The renin-angiotensin system and its receptors

Regulation of therapeutic apoptosis: a potential target in controlling hypertensive organ damage

Cell growth and survival are potential therapeutic targets for the control of complications associated with hypertension. In most cardiovascular disorders, cardiac fibroblasts and large-vessel smooth muscle cells can replicate and thus contribute to the disease. We propose that cardiovascular hyperplasia may be reversed via therapeutic apoptosis induction with drugs that are safe and already used in the clinic. We first reported that, irrespective of the drug class, those drugs that are able to induce regression of cardiovascular hypertrophy are also able to reverse cardiovascular hyperplasia via apoptosis. Drugs active in this regard include inhibitors of the renin-angiotensin system, calcium channel blockers, and beta-blockers. Moreover, the effects of these drugs on cell survival is not merely secondary to blood pressure reduction. Therapeutic apoptosis in the cardiovascular system of the spontaneously hypertensive rat is characterized by a rapid and transient onset following initiation of antihypertensive treatment. Herein, the induction and termination of therapeutic apoptosis during drug treatment of hypertension will be briefly reviewed and supported by novel data suggesting that reversal of cardiovascular hyperplasia is associated with reduced cell growth and a resistance to further induction of therapeutic apoptosis, as shown in spontaneously hypertensive rats receiving an intermittent regime of nifedipine therapy. We propose that the presence of a cell subpopulation with defective cell cycle regulation may determine organ susceptibility to undergo therapeutic apoptosis.Key words: apoptosis, hypertension, hyperplasia, growth, nifedipine.

Pressor and intra-renal effects of angiotensins I and II, and noradrenaline, in anaesthetized and conscious sheep

The pressor and intra-renal actions and effects of octa - and deca-peptides angiotensins II and I and of the catecholamine noradrenaline, in anaesthetized and conscious sheep, are considered. The halothane anaesthetic substantially lowers pressor sensitivity to both peptides but does not influence their ability to liberate K(+) ions into the circulating plasma. In comparison with angiotensin II, both angiotensin I and noradrenaline -- with direct presentation to the kidney -- are ineffective in decreasing intra-renal blood flow. However, with left ventricular injection, both pressor compounds immediately increase the blood pressure, as does angiotensin II. Combined doses of the decapeptide and catecholamine are thus highly effective in raising the blood pressure while having a minimal effect on blood flow through the kidney. This overall situation could provide a basis for treating clinical shock, especially regarding septicaemia and septic shock. The lowered hind-limb blood flow, with administration of the pressor compounds into the femoral artery, contrasts strongly with the raised flow resulting from intravenous injection. Experimental procedures to establish, or otherwise, relevant hypothetical situations are detailed.

Precocious activation of genes of the renin-angiotensin system and the fibrogenic cascade in IgA glomerulonephritis

BACKGROUND

The renin-angiotensin system (RAS) seems to play a pivotal role in progression of immunoglobulin A (IgA) nephropathy (IgAN). Accordingly, in patients with IgAN a relationship between the RAS and the fibrogenic cascade triggered by transforming growth factor-beta1 (TGF-beta1) should be observed. This study was carried out to obtain deeper insight into the regulation of RAS and the interaction with TGF-beta1 in the diseased kidney.

METHODS

Twenty renal biopsies from IgAN patients and five from renal cancer patients (controls) were analyzed in both microdissected glomerular and tubulointerstitial compartments by reverse transcription-polymerase chain reaction (RT-PCR). All patients had normal renal function. The expression of the following genes was determined: angiotensinogen (Agtg), renin, angiotensin-converting enzyme (ACE), angiotensin II (Ang II) type 1 and type II (AT1 and AT2 receptors), TGF-beta1, collagen IV (Coll IV), alpha-smooth muscle actin (alpha-SMA). Quantitative data were confirmed for TGF-beta1 and ACE genes by real-time PCR. Results. RAS genes were overexpressed in IgAN patients vs. control subjects. There was no difference between glomerular and tubulointerstitial RAS gene expression levels. On the contrary, the overactivation of fibrogenic cascade genes (TGF-beta1, Coll IV, alpha-SMA) in the tubulointerstitium was observed (TGF-beta1, glomerular 0.14 +/- 0.10 SD; tubulointerstial 0.34 +/- 0.20; P = 0.000) (alpha-SMA, glomerular 0.08 +/- 0.07; tubulointerstitial 0.35 +/- 0.19; P = 0.000) (Coll IV, glomerular 0.12 +/- 0.11; tubulointerstitial 0.22 +/- 0.10; P = 0.03). This fibrogenic cascade seems to be triggered by RAS as indicated by statistically significant correlations between the expression of their respective genes. A direct relationship between the putative Ang II activity and the expression of AT receptor genes was found in the tubulointerstitium, whereas in the glomeruli this relationship was negative. In the interstitium, statistically significant positive relationships emerged between interstitial infiltrates and the gene expression of Agtg, AT1 receptor, Coll IV, and TGF-beta1.

CONCLUSION

This study demonstrates that a tight regulation of the intrarenal RAS exists in IgAN and that it follows the general rules disclosed in animal models. Moreover, the RAS seems to be activated early in the diseased kidney and it appears that such activation drives inflammation and a parallel stimulation of the TGF-beta fibrogenic loop, particularly at the tubulointerstitial level.

Angiotensin II dose-effect curves and Schild regression plots for characterization of different angiotensin II AT1 receptor antagonists in clinical pharmacology

The 'Schild regression' method is based on the principle of assessing the rightward shift of agonist dose-effect curves in the presence of different doses/concentrations of the respective receptor antagonist and presenting their relationship in a double log plot (i.e. the 'Schild plot'). The original method was developed to quantitatively characterize antagonistic drugs in experimental pharmacology. The method was adopted for evaluation of various AT1 antagonists in humans utilizing (human) angiotensin II as the agonist. Angiotensin II (Ang II) in continuous intravenous dose-incremental administration resulted in a clearly dose-dependent increase in blood pressure. All AT1 antagonists tested after oral administration yielded concentration-dependent rightward shifts of those Ang II dose-effect curves that were quantified as dose ratio (DR). DR minus 1 (DR-1) enabled the assessment of antagonist time kinetics in humans and a quantitatively precise determination of the half-life of antagonism in vivo. Schild plots allowed for assessment of apparent Ki doses indicative of a twofold rightward shift of the Ang II effect, thus providing the means for a rational comparison of the pharmacological potency of many of these compounds, where the Ki doses obtained at 24 h after administration were in the range of 'therapeutic' doses. Schild plots of a variety of substances showed linear relations independent of whether the blockade was deemed surmountable or not. It is therefore assumed that this property does not play a role at clinical doses/concentrations. Slopes slightly below 1 in the Schild plots of all tested antagonists point to a second 'counterregulatory' vasodilatory mechanism of action of Ang II which becomes apparent with AT1 blockade in conditions of high doses/concentrations of Ang II. Concentration vs. effect relationships indicate that if assessed at the same degree of direct vascular antagonism, other effects, such as increase in plasma renin activity, may be present to a varying degree with different antagonists. Thus for irbesartan, the potency to stimulate renin release was found to be at least twice that of candesartan. These observations should stimulate further research into the relevance of these dynamic differences between the various compounds. Thus, methodologies relying on fundamental principles of experimental pharmacology can provide the clinical pharmacologist with powerful tools to measure accurately degree of antagonism and time kinetics and to investigate the nature of receptor antagonism in humans.

Skeletal muscle RAS and exercise performance

A local renin-angiotensin system (RAS) may be suggested by evidence of gene expression of RAS components within the tissue as well as physiological responsiveness of this gene expression. This review will focus on the evidence supporting the existence of the constituent elements of a physiologically functional paracrine muscle RAS. The effect of local skeletal muscle RAS on human exercise performance will be explored via its relation with pharmacological intervention and genetic studies. The most likely configuration of the muscle RAS is a combination of in situ synthesis and uptake from the circulation of RAS components. A reduction in angiotensin-converting enzyme (ACE) activity reverses the decline in physical performance due to peripheral muscle factors in those with congestive heart failure and may halt or slow decline in muscle strength in elderly women. Genetic studies suggest that increased ACE and angiotensin II (Ang II) mediate greater strength gains perhaps via muscle hypertrophy whereas lower ACE levels and reduced bradykinin (BK) degradation mediate enhanced endurance performance perhaps via changes in substrate availability, muscle fibre type and efficiency.

Effects of angiotensin II on vascular endothelial cells: formation of receptor-mediated reactive nitrogen species

Angiotensin II (ANG II) participates in many cardiovascular disease states, but the mechanisms involved are not completely defined. Doses of ANG II that do not affect blood pressure significantly can still cause early changes in vascular endothelial performance and cell-specific protein 3-nitrotyrosine formation (protein-3NT, marker of peroxynitrite formation) in vivo. Here, we have tested the hypothesis that ANG II induces endothelial cell peroxynitrite (ONOO-) formation in vitro, and investigated the mechanisms involved. Endothelial cells were incubated with ANG II (1nM-250 microM), and protein nitration was assessed by immunoblotting. ANG II caused concentration-dependent increases in protein-3NT above detectable basal control levels, at concentrations greater than 100nM. This response was inhibited significantly by co-incubation with losartan or diphenyleneiodonium chloride. Endothelial cell lysates incubated with nitrated protein standards demonstrated significant protein-3NT modification activity only in the presence of serum. However, endothelial cell lysates did not modify the free amino acid form of 3NT (free-3NT) in identical experimental conditions, assessed by capillary electrophoresis. Finally, free-3NT was cytotoxic to cultured endothelial cells (fitted LC(50)=98 microM). These data demonstrate that stimulation of angiotensin receptor subtype 1 by ANG II can cause increased endothelial cell protein nitration in vitro in the absence of other cell types or stimuli, at concentrations that are pathophysiologically relevant. Furthermore, endothelial cells selectively modified nitrated protein tyrosine residues only in the presence of a cofactor(s), and did not modify the free modified amino acid. Protein nitration may be a regulated endothelial signaling process, while free-3NT may be toxic to endothelial cells.

AT4 receptor is insulin-regulated membrane aminopeptidase: potential mechanisms of memory enhancement

Although angiotensin IV (Ang IV) was thought initially to be an inactive product of Ang II degradation, it was subsequently shown that the hexapeptide markedly enhances learning and memory in normal rodents and reverses the memory deficits seen in animal models of amnesia. These central nervous system effects of Ang IV are mediated by binding to a specific site, known as the AT(4) receptor, which is found in appreciable levels throughout the brain and is concentrated particularly in regions involved in cognition. This field of research was redefined by the identification of the AT(4) receptor as the transmembrane enzyme, insulin-regulated membrane aminopeptidase (IRAP). Here, we explore the potential mechanisms by which Ang IV binding to IRAP leads to the facilitation of learning and memory.

Sex and the renin angiotensin system: implications for gender differences in the progression of kidney disease

Two recognized risk factors implicated in the pathogenesis of progressive renal disease are overactivation of the renin angiotensin system and male gender. The peptide hormone, angiotensin II, produced by the renin angiotensin system cascade, plays a crucial role in maintaining blood pressure and electrolyte homeostasis. Medications that block the action of angiotensin II by either inhibiting its synthesis or by blocking its ability to bind its receptor are in wide clinical use because of their ability to significantly retard the progression of kidney disease. Analysis of data from national end-stage renal disease registries, clinical trials, and experimental animal models suggest that the progression of chronic kidney disease from several etiologies is more rapid in men than in women. In this review, we examine the data supporting the hypothesis that modulation of the activity of the renin angiotensin system by sex steroids markedly contributes to the gender differences observed in the pathophysiology of progressive kidney disease.

Role of C-terminal cytoplasmic domain of the AT2 receptor in ligand binding and signaling

A stop codon at position 322 was introduced to generate a truncated, C-terminal-deleted AT2 receptor. Expression studies in Xenopus oocytes showed that C-terminal-deleted AT2 had reduced affinity to [(125)I]angiotensin II (K(d)=1.7 nM) and enhanced binding of the AT2-specific peptidic ligand [(125)I]CGP42112A (K(d)=0.097 nM). AT2 activation by angiotensin II resulted in reduction of cGMP levels in oocytes and this reduction was further enhanced by C-terminal deletion, implying that the C-terminus may have a negative effect on the AT2-mediated cGMP reduction. Moreover, interaction of the AT2 with the ATP-binding domain of the human ErbB3 receptor in yeast two-hybrid assay was abolished by C-terminal deletion. In summary, the C-terminal cytoplasmic tail of AT2 modulates its ligand binding and signaling properties.

AT(2) receptor-dependent vasodilation is mediated by activation of vascular kinin generation under flow conditions

Physiological roles of angiotensin II type 2 receptor (AT(2)) are not well defined. This study was designed to investigate the mechanisms of AT(2)-dependent vascular relaxation by studying vasodilation in pressurized and perfused rat mesenteric arterial segments. Perfusion of angiotensin II in the presence of AT(1) antagonist elicited vascular relaxation, which was completely dependent on AT(2) receptors on endothelium. FR173657 (>1 microM), a bradykinin (BK) B(2)-specific antagonist, significantly suppressed AT(2)-dependent vasodilation (maximum inhibition: 68.5% at 10 microM). Kininogen-deficient Brown Norway Katholiek rats showed a significant reduction in AT(2)-mediated vasodilatory response compared with normal wild-type Brown Norway rats. Indomethacin (>1 microM), aprotinin (10 microM) and soybean trypsin inhibitor (10 microM) also reduced AT(2)-dependent vasodilation. Our results demonstrated that stimulation of AT(2) receptors caused a significant vasodilation through local production of BK in resistant arteries of rat mesentery in a flow-dependent manner. Such vasodilation counterbalances AT(1)-dependent vasoconstriction to regulate the vascular tone.

Differential effects of dietary cholesterol on aminopeptidase A, B and M in the frontal cortex of male and female mice

Although hypercholesterolemia and hypertension have been extensively associated, the regulatory mechanism underlying this relationship is poorly understood. Systemic and local renin-angiotensin systems are involved in the control of blood-pressure. Angiotensin II has been considered as the main effector peptide of renin-angiotensin system. However, other peptides derived from the metabolism of angiotensin II, as angiotensins III and IV have been shown to play significant roles. The aim of this study is to analyse the effect of dietary cholesterol on the activity of the enzymes involved in the metabolism of angiotensins II and III. Soluble and membrane-bound aminopeptidase A (aspartyl- and glutamyl-aminopeptidases), B (arginyl-aminopeptidase) and M (alanyl-aminopeptidase) activities were measured in the frontal cortex of male and female mice fed a cholesterol enriched-diet (1% cholesterol; 0.5 cholic acid). Soluble and membrane-bound aminopeptidases B and M did not change in male or female cholesterol groups. Significant increases were observed in membrane-bound aspartyl- and glutamyl-aminopeptidase activities in both cholesterol groups. Soluble aspartyl- and glutamylaminopeptidases did not change in male cholesterol group, but significant decreases were detected in female cholesterol group. Our results may indicate that the metabolism of angiotensin II to angiotensin III by aminopeptidase A is increased, but angiotensin III metabolism by aminopeptidases B and M is not modified after cholesterol intake; so cholesterol may enhance the effects of angiotensin III, at least, at the cortical level.

Pharmacological differences among angiotensin II receptor antagonists

Angiotensin II AT1 receptor antagonists (AIIRAs) have demonstrated efficacy similar to other classes of antihypertensive agents as well as "placebo-level" tolerability at all doses. Pharmacokinetic and pharmacodynamic studies provide a framework for understanding important intra-class dissimilarities. Disparity in antagonistic effects may be determined by in vivo responses to challenges of exogenous angiotensin II (Ang II) and by ex vivo/in vitro responses to a drug's biological activity by radioligand receptor assay (RRA). Two independent studies have been conducted in which irbesartan exhibited a more pronounced and longer-lasting antagonism to the effects of exogenous Ang II than losartan and valsartan. Comparative trials have indicated that both irbesartan and candesartan show greater clinical efficacy in lowering blood pressure than losartan. Recently, we have compared the Ang II antagonistic properties of irbesartan 150 mg/day and candesartan 8 mg/day. Both drugs block AT1 receptors with "insurmountable" antagonism and demonstrate a long duration of action. While both irbesartan and candesartan showed a similar degree of antagonistic activity in vivo, distinctly higher antagonistic activity in plasma was found for irbesartan by RRA at all time-points. Furthermore, plasma renin activity during periods with high antagonistic activity was significantly higher, and aldosterone levels following Ang II stimulation were blunted to a greater extent, following administration of irbesartan. In summary, in the doses tested, irbesartan exhibits the strongest antagonism when compared with losartan, valsartan and candesartan. This finding may have clinical implications.

Splanchnic vasoconstriction by angiotensin II is arterial pressure dependent

BACKGROUND

Our hypothesis was that splanchnic vasoconstriction by exogenous angiotensin II (Ang II) is significantly potentiated by local mechanisms increasing vasomotor tone and that splanchnic tissue oxygenation during administration of Ang II is perfusion pressure dependent. The aim was to study local splanchnic circulatory effects and tissue oxygenation during intravenous infusion of Ang II at different levels of regional arterial driving pressure in a whole-body large animal model.

METHODS

Ang II was infused in incremental doses (0-200 microg x h-1) in anaesthetised instrumented pigs (n=8). Mean superior mesenteric arterial pressure (PSMA) was adjusted by a local variable perivascular occluder. Perivascular ultrasound and laser-Doppler flowmetry were used for measurements of mesenteric venous blood flow and superficial intestinal blood flow, respectively. Intestinal oxygenation was evaluated by oxygen tissue tension (PtiO2) and lactate fluxes.

RESULTS

Ang II produced prominent and dose-dependent increases in mesenteric vascular resistance (RSMA) when the intestine was exposed to systemic arterial pressure, but Ang II increased RSMA only minimally when PSMA was artificially kept constant at a lower level (50 mmHg) by the occluder. Although Ang II decreased PtiO2 at a PSMA of 50 mmHg, splanchnic lactate production was not observed.

CONCLUSION

We demonstrate that splanchnic vasoconstriction by exogenous Ang II is dependent on arterial driving pressure, suggesting significant potentiation through autoregulatory increases in vasomotor tone. Intestinal hypoxaemia does not seem to occur during short-term infusion of Ang II in doses that significantly increases systemic arterial pressure.

Contribution of nitric oxide, angiotensin II and superoxide dismutase to exercise-induced attenuation of blood pressure elevation in spontaneously hypertensive rats

Moderate chronic exercise attenuates the elevation of blood pressure in young spontaneously hypertensive rats. In order to elucidate the physiological process of the effects of exercise, we examined the involvement of nitric oxide, angiotensin II, and superoxide dismutase in this process. Rats were exercised by voluntary running in a wheel-cage for 10 weeks. Systolic blood pressure in the exercised rats (195+/-4 mmHg, n=27) was significantly (p<0.05) lower than in the post-control rats (212+/-3 mmHg, n=28). The concentration of total plasma nitrite was significantly higher in exercised rats (14.9+/-1.5 micromol l(-1)) than in the post-control rats (9.9+/-0.7 micromol l(-1), p<0.05). Superoxide dismutase activity in the exercised rats was significantly higher (p<0.05) than in the post-control rats (thoracic aorta: 4.6+/-0.3 U mg protein(-1) vs 3.6+/-0.3 U mg protein(-1), heart: 12.7+/-0.6 U mg protein(-1) vs 10.2+/-0.6 U mg protein(-1), p<0.05). The plasma angiotensin II concentration was higher in the post-control rats (74.4+/-14.0 pg mL(-1)) than in the exercised rats (45.0+/-6.4 pg mL(-1), p<0.05), and in the pre-control rats (47.2+/-6.0 pg mL(-1)). The results suggest that exercise acts to decrease the level of superoxide by increasing superoxide dismutase activity in the aorta and heart and to decrease levels of angiotensin II, both of which, in turn, increase the effective concentration of nitric oxide. We conclude that the combination of these effects with the increased NO formation resulted in the low blood pressure seen in the exercised rats.

Acute effects of angiotensin II on myocardial performance

BACKGROUND

Specific angiotensin II (Ang II) receptors exist in many organs including peripheral blood vessels, cardiac myocytes and the central nervous system. This suggests multiple sites of actions for Ang II throughout the cardiovascular system. Cardiac effects of Ang II are not completely understood, though its prominent vasoconstrictor actions are well described. This study was designed to assess left ventricular function during administration of Ang II using relatively load-independent methods in a whole-animal model.

METHODS

Ang II was infused in incremental doses (0-200 microg x h(-1)) in anaesthetised instrumented pigs (n=10). Cardiac systolic and diastolic function were evaluated by analysis of the left ventricular pressure-volume relationship.

RESULTS

Heart rate (HR), mean arterial pressure (MAP) and systemic vascular resistance (SVR) increased dose-dependently with Ang II, while cardiac output (CO) remained unchanged. Systolic function indices, end-systolic elastance (Ees) and preload recruitable stroke work (PRSW), demonstrated dose-dependent increases. The diastolic function parameter tau (tau) did not change with increasing Ang II dose.

CONCLUSION

Ang II infusion caused increases in contractility indices in anaesthetised pigs in the doses used in this study. The mechanisms for these systolic function effects may be a direct myocardial effect or modulated through changes in autonomic nervous system activity.

No effect of angiotensin II AT(2)-receptor antagonist PD 123319 on cerebral blood flow autoregulation

Blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors (ACE-I) or angiotensin AT1-receptor antagonists shift the limits of autoregulation of cerebral blood flow (CBF) towards lower blood pressure (BP). The role of AT2-receptors in the regulation of the cerebral circulation is uncertain. Hence, the present study investigated the effect on CBF autoregulation of blocking of angiotensin AT2-receptors with PD 123319 in spontaneously hypertensive rats (SHR). Anaesthetised and ventilated SHR were given PD 123319, 0.36 mg/kg/min, intravenously, and compared with a control group. CBF was measured by the intracarotid 133xenon injection method and BP was raised by noradrenaline infusion and lowered by controlled haemorrhage in separate groups of rats. The limits of autoregulation were determined by computed least-sum-of-squares analysis. PD 123319 did not influence baseline CBF, but resulted in a minor BP decrease (10 control and 10 treated rats). The lower limit of CBF autoregulation (eight treated and eight control) as well as the upper limit of CBF autoregulation (eight treated and eight control) were not significantly different in PD 123319 and control animals (lower limit treated 102+/-4 mmHg and control 94+/-4; NS, and upper limit treated 171 +/- 10 mmHg and control 162+/-7; NS). These findings indicate that acute AT2-receptor blockade does not influence CBF autoregularion.

Contractile effects of angiotensin peptides in rat aorta are differentially dependent on tyrosine kinase activity

It has been suggested that tyrosine kinase activity participates in the regulation of signal transduction associated with angiotensin II (Ang II)-induced pharmaco-mechanical coupling in rat aortic smooth muscle. We further tested the effects of genistein, a tyrosine-kinase inhibitor, and its inactive analogue, daidzein, on angiotensin I (Ang I), angiotensin III (Ang III) and angiotensin IV (Ang IV) contractions, as compared with those on Ang II. Genistein partially inhibited Ang II- and Ang I-induced contractions. The genistein-induced inhibition was more evident on Ang III and especially important on Ang IV contractile effects. Thus, Ang IV- and Ang III-induced contractions seem to be more dependent on tyrosine kinase activity than those evoked by Ang II or Ang I. Daidzein did not significantly affect the contractile effects of any of angiotensin peptides tested. These results clearly suggest that the inhibition of the action of angiotensin peptides actions by genistein is mediated by inhibition of endogenous tyrosine kinase activity. Furthermore, our data show that the type and/or intensity of tyrosine kinase activity is differentially associated with the contractile effects of different angiotensin peptides in rat aorta. Nifedipine, a blocker of membrane L-type Ca2+ channels, strongly inhibited Ang IV-induced contractions. At the same time, it significantly inhibited Ang III contractile effects as compared with Ang II and Ang I contractions. Meanwhile, we observed a close relationship between calcium influx and tyrosine kinase phosphorylation activity under the stimulatory effects of angiotensin peptides. Furthermore, genistein did not significantly influence the phasic contractions induced by angiotensin peptides in Ca2+-free Krebs-Henseleit solution. Thus, it appears that Ca2+ influx, rather than the release of Ca2+ from IP3-sensitive stores, may play a major role in the contractile effects of angiotensin peptides in rat aorta via tyrosine kinase activation. One argument against a direct action of genistein on the Ca2+ channel itself is that it did not markedly affect the K+-induced contraction (depolarisation) in rat aorta. At the same time, a potential role for tyrosine kinase activity in the process of calcium entry is suggested. An elevation of intracellular calcium via tyrosine kinase-mediated processes may mediate the actions of G-protein coupled receptor agonists in smooth muscle, including angiotensin peptides.

Angiotensin receptor-like immunoreactivity in adult brain white matter astrocytes and oligodendrocytes

Most of the physiological effects of brain angiotensins are currently believed to be mediated by angiotensin receptors located principally on neurons. However, numerous studies in vitro have demonstrated the presence of functional angiotensin receptors on brain astrocytes, raising the possibility that glial cells may also participate in mediating the effects of the central renin-angiotensin system. Nevertheless, it is uncertain whether these cells in situ express angiotensin receptors, raising questions about the physiological significance of results observed in cell cultures. We have examined the distribution of angiotensin receptor-like immunoreactivity in glial cells in white matter tracts in the adult CNS, using a panel of antisera to the AT1 and AT2 angiotensin receptors. Antiserum preadsorption and/or Western blot demonstrated the specificity of the antisera in brain tissue. In immunohistochemical experiments, the AT1 antisera selectively labeled AT1-expressing neurons in the piriform cortex, whereas the AT2 antiserum stained cells in the trigeminal motor nucleus, these being nuclei known to express AT1 and AT2 receptors, respectively. Using double-label immunohistochemistry, we observed AT1- and AT2-immunoreactive astrocytes and oligodendrocytes in white matter tracts, which include the rat cerebellar white matter, periventricular white matter, and optic nerve, in addition to the bovine corpus callosum and human subcortical white matter. In contrast, astrocytes in the gray matter region of the cerebral cortex were not found to be angiotensin receptor-like immunoreactive. These results demonstrate the presence of AT1 and/or AT2 angiotensin receptor-like immunoreactivity in brain white matter macroglial cells in situ and support the idea that glial cells may play a more important role in the central renin-angiotensin system than previously thought.

Gene therapy to control hypertension: current studies and future perspectives

Hypertension is a complex pathophysiological state that leads to serious complications, including heart failure, coronary artery disease, and abnormal renal function. While traditional therapies can be effective in controlling the effects of hypertension, they offer no long-term cure and often lead to patient noncompliance, thereby diminishing their effectiveness. These reasons, coupled with the recent developments in gene transfer and somatic cell gene delivery, led researchers to explore alternative options that can produce long-term control of hypertension. Gene therapy offers the potential to yield lasting antihypertensive effects by influencing the genes associated with hypertension. In this review, we will discuss the merits of sense versus antisense strategies in controlling hypertension. We also discuss the advantages and disadvantages of both viral and nonviral vector types for the systemic delivery of genes for hypertension research. Results of our research group on the retrovirus-mediated delivery of the angiotensin type I receptor-antisense on the prevention of hypertension and related cardiovascular pathophysiology will be summarized. Finally, we discuss the future of this gene therapy approach in the reversal and long-term control of hypertension.

Protective effect of agiotensin II type I receptor antagonist, CV-11974, on ischemia and reperfusion injury of the liver

BACKGROUND

Microcirculatory disturbance has been shown to play a critical role in hepatic ischemia and reperfusion (I/R) injury. Angiotensin II (AngII) is one of the most potent endogenous vasoconstrictors. Angiotensin II type I (AT1) receptor antagonist has been reported to have protective effects on I/R injury of the heart and kidney. However, effect on hepatic I/R injury has not been determined. In this study, we investigate our hypothesis that AT1 receptor antagonist, CV-11974, attenuates hepatic I/R injury.

METHODS

Twelve beagle dogs underwent a 2-hr total hepatic vascular exclusion with veno-venous bypass. CV-11974 was given to animals at a dose of 0.002 mg/ kg/min for 5 min followed by 0.001 mg/kg/min for 25 min via portal vein before ischemia (group II, n=6). Nontreated animals were used as the control (group I, n=6). Animal survival, hemodynamics, hepatic tissue blood flow (HTBF), liver function, platelet count, renin activity, and AngII concentration of hepatic vein, energy metabolism, and histopathology were analyzed.

RESULTS

Two-week survival was 33% in group I, in contrast, 100% in group II. Mean arterial blood pressure during early reperfusion was maintained, and HTBF after reperfusion was significantly higher in group II. Treatment attenuated liver enzyme release and decrease of platelet count, increased renin and AngII, suppressed ATP degradation during ischemia and enhanced ATP resynthesis after reperfusion. Neutrophil infiltration and histopathological damages were lessened in group II.

CONCLUSIONS

Our data demonstrated that the local renin-angiotensin system might play a role in hepatic microcirculation. AT1 receptor blockade with CV-11974 attenuated hepatic microcirculatory disturbance and ameliorated I/R injury.

Angiotensin receptors--evolutionary overview and perspectives

The structure of the angiotensin molecule has been well preserved throughout the vertebrate scale with some amino acid variations. Specific angiotensin receptors (AT receptors) that mediate important physiological functions have been noted in a variety of tissues and species. Physiological and pharmacological characterization of AT receptors and, more recently, molecular cloning studies have elucidated the presence of AT receptor subtypes. Comparative studies suggest that an AT receptor subtype homologous to the mammalian type 1 receptor subtype (AT(1)), though pharmacologically distinct, is present in amphibians and birds, whereas AT receptors cloned from teleosts show low homology to both AT(1) and AT(2) receptor subtypes. Furthermore, receptors differing from both the AT(1)-homologue receptor and AT(2) receptor exist in some non-mammalian species. This may suggest that the prototype AT receptor evolved in primitive vertebrates and diverged to more than one type of AT receptor subtype during phylogeny. Furthermore, phenotypic modulation of AT receptors appears to occur during individual development/maturation.

Comparative analysis of amphibian and mammalian angiotensin receptors

Amphibian angiotensin receptors (xAT receptors) share many similarities with mammalian type 1 angiotensin receptors (AT(1) receptors). Both xAT and AT(1) receptors belong to the super family of seven transmembrane spanning G protein-coupled receptors and share approximately 60% amino acid homology. Highly stable secondary structure in the 5' leader sequences and the presence of the mRNA destabilizing sequence (AUUUA) in the 3' untranslated region (3'UTR) of the xAT and AT(1) receptor mRNAs suggest similar mechanisms exist for regulating gene expression. Amphibian and mammalian AT receptors bind angiotensin with equivalent affinities but show marked differences in their affinities towards mammalian AT(1) receptor subtype selective non-peptide ligands. Both xAT and AT(1) receptors couple to G proteins and to the phospholipase C (PLC) signal transduction pathway. Mammalian AT(1) receptors play a key role in maintaining blood pressure and fluid homeostasis and there is considerable evidence that xAT receptors play a similarly important role in amphibians. This review focuses on the comparison of amphibian xAT receptors with mammalian AT(1) receptors in terms of their structure, pharmacology, signaling, and function.

Angiotensin signaling and receptor types in teleost fish

Despite advances characterizing mammalian angiotensin receptors, the phylogeny of fish angiotensin receptors remains unclear. Three aspects of receptor function: (1) the nature of the ligand; (2) the second messenger system activated by it; and (3) the pharmacological profile of specific antagonists, are examined to provide insight into the fish receptor. (1) The octapeptide sequences of fish and mammalian angiotensin II (ANG II) are nearly homologous, differing only at the first and fifth residues. Both peptides are almost equally efficacious and equipotent in heterologous systems and both contain key agonist switches Tyr(4) and Phe(8) necessary to activate mammalian AT(1)-type receptors. (2) ANG II increases inositol trisphosphate production, and elevates intracellular calcium in fish tissues consistent with activation of the AT(1) receptor. (3) However, the specific mammalian sartan-type AT(1) antagonists, e.g. losartan, produce inconsistent results in fish often acting as partial agonists, or inhibiting only at elevated concentrations. Because sartans and ANG II act at distinct sites on the AT(1) receptor, we propose that the teleost receptor is an AT(1)-type receptor that is fairly well conserved with respect to both the ANG binding site and coupling to the second messenger system, whereas the sartan binding site has been poorly conserved. The evidence for non-AT(1) type ANG II receptors in teleosts is limited. Mammalian AT(2) receptor antagonists are generally ineffective but may block at elevated, non-specific doses. Truncated ANG II fragments, ANG III and ANG IV, are often less potent than ANG II, however, their receptors have not been examined. Preliminary studies in trout indicate that angiotensin 1-7 may have a mild vasodilatory effect; additional work is needed to determine if non-AT(1)-type receptors are involved.

Current perspectives on the use of gene therapy for hypertension

Systemic hypertension is a pathophysiological state that is manifested as high blood pressure and is a major risk factor for stroke, ischemic heart disease, peripheral vascular disease, and progressive renal damage. Pulmonary hypertension occurs in 3 distinct forms: primary pulmonary hypertension, pulmonary hypertension of the newborn, or secondary pulmonary hypertension attributable to a variety of lung and cardiovascular diseases. This review discusses the use of gene therapy in the control of systemic and pulmonary hypertension. Overexpression of vasodilator genes as well as antisense knockdown of vasoconstrictor genes has been successfully used in animal models of both forms of hypertension. Furthermore, the use of viral vectors to deliver these constructs has achieved long-term control of hypertension. The successful establishment of gene therapy techniques in the animal models of hypertension coupled with the anticipated advances in the genetic aspects of this disease would make it highly feasible to attempt gene delivery in the control of human hypertension.

The pharmacological potency of various AT(1) antagonists assessed by Schild regression technique in man

RATIONALE

A quantitative technique was used to compare the pharmacological potency in healthy volunteers of angiotensin II receptor antagonists (AIIA): candesartan cilexetil, losartan, irbesartan, valsartan, and telmisartan.

METHODS

In a randomised, double-blind, parallel-group (4x12 subjects) study, single oral doses of candesartan cilexetil 4, 8 and 16 mg, losartan potassium 25, 50 and 100 mg, valsartan 40, 80 and 160 mg, and irbesartan 75, 150 and 300 mg were administered on three consecutive days. Telmisartan 20, 40 and 80 mg was similarly evaluated in 12 volunteers in an open amendment. Angiotensin II (Ang II) antagonistic effects were determined in vivo from rightward shifts in Ang II dose-response curves for diastolic blood pressure (BP) and dose ratios were calculated. Apparent K(i)-doses, i.e. doses (in mg) required to induce a two-fold shift in Ang II dose-response curves (equivalent to approx. 50% blockade of receptors) were determined, using Schild regression analysis.

RESULTS

All treatments dose-dependently attenuated increases in diastolic BP induced by infusion of exogenous Ang II. Candesartan cilexetil appeared to have a more pronounced increase in effect following cumulative dosing. At 24 hours, apparent K(i)-doses were: candesartan cilexetil 6 mg, irbesartan 123 mg, valsartan 93.5 mg, and telmisartan 54 mg. It was not possible to determine an apparent K(i)-dose for losartan at 24 hours.

CONCLUSION

Consistent with results from experimental pharmacology, candesartan cilexetil displayed the highest pharmacological potency (i.e. antagonistic activity per mg substance) of the AIIAs tested. Apparent K(i)-doses at 24 hours were within the dose range recommended for clinical use in patients with hypertension.

Recent developments in gene therapy for cardiac disease

Cardiovascular[TRACE;del] disease is the leading cause of death in the US and world-wide. Advances in molecular biology and the human genome project have revealed opportunities for novel strategies for cardiac gene therapy. This review discusses general and specific aspects of gene transfer strategies in cardiac tissues. These include 1) the selection and/or optimization of the vector for gene transfer; 2) the identification of the target gene(s); 3) the use of cardiac-specific promoters; and 4) the use of an appropriate delivery system for administration. Currently, several vectors (e.g., viral and nonviral vectors) have been developed and many target genes have been identified (e.g., VEGF, FGF, beta-AR, etc.). Many investigations have provided experimental models for gene delivery systems but the most efficient cardiac gene transfer was obtained from intramyocardial injection or perfusion of explanted myocardium. The data available thus far have suggested favorable immediate effects following gene transfer, but long-term value of cardiac gene therapy has not been proven. Further refinements in appropriate vectors that provide cell or tissue selectivity and long-lasting effects are necessary as well as the development of minimally invasive procedures for gene transfer.

Role of the angiotensin AT(1) receptor in rat aortic and cardiac PAI-1 gene expression

Although the renin-angiotensin system has been implicated in increasing plasminogen activator inhibitor-1 (PAI-1) expression, the role of the angiotensin type 1 (AT(1)) receptor is controversial. This report examines the effects of angiotensin peptides, angiotensin-converting enzyme inhibition, and AT(1) antagonism on rat aortic and cardiac PAI-1 gene expression. In vitro, angiotensin (Ang) I, Ang II, and angiotensin Arg(2)-Phe(8) (Ang III) were potent agonists of PAI-1 mRNA expression in rat aortic smooth muscle cells (RASMCs), and stimulation of PAI-1 by these peptides was blocked by the AT(1) antagonist candesartan. Angiotensin Val(3)-Phe(8) (Ang IV) and angiotensin Asp(1)-Pro(7) (Ang [1-7]) did not affect PAI-1 expression in RASMCs. In neonatal rat cardiomyocytes, Ang II increased PAI-1 mRNA expression by 4-fold (P<0.01), and this response was completely blocked by AT(1) receptor antagonism. Continuous intrajugular infusion of Ang II into Sprague-Dawley rats for 3 hours increased aortic and cardiac PAI-1 mRNA expression by 17- and 9 fold, respectively, and these Ang II responses were completely blocked by coinfusion with candesartan. Aortic and cardiac PAI-1 expressions were compared in spontaneously hypertensive rats and Wistar-Kyoto rats. PAI-1 expression in the aorta and heart from spontaneously hypertensive rats was 5.8-fold and 2-fold higher, respectively, than in control Wistar-Kyoto rats (P<0.05). Candesartan treatment for 1 week reduced aortic and cardiac PAI-1 expression in spontaneously hypertensive rats by 94% and 72%, respectively (P<0.05), but did not affect vascular PAI-1 levels in Wistar-Kyoto rats. These results demonstrate a role for the AT(1) receptor in mediating the effects of Ang II on aortic and cardiac PAI-1 gene expression.

AT(1) and AT(2) receptors in the kidney: role in disease and treatment

All components of the renin-angiotensin system (RAS) are present in the kidneys and constitute a functioning renal RAS. Angiotensin II (Ang II) receptor subtypes AT(1) and AT(2) have been identified in the afferent and efferent arterioles, glomeruli, mesangial cells, and proximal tubules. AT(1) receptors regulate vasoconstriction and sodium and water reabsorption, as well as promote cell growth, proliferation, and collagen matrix deposition. Recent animal studies are elucidating the role of the less well understood AT(2) receptors. The AT(2) receptors appear to counterbalance the AT(1) receptors by increasing the production of bradykinin, nitric oxide, and cyclic guanosine monophosphate-mediating vasodilation and by promoting cell differentiation, antiproliferation, and apoptosis. Ang II subtype 1 receptor blockers prevent Ang II activation of the AT(1) receptor while leaving the AT(2) receptor open to Ang II stimulation.

Reinforcement of arteriolar myogenic activity by endogenous ANG II: susceptibility to dietary salt

The purpose of this study was to determine whether endogenous ANG II augments arteriolar myogenic behavior in striated muscle. Because circulating ANG II is decreased during high salt intake, we also investigated whether dietary salt could alter any influence of ANG II on myogenic behavior. Normotensive rats fed low-salt (0.45%, LS) or high-salt (7%, HS) diets were enclosed in a ventilated box with the spinotrapezius muscle exteriorized for intravital microscopy. Dietary salt did not affect resting arteriolar diameters. Microvascular pressure elevation by box pressurization caused greater arteriolar constriction in LS rats (up to 12 microm) than in HS rats (up to 4 microm). The ANG II-receptor antagonists saralasin and losartan attenuated myogenic responsiveness in LS rats but not HS rats. The bradykinin-receptor antagonist HOE-140 had no effect on myogenic responsiveness in LS rats but augmented myogenic responsiveness in HS rats. HOE-140 with the angiotensin-converting enzyme inhibitor captopril attenuated myogenic responsiveness to a greater extent in LS rats than in HS rats. We conclude that endogenous ANG II normally reinforces arteriolar myogenic behavior in striated muscle and that attenuated myogenic behavior associated with high salt intake is due to decreased circulating ANG II and increased local kinin levels.

Binding and signaling of angiotensin-(1-7) in bovine kidney epithelial cells involves the AT(4) receptor

Angiotensin-(1-7) decreased mitogen-activated protein (MAP) kinase (Erks) activation in cultured Mardin-Darby bovine kidney (MDBK) epithelial cells. Also, saturable, high-affinity (125)I-angiotensin-(1-7) binding was detected in MDBK cell membranes. Together, the data suggested the possible presence of an angiotensin-(1-7) receptor. However, ligand structure-binding studies revealed that angiotensin-(3-7) and AT(4) receptor ligands competed with high-affinity for (125)I-angiotensin-(1-7) binding. Furthermore, angiotensin-(3-7) and AT(4) receptor ligands decreased MAP kinase activation in MDBK cells. These results demonstrate that NH(2)-terminal-deleted metabolites of angiotensin-(1-7) can bind with high affinity to the AT(4) receptor and regulate the MAP kinase/Erk signaling pathway in renal epithelial cells.

Active immunization with angiotensin I peptide analogue vaccines selectively reduces the pressor effects of exogenous angiotensin I in conscious rats

1. Male, Sprague-Dawley rats were actively immunized with novel angiotensin vaccines, and their pressor responses to exogenous angiotensin I (AI) and angiotensin II (AII) were assessed in vivo. Serum antibody titres were also measured. 2. The most effective vaccine consisted of an AI analogue conjugated with a tetanus toxoid carrier protein and adjuvanted with aluminium hydroxide. When this vaccine was injected on days 0, 21 and 42, pressor responses to AI on day 63 were significantly inhibited (maximum, 8.9 fold shift), but responses to AII were unaffected. The anti-angiotensin antibody titre was increased 32,100 fold, and, uniquely, these antibodies also cross-reacted with angiotensinogen. 3. These findings indicate that active immunization against AI may be a useful approach for treating cardiovascular disorders involving the renin-angiotensin system.

Evaluation of three polymorphisms in the promoter region of the angiotensin II type I receptor gene

BACKGROUND

Angiotensin II induces vasoconstriction and growth via stimulation of the AT1 receptor. A genetic variant (+1166A/C) in the 3' untranslated region of this gene had been found to be associated with arterial hypertension, aortic stiffness and coronary artery disease.

OBJECTIVE

In order to evaluate further the potential implications of the genetic variability of the AT1 gene we explored three newly characterized single nucleotide polymorphisms (SNPs) in its promoter in a Caucasian population-based sample (n = 623). One of these (-2228G/A) is in complete linkage disequilibrium with six additional SNPs in the region such that, indirectly, potential functional implications of these sites were assessed as well. For comparison, we genotyped the previously described +1166A/C variant

RESULTS

The allele frequencies of the -2228G/A, -1424C/ G and -521 C/T SNPs were 0.82/0.18, 0.963/0.037 and 0.64/0.36, respectively. Statistical analysis by one-factor ANOVA revealed no significant relationship of any allele, genotype or haplotype with age, sex, body mass index, heart rate, systolic or diastolic blood pressure, hypertension, the intake of antihypertensive medication or left ventricular mass. Likewise, renin, angiotensinogen, angiotensin-converting enzyme, aldosterone or atrial natriuretic peptide levels were not found to be associated with any of these SNPs. Surprisingly, the -2228 A allele was found to be overrepresented in subjects with diabetes mellitus (n = 25, P = 0.006). However, this result could not be confirmed when additional individuals with diabetes mellitus (n = 45) were analysed. A weak linkage disequilibrium was observed between the -2228 A allele and the +1166 C allele (chi2 1 3.1; P = 0.010).

CONCLUSION

From the present data it is unlikely that any one of the nine newly characterized SNPs in the promoter region of AT1 gene is associated with arterial hypertension.

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.

Genetic control of fertility and embryonic waste in the mouse: A rolefor angiotensinogen

The purpose of this study was to evaluate the impact of angiotensinogen gene (Agt) deficiency on reproductive fitness in a rodent model. Mice with 0 (Agt(-/-)), 1 (Agt(-/+)), and 2 (Agt(+/+)) copies of Agt were bred according to the following schemes: 1) Agt(-/-) x Agt(-/-), 2) Agt(-/+) x Agt(-/+), 3) Agt(+/+) x Agt(+/+), and 4) Agt(+/+) female symbol x Agt(-/+) male symbol. There were 4 breeding pairs per scheme. Breedings were time mated. Mice and litters were weighed daily. Southern blotting was used for genotyping. We found that Agt(-/-) breeding pairs had fewer litters (2 [range 1-2] vs. 4 [range 3-5]; P = 0.01), fewer pups per litter (4 [range 1-7] vs. 6 [range 1-10]; P = 0.006), and longer interpregnancy intervals (43 days [range 31-44] vs. 35.5 days [range 22-58]; P = 0.04) compared to wild-type controls. The ratio of postcoital plugs to subsequent litters was 4.0 and 1.2 for Agt(-/-) and Agt(+/+) breedings, respectively (P = 0.03). Median maternal weights during all trimesters of pregnancy were significantly lower for Agt-deficient mice compared to wild-type controls. Among Agt(-/+) x Agt(-/+) breedings, the proportions of Agt(+/+) (n = 17), Agt(-/+) (n = 38), and Agt(-/-) (n = 4) offspring differed significantly from the expected 1:2:1 Mendelian inheritance pattern (P = 0.03). Neonatal survival among the offspring derived from the Agt(-/-) x Agt(-/-) breeding scheme was significantly reduced (P = 0. 001). We conclude that Agt deficiency is associated with an in utero lethal effect, decreased fertility, and impaired neonatal survival.

Angiotensin I-converting enzyme antisense gene therapy causes permanent antihypertensive effects in the SHR

The renin-angiotensin system plays a critical role in the control of blood pressure (BP), and its hyperactivity is associated with the development and maintenance of hypertension. Although traditional pharmacological therapies targeted toward the inhibition of the renin-angiotensin system are effective in the control of this disease, they pose significant limitations. We used an antisense gene delivery strategy to circumvent these limitations and established that a single intracardiac administration of angiotensin type 1 receptor antisense (AT(1)R-AS) causes permanent prevention of hypertension in the spontaneously hypertensive rat (SHR), an animal model of primary human hypertension. Our objectives in this study were 2-fold: to determine (1) whether the targeting of angiotensin I-converting enzyme (ACE) mRNA by a similar antisense strategy would prevent the SHR from developing hypertension and (2) whether the antihypertensive phenotype is transmitted to the offspring from the antisense-treated parents. Administration of a retroviral vector containing ACE antisense (LNSV-ACE-AS) caused a modest yet significant attenuation of high BP ( approximately 15+/-2 mm Hg) exclusively in the SHR. This was associated with a complete prevention of cardiac and renovascular pathophysiological alterations that are characteristic of hypertension. Like their parents, the F(1) generation offspring of the LNSV-ACE-AS-treated SHR expressed lower BP, decreased cardiac hypertrophy, and normalization of renal arterial excitation-coupling compared with offspring derived from the LNSV-ACE-tS (truncated sense)-treated SHR. In addition, the endothelial dysfunction commonly observed in the SHR renal arterioles was significantly prevented in both parents and offspring of the LNSV-ACE-AS-treated SHR. Polymerase chain reaction followed by Southern analysis revealed that the ACE-AS was integrated into the SHR genome and transmitted to the offspring. These observations suggest that transmission of ACE-AS by retroviral vector may be responsible for the transference of normotensive phenotypes in the SHR offspring.

Angiotensin I-converting enzyme antisense prevents altered renal vascular reactivity, but not high blood pressure, in spontaneously hypertensive rats

The renin-angiotensin system plays a critical role in the control of blood pressure, and its hyperactivity is associated with the development of human primary hypertension. Because low-dose angiotensin I-converting enzyme (ACE) inhibitors cause small reductions in blood pressure that are associated with the complete reversal of altered vascular pathophysiology, our objective in this study was to determine whether ACE antisense (ACE-AS) gene delivery prevents alterations in renal vascular physiology in the parents and F(1) offspring of AS-treated spontaneously hypertensive rats (SHR). A single bolus intracardiac injection of ACE-AS (2x10(8) colony-forming units) in SHR neonates caused a modest (18+/-3 mm Hg, n=7 to 9) lowering of blood pressure, which was maintained in the F(1) generation offspring (n=7 to 9). Alterations in renal vascular reactivity, electrophysiology, and [Ca(2+)](i) homeostasis are underlying mechanisms associated with the development and establishment of hypertension. Renal resistance arterioles from truncated ACE sense-treated SHR showed a significantly enhanced contractile response to KCl and phenylephrine (n=24 rings from 6 animals, P<0.01) and significantly attenuated acetylcholine-induced relaxations (n=24 rings from 6 animals, P<0.01) compared with arterioles from ACE-AS-treated SHR. In addition, compared with cells dissociated from arterioles of ACE-AS-treated SHR, cells from truncated ACE sense-treated animal vessels had a resting membrane potential that was 22+/-4 mV more depolarized (n=38, P<0.01), an enhanced L-type Ca(2+) current density (2.2+/-0.3 versus 1.2+/-0.2 pA/pF, n=23, P<0.01), a decreased Kv current density (16.2+/-1.3 versus 5.4+/-2.2 pA/pF, n=34, P<0.01), and increased Ang II-dependent changes in [Ca(2+)](i) (n=142, P<0.01). Similar effects of ACE-AS treatment were observed in the F(1) offspring. These results demonstrate that ACE-AS permanently prevents alterations in renal vascular pathophysiology in spite of the modest effect that ACE-AS had on high blood pressure in SHR.

Lipopolysaccharides and cytokines downregulate the angiotensin II type 2 receptor in rat cardiac fibroblasts

The present study examines the effect of lipopolysaccharides and proinflammatory cytokines on the expression of the second isoform of the angiotensin II receptor (AT(2)), which may have a role in lowering collagen deposition in cardiac tissue. Cardiac fibroblasts express high levels of both angiotensin II type 1 (AT(1)) and type 2 receptors. Incubation with lipopolysaccharides for 24 h dose- and time-dependently decreased angiotensin II AT(2) receptor expression with no apparent difference in the affinity. Actinomycin D, cycloheximide, N(omega)-nitro-L-arginine methyl ester and the protein tyrosine kinase inhibitor herbimycin A, but not the protein kinase C inhibitors bisindolylmaleimide and calphostin C, abolished the inhibitory action of lipopolysaccharides. The cytokines interleukin-1beta and tissue necrosis factor-alpha mimicked the effect of lipopolysaccharides. All three compounds induced inducible nitric oxide synthase (iNOS). The nitric oxide donor sodium nitroprusside and the cGMP analog 8-bromoguanosine cyclic monophosphate downregulated angiotensin II AT (2) receptor expression. The findings are consistent with the pathway in which lipopolysaccharides or cytokines induce iNOS. The data suggest that lipopolysaccharide- or cytokine-dependent induction of iNOS and resultant production of nitric oxide leads to the production of cGMP, which in turn downregulates expression of the angiotensin II AT (2) receptor in cardiac fibroblasts.