptation to constitutive RAS activation in mice results in a better glucose tolerance.

Sympathetic regulation of the renal functions in rats reciprocally congenic for chromosome 1 blood pressure quantitative trait locus

The role of the chromosome 1 blood pressure quantitative trait locus (QTL) on the sympathorenal interaction was studied using congenic strains. The two reciprocal congenic strains, WKYpch1.0 and SHRSPwch1.0, were respectively constructed by introgressing the stroke-prone spontaneously hypertensive rat (SHRSP)-derived fragment for the QTL into a Wistar-Kyoto rat (WKY) and vice versa. The role of the sympathetic nervous system in the kidney was evaluated by comparing the renal functions between denervated and sham-operated kidneys under anesthesia. The denervation was performed by stripping the adventitia off and applying 10% phenol to the blood vessels at the left renal hilus. Polyfructosan was continuously injected intravenously to determine the renal plasma flow and the glomerular filtration rate. A reciprocal and significant alteration in the renal norepinephrine (NE) content was observed between WKY and WKYpch1.0 and between SHRSP and SHRSPwch1.0. Concomitantly, the renal vascular resistance differed significantly between the congenic and the background parental strains. By contrast, no significant difference was observed in the fractional excretion of sodium, an index of the tubular function. While the denervation elicited a significant decrease of the renal NE content in all of the four strains studied, the significant effects of the denervation on the renal functions were observed only in SHRSP and WKYpch1.0, both of which harbored the SHRSP-derived QTL fragment. These results indicated that the chromosome 1 blood pressure QTL modulated the renal functions through the sympathetic nerve activity in the kidney.

Absence of peroxisome proliferator-activated receptor-alpha abolishes hypertension and attenuates atherosclerosis in the Tsukuba hypertensive mouse

Peroxisome proliferator-activated receptor-alpha is widely distributed in the vasculature where it is believed to exert pleiotropic antiatherogenic effects. Its role in the regulation of blood pressure is still unresolved; however, some evidence suggests that it may affect the renin-angiotensin system. We investigated its role in angiotensin II-induced hypertension in the Tsukuba hypertensive mouse (THM). This is a model of hypertension and atherosclerosis because of high angiotensin II and aldosterone levels as a result of the transgenic expression of the entire human renin-angiotensin system. Making the THM animals deficient in Peroxisome proliferator-activated receptor-alpha (THM/PPARKO) totally abolished hypertension and myocardial hypertrophy. This was accompanied by a reduction in plasma human active renin in THM/PPARKO mice compared with THM animals from 3525+/-128 mU/L to 1910+/-750 mU/L (P<0.05) and by a normalization of serum aldosterone (1.6+/-0.29 nmol/L versus 3.4+/-0.69 nmol/L; P=0.003). In the THM/PPARKO mice, the extent of atherosclerosis at the aortic sinus after a 12-week period on an atherogenic diet was decreased by >80%. In addition, the spontaneous formation of foam cells from peritoneal macrophages, a blood pressure-independent event, was reduced by 92% in the THM/PPARKO mice, suggesting protection from the usual oxidative stress in these animals, possibly because of lower prevailing angiotensin II levels. Finally, chronic fenofibrate treatment further elevated blood pressure in THM animals but not in THM/PPARKO animals. Taken together, these data indicate that peroxisome proliferator-activated receptor-alpha may regulate the renin-angiotensin system. They raise the possibility that its activation may aggravate hypertension and hasten atherosclerosis in the context of an activated renin-angiotensin system.

Blockade of angiotensin AT1a receptor signaling reduces tumor growth, angiogenesis, and metastasis

It was reported that angiotensin II stimulates angiogenesis in vivo, and angiotensin-converting enzyme (ACE) inhibitors inhibit angiogenesis. We found that an AT1-receptor (AT1-R) antagonist, TCV-116, inhibited tumor growth, tumor-associated angiogenesis, and metastasis in a murine model. Tumor growth of Sarcoma 180 (S-180) cells and of fibrosarcoma (NFSA) cells was strongly inhibited by administration of TCV-116 in the diet at a dose of approximately 100 mg/kg/day. This reduction was accompanied with a marked reduction in tumor-associated angiogenesis. The same treatment also reduced the lung metastasis of intravenously injected Lewis lung carcinoma cells. These effects of TCV-116 were equivalent to those of the ACE inhibitor, lisinopril. In S-180 and NFSA tumor tissues, ACE and AT1a receptor (AT1a-R) mRNAs were expressed when assessed with RT-PCR. AT1b receptor and AT2 receptor, however, were not detected. Immunoreactive AT1-R was detected mainly on the neovascularized vascular endothelial cells in which expression was reduced by TCV-116 and lisinopril. These results suggested that TCV-116 inhibits the angiogenesis, growth, and metastasis of tumors highly dependent on AT1a-R blockade. Blockade of AT1a-R signaling may therefore become an effective novel strategy for tumor chemoprevention.

Obesity is associated with tissue-specific activation of renal angiotensin-converting enzyme in vivo: evidence for a regulatory role of endothelin

In the C57BL/6J mice model, we investigated whether obesity affects the function or expression of components of the tissue renin-angiotensin system and whether endothelin (ET)-1 contributes to these changes. ACE activity (nmol. L His-Leu. mg protein(-1)) was measured in lung, kidney, and liver in control (receiving standard chow) and obese animals treated for 30 weeks with a high-fat, low cholesterol diet alone or in combination with LU135252, an orally active ET(A) receptor antagonist. ACE mRNA expression was measured in the kidney, and the effects of LU135252 on purified human ACE were determined. Aortic and renal tissue ET-1 protein content was measured, and the vascular contractility to angiotensin II was assessed. Obesity was associated with a tissue-specific increase in ACE activity in the kidney (55+/-4 versus 33+/-3 nmol/L) but not in the lung (34+/-2 versus 32+/-2 nmol/L). Long-term LU135252 treatment completely prevented this activation (13.3+/-0.3 versus 55+/-4 nmol/L, P<0.05) independent of ACE mRNA expression, body weight, or renal ET-1 protein but did not affect pulmonary or hepatic ACE activity. Obesity potentiated contractions in response to angiotensin II in the aorta (from 6+/-2% to 33+/-5% KCl) but not in the carotid artery (4+/-1% to 3.6+/-1% KCl), an effect that was completely prevented with LU135252 treatment (6+/-0.4% versus 33+/-5% KCl). No effect of LU135252 on purified ACE was observed. Thus, obesity is associated with the activation of renal ACE in vivo independent of its mRNA expression and enhanced vascular contractility to angiotensin II. These effects are regulated by ET in an organ-specific manner, providing novel mechanisms by which ET antagonists may exert organ protection.

Renin-angiotensin system stimulates cardiac and renal disorders in Tsukuba hypertensive mice

1. The role of the renin-angiotensin system (RAS) in cardiac hypertrophy and nephropathy was examined in Tsukuba hypertensive mice (THM) carrying both human renin and angiotensinogen genes. 2. Tsukuba hypertensive mice were treated with 20 mg/kg per day lisinopril, 30 mg/kg per day hydralazine or nothing. Administration of drugs was performed for 6 months from 12 weeks of age; water intake and urine volume were measured and urine albumin excretion, heart to bodyweight ratio and the glomerulosclerosis index were examined. 3. Systolic blood pressure was significantly lowered by treatment with lisinopril and hydralazine. Urine volume, water intake and urinary albumin excretion were significantly decreased by lisinopril. When hydralazine was administered to THM, these parameters were transiently decreased, but eventually reached almost the same levels as those in the untreated group. The heart to bodyweight ratio was significantly decreased by lisinopril, but not by hydralazine. The glomerulosclerosis index was significantly lowered by lisinopril, but the index in the hydralazine group was not significantly different from that in the untreated group. 4. These results suggest that the RAS plays an important role in the progression of cardiac hypertrophy in THM. In addition, the RAS may also play an important role in the progression of nephropathy; however, this may also be partially regulated by elevated blood pressure in the short term.