Increased vascular angiotensin formation in female rats harboring the mouse Ren-2 gene

Vitamin D depletion aggravates hypertension and target-organ damage

Background

We tested the controversial hypothesis that vitamin D depletion aggravates hypertension and target‐organ damage by influencing renin.

Methods and Results

Four‐week‐old double‐transgenic rats (dTGR) with excess angiotensin (Ang) II production due to overexpression of the human renin (hREN) and angiotensinogen (hAGT) genes received vitamin D‐depleted (n=18) or standard chow (n=15) for 3 weeks. The depleted group had very low serum 25‐hydroxyvitamin D levels (mean±SEM; 3.8±0.29 versus 40.6±1.19 nmol/L) and had higher mean systolic BP at week 5 (158±3.5 versus 134.6±3.7 mm Hg, P<0.001), week 6 (176.6±3.3 versus 162.3±3.8 mm Hg, P<0.01), and week 7 (171.6±5.1 versus 155.9±4.3 mm Hg, P<0.05). Vitamin D depletion led to increased relative heart weights and increased serum creatinine concentrations. Furthermore, the mRNAs of natriuretic peptides, neutrophil gelatinase‐associated lipocalin, hREN, and rRen were increased by vitamin D depletion. Regulatory T cells in the spleen and in the circulation were not affected. Ang metabolites, including Ang II and the counter‐regulatory breakdown product Ang 1 to 7, were significantly up‐regulated in the vitamin D‐depleted groups, while ACE‐1 and ACE‐2 activities were not affected.

Conclusions

Short‐term severe vitamin D depletion aggravated hypertension and target‐organ damage in dTGR. Our data suggest that even short‐term severe vitamin D deficiency may directly promote hypertension and impacts on renin‐angiotensin system components that could contribute to target‐organ damage. The findings add to the evidence that vitamin D deficiency could also affect human hypertension.

Oxidative stress contributes to pulmonary hypertension in the transgenic (mRen2)27 rat

The transgenic (mRen2)27 (Ren2) rat overexpresses mouse renin in extrarenal tissues, causing increased local synthesis of ANG II, oxidative stress, and hypertension. However, little is known about the role of oxidative stress induced by the tissue renin-angiotensin system (RAS) as a contributing factor in pulmonary hypertension (PH). Using male Ren2 rats, we test the hypothesis that lung tissue RAS overexpression and resultant oxidative stress contribute to PH and pulmonary vascular remodeling. Mean arterial pressure (MAP), right ventricular systolic pressure (RVSP), and wall thickness of small pulmonary arteries (PA), as well as intrapulmonary NADPH oxidase activity and subunit protein expression and reactive oxygen species (ROS), were compared in age-matched Ren2 and Sprague-Dawley (SD) rats pretreated with the SOD/catalase mimetic tempol for 21 days. In placebo-treated Ren2 rats, MAP and RVSP, as well as intrapulmonary NADPH oxidase activity and subunits (Nox2, p22phox, and Rac-1) and ROS, were elevated compared with placebo-treated SD rats (P < 0.05). Tempol decreased RVSP (P < 0.05), but not MAP, in Ren2 rats. Tempol also reduced intrapulmonary NADPH oxidase activity, Nox2, p22phox, and Rac-1 protein expression, and ROS in Ren2 rats (P < 0.05). Compared with SD rats, the cross-sectional surface area of small PA was 38% greater (P < 0.001) and luminal surface area was 54% less (P < 0.001) in Ren2 rats. Wall surface area was reduced and luminal area was increased in tempol-treated SD and Ren2 rats compared with untreated controls (P < 0.05). Collectively, the results of this investigation support a seminal role for enhanced tissue RAS/oxidative stress as factors in development of PH and pulmonary vascular remodeling.

Renal injury in streptozotocin-diabetic Ren2-transgenic rats is mainly dependent on hypertension, not on diabetes

Induction of streptozotocin (STZ) diabetes in hypertensive rats transgenic for the mouse ren-2 gene (TGR) has been described as a model of progressive diabetic nephropathy. We investigated the long-term course of STZ diabetes in TGR and appropriate Sprague-Dawley control rats (SD) and tested the role of angiotensin-dependent hypertension by treating rats with the angiotensin II type 1 receptor blocker losartan (1 mg·kg−1·day−1) via osmotic minipumps. Five weeks after STZ injection, diabetes developed in TGR and SD. Urinary albumin excretion was increased by diabetes and, to a much higher degree, by hypertension. The effects of hypertension and diabetes were not additive, and only the effects of hypertension were ameliorated by losartan. A similar pattern was observed for cell proliferation and macrophage infiltration in the kidney. In contrast, the effects of hypertension and diabetes on glomerular collagen IV accumulation were additive 5 wk after STZ injection. In a long-term study for 20 wk after STZ, survival was better in STZ-treated TGR than in normoglycemic TGR, whereas all SD survived. Impaired creatinine clearance and increased macrophage infiltration as well as glomerular and interstitial matrix deposition were prominent in TGR compared with SD, regardless of the presence or absence of diabetes. In conclusion, STZ diabetes in TGR may be useful to study glomerular and interstitial matrix deposition early in the course of diabetes. However, the long-term course of this animal model resembles severe hypertensive nephrosclerosis, rather than progressive diabetic nephropathy.

Effects of Dietary Salt Load and Salt Depletion on the Course of Hypertension and Angiotensin II Levels in Male and Female Heterozygous Ren-2 Transgenic Rats

BACKGROUND

In the present study we evaluated plasma and kidney angiotensin II (ANG II) levels in female and male Ren-2 transgenic rats (TGR) in comparison to age-matched female and male normotensive Hannover Sprague-Dawley rats.

METHODS

The rats were maintained on a normal sodium (NS) diet (0.6% NaCl) or fed a high sodium (HS) diet (2% NaCl) for 4 days or were sodium depleted by administration of 40 mg furosemide per liter drinking water overnight followed by 3 days of low sodium diet (0.01% NaCl) (LS + F). ANG II levels were determined by radioimmunoassay.

RESULTS

Female TGR at the age of 38 days were already hypertensive and had developed cardiac hypertrophy, whereas male TGR at this age still exhibited a normotensive phenotype. HS diet increased the blood pressure (BP) but did not alter the ANG II levels in TGR at any age. LS + F decreased the BP without significant change in ANG II concentrations in TGR. Female TGR responded to salt loading and salt depletion by more pronounced changes in BP than male TGR.

CONCLUSIONS

Female TGR develop hypertension more rapidly and the salt-sensitive component of hypertension is more pronounced in female than in male TGR.

Angiotensin II formation in the kidney and nephrosclerosis in Ren-2 hypertensive rats

BACKGROUND

Ren-2 transgenic hypertensive rats develop malignant hypertensive nephrosclerosis despite low to normal plasma angiotensin II and suppressed renal renin. We tested the hypothesis that local angiotensin II formation occurs at sites of renal vascular and interstitial injury in this model.

METHODS

Heterozygous Ren-2 transgenic rats were compared with normotensive Sprague-Dawley-Hannover control rats and Ren-2 transgenic rats treated with a very low dose of an angiotensin II type 1 (AT1) receptor antagonist, 1 mg/kg/day losartan, for 4 weeks. Blood pressure measurements, quantifications of urinary albumin, plasma and tissue angiotensin II as well as immunohistochemical analyses were performed.

RESULTS

Systolic blood pressure was not affected by losartan during the study but intra-arterial recordings revealed a decrease of blood pressure. Losartan reduced albumin excretion, cell proliferation, macrophage influx, collagen I and collagen IV deposition. Plasma angiotensin II was decreased, while kidney tissue angiotensin II content was increased in Ren-2 transgenic rats compared with control rats. In Ren-2 transgenic rats, juxtaglomerular renin and angiotensin II staining were reduced, but there was a marked angiotensin II staining at foci of tubulo-interstitial fibrosis and at proliferative malignant vascular lesions.

CONCLUSION

We conclude that local angiotensin II formation is increased in proliferative or fibrotic kidney lesions in the Ren-2 transgenic rat. Local angiotensin II formation may help to explain why the AT1 receptor antagonist prevents or ameliorates this transgenic model of malignant nephrosclerosis despite low to normal plasma angiotensin II and suppressed renal renin.

Effects of changes in sodium balance on plasma and kidney angiotensin II levels in anesthetized and conscious Ren-2 transgenic rats

OBJECTIVE

Since there is as yet no general agreement regarding the role of plasma and kidney angiotensin II (ANG II) in the development of hypertension in Ren-2 transgenic rats (TGR), in the present study we evaluated plasma and kidney ANG II levels in anesthetized and conscious TGR and in normotensive Hannover-Sprague-Dawley rats (HanSD) fed a normal salt diet (NS). Given the importance of ANG II in the development of salt-sensitive hypertension, and the fact that hypertensinogenic actions of ANG II are mediated via ANG II type 1 (AT1) receptors, the effects of high salt (HS) intake and of sodium depletion on blood pressure (BP), ANG II levels and kidney AT1 receptor protein expression in TGR and HanSD were also examined.

METHODS

Rats were maintained on a NS diet (0.6% NaCl) or fed a HS diet (2% NaCl) for 4 days or were sodium depleted (40 mg/l furosemide for 1 day followed by 3 days of 0.01% NaCl diet). They were sacrificed either by an overdose of anesthetic (thiopental sodium) or by decapitation (without anesthetic) and plasma and kidney ANG II levels were determined by radioimmunoassay during the prehypertensive (32 days old), the early (52 days) and the maintenance (90 days) phases of hypertension. Total kidney AT1 receptor protein levels were assessed by Western blot analysis.

RESULTS

In anesthetized animals fed the NS diet, plasma ANG II levels were lower in 32-day-old TGR than in HanSD, but at 52 and 90 days of age no significant differences were noted. ANG II concentrations in kidney tissue were similar in 32- and 90-day-old TGR and HanSD, but were higher in 52-day-old TGR than in HanSD. In contrast, in conscious animals immediately after decapitation, plasma and kidney ANG II levels were higher in TGR than in HanSD at all ages. HS diet did not change BP but suppressed ANG II levels in HanSD at all ages. In contrast, HS diet increased BP but did not decrease plasma and kidney ANG II levels in TGR at all ages. Sodium restriction did not alter BP and resulted in a marked increase in ANG II levels in HanSD, but caused a significant decrease in BP in TGR without altering plasma or tissue ANG II concentrations. There were no significant differences in renal AT1 receptor protein expression between HanSD and TGR at any age of any of the experimental groups.

CONCLUSIONS

On the basis of our present results we conclude that TGR exhibit a disrupted interaction between sodium homeostasis and the regulation of the renin-angiotensin system (RAS) activity which results in the loss of BP regulation in this model.

Adrenomedullin reduces mesangial cell number and glomerular inflammation in experimental mesangioproliferative glomerulonephritis

BACKGROUND

Adrenomedullin (ADM) is a vasodilator peptide that is abundantly expressed in the kidney. ADM has antiproliferative effects on glomerular mesangial cells (MC) in vitro. Whether or not treatment with ADM can reduce MC proliferation in vivo [i.e., in mesangioproliferative glomerulonephritis (GN)] is unknown. We tested the hypothesis that ADM substitution reduces MC proliferation in GN.

METHODS

GN in rats was induced by injection of an anti-Thy-1.1 antibody. Rats received osmotic minipumps, which continuously delivered rat ADM (500 ng/hour, N = 11), or vehicle (N = 13) from day 3 to day 6 after GN induction. Rats were sacrificed 6 days after induction of GN. On kidney sections, cells staining positive for proliferating cell nuclear antigen, mesangial cells, monocytes, and apoptotic cells were counted. Parameters of inflammation and fibrosis were measured in renal cortex and sieved glomeruli by real-time polymerase chain reaction (PCR).

RESULTS

Systolic blood pressure, diuresis, albuminuria, creatinine clearance, microaneurysm formation, and mesangial matrix expansion were not influenced by ADM infusion. However, ADM treatment significantly reduced the number of MC, showed a tendency to reduce total glomerular cell proliferation, and significantly increased apoptosis. ADM-treated GN animals showed significantly less glomerular monocyte infiltration. ADM treatment normalized transforming growth factor (TGF)-beta1 mRNA expression and reduced monocyte chemoattractant protein-1 (MCP-1), osteopontin, plasminogen activator inhibitor-1 (PAI-1), collagen I, and collagen III mRNA expression significantly.

CONCLUSION

Exogenous ADM infusion reduces MC number and glomerular monocyte infiltration in the state of mesangial proliferation during acute experimental mesangioproliferative GN. These findings indicate that ADM can influence the course of mesangioproliferative GN.

Local renin-angiotensin systems: the unanswered questions

The concept of local renin-angiotensin systems has been introduced almost 20 years ago to explain the beneficial blood pressure-independent effects of ACE inhibitors and AT(1) receptor antagonists in cardiovascular diseases. In the past decade, research has focussed on the local effects of angiotensin II rather than on the mechanism(s) of its local generation. This review addresses several of the unanswered questions with regard to tissue angiotensin II generation, focussing in particular on the heart and vascular wall: (1) what is the origin of the renin that is required to generate angiotensin II locally, (2) where does tissue angiotensin generation occur (intra- versus extracellular), (3) what is the importance of alternative (non-renin, non-ACE) angiotensin-generating enzymes, (4) do ACE inhibitors and AT(1) receptor antagonists exert local effects that are renin-angiotensin system independent (thereby incorrectly leading to the conclusion that they interfere with the local generation or effects of angiotensin II), and (5) to what degree do differences in tissue angiotensin generation underlie the association between cardiovascular diseases and renin-angiotensin system gene polymorphisms?

Local renin-angiotensin systems and their interactions with extra-adrenal corticosteroid production

Adrenal aldosterone production is regulated by the renin-angiotensin system (RAS). It is now known that several other tissues are capable of extra-adrenal aldosterone biosynthesis and that these tissues can also generate angiotensin II through local RAS. Therefore, the regulation of local aldosterone production by the local RAS is a distinct possibility. In this review, we present evidence for the existence of such systems in the vascular system, heart and brain. We then discuss the possibility of interactions between the RAS and aldosterone synthesis at the local level and speculate on the possible physiological effects of such systems in these tissues.

Dual ACE and NEP inhibitor MDL-100,240 prevents and regresses severe angiotensin II-dependent hypertension partially through bradykinin type 2 receptor

OBJECTIVE

To investigate the effects of the dual angiotensin-converting enzyme (ACE) + neutral endopeptidase (NEP) inhibitor, MDL-100,240 (MDL), on hypertension and cardiovascular damage in male heterozygous transgenic Ren2 rats.

METHODS

Blood-pressure-matched 5-week-old transgenic rats were allocated to receive a placebo, MDL (40 mg/kg body weight) or ramipril (5 mg/kg body weight) for 8 weeks. During the last 4 weeks, the bradykinin B2 receptor antagonist, icatibant (0.5 mg/kg body weight), was also administered subcutaneously via osmotic minipumps to 50% of the transgenic rats receiving MDL or ramipril. We measured blood pressure, heart weight, structural changes in the aorta and small resistance mesenteric arteries, and the plasma concentrations of adrenomedullin, aldosterone, atrial natriuretic peptide and cGMP. To verify if MDL could regress long-standing hypertension and full-blown cardiovascular damage, 3-month-old transgenic rats received MDL subcutaneously (3 and 10 mg/kg body weight, osmotic minipumps) for 4 weeks.

RESULTS

Compared with placebo, MDL decreased blood pressure (P < 0.001) and prevented left ventricular hypertrophy (P < 0.001), being as effective as ramipril. Hypertrophy and dilatation of the aorta and hypertrophy of the resistance arterioles were all prevented by MDL. Plasma aldosterone was decreased by MDL (P < 0.001), but not by ramipril. Icatibant blunted the decrease in blood pressure (P < 0.001), decreased cGMP concentrations and blunted the decrease in cross-sectional area of the resistance arteries in MDL-treated, but not in ramipril-treated, transgenic rats. In 3-month-old transgenic rats, MDL normalized blood pressure, regressed left ventricular hypertrophy and decreased adrenomedullin concentrations.

CONCLUSIONS

The dual ACE+NEP inhibitor MDL prevented and regressed severe hypertension and cardiovascular damage, even in this model of severe angiotensin II-dependent hypertension with pronounced cardiovascular damage. Enhancement of the effects of bradykinin has a role in such favourable outcomes.

Angiotensin-(1-7) is involved in the endothelium-dependent modulation of phenylephrine-induced contraction in the aorta of mRen-2 transgenic rats

1. The contribution of the local vascular production of angiotensin-(1-7) [Ang-(1-7)] to the control of alpha-adrenergic-induced contractions in the aorta of Sprague-Dawley (SD) and TGR(mRen-2)27 [mRen-2] rats was studied. 2. In mRen-2 rats, contractile responses to phenylephrine were diminished as compared to control SD rats in endothelium containing but not in endothelium-denuded vessels. L-NAME increased contractile responses to phenylephrine in mRen-2 rats and, after nitric oxide synthase blockade, responses to phenylephrine became comparable in both strains. 3. Inhibition of angiotensin-converting enzyme (ACE) by captopril potentiated contractile responses in mRen-2 rats and diminished contractile responses in SD rats, both effects being dependent on the presence of a functional endothelium. The effect of captopril in mRen-2 rats was abolished in vessels pre-incubated with Ang-(1-7). 4. Blockade of Ang-(1-7) and bradykinin (BK) receptors by A-779 and HOE 140 respectively, increased phenylephrine-induced contraction in mRen-2, but not in SD rats. This effect was seen only in endothelium-containing vessels. 5. Angiotensin II AT(1) and AT(2) receptor blockade by CV 11974 and PD 123319 did not affect the contractile responses to phenylephrine in aortas of transgenic animals but diminished the response in SD rats. This effect was only seen in the presence of a functional endothelium. 6. It is concluded that the decreased contractile responses to phenylephrine in aortas of mRen-2 rats was dependent on an intact endothelium, the local release and action of Ang-(1-7) and bradykinin.

Comparative effects of the dual ACE-NEP inhibitor MDL-100,240 and ramipril on hypertension and cardiovascular disease in endogenous angiotensin II-dependent hypertension

We investigated the effects of MDL-100,240 in a transgenic rat model (TGRen2) of hypertension with severe cardiovascular damage (CVD) due to enhanced tissue synthesis of angiotensin II (Ang II). Male heterozygous TGRen2 rats (5 weeks old) were allocated to receive MDL-100,240, ramipril (RAM) or placebo (PLAC) for 4 weeks, during which blood pressure (BP) was measured. We then evaluated: 1) left ventricle (LV) and right ventricle (RV), brain, kidney and adrenals weight; 2) structural changes in the aorta and the mesenteric arterioles wall; 3) tension responses of segments of the aorta to phenylephrine, KCl, and endothelin-1; and 4) creatinine, aldosterone, atrial natriuretic peptide (ANP), and cyclic GMP (cGMP) plasma levels. Compared to PLAC, both MDL-100,240 and RAM significantly (P < .001) lowered BP (after 4 weeks: 255 +/- 15 mm Hg PLAC, v 174 +/- 6 MDL-100,240, v 166 +/- 5 RAM). They hindered LV hypertrophy (3.73 +/- 0.25 mg/g body weight (PLAC) v 2.71 +/- 0.22 (MDL-100,240) P < .001; v 2.36 +/- 0.2 (RAM), P < .001). MDL-100,240 also prevented aortic dilatation and hypertrophy of the mesenteric arterioles (media thickness, 25.3 +/- 0.5 microm PLAC, v 21.1 +/- 0.9 MDL-100,240, P < .007; v 20.2 +/- 1.5 RAM, P = .033) and lowered the tension responses to phenylephrine (P < .01), KCl (P < .01), and endothelin-1 (P < .001). Plasma aldosterone (710 +/- 153 pmol/L PLAC, v 237 +/- 61 MDL-100,240, v 180 +/- 22 RAM) and creatinine levels (0.69 +/- 0.33 mg/dL PLAC, v 0.41 +/- 0.02 MDL-100,240, v 0.41 +/- 0.04 RAM) were also decreased (P < or = .001). Compared to PLAC, plasma ANP levels were 11% and 2.4% higher in MDL-100,240 and RAM, respectively (both P = not significant); cGMP levels were unaffected. Thus, severe hypertension and related CVD were regressed by MDL-100,240, which resulted to be as effective as a full dosage of ramipril in TGRen2.

Involvement of cysteinyl leukotrienes in angiotensin II-induced contraction in isolated aortas from transgenic (mRen-2)27 rats

OBJECTIVES

We have previously reported that 5-lipoxygenase-derived products, and particularly the cysteinyl leukotrienes (CysLTs), were involved in angiotensin II (Ang II)-induced contractions in isolated aortas from spontaneously hypertensive rats.

DESIGN

The aim of this study was to assess the role of CysLTs in the vascular response to Ang II in an Ang II-dependent model of hypertension, the (mRen-2)27 transgenic rats (TGs).

METHODS

Intact aortic rings from TG and normotensive Sprague-Dawley rats (SDs) were suspended in organ chambers for isometric tension development in response to Ang II. In addition, the release of CysLTs in response to Ang II (0.3 micromol/l) was measured by enzyme immunoassay.

RESULTS

In isolated aortas from TG rats, pretreatment with the 5-lipoxygenase inhibitor (AA861, 10 micromol/l) or the CysLT1 receptor antagonist (MK571, 1 micromol/l) significantly (P < 0.05) reduced Ang II-induced contractions by 52 and 42%, respectively. In addition, Ang II induced a 2.6-fold increase in CysLT release (pg/mg dry weight tissue: 58.3 +/- 17.9 (Ang II, n = 7) versus 22.5 +/- 5.9 (basal, n = 7) P < 0.05), which was inhibited by the AT1 receptor antagonist losartan (1 micromol/l). In contrast, in aortas from SD rats, pretreatment with AA861 or MK571 did not alter Ang II-induced contraction and CysLT production remained unchanged after exposure to Ang II.

CONCLUSION

These data suggest that CysLTs are involved in the contractile responses to Ang II in isolated aortas from TG but not from SD rats.

Renin uptake by the endothelium mediates vascular angiotensin formation

We investigated the role of the vascular endothelium in the local production of angiotensin. Angiotensin release from isolated rat hindquarters perfused with an artificial medium was measured by high-performance liquid chromatography and radioimmunoassay. Perfused hindquarters with endothelium released angiotensin I spontaneously, indicating ongoing renin-angiotensinogen reaction. Endothelium denudation (by a detergent, validated by electron microscopy and by the absence of a vasodilator response to acetylcholine) reduced angiotensin I release by >90%, whereas bilateral nephrectomy 24 hours before perfusion abolished the release completely. Infusion of renin into perfused hindquarters induced sustained local angiotensin I release in the presence of an intact endothelium but not after endothelium denudation. The conversion of angiotensin I to angiotensin II was abrogated by endothelium denudation, whereas the disappearance of angiotensin II was unchanged. Endothelium denudation diminished the pressor response to angiotensin II but abolished the response to renin and angiotensin I. Expression of renin messenger RNA, investigated by reverse-transcription polymerase chain reaction using 4 different primer combinations, was not detected in up to 5 microg vascular RNA, whereas a renin signal was readily detected with 5 ng kidney RNA. The effects of endothelium destruction on Ang I formation support the notion that the endothelium mediates vascular angiotensin formation by taking up renin.

Day-night variation in the in vitro contractility of aorta and mesenteric and renal arteries in transgenic hypertensive rats

TGR(mREN2)27 (TGR) rats develop severe hypertension and an inverted circadian blood pressure profile with peak blood pressure in the day-time rest phase. The present study investigated the in vitro responsiveness of different arteries of TGR rats during day and night. Twelve-week-old TGR rats and normotensive Sprague-Dawley (SPRD) controls, synchronized to 12h light, 12h dark (LD 12:12) (light 07:00-19:00), were killed at 09:00 (during rest) and 21:00 (during activity), and endothelium-dependent relaxation by acetylcholine and vascular contraction by angiotensin II were studied by measuring isometric force in ring segments of abdominal aorta and mesenteric and renal arteries. In SPRD rats, consistent day-night variation was found, with greater responses to angiotensin II during the daytime rest span. In TGR rats, biological time-dependent differences were found in the renal vasculature, but not in the aorta and mesenteric artery. Relaxation of SPRD rat aorta and mesenteric artery by acetylcholine was greater at 09:00, whereas in TGR rats, day-night variation was absent (mesenteric artery) or inverted (aorta). In conclusion, based on the study of two time points, day-night variation in vascular contractility of aorta and mesenteric artery is blunted in TGR rats, whereas renal artery segments showed an unchanged day-night pattern compared to SPRD controls.

Lack of correlation between Mbo I restriction fragment length polymorphism of renin gene and essential hypertension in Japanese

Predisposition to essential hypertension is associated with gene polymorphisms of the renin angiotensin system (RAS). Gene polymorphisms of the angiotensinogen and angiotensin converting enzyme genes are known to be risk factors for hypertension, while few studies concerning the renin gene polymorphism have been published. In the present investigation, we carried out a case control study using a Japanese population to examine the genetic influence of the renin gene on the predisposition to hypertension. Patients (n=235) recruited from outpatients at Osaka University Hospital and diagnosed with essential hypertension or receiving long-term antihypertensive medication participated in the study. Normotensive control subjects (n=510) without a history of hypertension and without diabetes mellitus were recruited from the same population, and were sex-matched with experimental subjects. A polymorphism in intron 9 of the human renin gene was determined as the Mbo I restriction fragment length polymorphism (Mbo I-RFLP). There was no significant association between Mbo I-RFLP of the renin gene and predisposition to essential hypertension in Japanese (p>0.05, chi2=2.1). These results suggest that the Mbo I (+) allele of the renin gene does not increase the risk for hypertension in Japanese.

Monocyte chemoattractant protein-1 and macrophage infiltration in hypertensive kidney injury

BACKGROUND

We investigated whether monocyte chemoattractant protein-1 (MCP-1) is expressed in hypertensive nephrosclerosis, and tested the effect of angiotensin II type 1 receptor blockade on MCP-1 expression and macrophage (MPhi) infiltration.

METHODS

Rats with two-kidney, one-clip (2K1C) hypertension with and without treatment with the angiotensin II type 1 receptor antagonist valsartan (3 mg/kg/day) were studied. In these animals as well as in spontaneously hypertensive rats (SHR), stroke-prone SHR (SHR-SP), hypertensive mRen-2 transgenic rats (TGR), and respective control strains, MCP-1 expression in the kidney was investigated by Northern and Western blots and by immunohistochemistry. Glomerular and interstitial MPhis were counted.

RESULTS

In the nonclipped kidney of 2K1C rats, MCP-1 expression was elevated at 14 and 28 days when significant MPhi infiltration was present. MCP-1 was localized to glomerular endothelial and epithelial cells, interstitial and tubular cells, MPhis, and vascular smooth muscle cells. A similar pattern of MCP-1 staining was present in TGR kidneys, whereas MCP-1 expression was not increased in SHR and SHR-SP. Valsartan reduced but did not normalize blood pressure, blocked the induction of MCP-1 protein in 2K1C kidneys, and decreased interstitial MPhi infiltration significantly.

CONCLUSION

MCP-1 expression is increased in angiotensin II-dependent models of hypertensive nephrosclerosis and is temporally and spatially related to MPhi infiltration. The angiotensin II type 1 receptor mediates the induction of MCP-1.

Blockade of angiotensin II type 1 receptor and not of endothelin receptor prevents hypertension and cardiovascular disease in transgenic (mREN2)27 rats via adrenocortical steroid-independent mechanisms

We investigated the role of angiotensin II (Ang II) and endothelin-1 (ET-1) in transgenic (mREN2)27 rats, a model of the monogenic renin-dependent form of severe hypertension and cardiovascular disease. Four-week-old heterozygous male transgenic (mREN2)27 rats (n=24) were matched according to body weight (BW) and blood pressure (BP) and randomly allocated to receive a placebo (group P), the mixed endothelin type A and B receptor antagonist bosentan (100 mg/kg BW PO, group B), the Ang II type 1-specific receptor antagonist irbesartan (50 mg/kg BW PO, group I), or the endothelin type A-selective antagonist BMS-182874 (52 mg/kg BW PO, group BMS). After 4 weeks of treatment, during which BW and BP were measured weekly, animals were euthanized, and the heart, left ventricle, right ventricle, adrenal gland, brain, and kidney were weighed. The plasma levels of adrenocortical steroids were measured by high-performance liquid chromatography. The tension responses of ET-free segments of the thoracic aorta to 5 x 10(-6) mmol/L phenylephrine, 60 mmol/L KCl, and cumulative doses of ET-1 were assessed. The density of ET-1 receptor subtypes in the aorta and vascular structural changes in the mesenteric arterioles (100 to 200 microm ID) were also measured with autoradiography and myography, respectively. Compared with all other groups, group I rats showed significantly (P<0.001) lower systolic BP (group I, 161+/-8 mm Hg; group P, 269+/-23 mm Hg; group B, 275+/-17 mm Hg; and group BMS, 254+/-21 mm Hg), left ventricular weight (2.28+/-0.15 versus 3. 71+/-0.26, 3.38+/-0.27, and 3.96+/-0.51 mg/g BW, respectively), tension responses to vasoconstrictors, and normalized media thickness of the mesenteric arterioles (22.3+/-0.6 versus 25.3+/-0.5, 25.5+/-0.7, and 24.1+/-1.5 microm, respectively). Compared with levels in group P (78+/-25 pmol/mL), plasma aldosterone levels were significantly decreased in group B (51+/-11 pmol/mL) and group I (40+/-16 pmol/mL). Thus, endogenous ET-1 and Ang II contribute to the regulation of aldosterone, but only Ang II is crucial for the development of hypertension and related target organ damage via the Ang II type 1 receptor. Endogenous Ang II does not appear to enhance cardiovascular production of ET-1 in this model of hypertension within the time span of our experiment.

Release of angiotensin-(1-7) from the rat hindlimb: influence of angiotensin-converting enzyme inhibition

The results of recent studies have demonstrated that angiotensin (Ang)-(1-7) contributes to the antihypertensive actions of either combined ACE/Ang II type 1 receptor blockade or ACE inhibition alone. The vasculature is a key site of action for either drug regimen, and evidence favors a local Ang system within these tissues. Because ACE may degrade Ang-(1-7), we determined whether ACE inhibition alters Ang-(1-7) release from the rat hindlimb perfused with Krebs-Ringer buffer containing Ficoll. Ang-(1-7) release averaged 36+/-13 fmol (period 1, 15-minute collection) and 44+/-11 fmol (period 2) in the control buffer. The addition of the ACE inhibitor lisinopril to the perfusion buffer augmented levels of Ang-(1-7) in periods 3 (144+/-39 fmol) and 4 (163+/-35 fmol; P<0.05 versus 1 or 2, n=8). HPLC and radioimmunoassay of effluent from control or lisinopril treatment demonstrated a single immunoreactive peak with a retention time identical to that of Ang-(1-7). The addition of the neprilysin inhibitor SCH 39370 reduced Ang-(1-7) release in the lisinopril buffer from 177+/-32 (period 1) and 173+/-39 (period 2) fmol to 112+/-24 (period 3) and 87+/-23 fmol (period 4; P<0.05 versus 1 or 2, n=6). Ang I metabolism in the collected perfusate revealed the formation of Ang-(1-7) that was sensitive only to thimet oligopeptidase inhibition; Ang II generation was not detected. The present study demonstrates the recovery of endogenous Ang-(1-7) from the perfused hindlimb. The release of Ang-(1-7) is significantly influenced by inhibition of ACE, which may reflect both increased substrate (Ang I) levels and reduced metabolism of the peptide. Neprilysin inhibition reduced but did not abolish Ang-(1-7) release, which suggests that other endopeptidases may contribute to the release of the peptide.

Cardiovascular responses to angiotensins I and II in normotensive and hypertensive rats; effects of NO synthase inhibition or ET receptor antagonism

1. We compared the cardiovascular responses to angiotensins (I and II), and any possible modulatory influences thereupon of nitric oxide (NO) or endothelin (ET) in conscious male, normotensive, Hannover Sprague-Dawley (SD) rats, and hypertensive, heterozygous ((mRen-2)27), transgenic (TG) rats. 2. The pressor effects of angiotensin I or of angiotensin II were not consistently different in SD and TG rats. The accompanying absolute reductions in renal and mesenteric vascular conductances were smaller in TG rats, but probably due to the baseline vasoconstriction in those animals. 3. Inhibition of NO synthase with L-NAME had no significant effects on the pressor responses to angiotensin I or angiotensin II in either SD or TG rats. L-NAME reduced the absolute, but not percentage, reductions in renal and mesenteric vascular conductances in response to angiotensin I and angiotensin II. L-NAME abolished the hindquarters vasodilator effects of angiotensin I and angiotensin II in both strains of rat. 4. ET receptor antagonism (with SB209670) had no significant influence on the pressor or renal or mesenteric vasoconstrictor effects of angiotensin II in SD rats. In TG rats, the pressor responses to angiotensin II were unaffected by SB209670; the accompanying falls in renal and mesenteric vascular conductances were enhanced in absolute, but not in percentage terms. 5. These results provide no evidence for a buffering action of NO, or a modulatory influence of ET, on the pressor or vasoconstrictor effects of angiotensin I and/or angiotensin II in SD rats. Furthermore, there is no evidence for an altered sensitivity to angiotensin I or angiotensin II, and no evidence for a differential modulatory influence of either NO or ET in TG, compared to SD, rats.

Cardiac interstitial fluid levels of angiotensin I and II in the pig

OBJECTIVE

To study whether cardiac interstitial fluid levels of angiotensin I and II (Ang I and II) can be monitored in vivo, using the microdialysis technique, and to assess the contribution of plasma-derived angiotensins to the interstitial fluid levels of these peptides.

DESIGN AND METHODS

Microdialysis probes were placed in the left ventricular (LV) myocardium of eight anaesthetized pigs, three of which were untreated and five treated with the angiotensin II type 1 (AT1) receptor antagonist L-158,809 (10 mg intracoronary). All pigs were given a 1 h intracoronary infusion of 125I-Ang II. Aortic and coronary venous blood samples were taken under steady-state conditions, and interstitial dialysate was collected during the entire infusion period. Immediately after stopping the infusion, LV tissue pieces were obtained at various time points.

RESULTS

L-158,809 did not affect the levels of endogenous Ang I and II or the levels of plasma 125I-Ang II. Aortic Ang I and II levels (22 and 16 fmol/ml; geometric mean of eight pigs) were comparable to coronary venous Ang I and II levels, whereas the coronary venous 125I-Ang II levels (6650 c.p.m./ml) were approximately 30 times higher than those in the aorta. Tissue Ang I and II levels were 5 and 17 fmol/g, respectively. In untreated animals, the 125I-Ang II levels per g LV tissue were similar to the levels per ml coronary venous plasma, and the ex vivo half-life of tissue 1251-Ang II was > 30 min. In treated animals, tissue 125I-Ang II was < 5% of coronary venous 125I-Ang II and became undetectable within 15 min. 125I-Ang II, Ang I and Ang II levels in the interstitial fluid were close to or below the detection limit (200 c.p.m., 60 fmol and 20 fmol per ml, respectively) in all animals.

CONCLUSIONS

Plasma and myocardial interstitial fluid angiotensin levels are of the same order of magnitude. Plasma Ang II does not contribute to the interstitial fluid level of Ang II, most likely because of its rapid metabolism in the vascular wall. Binding to AT1 receptors protects Ang II against metabolism.

Angiotensin II AT1-receptor blockade inhibits monocyte activation and adherence in transgenic (mRen2)27 rats

This study investigated whether angiotensin II AT1-receptor blockade with losartan inhibits endothelium-monocyte interactions originating from long-term activation of the renin-angiotensin system in hypertensive transgenic rats [TGR(mRen2)27]. The number of circulating activated monocytes, monocytes adhered to thoracic aorta endothelium, and the extent of endothelial cell injury were compared in adult male transgenic (mRen2)27 and age-matched Hannover Sprague-Dawley (SD) rats after 12 days of continuous subcutaneous administration of saline (120 microl/24 h), losartan (10 mg/kg/24 h), or the vasodilator hydralazine (3 mg/kg/24 h). At the doses administered in this experiment, both losartan and hydralazine normalized mRen2 rat blood pressures equal to values in similarly treated SD rats. Compared with saline infusion, administration of either antihypertensive in mRen2 rats reduced (p<0.05) endothelial cell injury, but only losartan significantly (p<0.05) decreased the number of activated circulating and endothelium-adherent monocytes. Infusion of antihypertensives in SD rats had no effect on blood pressures, monocyte activity, or endothelial injury compared with saline administration. These findings suggest that the recruitment and infiltration of leukocytes into the subendothelium associated with renin-angiotensin system-induced hypertension is partly mediated by pressure-independent AT1-receptor pathways.

Increased central angiotensin and osmotic responses in the Ren-2 transgenic rat

We previously demonstrated that the Ren-2 transgenic (TG) rat is sensitive to salt, showing a sodium-induced pressor response. The present studies determined the effect of central stimulation with hypertonic saline (HS) and angiotensin II (Ang II) on mean arterial pressure (MAP), heart rate (HR), and plasma vasopressin. HS (1 mol/L NaCl, 5 microL) or Ang II (100 ng, 5 microL) was injected into the lateral ventricle of conscious male TG and control rats. The pressor responses to HS and Ang were greater in TG than in control rats, increases of 42+/-4 and 41+/-4 mm Hg versus 25+/-3 and 18+/-2 mm Hg (HS and Ang II and TG and control rats, respectively). The TG rats also showed an increased vasopressin response to Ang II, peak levels of 14+/-3 versus 28+/-3 pg/mL (control versus TG rats). HS increased plasma vasopressin levels, although the group responses were not different. HR was not significantly altered by either stimulus. Results demonstrate an increased responsiveness to intraventricular HS and Ang II in Ren-2 transgenic rats, suggesting a relationship between the enhanced angiotensinergic drive and central cardiovascular and vasopressin responses.

Dissociation of blood pressure reduction from end-organ damage in TGR(mREN2)27 transgenic hypertensive rats

OBJECTIVE

Since the biochemical disturbance underlying hypertension may be an important determinant of patient outcome, we compared the effects of early treatment with different antihypertensive drugs on end-organ damage in the TGR(mREN2)27 transgenic rat (REN-2). In these REN-2 rats, hypertension is primarily caused by increased activity of the tissue renin-angiotensin system.

DESIGN AND METHODS

Seven-week-old REN-2 rats were either untreated or treated orally with an optimal daily dose of carvedilol (30 mg/kg), hydralazine (30 mg/kg), losartan (10 mg/kg) or quinapril (15 mg/kg). Nontransgenic littermates served as normotensive controls. After 11 weeks of treatment, we determined plasma norepinephrine concentrations, left ventricular atrial natriuretic factor messenger RNA and cardiac and vascular function and hypertrophy.

RESULTS

Chronic treatment with carvedilol and hydralazine significantly decreased blood pressure to a similar level but failed to normalize it, whereas both losartan and quinapril completely normalized blood pressure. Despite a blood pressure reduction in all treatment groups, only losartan, quinapril and hydralazine preserved endothelial function, while carvedilol did not. Furthermore, losartan and quinapril prevented cardiac and medial hypertrophy. The expression of atrial natriuretic factor messenger RNA paralleled the hemodynamic changes. Plasma norepinephrine levels were normalized by losartan or quinapril but remained increased after carvedilol and hydralazine treatment.

CONCLUSIONS

In REN-2 hypertensive rats, end-organ damage can be prevented by both inhibition of the angiotensin converting enzyme and blockade of the angiotensin II type 1 receptor, but not by merely lowering blood pressure. When blood pressure is not fully normalized, the effects on end-organs are clearly dissociated from the antihypertensive effects.

Vascular beta-adrenergic receptor adenylyl cyclase system from renin-transgenic hypertensive rats

In transgenic rats harboring the mouse Ren-2d gene [TG(mREN2)27], downregulation of the myocardial beta-adrenergic receptor adenylyl cyclase system has been demonstrated previously. Because a reduced vasodilatory reactivity may significantly contribute to hypertension in this model of an activated tissue renin-angiotensin system, the present study investigated alterations of the vascular beta-adrenergic receptor adenylyl cyclase system. In freshly harvested aortas from transgenic rats, the activity of adenylyl cyclase was reduced significantly (P<.05) in the presence of isoprenaline (10 micromol/L; -28+/-4.5%), guanosine 5'-triphosphate, 5'-guanylylimidodiphosphate [Gpp(NH)p] (100 micromol/L; -29+/-4.7%), and forskolin (100 micromol/L) with (-42+/-6%) and without (-40+/-4.3%) MnCl2. Densities of beta-adrenoceptors were similar in both strains. In situ hybridization demonstrated the expression of the transgene in aortic smooth muscle cells. These data indicate a reduced catalyst function as a major contributing factor involved in the maintenance of high blood pressure in TG(mREN2)27. However, in cultivated aortic smooth muscle cells, cAMP production after stimulation with isoprenaline, forskolin, and Gpp(NH)p in the presence or absence of MnCl2 was not different. Affinities and densities of beta-adrenoceptors and amounts of immunochemically detected inhibitory and stimulatory G-protein alpha-subunits were unchanged. Desensitization after incubation with 10 micromol/L isoprenaline for 72 hours was identical in smooth muscle cells from both strains. Cell cultivation and isoprenaline treatment had no effect on transgene expression. We concluded that in transgenic rats the downregulation of the aortic beta-adrenergic adenylyl cyclase system is due to humoral and hemodynamic factors present in vivo rather than to transgenicity itself.

Effects of quinapril, losartan and hydralazine on cardiac hypertrophy and beta-adrenergic neuroeffector mechanisms in transgenic (mREN2)27 rats

1. Desensitization of the myocardial beta-adrenergic signal transduction pathway is an important mechanism which is involved in the progression of hypertensive heart disease. The aim of the present study was to evaluate the differential effects of chronic pharmacotherapy with an angiotensin converting enzyme (ACE)-inhibitor, an AT1-receptor antagonist and a direct vasodilator on blood pressure, cardiac hypertrophy and the beta-adrenergic signal transduction. Therefore, transgenic TG(mREN2)27 (TG) rats overexpressing the mouse renin gene were used. This strain is characterized by the development of fulminant hypertension with cardiac hypertrophy. 2. Seven week old heterozygous TG(mREN2)27 rats were treated for 11 weeks with the AT1-receptor antagonist losartan (10 mg kg[-1]), the ACE-inhibitor quinapril (15 mg kg[-1]) and the direct vasodilator hydralazine (30 mg kg[-1]). Untreated TG and normotensive Sprague-Dawley rats (SD) served as controls. 3. TG(mREN2)27-rats were characterized by arterial hypertension (TG 194+/-3.2 mmHg vs SD 136+/-2.9 mmHg systolic blood pressure), increased left ventricular weights (TG 4.3+/-0.3 vs SD 3.0+/-0.1 mg g(-1) body weight), decreased myocardial neuropeptide Y (NPY) concentrations (TG 1143+/-108 vs SD 1953+/-134 pg g(-1) wet weight), reduced beta-adrenoceptor densities (TG 51.1+/-1.9 vs SD 63.4+/-3.7 fmol mg[-1]) as assessed by [125I]-cyanopindolol binding studies, and increased Gi(alpha)-activities (TG 4151+/-181 vs SD 3169+/-130 densitometric units) as assessed by pertussis toxin catalyzed [32P]-ADP-ribosylation. Downregulation of beta-adrenoceptors and increased Gi(alpha) were accompanied by significantly reduced isoprenaline-, Gpp(NH)p- and forskolin-stimulated adenylyl cyclase activity. Catalyst activity as determined by forskolin plus Mn2+ co-stimulation of adenylyl cyclase did not differ between TG(mREN2)27- and SD control-rats. 4. Losartan and quinapril significantly restored systolic blood pressures, left ventricular weights, beta-adrenoceptor densities, myocardial neuropeptide Y-concentrations, adenylyl cyclase activities and Gi(alpha)-activities towards the values in Sprague-Dawley-controls. No differences were observed between the effects of quinapril- and losartan-treatment. In contrast, hydralazine had only minor effects on blood pressure reduction, regression of left ventricular hypertrophy and neuroeffector defects in TG(mREN2)27. 5. In conclusion, direct vasodilatation is not able to overcome the pathophysiological alterations in TG caused by transgene overexpression. In contrast, ACE-inhibitors and AT1-receptor antagonists, which inhibit the renin angiotensin system, equally exert beneficial effects on blood pressure, myocardial hypertrophy and neuroeffector mechanisms. Modulation of the sympathetic tone and resensitization of the beta-adrenergic signal transduction system may contribute to the special effectiveness of these drugs in the treatment of the hypertensive cardiomyopathy.

Angiotensinases restrict locally generated angiotensin II to the blood vessel wall

We tested the hypothesis that angiotensinases limit the spillover of locally formed angiotensin II into the circulation. The release of angiotensin peptides from isolated rat hindquarters perfused with an artificial medium was measured by high-performance liquid chromatography and radioimmunoassay. The spontaneous release of angiotensins was increased by the angiotensinase inhibitors phenanthroline (850+/-195 versus 95+/-33 fmol of angiotensin I per 30 minutes in controls, P<.05, n=5 each) and amastatin (P<.05, n=5 each). Infusion of renin induced sustained local angiotensin I formation, which was also increased by phenanthroline. Stimulation of local angiotensin formation by renin infusion was compared with infusion of exogenous angiotensin II. Renin caused similar increases of perfusion pressure (11.1+/-2.2 versus 7.6+/-1.9 mm Hg after angiotensin II, P>.05) despite lower angiotensin II levels in the venous effluent than during infusion of exogenous angiotensin II (65+/-2 versus 482+/-33 fmol/mL, P<.05, n=7 each). Thus, renin must have caused higher angiotensin II tissue levels than indicated by the measurements in the venous effluent. The pressor response to renin was abolished by the type 1 angiotensin II receptor antagonist losartan. We conclude that the major part of locally generated angiotensins is not released into the circulation but degraded by angiotensinases within the tissue compartment.

Angiotensin II mediates cell hypertrophy in vascular smooth muscle cultures from hypertensive Ren-2 transgenic rats by an amiloride- and furosemide-sensitive mechanism

We have reported that cultured vascular smooth muscle cells (VSMC) from hypertensive Ren-2 transgenic rats (TGR) are constitutively hypertrophic when compared to matched cells from normotensive Sprague-Dawley rats (SD), by a mechanism involving the endogenous production of angiotensin II (AII). In the present work, we analyzed the possible involvement of two Na+ transport mechanisms in TGR-VSMC hypertrophy. In both SD- and TGR-VSMC, AII increased both cell size, by a furosemide- and amiloride-sensitive mechanism, and Na+/K+/2Cl- cotransport activity, by an amiloride-sensitive mechanism. Under basal unstimulated conditions, TGR-VSMC showed higher cell size and Na+/K+/2Cl- cotransport activity than SD-VSMC. Under these same conditions, losartan, furosemide, or amiloride reduced cell size only in TGR-VSMC. Similarly, basal cotransport activity was reduced by losartan and amiloride to levels similar to those observed in SD-VSMC. We conclude that hypertrophy of TGR-VSMC is dependent on the endogenous production of AII and mediated by increased Na(+)-H+ exchange and Na+/K+/2Cl- cotransport activities.

Effects of captopril, losartan, and nifedipine on cell hypertrophy of cultured vascular smooth muscle from hypertensive Ren-2 transgenic rats

1. We hypothesized that tissular renin-angotensin system (RAS) induces vascular hypertrophy in hypertensive Ren-2 transgenic rats (TGR; strain name TGR(mRen2)L27). This assumption was tested in cell cultures of vascular smooth muscle (VSMC) from both hypertensive TGR and control normotensive Sprague-Dawley (SD) rats. Planar cell surface area, protein synthesis, and protein content per cell were studied, the role for locally produced angiotensin II (AII) was evaluated and the possible pharmacological interference by different drugs was analysed. 2. By use of radioimmunoassay techniques, AII could be determined in TGR cultures (10.25 +/- 0.12 pg per 10(7) cells) while it could not be detected in SD ones. 3. Under serum-free conditions, VSMC from hypertensive TGR were hypertrophic when compared to SD VSMC, as they presented a higher protein content per cell (335 +/-18 and 288 +/- 7 pg per cell respectively; P<0.05) and increased mean planar cell surface area, as determined by image analysis (4,074 +/- 238 and 4,764 +/- 204 microm2, respectively; P < 0.05). 4. When exogenously added to cultured SD and TGR VSMC, AII (100 pM to 1 microM) promoted protein synthesis and protein content in a concentration-dependent manner without affecting DNA synthesis. Maximal effects were observed at 100 nM. At this concentration, AII effectively increased planar cell surface area in both SD and TGR cultures by approximately 20%. 5. Treatment of TGR cultures, in the absence of exogenous AII, with the angiotensin-converting enzyme inhibitor captopril or the angiotensin AT1 receptors antagonist losartan (100 nM to 10 microM) reduced planar cell surface area in a concentration-dependent manner. In addition, both captopril and losartan (10 microM), decreased protein synthesis by approximately 15%. 6. Treatment of SD VSMC, in the absence of exogenous AII, with both captopril and losartan had no effect either on planar cell surface area or protein synthesis. 7. Treatment with the Ca2+ antagonist nifedipine (100 nM to 10 microM) reduced cell size in both SD and TGR cultures. Maximal cell reduction reached by nifedipine averaged 906 +/- 58 and 1,292 +/- 57 microm2, in SD and TGR, respectively (P<0.05). In addition, nifedipine, nitrendipine and nisoldipine (all at 10 microM) decreased protein synthesis in both cell types by 15-25%. 8. We concluded that cultured VSMC from TGR are hypertrophic in comparison with those from SD. This cell hypertrophy can be the consequence of the expression of the transgene Ren-2 that activates a tissular RAS and locally produces AII, which acts in a paracrine, autocrine, or intracrine manner. Cell hypertrophy in TGR cultures could be selectively reduced by RAS blockade, while nifedipine decreased cell size and protein synthesis in both hypertrophic and non hypertrophic cells.

Differential alteration in vascular structure of resistance arteries isolated from the cerebral and mesenteric vascular beds of transgenic [(mRen-2)27], hypertensive rats

In this study we examined the structural properties of cerebral and mesenteric resistance arteries isolated from normotensive, Sprague-Dawley (SD) rats (mean arterial pressure [MAP], 110 +/- 3 mm Hg) and hypertensive, transgenic (TG) rats (MAP, 167 +/- 4 mm Hg), which express the mouse Ren-2 renin gene. Vessels were set up in a pressure myograph, and ID and vascular wall thickness were determined at increasing intraluminal pressures. Arteries were subsequently pressurized to the MAP of the animal from which they were isolated and were fixed with glutaraldehyde before being embedded in araldite, sectioned, and examined histologically. The middle cerebral artery (MCA) isolated from SD rats and TG rats had similar media cross-sectional areas. There was no difference in MCA diameter at 10 mm Hg in vessels from TG rats compared with SD rats. However, at higher distending pressures, the diameter of the MCA from TG rats was significantly smaller than that of vessels from SD rats. This reduced ID at the higher pressures was a consequence of a decreased distensibility of the MCA from TG rats (as shown by a leftward shift of the stress-strain relationship in arteries from TG rats) and was not caused by an increase in wall thickness. First- and second-order mesenteric resistance arteries isolated from TG rats displayed an increased wall thickness and media content compared with vessels from SD rats. However, this alteration in mesenteric artery structure did not impinge on the ID of arteries from TG rats; there was no difference in the IDs of mesenteric resistance arteries between the two strains at any distending pressure. These observations show that there are distinct regional alterations in vascular structure in hypertensive TG rats expressing the mouse Ren-2 renin gene. Mesenteric resistance arteries isolated from TG rats display signs of vascular growth, although this structural alteration does not produce a reduction in the ID of these arteries per se. In contrast, cerebral arteries from TG rats do not show increased growth but have a reduced vascular distensibility, which results in a smaller ID compared with vessels from SD rats.

Down-regulation of aortic and cardiac AT1 receptor gene expression in transgenic (mRen-2) 27 rats

1. Transgenic(TG) (mRen-2) rats overexpressing the mouse renin gene develop fulminant hypertension and cardiac hypertrophy. Since the activation of AT1 receptor by angiotensin II is involved in blood pressure regulation, cardiac performance and myocardial growth, we investigated the biological effects of angiotensin II and the regulation of the AT1 receptor in the heart and aorta of TGR (mRen-2)27 rats in comparison to control animals. 2. Contraction studies on isolated cardiac muscle strips reveal that angiotensin II exerts no positive inotropic effect on the left ventricular myocardium of both, transgenic and control rats. In contrast, angiotensin II leads via AT1 receptor activation in the left atrium of control rats to a significant contraction (130 +/- 5% of basal contraction) which is not detectable in left atrium preparations of the transgenic animals. Furthermore, AT1 receptor activation causes a profound contraction of aortic rings isolated from control rats amounting to 1.39 +/- 0.2 mN mg-1 wet weight, whereas aortic rings from TGR (mRen-2)27 rats contract only minimally upon angiotensin II stimulation (0.2 +/- 0.02 mN mg-1 wet weight). 3. These altered physiological responses of angiotensin II in the transgenic rats are in part due to a marked down-regulation of the AT1 receptor in atrial, ventricular and aortic tissue of these transgenic animals in comparison to control Sprague-Dawley rats, as shown by radioligand binding assays and quantitative polymerase chain reaction (PCR) experiments. The AT1 receptor density Bmax in the left atrium was 1.3 +/- 0.08 fmol mg-1 protein in control rats (KD 1.1 +/- 0.18 nmol l-1) and 0.94 +/- 0.15 fmol mg-1 protein (KD 2.1 +/- 0.3 nmol l-1. In the aorta Bmax values were 15.1 +/- 0.5 fmol mg-1 protein (KD 1.9 +/- 0.27 nmol l-1) for control rats and 11.3 +/- 0.76 fmol mg-1 protein (KD 1.9 +/- 0.27 nmol l-1) for the TGR(mRen-2)27 rats AT1 receptor mRNA was reduced in the transgenic animals to 46 +/- 3% in the left atrium, 50 +/- 11% in the left ventricle and 40 +/- 3% in the aorta, respectively. 4. Together, the AT1 receptor is down-regulated in TGR (mRen-2)27 rats in comparison to wildtype Sprague Dawley rats leading to a profoundly decreased response of cardiac and aortic tissue upon stimulation with angiotensin II.

Nifedipine, losartan and captopril effects on hyperplasia of vascular smooth muscle from Ren-2 transgenic rats

Vascular smooth muscle cells from hypertensive transgenic rats for the mouse Ren-2 gene exhibited radioimmunoassayable angiotensin II and hyperplasia in comparison with cells from Sprague-Dawley rats. However, neither captopril, losartan, saralasin, nor PD123319 (all at 10 microM) modified DNA synthesis or cell number observed in 4-day growth curves with 10% fetal calf serum. Nifedipine reduced DNA synthesis in both cell types, the concentration required being significantly higher in Sprague-Dawley- (1 microM) than in transgenic-derived cultures (100 nM). The EC50 values were of 2.43 +/- 0.32 and 1.0 +/- 0.17 microM, respectively (P < 0.05). In both cell types, only 10 microM nifedipine reduced serum-induced cell proliferation, but inhibition percentage was higher in transgenic-derived cultures. In conclusion, hyperplasia of transgenic-derived vascular smooth muscle cells is not blocked by angiotensin-converting enzyme inhibitors or angiotensin receptor antagonists, but these cells are more sensitive to the antiproliferative effects of nifedipine.

Angiotensin-(1-7) augments bradykinin-induced vasodilation by competing with ACE and releasing nitric oxide

Recent studies have shown that angiotensin-(1-7) [Ang-(1-7)] interacts with kinins and augments bradykinin (BK)-induced vasodilator responses by an unknown mechanism. In this study, we evaluated whether the potentiation of the BK-induced vasodilation by Ang-(1-7) may be attributable to inhibition of BK metabolism, release of nitric oxide, or both. Isometric tension was measured in intact canine coronary artery rings suspended in organ chambers. 125I-[Tyr0]-BK metabolism was determined in vascular rings by assessing the degradation of the peptide by high-performance liquid chromatography. Ang-(1-7) augmented the vasodilation induced by BK in a concentration-dependent manner in rings preconstricted with the thromboxane analog U46619. The EC50 of BK (2.45 +/- 0.51 nmol/L versus 0.37 +/- 0.08 nmol/L) was shifted leftward by 6.6-fold in the presence of 2 mumol/L concentration of Ang-(1-7). The response was specific for BK. since Ang-(1-7) did not augment the vasodilation induced by either acetylcholine (0.05 mumol/L) or sodium nitroprusside (0.1 mumol/L). Moreover, neither angiotensin I nor angiotensin II (Ang II) duplicated the augmented BK response of Ang-(1-7). Pretreatment of vascular rings with the nitric oxide synthase inhibitor, N omega-nitro-L-arginine (L-NA; 100 mumol/L) completely abolished the effects of Ang-(1-7) on BK-induced vasodilation whereas pretreatment with indomethacin (10 mumol/L) was without effect. The potent specific BK B2 receptor antagonist, Hoe 140. nearly abolished the BK and the Ang-(1-7) potentiated responses at 2 mumol/L, whereas at a lower concentration (20 nmol/L) Hoe 140 shifted the response curve to the right for both Ang-(1-7) and vehicle; however, the augmented response to Ang-(1-7) persisted. Preincubation of vascular rings with 20 mumol/L of the AT1 (CV11974), AT2 (PD123319), or nonselective (Sar1 Thr8-Ang II) receptor antagonists had no significant effect on the Ang-(1-7)-enhanced vasodilator response to BK. Lisinopril (2 mumol/L) significantly enhanced the BK-induced vasodilator response while at the same time it abolished the synergistic action of Ang-(1-7) on BK. In addition, pretreatment with 2 mumol/L Ang-(1-7) significantly inhibited the degradation of 125I-[Tyr0]-BK and the appearance of the BK-(1-7) and BK-(1-5) metabolites in coronary vascular rings. Ang-(1-7) inhibited purified canine angiotensin converting enzyme activity with an IC50 of 0.65 mumol/L. In conclusion. Ang-(1-7) acts as a local synergistic modulator of kinin-induced vasodilation by inhibiting angiotensin converting enzyme and releasing nitric oxide.

Synthesis and secretion of natriuretic peptides in the hypertensive TGR(mREN-2)27 transgenic rat

To examine the pathophysiological mechanisms in transgenic rats carrying the murine Ren-2d renin gene, we studied atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) gene expression and secretion in 12-week-old hypertensive TGR(mREN-2)27 and normotensive Sprague-Dawley rats. Hypertension and marked left ventricular hypertrophy in TGR(mREN-2)27 rats were associated with high baseline plasma levels of immunoreactive ANP (148 +/- 18 versus 34 +/- 3 pmol/L, hypertensive versus normotensive rats; P < .001), whereas plasma immunoreactive BNP levels did not differ significantly between the strains (19 +/- 4 versus 12 +/- 3 pmol/L, P = .06). ANP mRNA and immunoreactive ANP levels in the left ventricular endocardial and epicardial layers in TGR(mREN-2)27 rats were about 20 to 40 times higher (P < .001) than those in normotensive rats. There were no statistically significant differences between atrial and ventricular BNP mRNA levels, but left ventricular immunoreactive BNP concentrations were twofold higher in hypertensive TGR(mREN-2)27 than in normotensive rats. Infusion of [Arg8]-vasopressin (0.05 microgram/kg per minute IV, for 2 hours) in normotensive rats produced rapid increases (twofold, P < .05 to .01) in left ventricular BNP mRNA and immunoreactive BNP levels, whereas ventricular BNP mRNA and peptide levels did not change significantly in hypertensive rats. The increase in left atrial BNP mRNA levels in response to acute pressure overload was also significantly smaller in the hypertensive than normotensive rats (3.5-fold versus 5.2-fold, P < .01). Furthermore, the proportional but not absolute (in picomoles per liter) increase in plasma immunoreactive ANP was smaller in transgenic rats in response to acute saline and [Arg8]-vasopressin infusions (0.9% NaCl: 1.9-fold increase versus 4.4-fold increase in normotensive rats, P < .001; [Arg8]-vasopressin: 2.2-fold versus 4.8-fold increase, P < .001). These results show that baseline and cardiac overload-induced increases in BNP synthesis are markedly attenuated in transgenic rats carrying the murine Ren-2d renin gene. In addition, acute volume and pressure overload produced a smaller proportional increase in ANP secretion in hypertensive rats than normotensive rats. These alterations in the natriuretic peptide system may contribute to the pathogenesis of hypertension and cardiovascular complications in the TGR(mREN-2)27 rat.

Vascular damage without hypertension in transgenic rats expressing prorenin exclusively in the liver

We have developed a transgenic animal model to investigate the effects of overexpression of rat prorenin on the cardiovascular system. Two transgenic rat lines were generated in which rat prorenin expression was directed to the liver by a human alpha1-antitrypsin promoter. Liver-specific expression was confirmed by RNase protection assay. Plasma prorenin concentrations in transgenic rats were increased 400-fold in the males of both lines but were increased only two- to threefold in the females. Thus, transgene expression exhibited sexual dimorphism. Blood pressures were not significantly higher in transgenic rats than in nontransgenic controls. The ratio of heart weight to body weight was greater in male transgenic rats than in the nontransgenic controls. Histological analysis revealed severe renal lesions and hypertrophic cardiomyocytes in transgenic males only. This transgenic model demonstrates a likely role of prorenin in the development of cardiac and renal pathology independent of hypertension. These animals will facilitate studies of the effects of blockade of the renin-angiotensin system and other pharmacological interventions on the development and treatment of cardiac, vascular, and renal lesions induced by changes in this system in the absence of chronic hypertension.

Disproportional arterial hypertrophy in hypertensive mRen-2 transgenic rats

In the present study, we investigated the role of enhanced vascular renin-angiotensin activity in vascular hypertrophy. We used transgenic (mRen-2)27 (renin TGR) rats, spontaneously hypertensive rats (SHR), and their respective normotensive control rats to study in situ pressure-diameter relationships in second-generation mesenteric arterial branches (in vivo diameter, 400 to 500 microns) over a pressure range of 0 to 200 mm Hg. We studied pressure-diameter curves under both control (Tyrode's solution) and fully relaxed (Tyrode's solution containing 100 mg/L potassium cyanide) conditions. From these curves, we determined mechanical properties at operating blood pressure. In both hypertensive strains, mesenteric arterial media cross-sectional area was increased, with a significantly (P < .05) stronger degree of hypertrophy in renin TGR rats. Arterial distensibility of relaxed vessels was decreased to an equal degree in both hypertensive strains. Under control conditions, distensibility was higher in SHR than in renin TGR rats but still significantly reduced compared with distensibility in normotensive rats. Wall tension was increased to an equal degree in both hypertensive strains, whereas circumferential wall stress was normal in SHR but significantly (P < .05) reduced in renin TGR rats. These results indicate that whereas vascular hypertrophy in SHR causes adaptive normalization of arterial wall stress, enhanced vascular renin-angiotensin activity causes vascular hypertrophy in excess of the hypertrophy associated with pressure elevation alone.

Role of the circulating renin-angiotensin system in the pathogenesis of hypertension in transgenic rats. TGR(mREN2)27

Transgenic rats, termed TGR(mREN2)27, which carry the mouse ren2d renin gene, develop fulminant hypertension. To evaluate the role of the circulating renin-angiotensin system (RAS) in hypertension of TGR(mREN2)27, we determined plasma levels of its components and their regulation by ether-stress. Plasma prorenin was elevated in prehypertensive and in adult heterozygous TGR(mREN2)27 (fourtyfold), when compared with Sprague Dawley (SD) controls, whereas plasma renin concentration (PRC) and angiotensin II were not in SD rats ether anesthesia increased PRC at day (11 a.m.; fivefold), but not at night (11 p.m.). Ether had no effect on PRC in TGR(mREN2)27. In contrast, ether increased plasma corticosterone levels at day and night in both strains to a similar degree. Our data indicate that plasma active renin is not a pathogenetic factor for hypertension in TGR(mREN2)27 and suggest a primary role of circulating prorenin. The lack of stimulation of PRC by ether in TGR(mREN2)27 probably reflects predominant extrarenal origin of renin.

Reduction of cardiac hypertrophy in TGR(mREN2)27 by angiotensin II receptor blockade

TGR(mREN2)27 is a transgenic rat harboring the murine Ren-2 gene and exhibit fulminant hypertension and marked heart hypertrophy. In order to study the role of angiotensin II in the increase of cardiac mass, these animals were treated with antihypertensive and non-antihypertensive doses of the angiotensin II receptor AT1 antagonist Telmisartan for 9 weeks. All doses led to significant reductions of heart hypertrophy detected by the evaluation of the diameter of cardiac muscle bundles. We conclude from this study that cardiac hypertrophy in TGR(mREN2)27 is characterized by an increased volume of cardiomyocytes and an unchanged amount of fibrous tissue and that angiotensin II plays an important role in the mechanisms leading to this phenotype.

Noradrenergic transmission in the tail artery of hypertensive rats transgenic for the mouse renin gene Ren-2

1. The aim of the present study was to analyse the noradrenergic transmission in the tail artery of hypertensive rats transgenic for the mouse renin gene Ren-2 (TGR) in comparison with its control, the Sprague-Dawley (SD) rat. 2. Electrical field stimulation (EFS) of vascular segments produced frequency-dependent vasoconstrictions that were significantly greater in TGR arteries. 3. These contractions were abolished by tetrodotoxin (0.1 microM). Phentolamine (50 nM) and prazosin (1 - 10 nM) produced an inhibition of these responses that was significantly greater in SD arteries, whereas that produced by yohimbine (0.5-1 microM) was higher in TGR arteries. In both strains, propranolol (1 microM) potentiated the responses to EFS, and this increase was observed at lower frequencies in TGR arteries. 4. The EFS-evoked [3H]-noradrenaline (NA) release was significantly greater in TGR than in SD rats. However, NA (10 nM-10 microM) reduced and yohimbine and phentolamine (10 nM-10 microM) increased the tritium outflow to a similar degree in both strains. 5. Exogenous NA also induced greater vasoconstriction in TGR arteries. 6. These results suggest the existence in TGR tail artery of an increase in: (a) NA-release and alpha 2-adrenoceptor-mediated contractions, which could contribute to the elevated blood pressure in these rats; and (b) beta-adrenoceptor-mediated vasodilatations, which may be a mechanism to counteract high blood pressure.

The renin-angiotensin system in transgenic rats

Transgenic animals are used to study the function, regulation and in vivo expression of genes. The effects of the genes of the renin-angiotensin system on blood pressure regulation and hypertension were invested in transgenic rats. The role of the renin-angiotensin system in the development of the cardiovascular hypertrophy or hypertensive renal damage was analysed, as well as its interaction with other hormonal systems, i.e., adrenal steroids. The development of a transgenic rat strain carrying the mouse REN-2 gene has provided a new model of hypertension with systolic blood pressure values of 200 mmHg. This model is characterised by low active plasma renin, hyperproreninaemia and high expression of renin in the adrenal gland and other external tissues. Transgenic rats with the human components of the renin-angiotensin system expressed the human renin and angiotensinogen proteins which interacted species-specifically in transgenic rats. These transgenic models demonstrate the feasibility of studying the function of candidate hypertension genes in transgenic animals. In the future, further refinements in transgene construction, mutation, and modification can be tested in such transgenic animal models.

Effect of captopril and angiotensin II receptor blockade on pressure natriuresis in transgenic TGR(mRen-2)27 rats

The pressure-natriuresis curve of transgenic rats harboring an extra mouse renin gene [TGR(mRen-2)27] is shifted rightward compared with controls; however, whether intrarenal angiotensin II effects are responsible for the rightward shift is unknown. To clarify this issue we infused the converting enzyme inhibitor captopril or the angiotensin II receptor blocker CV 11974 into transgenic and normotensive Sprague-Dawley Hannover control rats. We eliminated any other neural or endocrine regulatory differences between transgenic and control rats by renal denervation and infusion of vasopressin, aldosterone, corticosterone, and norepinephrine in sufficient quantities to occupy all receptors. Sodium excretion increased from 3.4 +/- 1.2 to 10.1 +/- 0.5 mumol/min per gram kidney weight in transgenic rats when renal perfusion pressure was increased from 158 to 201 mm Hg. Captopril (4 mg/kg) and CV 11974 (0.1 mg/kg) shifted the pressure-natriuresis curve of transgenic rats leftward, so that sodium excretion was threefold higher at similar renal perfusion pressures (150 to 160 mm Hg). Similarly, fractional sodium and water excretion curves were shifted leftward, so that values for transgenic and control rats were no longer different. Over the pressure range, renal blood flow in transgenic rats ranged from 3.1 +/- 0.7 to 4.4 +/- 0.5 mL/min per gram kidney weight and increased (P < .05) with both captopril and CV 11974 to ranges from 4.8 +/- 0.9 to 6.8 +/- 0.6 or from 4.5 +/- 0.7 to 6.9 +/- 1.0 mL/min per gram kidney weight, respectively. Glomerular filtration rate in transgenic rats, on the other hand, was not increased. Transgenic kidneys showed severe hypertension-induced nephrosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of human renin in the vasculature of rats transgenic for human angiotensinogen

Transgenic rats, which express the human angiotensinogen gene, provide a unique model for studying local vascular effects of human renin. We examined the cleavage of human angiotensinogen to angiotensin I (Ang I) by human renin and its inhibition by a human renin inhibitor in an isolated perfused hindlimb preparation from such rats. Perfusion resulted in the sustained release of human angiotensinogen, which decreased from 19.4 to 11.8 pmol/mL over 45 minutes. Active human renin at doses of 3, 10, and 30 ng/mL perfusate for 15 minutes increased Ang I release from undetectable levels (mean +/- SEM) to 31.9 +/- 3.3, 147.1 +/- 26.2, and 206.4 +/- 17.1 fmol/mL, respectively, by 9 minutes. In separate experiments aimed at the quantification of renin-induced vasoconstriction, captopril decreased the perfusion pressure and lowered Ang II concentrations to nondetectable levels, whereas Ang I values increased sharply. When renin (30 ng/mL) was infused for 15 minutes, renin values in the perfusate decreased to barely detectable levels within minutes after termination of the infusion. However, Ang I values remained high for at least 30 minutes thereafter. The addition of a human renin inhibitor during renin infusion caused Ang I values to promptly decrease within minutes to undetectable levels. Hindlimbs from non-transgenic control rats released no detectable amounts of Ang I, with or without human renin. Finally, by in situ hybridization we documented the presence of human angiotensinogen message in the vessels of the hindlimb. We conclude that renin acts on angiotensinogen at a site in the vascular wall. The cleavage depends on renin and not on other lysosomal proteases.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin and bradykinin peptides in the TGR(mRen-2)27 rat

The transgenic TGR(mRen-2)27 rat, in which the Ren-2 mouse renin gene is transfected into the genome of the Sprague-Dawley rat, develops severe hypertension at a young age that responds to inhibitors of angiotensin-converting enzyme and to antagonists of the type 1 angiotensin II (Ang II) receptor. Despite this evidence that the hypertension is Ang II dependent, TGR(mRen-2)27 rats have suppressed renal renin and renin mRNA content, and there is controversy concerning the plasma levels of renin and Ang II in these rats. We investigated the effect of the transgene on circulating and tissue levels of angiotensin and bradykinin peptides in 6-week-old male homozygous TGR(mRen-2)27 rats. Systolic blood pressure of TGR(mRen-2)27 rats was 212 +/- 4 mm Hg (mean +/- SEM, n = 25) compared with 108 +/- 2 mm Hg (n = 29) for age- and sex-matched Sprague-Dawley rats. Compared with control rats, TGR(mRen-2)27 rats had increased plasma levels of active renin (4.5-fold), prorenin (300-fold), and Ang II (fourfold) as well as tissue levels of Ang II (twofold to fourfold in kidney, adrenal, heart, aorta, brown adipose tissue, and lung and 18-fold in brain). Plasma angiotensinogen levels were reduced to 73% of control, and plasma aldosterone levels were increased fourfold. Plasma angiotensin-converting enzyme was reduced to 64% of control. Compared with control rats, TGR(mRen-2)27 rats had increased bradykinin levels in brown adipose tissue (1.9-fold) and lung (1.6-fold).(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of angiotensin-converting enzyme in renovascular hypertensive rat kidney

We hypothesized that the gene expression of angiotensinogen, angiotensin-converting enzyme, and angiotensin II type 1 receptor, in addition to renin, is increased in kidneys after renal artery stenosis. Two-kidney, one clip renovascular hypertension was initiated in Sprague-Dawley rats by clipping of the left renal artery; control rats were sham operated. Blood pressure was not changed for the first 2 days after clipping but was elevated on day 4 (mean arterial pressure, 104 +/- 4 versus 87 +/- 2 mm Hg in sham-operated control rats, P < .002) and increased further during the next 24 days. Rats were killed 2, 4, 7, 14, and 28 days after clipping or sham operation, and poly(A)(+)-purified renal cortical RNA was analyzed by Northern blotting. Autoradiographs were quantitated by densitometry and normalized for the expression of a housekeeping gene. Renin expression was increased in the clipped kidney (by 149% on day 2) and decreased in the nonclipped kidney (by 82% on day 2), compared with kidneys of control rats. Expression of the angiotensin-converting enzyme was increased in clipped kidneys from the first day after clipping (158%) and throughout the experiment (66% on day 28), but was unchanged or slightly decreased in nonclipped kidneys. Angiotensinogen mRNA showed little change. Angiotensin II type 1 receptor expression was decreased in nonclipped kidneys but unchanged during the first 7 days in clipped kidneys. Our results show that components of the renin-angiotensin system other than renin are also differentially expressed in clipped kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)