Circulating and tissue angiotensin systems

Aldosterone induces angiotensin-converting-enzyme gene expression in cultured neonatal rat cardiocytes

BACKGROUND

The cardiac renin-angiotensin-aldosterone system is activated in failing hearts in proportion to the severity of the disease. We hypothesized that a positive feedback mechanism might exist within this system and contribute to the progression of the heart failure. Methods and Results-- To test this hypothesis, we examined whether angiotensin II or aldosterone induces the expression of angiotensin-converting-enzyme (ACE) mRNA in cultured neonatal rat ventricular cardiocytes. Expression of ACE mRNA was detected and quantified using real-time reverse transcription-polymerase chain reaction. Exposure to angiotensin II (10(-5) mol/L) for 24 hours had no significant effect on the expression of ACE mRNA (0.7+/-0.5-fold versus control, P=NS), but similar treatment with aldosterone (10(-5) mol/L) induced a 23.3+/-7.9-fold increase (P<0.01) in ACE mRNA expression. The effect of aldosterone was both time- (maximal effect, 24 hours) and dose-dependent (EC(50), 4x10(-7) mol/L), and it was significantly (P<0.01) inhibited by spironolactone, a specific mineralocorticoid receptor antagonist.

CONCLUSIONS

Aldosterone upregulates ACE mRNA expression, which is blocked by spironolactone in neonatal rat cardiocytes. Thus, spironolactone may suppress the progression of heart failure by blocking the effects of aldosterone and angiotensin II.

Metabolism of angiotensin I by guinea pig aqueous humor

We investigated the degradation of angiotensin I (Ang I) by guinea pig aqueous humor at physiological pH (pH 7.4) and assessed the activity of responsible enzymes using various enzyme inhibitors. The aqueous humor was incubated with Ang I in the presence or absence of an enzyme inhibitor at 37°C for the appropriate time period. The resulting peptides were analyzed by a Beckman HPLC system with a Waters µBondapak C18 analytical column using a 30-min increasing linear gradient of 10 to 40% acetonitrile containing 0.05% trifluoroacetic acid (TFA) and H2O containing 0.05% TFA at a flow rate of 1 mL/min. Detection was done by absorbance at 214 nm. Angiotensin II (Ang II) was a major product (39.3 ± 4.10 nmol·h–1·mL–1, n = 5) of Ang I hydrolysis. Traces of angiotensin 1–9, angiotensin IV, and angiotensin 1–7 were also produced. Chymostatin (0.05 mmol/L), EDTA (1 mmol/L), enalaprilat (0.1 mmol/L), and ebelacton B (0.01 mmol/L) inhibited generation of Ang II from Ang I by guinea pig aqueous humor by 89 ± 4.6, 56 ± 7.6, 33 ± 5.1, 20 ± 6.5 %, respectively. Our findings indicate that guinea pig aqueous humor contains several enzymes that can form Ang II. The chymostatin-sensitive type of enzyme was the most active one found in guinea pig aqueous humor. Angiotensin I converting enzyme, carboxypeptidase A, and deamidase may also contribute to angiotensin II formation in guinea pig ocular fluid.Key words: aqueous humor, angiotensin I, angiotensin II, chymase-like activity, ACE, guinea pig.

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.

KT3-671, an angiotensin AT1 receptor antagonist, attenuates vascular but not cardiac responses to sympathetic nerve stimulation in pithed rats

Effects of KT3-671 on vascular and cardiac sympathetic neurotransmission were investigated in pithed rats. The pressor response to spinal stimulation (5 Hz) of the pithed rat without the adrenals was approximately 75% of that with the adrenals. Guanethidine (8 mg/kg, i.v.) decreased by about 76% the pressor response to sympathetic stimulation in the pithed rat with intact adrenals and the guanethidine-resistant response was almost completely abolished by bilateral adrenalectomy. Therefore, the following experiments were done using the pithed rat without the adrenals. KT3-671 (1-10 mg/kg, i.v.) as well as losartan (1-10 mg/kg, i.v.) inhibited dose-dependently the pressor response to sympathetic stimulation. KT3-671 was approximately four times more potent than losartan in inhibiting the pressor response. The two angiotensin II subtype 1 receptor antagonists (10 mg/kg, i.v.) did not affect the pressor response to exogenously administered norepinephrine. Neither KT3-671 nor losartan influenced the tachycardia induced by spinal stimulation and isoprenaline. Intravenous infusion of angiotensin II (100 ng/kg/min) did not affect both pressor and tachycardic responses to sympathetic stimulation. In conclusion, KT3-671 as well as losartan inhibits vascular but not cardiac sympathetic neurotransmission of the pithed rats, which may contribute to its overall antihypertensive efficacy.

Upregulation of immunoreactive angiotensin II release and angiotensinogen mRNA expression by high-frequency preganglionic stimulation at the canine cardiac sympathetic ganglia

The possible involvement of the local angiotensin system in ganglionic functions was investigated in the canine cardiac sympathetic ganglia. Positive chronotropic responses to preganglionic stellate stimulation at high frequencies, after intravenous administration of pentolinium plus atropine, were inhibited by the nonpeptide angiotensin AT(1) receptor antagonist forasartan or the angiotensin I-converting enzyme inhibitor captopril, whereas the rate increases elicited by the postganglionic stellate stimulation and norepinephrine given intravenously failed to be inhibited by these antagonists. The levels of endogenous immunoreactive angiotensin II, as determined by radioimmunoassay in the incubation medium of the stellate and inferior cervical ganglia, were increased after the high-frequency preganglionic stimulation of the isolated ganglia. The increment of the peptide was also antagonized by the pretreatment with captopril but not by a chymase inhibitor, chymostatin. The expression of angiotensinogen mRNA was observed in the stellate ganglion, adrenal, liver, and lung but not in the ovary and spleen. The expression of the mRNA in the stellate and inferior cervical ganglia increased after high-frequency preganglionic stimulation of the in vivo dogs for a period of 1 hour. These results indicate that an intrinsic angiotensin I-converting enzyme-dependent angiotensin system exists in the cardiac sympathetic ganglia, which is activated by high-frequency preganglionic stimulation.

Evolution and pathophysiology of chronic systolic heart failure

Understanding of the pathophysiology of chronic systolic heart failure evolved from a purely mechanical model to one in which a cascade of neurohormones and biologically active molecules are thought to be critical in the development, maintenance, and progression of the disease. Two important neurohormonal systems are the sympathetic nervous and renin-angiotensin-aldosterone systems. Initially, increases in norepinephrine concentrations from the sympathetic nervous system and in angiotensin II and aldosterone are beneficial in the short term to maintain cardiac output after an insult to the myocardium. However, long-term exposure to these neurohormones causes alterations of myocytes and interstitial make-up of the heart. These alterations in myocardium lead to progression of heart failure and, eventually, death.

Antisense oligonucleotide inhibition of angiotensinogen in the brains of rats and sheep

Phosphorothioated antisense oligodeoxynucleotides (ODNs) that were complementary to various parts of the rat or sheep mRNA encoding angiotensinogen were synthesized by conventional techniques. Their effectiveness as blockers of angiotensinogen synthesis in the brain was tested by bioassay. This involved measuring the effect of centrally administered antisense ODNs on water drinking that occurred in response to intracerebroventricular injection of hog renin. Renin-induced drinking requires brain angiotensinogen for the generation of angiotensin I and then angiotensin II to stimulate thirst. Intracerebroventricular injection of an 18-mer antisense ODN (0.5 microg twice in 24 h) complementary to the 5'-end start codon for rat angiotensinogen mRNA caused a pronounced inhibition of renin-induced drinking. This effect appeared to be specific for this region of the codon because antisense ODNs directed against other regions of rat angiotensinogen mRNA were ineffective, and renin-induced drinking was not inhibited by intracerebroventricular injection of scrambled or mismatched sequences of the effective ODN or by intraperitoneal injection of it. Intracerebroventricular injection of antisense ODN (0.5 microg twice in 24 h) did not inhibit appetite or affect water drinking in response to some other dipsogenic stimuli, thus demonstrating the specificity of its action against renin-induced drinking. By contrast, intracerebroventricular administration of 625 microg of an antisense ODN directed against the corresponding 5'-end start codon region of sheep angiotensinogen mRNA did not inhibit intracerebroventricular renin-induced drinking in sheep. These data show that while intracerebroventricularly administered antisense may be used effectively in rodents, the method is not necessarily applicable in larger mammals.

Angiotensin II induces gene transcription through cell-type-dependent effects on the nuclear factor-kappaB (NF-kappaB) transcription factor

The vasopressor octapeptide, angiotensin II (Ang II), exerts homeostatic responses in cardiovascular tissues, including the heart, blood vessel wall, adrenal cortex and liver (a major source of circulating plasma proteins). One of the effects of Ang II is to induce expression of regulatory, structural and cytokine genes that play important roles in long-term control of blood pressure, vascular remodeling, cardiac hypertrophy and inflammation. The identification of nuclear signaling pathways and target transcription factors has provide important insight into cellular responses and the spectrum of genes controlled by Ang II. Here we will review how Ang II activates the transcription factors, Activator Protein 1 (AP-1), Signal Transducer and Activator of Transcription (STATs), and Nuclear Factor-kappaB (NF-kappaB). NF-kappaB is of particular interest because it is an important mediator of resynthesis of the Ang II precursor, angiotensinogen AGT. Through this positive feedback loop, long-term changes in the activity of the renin angiotensin system occur. Although NF-kappaB is ubiquitously expressed, surprisingly the mechanism for Ang II-inducible NF-kappaB regulation differs between aortic smooth muscle cells (VSMCs) and hepatocytes. In VSMC, Ang II induces nuclear translocation of cytoplasmic transactivatory NF-kappaB proteins through proteolysis of its inhibitor, IkappaB. By contrast, in hepatocytes, Ang II induces large nuclear isoforms of NF-kappaB1 to bind DNA through a mechanism independent of changes in IkappaB turnover. NF-kappaB activation depends upon the activity of DAG-sensitive PKC isoforms and ROS signaling pathway. These observations indicate that significant differences exist in Ang II signaling depending upon cell-type involved and suggest the possibility that tissue-selective modulation of Ang II effects is possible in the cardiovascular system.

Definitive molecular evidence of renin-angiotensin system in human uterine decidual cells

The tissue renin-angiotensin system (RAS) has been suggested to be present in human gestational tissues, but uncertainty exists about the authenticity of this RAS, and the cellular origin of this RAS has not been defined. In the present study, we confirmed the presence of authentic renin and angiotensinogen in the prolactin-producing decidual tissue by sequencing the cDNAs generated through reverse transcription-polymerase chain reaction, confirming cDNA product sizes, and by performing Northern blot analysis of the RNA. Our comparative data demonstrate that prolactin has the highest expression in the decidual tissue, followed by renin, and that angiotensinogen has the least expression. We demonstrated with fluorescent in situ hybridization that prolactin-expressing endocrine decidual cells are the same cells that express both renin and angiotensinogen. These results have implications in regard to how the decidual RAS may be regulated and what potential role this local RAS may have in the pathogenesis of preeclampsia.

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.

Tissue angiotensin II and endothelin-1 modulate differently the response to flow in mesenteric resistance arteries of normotensive and spontaneously hypertensive rats

In resistance arteries pressure-induced (myogenic) tone (MT) and flow (shear stress)-induced dilation (FD) are potent determinant of vascular resistance. We investigated the role of angiotensin II and endothelin-1 in FD and MT in resistance arteries and their potential change in hypertension. Flow - diameter - pressure relationship was established in situ, under anaesthesia, in two daughter branches of a mesenteric resistance artery (180 microM, n=7 per group) from spontaneously hypertensive (SHR) or normotensive (WKY) rats. One artery was ligated distally, so that it was submitted to pressure only, while the other was submitted to pressure and flow. Drugs were added to the preparation and external diameter, pressure and flow measured continuously. External diameter (with flow) ranged from 150+/-3 to 191+/-7 microM in WKY (n=28) rats and from 168+/-6 to 186+/-6 microM in SHR (n=28). Flow induced a dilation of the non-ligated arteries which was lower in SHR (13+/-5 - 31+/-4 microM vs WKY: 5+/-5 - 44+/-4 microM). In the ligated artery, the diameter did not significantly change, due to MT. In the vessels submitted to flow angiotensin converting enzyme inhibition (perindopril, 10 micromol L(-1)) increased the diameter in SHR (+11+/-2 microM) significantly more than in WKY (+2+/-1 microM). Angiotensin type 1 receptor (AT(1)R) blockade (losartan, 10 micromol L(-1)) increased the diameter in the vessels with flow in SHR only (+6+/-1 microM). Angiotensin type 2 receptor (AT(2)R) blockade (PD 123319, 1 micromol L(-1)) decreased arterial diameter in WKY only (9+/-2). Endothelin-1 type A receptor (ET(A)R) blockade (LU135252, 0.1 micromol L(-1)) increased the diameter only in SHR in the artery submitted to flow (by 6+/-1 microM). Thus FD was counteracted by a flow-dependent AT(1) and ET(A) receptors-activation in SHR whereas in WKY FD AT(2)-dependent dilation is involved.

CD143 in the development of atherosclerosis

The expression of CD143 (angiotensin-I-converting enzyme, ACE) in cardiovascular diseases may be an important determinant of local angiotensin and kinin concentrations. Much of the experimental and clinical evidence suggests a crucial role for Ang II in fibrogenesis and the development of atherosclerosis. Therefore, we have studied the distribution of CD143 in atherosclerotic and non-atherosclerotic segments isolated from different parts of the human vascular tree, including aorta and coronary, carotid, brachial, renal, iliac and femoral arteries, and staged according to the AHA. Two hundred and thirty native and formalin-fixed specimens of 80 patients were analysed by sensitive APAAP-technique using ten different monoclonal and polyclonal antibodies to human CD143 and several controls. In non-atherosclerotic segments or intimal thickening, CD143 was found almost restricted to the endothelial cells of adventitial arterioles and small muscular arteries. In contrast, a striking accumulation of CD143 was detected in all early and advanced atherosclerotic lesions. This de-novo occurrence of CD143 within the intimal vascular wall was caused by spindle-shaped subendothelial cells with macrophagic/histocytic features, activated macrophages and foam cells. In addition, advanced lesions of atherosclerosis showed a marked neo-expression of CD143 in newly formed intimal microvessels. Hypocellular fibrotic plaques depleted in microvessels and macrophages showed only little CD143. The de-novo occurrence of CD143 was dependent on the stage of atherosclerosis but not on its particular localisation within the vascular system. This early and obligatory CD143 expression at an unusual vascular site may contribute to unusual tissue levels of angiotensins as indicated by co-localisation of immunoreactive Ang II. Thus, it may be an important pathogenetic step in the development of atherosclerosis and an established target for pharmacological prevention.

Paracrine effects of angiotensin-converting-enzyme- and angiotensin-II-receptor- inhibition on transcapillary glucose transport in humans

The paracrine renin-angiotensin-system (RAS) is increasingly recognized to play an important role in the regulation of both, regional vascular tone and regional glucose metabolism. To date, however, a selective investigation of paracrine RAS effects in an in vivo clinical setting was beyond technical reach. We here set out to selectively study the metabolic effects of paracrine RAS inhibition at different levels in healthy volunteers (n = 8). For this purpose bradykinin, enalaprilate and losartan were administered locally to the interstitial space fluid in skeletal muscle by means of reverse microdialysis and transcapillary glucose transport was measured simultaneously. During reverse microdialysis with bradykinin and enalaprilate a significant decrease in arterial-interstitial-gradient for glucose (AIG(glu)) was observed (from 1.49 +/- 0.08 mM to 0.12 +/- 0.63 mM (p = 0.018) for bradykinin and from 1.5 +/- 0.07 mM to 0.24 +/- 0.67 mM (p = 0.043) for enalaprilate). In contrast, losartan had no effect on AIG(glu). The changes in transcapillary glucose transport during bradykinin and enalaprilate administration were accompanied by significant increases in interstitial lactate levels which was most pronounced for bradykinin (from 0.14 +/- 0.01 mM to 0.40 +/- 0.07 mM, p = 0.018). We conclude that paracrine angiotensin-converting-enzyme (ACE) inhibition but not angiotensin II (AT-II) receptor blockade decreases AIG(glu) and facilitates transcapillary glucose transport due to an increase in interstitial bradykinin concentration. These results support the concept that blood pressure control with ACE-inhibitors but not with AT-II-receptor-antagonists has beneficial long term metabolic consequences in hypertensive, hyperinsulinemic subjects.

Activation of local renin-angiotensin system by chronic hypoxia in rat pancreas

Previous studies have provided evidence that several key elements of renin-angiotensin system (RAS) are present in the rat pancreas, notably angiotensinogen, which is mandatory for intracellular generation of physiologically active angiotensin II. The data support the existence of an intrinsic RAS, which may be important for pancreatic blood flow and ductal anion secretion. In the present study, the effect of chronic hypoxia on the expression of RAS components, particularly at the levels of its precursor angiotensinogen and its receptor subtypes AT(1) and AT(2), were investigated in the rat pancreas. Results from western blot and semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) analyses unequivocally showed that chronic hypoxia caused a marked increase in angiotensinogen both at the protein and gene levels when compared with that in the normoxic pancreas. However, results from RT-PCR showed that there was a differential effect of chronic hypoxia on the expression of AT(1) and AT(2) receptor subtypes, which exhibited subtype-specific changes in gene expression. For AT(1), chronic hypoxia did not cause a significant change in mRNA expression for AT(1a) but a significant increase in mRNA expression for AT(1b). For AT(2), chronic hypoxia caused a marked increase in its mRNA expression. The increased expression of RAS component genes by chronic hypoxia and its significance of changes may be important for physiological and pathophysiological aspects of the pancreas.

Angiotensin II induces nuclear factor (NF)-kappaB1 isoforms to bind the angiotensinogen gene acute-phase response element: a stimulus-specific pathway for NF-kappaB activation

The vasopressor angiotensin II (AII) activates transcriptional expression of its precursor, angiotensinogen. This biological "positive feedback loop" occurs through an angiotensin receptor-coupled pathway that activates a multihormone-responsive enhancer of the angiotensinogen promoter, termed the acute-phase response element (APRE). Previously, we showed that the APRE is a cytokine [tumor necrosis factor-alpha (TNFalpha)]- inducible enhancer by binding the heterodimeric nuclear factor-kappaB (NF-kappaB) complex Rel A x NF-kappaB1. Here, we compare the mechanism for NF-kappaB activation by the AII agonist, Sar1 AII, with TNFalpha in HepG2 hepatocytes. Although Sar1 AII and TNFalpha both rapidly activate APRE-driven transcription within 3 h of treatment, the pattern of inducible NF-kappaB binding activity in electrophoretic mobility shift assay is distinct. In contrast to the TNFalpha mechanism, which strongly induces Rel A x NF-kappaB1 binding, Sar1 AII selectively activates a heterogenous pattern of NF-kappaB1 binding. Using a two-step microaffinity DNA binding assay, we observe that Sar1 AII recruits 50-, 56-, and 96-kDa NF-kappaB1 isoforms to bind the APRE. Binding of all three NF-kappaB1 isoforms occurs independently of changes in their nuclear abundance or proteolysis of cytoplasmic IkappaB inhibitors. Phorbol ester-sensitive protein kinase C (PKC) isoforms are required because PKC down-regulation completely blocks AII-inducible transcription and inducible NF-kappaB1 binding. We conclude that AII stimulates the NF-kappaB transcription factor pathway by activating latent DNA-binding activity of NF-kappaB subunits through a phorbol ester-sensitive (PKC-dependent) mechanism.

Prejunctional effects of angiotensin II and bradykinin in the heart and blood vessels

1. Angiotensin and bradykinin facilitate the release of noradrenaline from sympathetic nerve terminals and cause positive inotropy in rat isolated atria and ventricles. The effect of bradykinin was enhanced by the ACE inhibitor, ramiprilat. 2. The facilitated release of noradrenaline in rat ventricle by bradykinin was blocked by the beta2-receptor antagonist HOE-140. This response is also reduced by removing the endocardium, suggesting the release of a mediator from the endocardium. 3. The facilitated noradrenaline release by angiotensin II and bradykinin was blocked by the angiotensin receptor antagonist saralasin to the same extent. In contrast, losartan caused only minor blockade in a range of vascular and cardiac tissues. This suggests that angiotensin and bradykinin exert these responses by interacting with a prejunctional receptor different from the established AT1 subtype. 4. These results suggest that bradykinin mediates facilitation of noradrenaline release via the local release of angiotensin onto an atypical AT1 receptor.

Cardiac angiotensin-converting enzyme activity in myocardial infarction

The cardiac renin-angiotensin system is regarded as an important modulator in the infarct heart. Little is known about their presence and regulation in human hearts. We measured angiotensin-converting enzyme (ACE) and renin activities at the aortic root and anterior interventricular vein (AIV) in 51 patients with previous myocardial infarction (MI): anterior wall MI in 31 and inferior wall MI in 20 and 33 control subjects. In the anterior wall MI group, the serum ACE activity was increased significantly in the AIV than in the aortic root (16.2 +/- 5.3 vs 15.3 +/- 5.0 nmol/min/ml, p <0.001), whereas the activity was not different between the aortic root and AIV in the control (14.4 +/- 3.7 vs 14.4 +/- 3.7 nmol/min/ ml) and in the inferior wall MI (16.5 +/- 4.8 vs. 17.0 +/-5.2 nmol/min/ml) groups. On the other hand, there was no significant difference in plasma renin activity between the AIV and aortic root in the 3 groups (control group, 1.0 +/- 0.5 vs 1.0 +/- 0.5 pg/ml/hour; anterior wall MI group, 1.3 +/- 0.8 vs 1.3 +/- 0.8 pg/ml/hour; inferior wall MI group, 1.2 +/- 0.7 vs 1.3 +/- 0.8 pg/ml/ hour). The difference in serum ACE activity between the AIV and aortic root had a significant positive linear correlation with pulmonary capillary wedge pressure (r = 0.606, p <0.001), and had a significant negative linear correlation with left ventricular ejection fraction (r = -0.620, p <0.001) in the anterior wall MI group. Serum ACE activity from the infarct region of the left ventricle was augmented in patients with MI, and the activity was increased in proportion to the severity of left ventricular dysfunction.

Larger anastomoses in angiotensinogen-knockout mice attenuate early metabolic disturbances after middle cerebral artery occlusion

Abnormalities in the homeostasis of the renin-angiotensin system have been implicated in the pathogenesis of vascular disorders, including stroke. The authors investigated whether angiotensinogen (AGN) knockout mice exhibit differences in brain susceptibility to focal ischemia, and whether such differences can be related to special features of the collateral circulation. Wild-type and AGN-knockout mice were submitted to permanent suture occlusion of the middle cerebral artery (MCA). The collateral vascular system was visualized by systemic latex infusion, and the ischemic lesions were identified by cresyl-violet staining. The core and penumbra of the evolving infarct were differentiated by bioluminescence and autoradiographic imaging of ATP and protein biosynthesis, respectively. In wild-type mice, mean arterial blood pressure was 95.0 +/- 8.6 mm Hg, and the diameter of fully relaxed anastomotic vessels between the peripheral branches of the anterior and middle cerebral arteries 26.6 +/- 4.0 microm. In AGN knockouts, mean arterial blood pressure was significantly lower, 71.5 +/- 8.5 mm Hg (P < .01), and the anastomotic vessels were significantly larger, 29.4 +/- 4.6 microm (P < .01). One hour after MCA occlusion, AGN-knockout mice exhibited a smaller ischemic core (defined as the region of ATP depletion) but a larger penumbra (the area of disturbed protein synthesis with preserved ATP). At 24 hours after MCA occlusion, this difference disappeared, and histologically visible lesions were of similar size in both strains. The observations show that in AGN-knockout mice the more efficient collateral blood supply delays ischemic injury despite the lower blood pressure. Pharmacologic suppression of angiotensin formation may prolong the therapeutic window for treatment of infarcts.

Relationship between the circulating and vascular renin-angiotensin system and the vasodilating effect of captopril in human hypertension

A vascular renin-angiotensin system (RAS) is present in the forearm vasculature of essential hypertensive patients and is closely related to the circulating renin profile. To test whether the haemodynamic effect of acute intrabrachial administration of captopril is related to the circulating and/or vascular RAS, 31 hypertensive patients were selected and divided into four groups according to their different circulating RAS profile (n = 7 hypertensive patients with primary aldosteronism and suppressed plasma renin activity; n = 7 low renin essential hypertensive patients; n = 8 normal renin essential hypertensive patients; n = 9 high renin renovascular hypertensive patients). The forearm net balance of active renin, plasma renin activity and angiotensin II, obtained by intrabrachial infusion of the beta-adrenergic receptor agonist isoproterenol (0.03, 0.1, 0.3 microg/100 ml/min) and calculated as the product of the venous-arterial plasma concentration gradient and forearm blood flow (FBF), was closely related to the circulating RAS. Captopril (0.25, 2.5, 25 microg/100 ml/min per 20 min each dose) unchanged basal FBF in the primary aldosteronism and low renin groups (FBF increase: from 3.9 +/- 0.4 to a maximum of 4.1 +/- 0.5 and from 3.8 +/- 0.3 to a maximum of 4.3 +/- 0.5 ml/100 ml/min, respectively), whereas it caused slight vasodilation in the normal renin group (from 3.9 +/- 0.3 to a maximum of 5.3 +/- 0.7 ml/100 ml/min), and pronounced vasodilation in the high renin group (from 4.0 +/- 0.4 to a maximum of 6.4 +/- 0.5 ml/100 ml/min). Captopril-induced vasodilation showed a significant direct correlation with the circulating and vascular RAS. The present data, while confirming the existence of a vascular RAS in the forearm of hypertensive patients indicate that the acute vasodilating effect of intrabrachial captopril is linked to a stimulated RAS, either circulating or vascular, supporting the evidence that, in acute conditions, ACE inhibitors exert their vasodilating effect through the RAS blockade.

Transcriptional regulation of angiotensinogen gene expression

The renin--angiotensin system (RAS) is an extracellular hormonal system implicated in acute, homeostatic control of peripheral vascular resistance and electrolyte homeostasis. In this tightly regulated system, physiological regulators of blood pressure and fluid balance induce the production of the potent vasoactive angiotensin peptides by sequential proteolysis of the angiotensinogen (AGT) prohormone. AGT is the only known precursor of the angiotensin peptides, whose circulating concentrations influence the tonic activity of the RAS. AGT abundance is regulated at the transcriptional level through hormonal and cell-type specific regulators. In this review, we will discuss the identified mechanisms controlling AGT expression separately for the rodent and human genes. The most intensively investigated gene (rodent AGT) is regulated constitutively by multiple positive- and negative-acting cis factors that function in a cell-type dependent fashion. Inducible rodent AGT expression is mediated through a multihormone-inducible enhancer that integrates signals from steroid and cytokine hormones into AGT transcription. We review recent advances in understanding the mechanism of the nuclear factor-kappa B (NF-kappa B) family in mediating cytokine-induced AGT expression and our recent discoveries on the existence of differentially inducible pools of cytoplasmic NF-kappa B. Constitutive control of the human AGT gene will be discussed; there is surprisingly little information on the cis- and trans-acting regulators controlling inducible expression of human AGT. Finally, we will explore some of the recent developments in gene linkage studies where human AGT alleles have been associated with hypertensive phenotypes through a mechanism that may involve enhanced transcription. These studies have provided a molecular explanation for a subset of heritable hypertensive disorders in humans.

Adenosine causes the release of active renin and angiotensin II in the coronary circulation of patients with essential hypertension

OBJECTIVES

The aim of the study was to evaluate whether adenosine infusion can induce production of active renin and angiotensin II in human coronary circulation.

BACKGROUND

Adenosine can activate angiotensin production in the forearm vessels of essential hypertensive patients.

METHODS

In six normotensive subjects and 12 essential hypertensive patients adenosine was infused into the left anterior descending coronary artery (1, 10, 100 and 1,000 microg/min x 5 min each) while active renin (radioimmunometric assay) and angiotensin II (radioimmunoassay after high performance liquid chromatography purification) were measured in venous (great cardiac vein) and coronary arterial blood samples. In five out of 12 hypertensive patients adenosine infusion and plasma samples were repeated during intracoronary angiotensin-converting enzyme inhibitor benazeprilat (25 microg/min) administration. Finally, in adjunctive hypertensive patients, the same procedure was applied during intracoronary sodium nitroprusside (n = 4) or acetylcholine (n = 4).

RESULTS

In hypertensive patients, but not in control subjects, despite a similar increment in coronary blood flow, a significant (p < 0.05) transient increase of venous active renin (from 10.7 +/- 1.4 [95% confidence interval 9.4 to 11.8] to a maximum of 13.8 +/- 2.1 [12.2 to 15.5] with a consequent drop to 10.9 +/- 1.8 [9.7 to 12.1] pg/ml), and angiotensin II (from 14.6 +/- 2.0 [12.7 to 16.5] to a maximum of 20.4 +/- 2.7 [18.7 to 22.2] with a consequent drop to 16.3 +/- 1.8 [13.9 to 18.7] pg/ml) was observed under adenosine infusion, whereas arterial values did not change. Calculated venous-arterial active renin and angiotensin II release showed a strong correlation (r = 0.78 and r = 0.71, respectively; p < 0.001) with circulating active renin. This adenosine-induced venous angiotensin II increase was significantly blunted by benazeprilat. Finally, both sodium nitroprusside and acetylcholine did not affect arterial and venous values of active renin and angiotensin II.

CONCLUSIONS

These data indicate that exogenous adenosine stimulates the release of active renin and angiotensin II in the coronary arteries of essential hypertensive patients, and suggest that this phenomenon is probably due to renin release from tissue stores of renally derived renin.

Cardiac production of angiotensin II and its pharmacologic inhibition: effects on the coronary circulation

Angiotensin II (AII), produced systemically as well as locally in the heart, affects the coronary circulation, as do consequences of its pharmacologic inhibition. AII is a powerful vasoconstrictor directly acting on vascular smooth muscle cells, modulating sympathetic innervation and calcium ion influx, and releasing other vasoconstrictor factors. In addition to these immediate actions, AII has longer-term biologic actions that influence cardiac endothelial function, vascular smooth muscle cell phenotype expression, and fibroblast proliferation. Moreover, the production of AII is interrelated with the vasodilator substances bradykinin, nitric oxide, and prostaglandins E2 and I2 (prostacyclin). Circulating hormonal actions of AII include fluid retention, direct vasoconstriction, and sympathetic neuromodulation, all resulting in increased left ventricular preload and afterload. Because of these local and hormonal characteristics, AII can immediately affect the myocardial balance of metabolic demand and supply and long term can induce structural vascular and myocardial alterations. Pharmacologic inhibition of AII production likely conveys myocardial and vascular protection in situations of acute myocardial oxygen debt. In the long term, inhibition of AII may attenuate structural changes in the coronary microcirculation related to various cardiomyopathies or acute tissue injury, and direct antiatherogenic effects may also occur.

Association of 3 gene polymorphisms with atopic diseases

BACKGROUND

Various peptidases, including angiotensin-converting enzyme (ACE), inactivate some inflammatory peptides that are considered to influence the pathogenesis of atopic diseases. This enzyme is also involved in the conversion or activation of 2 bronchoconstriction mediators: angiotensin II from angiotensinogen and endothelin (ET), respectively.

OBJECTIVE

We tested a hypothesis that asthma or other atopic diseases are associated with insertion/deletion ACE, M235T angiotensinogen, and TaqI ET-1 gene polymorphisms.

METHODS

A case-control approach was used in the study. Healthy subjects (141 persons) were used as control subjects, and 231 patients with histories of atopic asthma, allergic rhinitis, atopic dermatitis, or a combination thereof were studied. ACE genotype was determined by PCR, angiotensinogen M235T and ET-1 by PCR, and restriction analysis by AspI and TaqI, respectively.

RESULTS

We found the significant association of the insertion/deletion polymorphism of the ACE, as well as that of M235T polymorphism of the angiotensinogen genes, with the group of patients with atopic diseases ( P =.0025 and P =.0204, respectively). No difference was proved for the intron 4 (position 8000) polymorphism in the ET-1 gene when comparing the atopic patients with the control group (P =.1774). A significant difference was found between groups of patients with both asthma and rhinitis and patients without both respiratory atopic diseases (P =.0033).

CONCLUSION

It follows that the examined polymorphisms in the genes for ACE, angiotensinogen, and ET-1 could participate in the etiopathogenesis of atopic diseases.

Expression of endothelin-1, ETA and ETB receptors, and ECE and distribution of endothelin-1 in failing rat heart

Endothelin (ET)-1 has a positive inotropic effect and induces hypertrophy in cardiomyocytes. We previously reported that the peptide level of ET-1 is increased in the failing heart of rats with chronic heart failure (CHF) and that treatment with an ETA-receptor antagonist greatly improves survival in rats with CHF. However, precise analysis for alteration of the myocardial ET system in the failing heart is not known. In this study, we used rats with CHF due to chronic myocardial infarction. Sham-operated rats served as a control. The results showed that the level of preproendothelin (preproET)-1 mRNA and the peptide level of ET-1 were markedly increased in the heart of rats with CHF, whereas the expression of endothelin-converting enzyme (ECE)-1 mRNA in the heart did not differ between CHF and control rats. The intensity of ET-1 staining (ET-1-like immunoreactivity) in cardiomyocytes was markedly stronger in rats with CHF than in control rats, and the fibrotic tissues of the infarcted area were not stained. The mRNA and protein levels of both ETA and ETB receptors in the heart were significantly higher in rats with CHF than in control rats. The present study suggests that the increase in ET-1 peptide level in the heart of the rats with CHF originated from upregulation of preproET-1 mRNA, which was not attendant with the alteration of ECE-1 mRNA expression, and that both the ETA- and ETB-receptor systems are greatly accelerated in the failing heart.

Differential effects of isoproterenol on the activity of angiotensin-converting enzyme in the rat heart and aorta

The excessive stimulation of beta-adrenergic receptors in the heart induces myocardial hypertrophy. There are several experimental data suggesting that this hypertrophy may also depend, at least partially, on the increase of local production of angiotensin II secondary to the activation of the cardiac renin-angiotensin system. In this study we investigated the effects of isoproterenol on the activity of angiotensin-converting enzyme (ACE) in the heart and also in the aorta and plasma. Male Wistar rats weighing 250 to 305 g were treated with a dose of (+/-)-isoproterenol (0.3 mg kg-1 day-1, N = 8) sufficient to produce cardiac hypertrophy without deleterious effects on the pumping capacity of the heart. Control rats (N = 7) were treated with vehicle (corn oil). The animals were killed one week later. ACE activity was determined in vitro in the four cardiac chambers, aorta and plasma by a fluorimetric assay. A significant hypertrophy was observed in both ventricular chambers. ACE activity in the atria remained constant after isoproterenol treatment. There was a significant increase (P < 0.05) of ACE activity in the right ventricle (6.9 +/- 0.9 to 8.2 +/- 0.6 nmol His-Leu g-1 min-1) and in the left ventricle (6.4 +/- 1.1 to 8.9 +/- 0.8 nmol His-Leu g-1 min-1). In the aorta, however, ACE activity decreased (P < 0.01) after isoproterenol (41 +/- 3 to 27 +/- 2 nmol His-Leu g-1 min-1) while it remained unchanged in the plasma. These data suggest that ACE expression in the heart can be increased by stimulation of beta-adrenoceptors. However, this effect is not observed on other local renin-angiotensin systems, such as the aorta. Our data also suggest that the increased sympathetic discharge and the elevated plasma concentration of catecholamines may contribute to the upregulation of ACE expression in the heart after myocardial infarction and heart failure.

The renin-angiotensin system and its receptors

The renin-angiotensin system (RAS) plays an important role in blood pressure control and in water and salt homeostasis. It is involved in the pathophysiology of hypertension and structural alterations of the vasculature, kidney, and heart, including neointima formation, nephrosclerosis, postinfarction remodeling, and cardiac left ventricular hypertrophy (LVH). Recently, an increased knowledge of the effector peptides of the RAS, their receptors, and their respective functions has led to a new principle of treatment for hypertension: the inhibition of angiotensin (Ang) II via angiotensin-converting enzyme inhibitors or Ang II-receptor antagonists. In this review, the Ang receptors AT1 and AT2 and the potential roles of shorter angiotensin fragments, including Ang III(2-8), Ang IV(3-8), and Ang(1-7), are discussed.

New insights into the genetics of preeclampsia

Preeclampsia is familial. Pedigree analyses suggest that one or more common alleles may act as "preeclampsia susceptibility genes." The authors speculate that genes involved in blood pressure control, volume regulation, placental health, vascular disease, and vascular remodeling, underlie familial susceptibility to preeclampsia. Several candidate genes have been examined. These data suggest that a common mutation in the angiotensinogen promoter, A(-6), leads to elevated expression of this gene and pleiotropic effects, including abnormal spiral artery remodeling and failed hypervolemia of pregnancy. The factor V Leiden mutation, which predisposes women to thromboembolic disorders during pregnancy, has been implicated as another preeclampsia susceptibility gene. New insights into the genetics of preeclampsia will contribute to the understanding of this disease and should ultimately lead to improved diagnosis and treatment.

Local renin-angiotensin system and mitogen-activated protein kinase activation in rat aorta

We previously reported that endogenous angiotensin II is released to cause mitogen-activated protein (MAP) kinase stimulation in the media portion of the vasculature. In this study, we examined whether a functional renin-angiotensin system is indeed present within the media of the vasculature. In rat aortic strips, endothelium removal produced an increase of MAP kinase activity. The MAP kinase activation was inhibited either by the renin inhibitor pepstatin A or by the angiotensin-converting enzyme inhibitor captopril. The degree of the inhibition of the MAP kinase activation by pepstatin A, captopril and the angiotensin receptor antagonist losartan was almost the same. Pepstatin A inhibited MAP kinase activation induced by renin but not by angiotensin I and angiotensin II. Captopril inhibited the MAP kinase activation induced by angiotensin I but not by angiotensin II. In nephrectomized rat aortic strips, endothelium removal also produced an increase in MAP kinase activity, but the MAP kinase activation was considerably small and minimally inhibited by losartan. Nephrectomy produced a marked decrease in plasma renin activity. These findings suggest that an apparently fully intact and functional renin-angiotensin system is present in the media of the rat vasculature and this system serves to increase MAP kinase activity. It appears that renin plays the determining role in the regulation of angiotensin generation also in the media and the major source of the renin is renin of kidney origin.

Inhibition of angiotensin-converting enzyme in human hand veins

Conversion of angiotensin I to angiotensin II likely occurs in human veins, supporting the existence of endothelial angiotensin-converting enzyme (ACE) activity in these vessels. Using the dorsal hand vein technique, we investigated the effects of 2 ACE inhibitors, captopril (single oral dose of 6.25 mg) and enalaprilat (local infusion of 1 microgram/min), on venous responsiveness in healthy subjects. Orally administered captopril induced a marked decrease in angiotensin I- but not angiotensin II-induced venoconstriction. This blunted response persisted for at least 4 hours. Enalaprilat and captopril increased the sensitivity to bradykinin, decreasing the dose producing half-maximal response (ED50) of bradykinin 18-fold and 5-fold, respectively, without changing the maximal venodilatory response. These results confirm that there is substantial rapid metabolism of angiotensin I in human veins and suggest that a single dose of locally infused angiotensin I can be used with the dorsal hand vein technique to assess the time-course effect of vascular ACE inhibition after oral administration. Our findings also extend previous in vitro observations in human veins by showing that these agents potentiate the venodilatory effects of bradykinin in vivo.

Effects of human prorenin in rats transgenic for human angiotensinogen

The physiological role of prorenin is unknown; however, the possibility that prorenin inhibits renin locally has been suggested. We tested the hypothesis that prorenin may be an endogenous competitor for renin uptake in the tissue. We also investigated whether prorenin can be activated to active renin and affect mean arterial pressure (MAP). Isolated perfused hindquarters of rats transgenic for human angiotensinogen were infused with human renin and/or prorenin. The plateau phase of angiotensin (Ang) I release 15 minutes after cessation of infusions was used as a parameter for renin uptake. Renin (10 ng/mL for 15 minutes) caused sustained release of Ang I (153+/-16 fmol/mL). Coinfusion with a 15-fold excess of prorenin did not affect local Ang I formation (153+/-19 fmol/mL). Prorenin infusion alone showed no activation to active renin. In addition, we investigated MAP and plasma Ang II levels after injection of saline (DeltaMAP, -1+/-2 mm Hg; 40+/-5 fmol/mL Ang II), 9 ng renin (DeltaMAP, +37+/-3 mm Hg; 378+/-39 fmol/mL), and 144 ng prorenin (DeltaMAP, +10+/-5 mm Hg; 61+/-5 fmol/mL) and the coinjection of renin and prorenin (DeltaMAP, +41+/-4 mm Hg; 305+/-23 fmol/mL) in anesthetized rats. The data show that prorenin was not activated to active renin and did not affect MAP in short-term experiments. Renin-induced Ang formation was not affected by prorenin. Renin may have been taken up specifically because of its physical and chemical properties or because of nonspecific sequestration in the extravascular space. We conclude that prorenin does not act as an endogenous antagonist for the long-lasting effects of renin in the vascular wall. Moreover, prorenin does not affect acute renin-related effects on blood pressure.

Hyperhomocysteinemia induces elastolysis in minipig arteries: structural consequences, arterial site specificity and effect of captopril-hydrochlorothiazide

Hyperhomocysteinemia is a risk factor for arterial diseases, and the deterioration of the arterial elastic structures is one of the possible mechanisms underlying this epidemiological association. The aim of this paper is to quantitatively characterize such structural alterations and to explore their causes in a previous model of dietary induced mild hyperhomocysteinemia in minipigs. After four months, both a morphodensitometrical analysis of the elastic structure and a biochemical analysis of elastin and elastase activities were performed on the infrarenal abdominal aorta (IRAA) and the proximal left interventricular coronary artery (LIVCA) of control (C), hyperhomocysteinemic (H) and captopril-hydrochlorothiazide (Cp-Htz, 25 + 12.5 mg/d)-treated (H+/-Cp) minipigs (n = 8/group). Hyperhomocysteinemia was found to induce an increase in parietal elastolytic metalloproteinase activities. It resulted in opening and enlargement of fenestrae through the medial elastic laminae and in a decrease in medial elastin content (p < 10(-3)), expressed as well as volume density (%) as weight concentration (microg elastin/mg dry tissue). The thickness of the media and its basic lamellar organization was unchanged. The reduction in volume density was more dramatic in LIVCA (H: 4.7 +/- 0.9 vs C: 8.8 +/- 2.4), where it was evenly distributed within the media, than in IRAA (H: 6.7 +/- 1.1 vs C: 9.3 +/- 1.2), where the deep medial layers were less affected. Cp-Htz partly prevented the hyperhomocysteinemia-induced reduction of the medial elastin content in LIVCA (5.7 +/- 1.2) and IRAA (7.9 +/- 1.4). This effect, occurring in the subintimal layers of the media in both arteries but not in the deeper layers, resulted in a less beneficial effect in LIVCA than in IRAA. This result parallels the moderate beneficial therapeutic effect of ACE inhibitors against coronary atherosclerosis in humans. This paper reports for the first time a quantitative analysis of the arterial site-dependent deterioration of the elastic structure caused by mild hyperhomocysteinemia and the involvement of metalloproteinases in this process. These results confirm that the plaque-independent damage to elastic structure previously described in hyperhomocysteinemic-atherosclerotic minipigs was mainly due to homocysteine. This highlights that the metalloproteinase-related elastolysis and the subsequent structural deterioration is one of the major events underlying the epidemiological association between mild hyperhomocysteinemia and arterial diseases.

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.

Differences in tissue angiotensin II-forming pathways by species and organs in vitro

Angiotensin (Ang) II plays an important role in cardiovascular homeostasis, not only in the systemic circulation but also at the tissue level, and is involved in the remodeling of the heart and vasculature under pathological conditions. Although alternative Ang II-forming pathways are known to exist in various tissues, the details of such pathways remain unclear. The aim of this study was to examine tissue Ang II-forming activities and to identify the responsible enzyme in several organs (lung, heart, and aorta) in various species (human, hamster, rat, rabbit, dog, pig, and marmoset). Among the organs examined, the lung contained the highest Ang II-forming activity. The responsible enzyme for pulmonary Ang II formation was angiotensin I-converting enzyme (ACE) in all of the species except the human lung, in which a chymaselike enzyme was dominant. In the heart, the highest total Ang II-forming activity was observed in humans, and a chymaselike enzyme was dominant in all of the species except rabbit and pig. Aorta exhibited a relatively high total Ang II-forming activity, with a predominance of chymaselike activity in all of the species except rabbit and pig, in which ACE was dominant. Our results indicate that there were remarkable differences in Ang II-forming pathways among the species and organs we examined. To study the pathophysiological roles of ACE-independent Ang II formation, one should choose species and/or organs that have Ang II-forming pathways similar to those in humans.

Control of the renal renin system by local factors

Local factors, such as prostaglandins (PGs), nitric oxide (NO), and endothelins (ETs), produced in the immediate vicinity of juxtaglomerular (JG) cells can exert significant effects on renin secretion and renin gene expression. PGE2, as the main renotubular PG, and PGI2, as the main endothelial prostanoid, both stimulate renin secretion and renin gene expression by activating cAMP formation in JG cells. Although the direct effect of NO on JG cells is less clear, its overall effect in vivo seems to be to stimulate the renin system. Evidence is emerging that stimulation by NO is related to the cAMP pathway, and cGMP-induced inhibition of cAMP-phosphodiesterase III (PDE-III) may mediate this effect. ETs, on the other hand, appear to inhibit the renin system, in particular in those pathways activated by cAMP, acting via Ca2+- and protein kinase C-related mechanisms. There is increasing evidence that both NO and PGs could be involved in the physiological regulatory mechanisms by which salt intake affects the renin system.

Angiotensin-Converting Enzyme Inhibitors an Angiotensin II-Receptor Antagonists

The renin-angiotensin-aldosterone system (RAAS) is one of the main targets in the pharmacotherapy of cardiovascular diseases. Inhibitors of the angiotensin- converting enzyme (ACE) have been in clinical use for years and a great deal of experience exists with this particular group of drugs. However, the therapeutic effect is based on the inhibition of an enzyme (ACE) that is not very specific. Another substrate is bradykinin, a well-known mediator of inflammation and a potent inductor of vasodilatation and bronchoconstriction. Dur ing therapy with an ACE inhibitor, the inactivation of bradykinin by cleavage of the carboxyterminal end of this nonpeptide is blocked as well, with the result of bradykinin accumulation. The pattern of adverse effects seen with ACE inhibitors is mainly determined by bradykinin-mediated actions such as edema and cough. Therefore, the inhibition of the RAAS at the level of the transmitter-receptor interaction seems to be a logical development. Because nonpeptide (ie, orally active) angiotensin II (AT) receptor antagonists are available, this concept can be proven.

Effect of long-term treatment with enalapril in streptozotocin diabetic and DOCA hypertensive rats

We studied the effects of long-term treatment with enalapril (5 mg/kg/day orally) on various biochemical and cardiovascular complications in streptozotocin (STZ) diabetic and deoxycorticosterone acetate (DOCA) hypertensive rats. Female Wistar rats made diabetic or hypertensive or both by streptozotocin (STZ; 45 mg/kg) or deoxycorticosterone acetate (DOCA; 10 mg/kg, p.o., daily) or both. Enalapril (5 mg/kg) was administered daily by the oral route for 6 weeks. At the end of 6 weeks, blood samples were taken to analyze glucose, insulin, and lipids. Blood pressure and heart rate were recorded by a noninvasive technique, and cardiac functions were recorded by Neely's working heart preparation. Injection of STZ produced severe glycosuria (>2%), hyperglycemia, hypoinsulinemia, and loss of body weight. It also produced hypercholesterolemia, hypertriglyceridemia, hypertension, bradycardia, and decreased left ventricular developed pressure (LVDP) and increase in angiotensin-converting enzyme (ACE) in left ventricular tissue. DOCA by itself did not produce any change in blood glucose but reduced serum insulin levels in nondiabetic animals. However, in the diabetic group, DOCA reduced blood sugar levels. Treatment with enalapril prevented an increase in the blood pressure and the heart weight. Decrease in the heart rate, reduction in LVDP, and increase in intracardiac activity were observed in diabetic rats; these were also prevented by enalapril treatment. Enalapril had no effect on plasma glucose and did not modify plasma insulin levels in diabetic animals. The effects of STZ and DOCA together were not additive on the investigated parameters, and enalapril was similarly efficient in diabetic and diabetic hypertensive animals.

Angiotensin, LDL peroxidation and atherosclerosis

Hypertension is a known risk factor for the development of atherosclerosis. However, in most of the studies, no effect of blood pressure reduction was demonstrated on the incidence of coronary artery disease, except in the SHEP study in which it was shown that in older persons, with isolated systolic hypertension, antihypertensive stepped-care drug treatment reduced the incidence of total stroke and major cardiovascular event. In hypertensive patients with elevated plasma renin activity, a 5-fold increased incidence of myocardial infarction was demonstrated. As oxidation of low density lipoprotein (LDL) was suggested to be a major risk factor for atherosclerosis, we studied the relationship between hypertension and LDL oxidation. We demonstrated increased propensity of LDL obtained from hypertensive patients to oxidative modification, in comparison with LDL obtained from normotensive subjects and suggested that angiotensin II (Ang-II) may be involved in this effect. Ang-II was shown to enhance macrophage lipid peroxidation both in vivo and in vitro. This effect was dose-dependent and involved the binding of Ang-II to its receptor on the macrophage surface. In addition, these lipid peroxidized Ang-II-treated macrophages could substantially oxidize LDL. Ang-II was shown to possess additional atherogenic properties such as increasing the activity of the macrophage oxidized LDL receptors. It also binds to LDL, thus leading to the formation of a modified lipoprotein, which is taken up by macrophages at enhanced rate through the scavenger receptor. Inhibition of Ang-II formation by angiotensin converting enzyme inhibitors reduced LDL peroxidation in hypertensive patients as well as in the atherosclerotic apo E deficient mice. The reduction in LDL peroxidation in these mice was accompanied by a 70-90% reduction in the atherosclerotic lesion area. A similar effect in these mice was demonstrated with the Ang-II receptor antagonist, Losartan. Thus, we suggest that Ang-II is involved in the development of atherogenesis in hypertensive patients and inhibition of Ang-II formation or prevention of its interaction with its receptor may attenuate the atherosclerotic process.

Should we aim at tissue renin-angiotensin systems?

Recent developments in our knowledge of the renin-angiotensin system (RAS) necessitate an update of the classical view on this system. These developments pertain to the pathways leading to formation of angiotensin II and other active metabolites, their receptors, biological functions and the presence of renin-angiotensin systems in tissues. The implications of the above new developments for the current interest in tissue renin-angiotensin systems as potential targets for drug therapy in cardiovascular disease are discussed in this review.

Endothelin-converting enzyme and angiotensin-converting enzyme in failing hearts of rats with myocardial infarction

We have previously reported that production of endothelin (ET)-1 is markedly increased in failing hearts of rats with chronic heart failure (CHF). It was also reported that the production of angiotensin II (Ang II) is increased in the failing heart. In this study we investigated both converting enzymes of the ET-1 system and the angiotensin system. We used left coronary artery-ligated rats as a model of CHF. The peptide level of ET-1 in the left ventricle (LV) was markedly higher in CHF rats than in control rats. In the LV, expression of preproET-1 mRNA was also markedly higher in CHF rats than in controls. The expression of endothelin-converting enzyme (ECE)-1 mRNA in the rats with CHF was similar to that in controls. Therefore, we believed that the increase in ET-1 production in the failing heart originated from an increase in preproET-1 production rather than increase in ECE. The expression of angiotensin-converting enzyme (ACE) mRNA in failing hearts of CHF rats was significantly higher than that of the sham-operated rats. The expression of angiotensinogen mRNA in failing hearts of these CHF rats was slightly higher than that of the sham-operated rats. This study suggests that there is a difference in the role of peptide synthesis between the ECE system and the ACE system in rats with CHF.