Obese female SHHF/Mcc-fa(cp) rats resist antihypertensive effects of renin-angiotensin system inhibition.

Gender and obesity may influence response to pharmacological modulation of the renin-angiotensin system. We used SHHF/Mcc-fa(cp) rats to study effect of obesity and gender on the ability of an AT1 receptor antagonist to decrease blood pressure. After 2 weeks treatment with irbesartan (50 mg/kg), only lean and obese males showed significant decreases in blood pressure, while obese females were completely resistant. Lean females showed a trend toward lowering of pressure (p=0.06). However, irbesartan similarly shifted angiotensin II dose response curves to the right in all groups. Twelve weeks of irbesartan also failed to decrease blood pressure, but did significantly reduce heart weight in obese females. In untreated rats, obese females had lower plasma renin activity and serum angiotensin converting enzyme activity compared to lean males, while lean and obese females had increased urinary endothelin excretion. Despite an otherwise similar genetic background contributing to hypertension and heart failure, obese females have different patterns of humoral activation compared to lean males, which may contribute to their resistance to the depressor effects of irbesartan.

Microsphere-adenoviral complexes target and transduce the glomerulus in vivo.

BACKGROUND: Developing new treatments for glomerulonephritis makes the glomerulus a logical target for gene therapy. Microspheres may lodge in the glomerulus, and replication-deficient recombinant adenoviruses are potent mediators of gene transfer. We postulated that adenoviral-microsphere complexes could result in DNA transfer (transduction) into glomerular cells in vivo. METHODS: Two adenoviruses, each one containing a luciferase or beta-galactosidase (beta-gal) transgene expression cassette, were complexed to polystyrene microspheres. To assess in vivo glomerular transduction with this tool, male Sprague-Dawley rats underwent aortic injections with adenovirus linked to 11 or 16 microm diameter microspheres. RESULTS: After 48 hours, adenoviral-microsphere complexes resulted in transduction of up to 19% of glomeruli per kidney section. Endothelial and mesangial cells were transduced with this approach, and transprotein expression persisted for 21 days. Transduction efficiency was greater in the 16 microm group. For all rats, there was a strong correlation between kidney luciferase levels and the number of beta-gal-positive glomeruli (r = 0.87), indicating that transgene expression was primarily glomerular in location. This was supported by reverse transcriptase in situ polymerase chain reaction, which demonstrated glomerular localization of the beta-gal transgene. CONCLUSIONS: The aortic injection of adenoviral-microsphere complexes transduces the glomerulus in vivo and may be a useful tool in developing approaches to gene therapy of glomerular disease.

Endothelial dysfunction and peroxynitrite formation are early events in angiotensin-induced cardiovascular disorders.

Angiotensin II (ANG II) is a well-established participant in many cardiovascular disorders, but the mechanisms involved are not clear. Vascular cell experiments suggest that ANG II is a potent stimulator of free radicals such as superoxide anion, an agent known to inactivate nitric oxide and promote the formation of peroxynitrite. Here we hypothesized that ANG II reduces the efficacy of NO-mediated vascular relaxation and promotes vascular peroxynitrite formation in vivo. ANG II was infused in rats at sub-pressor doses for 3 days. Systolic blood pressure and heart rate were unchanged on day 3 despite significant reductions in plasma renin activity. Thoracic aorta was isolated for functional and immunohistochemical evaluations. No difference in isolated vascular contractile responses to KCI (125 mM), phenylephrine, or ANG II was observed between groups. In contrast, relaxant response to acetylcholine (ACh) was decreased sixfold without a change in relaxant response to sodium nitroprusside. Extensive prevalence of 3-nitrotyrosine (3-NT, a stable biomarker of tissue peroxynitrite formation) immunoreactivity was observed in ANG II-treated vascular tissues and was specifically confined to the endothelium. Digital image analysis demonstrated a significant inverse correlation between ACh relaxant response and 3-NT immunoreactivity. These data demonstrate that ANG II selectively modifies vascular NO control at sub-pressor exposures in vivo. Thus, endothelial dysfunction apparently precedes other established ANG II-induced vascular pathologies, and this may be mediated by peroxynitrite formation in vivo. Wattanapitayakul, S., Weinstein, D. M., Holycross, B. J., Bauer, J. A. Endothelial dysfunction and peroxynitrite formation are early events in angiotensin-induced cardiovascular disorders.

Myocardial tumor necrosis factor-alpha secretion in hypertensive and heart failure-prone rats.

Acute increases in blood pressure (BP) increase myocardial tumor necrosis factor (TNF)-alpha production, but it is not known whether chronic hypertensive stress elevates myocardial TNF-alpha production, possibly contributing to cardiac remodeling, decreased cardiac function, and faster progression to heart failure. BP, cardiac function, and size were evaluated in normotensive [Sprague-Dawley (SD)], spontaneously hypertensive (SHR), and spontaneously hypertensive heart failure-prone (SHHF) rats at 6, 12, 15, and 18 mo of age and in failing SHHF. Left ventricular tissues were evaluated for secretion of bioactive TNF-alpha and inhibition of TNF-alpha secretion by phosphodiesterase inhibitors. All ventricles secreted bioactive and immunoreactive TNF-alpha, but secretion decreased with age. SHR and SHHF rats secreted more TNF-alpha than SD rats at 6 mo of age, but only failing SHHF rats secreted significantly more TNF-alpha at 18 mo. Amrinone inhibited TNF-alpha secretion in all rats and was less potent but more efficacious than RO-201724 in all strains. TNF-alpha secretion correlated with BP and left ventricular mass in 6-mo-old rats, but this relationship disappeared with age. Results suggest that hypertension and/or cardiac remodeling is associated with elevated myocardial TNF-alpha, and, although hypertension, per se, did not maintain elevated cardiac TNF-alpha levels, SHHF rats increase TNF-alpha production during the end stages of failure.

Effect of ovariectomy and estrogen replacement on cardiovascular disease in heart failure-prone SHHF/Mcc- fa cp rats.

The importance of endogenous and exogenous estrogen levels to the development of cardiovascular disease in women in controversial. The purpose of our study was to examine the effect of estrogen on the development of hypertension, cardiac hypertrophy, ventricular function, and gene expression for atrial natriuretic peptide (ANP) and components of the renin angiotensin system in spontaneously hypertensive heart failure rats (SHHF/Mcc- facp). Development of hypertension was prevented in 3-month-old ovariectomized rats receiving subcutaneous 17 beta -estradiol implants (EST) compared to ovariectomized (OVX) and controls (CON). EST had the least left ventricular hypertrophy, CON were intermediate, and OVX had the most (P<0.05), correlating well with systolic blood pressure. OVX had significantly lower percentage V(1)myosin isoform compared to EST and CON, indicating reversion to a more immature phenotype associated with hypertrophy. Similarly, OVX had decreased percentage left ventricular shortening fraction by echocardiography compared to EST and CON. These changes were not accompanied by alterations in plasma ANP, or in expression of mRNA for left ventricular ANP, renal renin, or hepatic angiotensinogen. Serum angiotensin converting enzyme activity was lower in EST compared to CON or OVX. When 17 beta -estradiol was given to 17-month-old rats that had naturally ceased estrous cycling, there was no effect on hypertension, progression of cardiac functional decline, or survival. In conclusion, estradiol treatment given prior to the development of hypertension in SHHF prevented left ventricular hypertrophy and hypertension. Development of congestive heart failure was not delayed if 17 beta -estradiol was begun in the post-menopausal period. Effectiveness of estrogen therapy may depend on age or whether hypertension is already established at the time treatment is begun.

Comparison of irbesartan with captopril effects on cardiac hypertrophy and gene expression in heart failure-prone male SHHF/Mcc-fa(cp) rats.

Angiotensin-converting enzyme (ACE) inhibitors have proven an effective means to control hypertension and manage cardiac hypertrophy. It is presently unknown if newer specific angiotensin II subtype 1 receptor (AT1R) antagonists are as effective or more effective in treating these conditions compared with ACE inhibitors. There is evidence that these classes of drugs may affect cardiac hypertrophy by different mechanisms. This study compared the effect of irbesartan, an AT1R antagonist, with that of captopril, an ACE inhibitor, on expression of early genetic markers of cardiac hypertrophy in lean male SHHF/Mcc-fa(cp) rats. SHHF/Mcc-fa(cp) rats (n = 10/group) were given captopril (100 mg/kg/day), irbesartan (50 mg/kg/day), or placebo for 16 weeks. Irbesartan and captopril significantly reduced systolic pressure and produced similar rightward shifts in the angiotensin I dose-response curve. Renal renin gene expression was increased 8.6-fold by irbesartan and 17.7-fold by captopril. The only effect on echocardiographic findings was a similar decrease in aortic peak velocity, an index of systolic function, by both treatments. Early markers of cardiac hypertrophy were significantly attenuated by both drugs. Both drugs produced marked and equivalent reductions in left ventricular atrial natriuretic peptide (ANP) messenger RNA (mRNA) levels compared with controls. This decrease in ANP gene expression was accompanied by a decrease in plasma ANP concentration in the treatment groups. The shift from V1 to V3 myosin isozymes was similarly decreased in both treatment groups, compared with controls. These data suggest that captopril and irbesartan are similarly effective in controlling expression of genes associated with ventricular hypertrophy in heart failure-prone SHHF/Mcc-fa(cp) rat.

Effect of ovariectomy in heart failure-prone SHHF/Mcc-facp rats.

The importance of the loss of ovarian function to the progression of hypertension and heart disease in women is controversial. We investigated whether ovariectomy would accelerate development of hypertension, congestive heart failure, and neurohumoral activation in adult spontaneous hypertension heart failure (SHHF) rats, a genetic model of heart failure. Six months after ovariectomy, no significant differences between control and ovariectomized rats were seen in systolic or diastolic blood pressure, left ventricular fractional shortening by echocardiography, or heart weight. Percent V1 myosin isozyme was significantly lower in ovariectomized rats. Northern blot analysis failed to show significant differences between groups in expression of hepatic angiotensinogen, renal renin, or left ventricular atrial or brain natriuretic peptide mRNA. In a second experiment, serial measures of systolic pressure and left ventricular shortening fractions failed to document a significant difference between control and ovariectomized rats as they developed heart failure, although there was a significant decline in shortening fraction in both groups at the age when regular estrous cycling naturally ceases. Survival time was similar between groups. In summary, ovariectomy of adult SHHF rats does not appear to affect the progression of genetically programmed hypertension and heart failure in this model.

Age-dependent augmentation of cardiac endothelial NOS in a genetic rat model of heart failure.

Alterations in nitric oxide (NO) biosynthesis in the heart have been implicated in the pathophysiology of heart failure. We compared changes in cardiac nitric oxide synthase (NOS) activity and expression in genetically heart failure-prone (SHHF) rats at 6, 12, and 18 mo of age with those in age-matched spontaneously hypertensive (SHR) and Sprague-Dawley (SD) rats. Systolic blood pressure was significantly higher in SHHF and SHR rats compared with SD rats; however, it declined with age in SHHF rats only. Left ventricular mass increased with age in SHR and SHHF, but not in SD rats. Plasma nitrate and nitrite level was elevated in SHHF and SHR rats at 18 mo only. In left ventricular homogenates from SHHF rats, Ca(2+)-dependent NOS activity increased markedly with age and was accompanied by enhanced expression of endothelial NOS (eNOS). In contrast, SHR rats showed a much smaller increase in Ca(2+)-dependent NOS activity over time without changes in eNOS expression; neither parameter was altered with age in SD rats. Ca(2+)-independent NOS activity was not detected in any heart. This is the first report of a unique alteration in myocardial NOS activity in hypertensive rats genetically prone to heart failure.

Plasma renin activity in heart failure-prone SHHF/Mcc-facp rats.

Plasma renin activity (PRA) increases during heart failure; however, PRA is altered by drug therapy, and it is difficult to study the natural progression of elevated PRA in humans and the possible factors that contribute to its rise. This study evaluated PRA in a drug-naive hypertensive rat model (SHHF/Mcc-facp) that has a genetic program resulting in heart failure (HF). Mean arterial blood pressure and PRA were determined and correlated to heart weight index in conscious normotensive, spontaneously hypertensive rats and HF rats of various ages. PRA, atrial natriuretic peptide, and aldosterone levels progressively increase with age in male HF rats. PRA and blood pressure are independently correlated to cardiac hypertrophy in male HF rats. Atrial natriuretic peptide was elevated in spontaneously hypertensive compared with normotensive rats. Female HF rats have elevated PRA, but the increase is temporally delayed compared with that in male HF rats. Hypertension, PRA, and male gender are independent factors contributing to cardiac hypertrophy and heart failure in the HF model. The HF rat model may prove useful in determining the contribution of these factors in the progression from cardiac hypertrophy to heart failure.

Pharmacological modulation of myocardial tumor necrosis factor alpha production by phosphodiesterase inhibitors.

Phosphodiesterase (PDE) inhibitors are used as therapeutic agents for management of congestive heart failure. PDE inhibitors are potent inotropic and vasodilator drugs, which have also been shown to inhibit tumor necrosis factor alpha (TNF-alpha) production. TNF-alpha is a pleiotropic cytokine that has the ability to produce cardiac depressant and other cardiovascular effects in many disease conditions. TNF-alpha levels are elevated in patients with chronic congestive heart failure, and it is possible that TNF-alpha may play a role in this condition. The effects of PDE inhibitors on TNF-alpha secretion from rat heart were evaluated in this study. Rat left ventricle was minced and incubated for 4 hr with various PDE inhibitors, and the amount of TNF-alpha secretion was evaluated by cytotoxicity assay. Ro-20, 1724, etazolate, amrinone, milrinone and pentoxifylline inhibited unstimulated TNF-alpha production, with IC50 values of 1.87, 2.07, 13.9, 153 and 201 microM, respectively. Lipopolysaccharide-induced TNF-alpha secretion from rat left ventricle was also evaluated in this study. Amrinone, milrinone and pentoxifylline inhibited lipopolysaccharide-induced TNF-alpha secretion, with IC50 values of 14.8, 81.6 and 748 microM, respectively, whereas Ro-2D, 1724 and etazolate had no effect on lipopolysaccharide-induced TNF-alpha secretion. These results demonstrated that TNF-alpha was secreted from rat left ventricle after 4 hr and different pharmacological manipulations were able to inhibit the secretion of TNF-alpha from left ventricle. These initial pharmacological results may provide an important tool for further investigation into the beneficial effects of PDE inhibitors in congestive heart failure or other conditions where TNF-alpha levels are elevated.

Angiotensin II stimulates increased protein synthesis, not increased DNA synthesis, in intact rat aortic segments, in vitro.

There is considerable controversy regarding whether angiotensin II (AngII) stimulates hypertrophy or hyperplasia of vascular smooth muscle cells (SMC). The purpose of the present study was to determine whether stretch of the vessel wall or AngII treatment increased protein or DNA synthesis in intact aortic rings in vitro and whether stretch of the vessel wall altered the growth responses to AngII. Rat aortic rings were mounted on steel supports in serum-free medium for 16 h and subjected to 0 or 1.5 g of preload (i.e. passive stretch). Fetal bovine serum (13%, FBS) or AngII [1 microM, in the presence or absence of angiotensin receptor antagonist, losartan (DuP753) 10 microM] was administered and isometric tension development was measured. 35S-methionine (3 microCi/ml) was added to the baths at 14-16 h for measurement of protein synthesis. Passive stretch did not increase protein synthesis as compared to vessels mounted under no-preload conditions. AngII and FBS elicited similar increases in isometric tension development, but tension development in FBS-treated rings was sustained 4 times longer than in rings treated with AngII. AngII and FBS increased protein synthesis by 35 and 121%, respectively, but there was no difference in the extent of contractile agonist-induced protein synthesis between rings subjected to 0 or 1.5 g of passive stretch. Losartan totally abolished AngII-induced tension development and protein synthesis. AngII and FBS did not stimulate increased DNA synthesis in aortic rings, as measured by 3H-thymidine incorporation. These results suggest that AngII stimulates hypertrophy rather than hyperplasia of fully contractile SMC in an intact vessel.

Platelet-derived growth factor-BB-induced suppression of smooth muscle cell differentiation.

Previously, we demonstrated that treatment of postconfluent quiescent rat aortic smooth muscle cells (SMCs) with platelet-derived growth factor (PDGF)-BB dramatically reduced smooth muscle (SM) alpha-actin synthesis. In the present studies, we focused on the expression of two other SM-specific proteins, SM myosin heavy chain (SM-MHC) and SM alpha-tropomyosin (SM-alpha TM), to determine whether the actions of PDGF-BB were specific to SM alpha-actin or represented a global ability of PDGF-BB to inhibit expression of cell-specific proteins characteristic of differentiated SMCs. SM-MHC and SM-alpha TM expression were assessed by one- or two-dimensional gel electrophoretic analysis of proteins from cells labeled with [35S]methionine, as well as by Northern analysis of mRNA levels. Synthesis of both SM-specific proteins was decreased by 50-70% in PDGF-BB--treated cells as compared with cells treated with PDGF vehicle. Treatment of cells with 10% fetal bovine serum, which produced a mitogenic effect equivalent to that of PDGF-BB, decreased SM-MHC synthesis by 40% but increased SM-alpha TM synthesis. SM-MHC and SM-alpha TM mRNA expression was decreased by 80% at 24 hours in PDGF-BB--treated postconfluent SMCs, whereas treatment with 10% fetal bovine serum did not decrease the expression of SM-alpha TM mRNA but did inhibit SM-MHC mRNA expression by 36%. Consistent with the absence of detectable PDGF alpha-receptors on these cells, PDGF-AA had no effect on either mitogenesis or expression of SM-MHC or SM-alpha TM.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic treatment with caffeine on kidney responses to angiotensin II.

Previous studies demonstrate that chronic administration of caffeine causes glomerular filtration to deteriorate in rats with high-renin renovascular hypertension. A partial explanation for these findings could be that chronic administration of caffeine alters the effects of angiotensin II on the kidney. As an initial test of this hypothesis, we compared the acute effects of intrarenal infusions of angiotensin II (3 ng/min) on renal function in control rats versus rats treated with 0.1% caffeine in their drinking water for 1 week. The renal responses to angiotensin II in a group of animals receiving acute intrarenal infusions of adenosine (10 micrograms/min) were also measured to determine whether caffeine and adenosine modulated renal responses to angiotensin II in opposite directions. All studies were performed in the in situ blood perfused rat kidney. Neither caffeine nor adenosine significantly altered angiotensin II-induced changes in renal blood flow, urinary excretory function or renin release. However, caffeine augmented and adenosine attenuated the increase in filtration fraction caused by angiotensin II. The fact that caffeine potentiates angiotensin II-induced increases in filtration fraction without affecting angiotensin II-induced reductions in renal blood flow is consistent with, but does not prove, the hypothesis that chronic administration of caffeine modifies the effects of angiotensin II on the renal microvasculature. If this inference is correct, caffeine could facilitate renal damage in high-renin hypertension by exacerbating angiotensin II-induced increases in glomerular capillary hydrostatic pressure.

Polymerase chain reaction analysis of renin in rat aortic smooth muscle.

Controversy exists whether vascular smooth muscle cells in vivo synthesize renin, thereby providing a critical component of the hypothesized vascular renin-angiotensin system. To examine this question, we enzymatically isolated and pooled the medial layer of thoracic aortas from Sprague-Dawley rats that were either untreated or enalapril treated for 3 days, isolated messenger RNA (mRNA), and performed Northern blot analysis with rat complementary DNA (cDNA) probes for renin, cathepsin D, and cathepsin E. Renin mRNA was detected in kidney but was not detected in aortic smooth muscle from the untreated or enalapril-treated groups. Cathepsin E mRNA was detected in enalapril-treated aorta and kidney, and cathepsin D mRNA was detected in all tissues examined. cDNA was synthesized and subjected to polymerase chain reaction analysis by using primers corresponding in sequence to regions conserved throughout the aspartic proteinases. Cathepsins D and E were amplified from kidney and aortic cDNA. Renin was less consistently amplified from the aortic cDNA and was much less abundant than cathepsin E or cathepsin D. These results suggest that 1) renin mRNA is present in aortic smooth muscle cells in vivo in quantities detectable only after multiple rounds of polymerase chain reaction amplification, 2) renin mRNA is not upregulated in aortic smooth muscle after converting enzyme inhibition, and 3) cathepsins D and E are the predominant aspartic proteinases in aortic smooth muscle.

Adenosine-angiotensin II interactions. Part I. Role of adenosine in regulating angiotensin II-induced potentiation of noradrenergic neurotransmission and angiotensin II-induced vasoconstriction.

The pharmacology of adenosine and angiotensin II (AII) suggests that endogenous adenosine could function to regulate some of the biological effects of AII. The goal of this study was to test the hypothesis that endogenous adenosine inhibits the ability of AII to potentiate noradrenergic neurotransmission and/or to directly contract vascular smooth muscle. Two approaches were used to assess the physiological import of adenosine-AII interactions on neurotransmission and vascular tone. First, the effects of exogenous adenosine and AII, separately and in combination, on vascular responses to periarterial nerve stimulation (PNS) and vascular tone were determined. Second, the effects of an adenosine receptor antagonist, 1,3-dipropyl-8-p-sulfophenylxanthine, on AII-induced potentiation of vascular responses to PNS and on AII-induced direct vasoconstriction were examined. All studies were conducted in the in situ blood perfused rat mesentery. Intra-arterial and i.v. infusions of AII potentiated responses to PNS and increased vascular tone, whereas i.a. infusions of adenosine had the opposite effects. Intra-arterial infusions of adenosine potentiated the ability of i.a. AII to enhance responses to PNS; however, i.a. adenosine attenuated the direct vasoconstrictive action of i.a. AII. Intra-arterial infusions of 1,3-dipropyl-8-p-sulfophenylxanthine, at a dose which antagonized the effects of exogenous adenosine, did not alter the effects of either i.a. AII or i.v. AII on vascular responses to PNS or on vascular tone. These results indicate that although adenosine has the potential to regulate AII-induced enhancement of noradrenergic neurotransmission and AII-induced direct vasoconstriction, such regulation does not occur under the conditions of this study.

Adenosine-angiotensin II interactions. Part II. The role of adenosine in regulating angiotensin II-induced changes in heart rate and aldosterone release.

The purpose of the present study was to determine whether endogenous adenosine (ADO) participates in angiotensin II (AII)-induced decreases in heart rate (HR) and regulates AII-induced aldosterone (ALDO) release. To test these hypotheses we investigated: 1) the effects of ADO and AII on base-line HR and ALDO levels; 2) the effects of ADO on AII-induced bradycardia and AII-induced increases in ALDO levels; 3) the effects of ADO receptor antagonists [caffeine and/or 1,3-dipropyl-8-p-sulfophenylxanthine (DPSPX)] on AII-induced bradycardia and AII-induced increases in ALDO levels; and 4) the effects of ADO receptor hypersensitivity on AII-induced bradycardia. In the latter experiments, the animals were rendered hypersensitive to the bradycardic effects of ADO by administering caffeine for 1 week then abruptly withdrawing caffeine 18 hr before the experiment, i.e., caffeine withdrawal. Intravenous infusions of either ADO or AII decreased base-line HR and ADO reduced the bradycardic response to AII. Intravenous infusions of DPSPX attenuated and caffeine withdrawal potentiated AII-induced bradycardia without modifying AII-induced increases in arterial blood pressure. AII increased and ADO did not alter base-line plasma ALDO levels; however, ADO attenuated by 50% AII-induced increases in ALDO levels. Neither DPSPX nor caffeine altered the ability of AII to increase plasma ALDO levels. These results indicate that although ADO has the potential to modulate AII-induced increases in plasma ALDO concentrations, endogenous ADO does not regulate the effects of AII on plasma ALDO levels under the conditions of these studies. However, endogenous ADO, in some way, contributes substantially to AII-induced bradycardia.