Angiotensin I converting enzyme

Effect of ACE inhibitor on DOCA-salt- and aortic coarctation-induced hypertension in mice: do kinin B2 receptors play a role?

Kinins have been shown to play an important role in the cardioprotective effect of ACE inhibitors (ACEi) during heart failure and ischemia-reperfusion. However, it is controversial as to whether kinins oppose the hypertensinogenic effect of deoxycorticosterone acetate plus salt (DOCA-salt) or aortic coarctation and whether they mediate both chronic antihypertensive and cardiac antihypertrophic effects of ACEi in hypertension. Using normal 129/SvEvTac mice and mice lacking the bradykinin B2 receptor gene (B2-KO), we investigated whether (1) the hypertensinogenic effect of DOCA-salt or aortic coarctation is enhanced in B2-KO mice and (2) the chronic antihypertensive and antihypertrophic effects of an ACEi (ramipril, 4 mg. kg-1. d-1) are mediated by B2 receptors in aortic coarctation (6 weeks)- and DOCA-salt (4 weeks)-induced hypertension. Before surgery, there was no difference between 129/SvEvTac and B2-KO mice in terms of blood pressure and heart weight, suggesting that kinins are not essential to maintaining normal blood pressure. DOCA-salt (volume expansion) or aortic coarctation (renin-dependent) induced similar hypertension and left ventricular hypertrophy (LVH) in 129/SvEvTac and B2-KO mice, suggesting that kinins do not play an essential role in the development of DOCA-salt- or aortic coarctation-induced hypertension. We found that B2 receptors mediate only the early (1 week) but not the late phase (4 weeks) of the chronic hypotensive effect of ACEi in DOCA-salt hypertension. On the other hand, chronic ACE inhibition prevented the development of hypertension and LVH in both 129/SvEvTac and B2-KO mice given DOCA-salt or subjected to aortic coarctation, suggesting that kinins do not participate in the chronic antihypertensive and antihypertrophic effects of ACEi in these 2 models of hypertension. Thus, in mice, kinins acting via B2 receptors do not participate in (1) maintenance of normal basal blood pressure, (2) establishment and maintenance of hypertension induced by DOCA-salt or aortic coarctation, and (3) chronic antihypertensive and cardiac antihypertrophic effects of ACEi in DOCA-salt and aortic coarctation hypertension.

Protective effect of perindoprilat in the hypoxemia-induced renal dysfunction in the newborn rabbit

The renal effects of acute hypoxemia and the ability of perindoprilat, a potent angiotensin-converting enzyme inhibitor, to prevent these effects were assessed in 31 anesthetized and mechanically ventilated newborn (5 to 8 d of age) rabbits. Renal blood flow (RBF) and GFR were determined by the clearances of para-aminohippuric acid and inulin, respectively. Each animal acted as its own control. In eight normoxemic rabbits (group 1), the i.v. infusion of saline did not change renal and hemodynamic functions. In eight additional rabbits, acute hypoxemia (PaO2= 40 mm Hg) induced a significant decrease in mean blood pressure (-8+/-2%), RBF (-36+/-3%), and GFR (-31+/-3%) and an increase in renal vascular resistance (+50+/-12%). A third group of newborn animals (n=7) was used to determine the renal effects of perindoprilat administration (20 microg/kg) under normoxemic conditions. RBF significantly increased (+15+/-2%) and renal vascular resistance significantly decreased (-15+/-3%), whereas GFR, mean blood pressure, and filtration fraction did not change significantly. In group 4 (n=7), perindoprilat infusion completely prevented the hypoxemia-induced alterations in GFR and renal vascular resistance and partially prevented the fall in RBF. These results demonstrate that angiotensin II modulates the renal immature microcirculation and that inhibition of its formation effectively prevents the hypoxemia-induced decrease in GFR.

Angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists in the treatment of heart failure caused by left ventricular systolic dysfunction

Activation of the renin-angiotensin-aldosterone system (RAAS) in left ventricular systolic dysfunction is a critically important determinant in the pathophysiologic processes that lead to progression of heart failure and sudden death. Angiotensin II, acting at the specific angiotensin receptor (AT1-R), activates a series of intracellular signaling sequences which are ultimately expressed within the cardiovascular system as vasoconstriction and associated vascular hypertrophy and remodeling. Angiotensin converting enzyme (ACE) inhibition leads to increases in the vasodilatory peptides bradykinin and substance P and at least an initial reduction in angiotensin II concentrations. AT1-R blocking drugs prevent access of angiotensin II to the AT1-R and thus prevent cellular activation. ACE inhibitors have clearly been demonstrated through a large number of clinical trials to increase survival in congestive heart failure, primarily by reducing the rate of progression of left ventricular dilatation and decompensation. However, this beneficial effect diminishes over time. Preliminary short-term clinical studies evaluating the efficacy of AT1-R blocking drugs in the treatment of heart failure have suggested that they elicit similar hemodynamic and neuroendocrine effects as do the ACE inhibitors. The combination ACE inhibitors and AT1-R blocking drugs offer the theoretical advantage of increasing bradykinin while blocking the actions of angiotensin II, and thus possibly show a synergistic effect. Again, preliminary studies have yielded encouraging results that are difficult to interpret because neither ACE inhibitor nor the AT1-R blocking drug doses were titrated to tolerance. Pharmacological manipulation of the RAAS has led to better understanding of its role in heart failure and improved clinical outcomes.

Cardiovascular kinin-generating capability in hypertensive fructose-fed rats

OBJECTIVE

The hypertensive state is often associated with metabolic abnormalities, including glucose intolerance. Tissue kallikrein, a potent kinin-generating enzyme, is present in the vascular wall and heart tissue. High dietary fructose consumption is reported to induce hyperinsulinemia, hypertriglyceridemia and hypertension. The objective of the present study was to examine the status of kallikrein in vascular and cardiac tissue from highly fructose-fed rats and to delineate the effect of kinins and the angiotensin converting enzyme inhibitor ramipril in this animal model of glucose intolerance.

DESIGN AND METHODS

Male Wistar rats (350 g body weight) were divided into four groups of 10 rats each: (1) controls; (2) oral ramipril at 500 microg/kg per day for the last 2 study weeks; (3) fructose in drinking water as a 10% (w/v) solution for 4 weeks; and (4) fructose + ramipril, with fructose administered as in group 3 plus the administration of ramipril for the last 2 study weeks. Systolic blood pressure (tail-cuff method), glucose tolerance (2 g/kg body weight intraperitoneally) and metabolic parameters were recorded. Kallikrein activity in tail artery and heart tissue homogenates was estimated at the end of the 4th study week from measurements of kininogenase activity and kinins generated by a radioimmunoassay.

RESULTS

The area under the curve for the glucose tolerance test increased from 1265 +/- 103 mmol/l after 120 min in the control and 1152 +/- 36 mmol/l in the ramipril group (NS) to 2628 +/- 143 mmol/l in the fructose group (P<0.01). The administration of ramipril to fructose-treated rats in group 4 improved glucose tolerance (2160 +/- 100 mmol/l; P<0.05 versus group 3). Blood pressure increased significantly in fructose-fed rats but fell markedly in fructose-fed rats treated with ramipril (P<0.01). Kallikrein activity measured in the heart and vessels increased as a consequence of fructose administration (P<0.05), but the administration of ramipril increased this parameter to a much greater extent (P<0.01 versus control group), which correlated closely with the decrease in blood pressure and the improvement in glucose tolerance observed in the fructose + ramipril group.

CONCLUSIONS

The administration of fructose as a solution in the drinking water induced glucose intolerance and increased blood pressure. Treatment with the angiotensin converting enzyme inhibitor ramipril improved glucose tolerance and significantly diminished blood pressure. Cardiovascular kinin-generating capability increased in treated animals and this increase was even higher when rats were treated with ramipril, suggesting that kinins, acting as a paracrine hormonal system, can exert cardiovascular protection and contribute to the beneficial effects of angiotensin converting enzyme inhibitor.

Effect of chronic bradykinin administration on insulin action in an animal model of insulin resistance

The nonapeptide bradykinin (BK) has been implicated as the mediator of the beneficial effect of angiotensin-converting enzyme inhibitors on insulin-stimulated glucose transport in insulin-resistant skeletal muscle. In the present study, the effects of chronic in vivo BK treatment of obese Zucker (fa/fa) rats, a model of glucose intolerance and severe insulin resistance, on whole body glucose tolerance and skeletal muscle glucose transport activity stimulated by insulin or contractions were investigated. BK was administered subcutaneously (twice daily at 40 microg/kg body wt) for 14 consecutive days. Compared with a saline-treated obese group, the BK-treated obese animals had significantly (P < 0.05) lower fasting plasma levels of insulin (20%) and free fatty acids (26%), whereas plasma glucose was not different. During a 1 g/kg body wt oral glucose tolerance test, the glucose and insulin responses [incremental areas under the curve (AUC)] were 21 and 29% lower, respectively, in the BK-treated obese group. The glucose-insulin index, the product of the glucose and insulin AUCs and an indirect index of in vivo insulin action, was 52% lower in the BK-treated obese group compared with the obese control group. Moreover, 2-deoxyglucose uptake in the isolated epitrochlearis muscle stimulated by a maximally effective dose of insulin (2 mU/ml) was 52% greater in the BK-treated obese group. Contraction-stimulated (10 tetani) 2-deoxyglucose uptake was also enhanced by 35% as a result of the BK treatment. In conclusion, these findings indicate that in the severely insulin-resistant obese Zucker rat, chronic in vivo treatment with BK can significantly improve whole body glucose tolerance, possibly as a result of the enhanced insulin-stimulated skeletal muscle glucose transport activity observed in these animals.

Irreversible inhibition of zinc-containing protease by oxazolidinone derivatives. Novel inactivation chemistry

alpha-Benzyl-2-oxo-1,3-oxazolidine-4-acetic acid (BOOA) having (alpha R,4S) and (alpha S,4R) configurations were designed and synthesized as a novel type of mechanism-based inactivators for carboxypeptidase A (CPA), and kinetic analysis demonstrated that they indeed inhibit the enzyme in a time-dependent manner with the second order inhibitory rate constants (kinact/KI) of 1.52 and 1.39 M-1 s-1 for (alpha S,R4)-BOOA and (alpha R,4S)-BOOA, respectively.

Role of bradykinin in the neonatal renal effects of angiotensin converting enzyme inhibition

The vascular effects of angiotensin converting enzyme inhibitors are mediated by the inhibition of the dual action of angiotensin converting enzyme (ACE): production of angiotensin II and degradation of bradykinin. The deleterious effect of converting enzyme inhibitors (CEI) on neonatal renal function have been ascribed to the elevated activity of the renin-angiotensin system. In order to clarify the role of bradykinin in the CEI-induced renal dysfunction of the newborn, the effect of perindoprilat was investigated in anesthetized newborn rabbits with intact or inhibited bradykinin B2 receptors. Inulin and PAH clearances were used as indices of GFR and renal plasma flow, respectively. Perindoprilat (20 microg/kg i.v.) caused marked systemic and renal vasodilation, reflected by a fall in blood pressure and renal vascular resistance. GFR decreased, while urine flow rate did not change. Prior inhibition of the B2 receptors by Hoe 140 (300 microg/kg s.c.) did not prevent any of the hemodynamic changes caused by perindoprilat, indicating that bradykinin accumulation does not contribute to the CEI-induced neonatal renal effects. A control group receiving only Hoe 140 revealed that BK maintains postglomerular vasodilation via B2 receptors in basal conditions. Thus, the absence of functional B2 receptors in the newborn was not responsible for the failure of Hoe 140 to prevent the perindoprilat-induced changes. Species- and/or age-related differences in the kinin-metabolism could explain these results, suggesting that in the newborn rabbit other kininases than ACE are mainly responsible for the degradation of bradykinin.

Early induction of angiotensin I-converting enzyme in rat carotid artery after balloon injury

Several studies have demonstrated the effectiveness of angiotensin I-converting enzyme (ACE) inhibitors in preventing the neointima formation found after denudation of the rat carotid artery by balloon injury. The aim of the present study was to determine the role of ACE in this model and to compare the treatment with the ACE inhibitor ramiprilat with that with the angiotensin II antagonist HR 720. The endothelial layer of the left carotid artery was removed using an inflated balloon catheter. Injured and control vessels were both submitted to histomorphological analysis and DNA content quantification at 2, 4, 6, 8, 12, and 14 days after injury. Evaluation of neointima thickening demonstrated a slow but steady increase of neointima that was significant after day 6 and reached 30% of the lumen in 2 weeks. This was paralleled by an increase in DNA content, which was significant 4 days after injury. ACE mRNA levels were quantified by polymerase chain reaction after reverse transcription. Measurement of ACE mRNA levels revealed a significant upregulation 2 and 8 days after injury, with no significant difference when compared with control tissue at later time points. ACE activity was also significantly enhanced at 2 and 8 days after injury, with no significant difference when compared with control tissue at later time points. In addition, the treatment with ramiprilat was more efficient in reducing neointima formation than that with HR 720. These data underlie the role of ACE in this model of restenosis. The early induction of ACE expression after endothelial injury but before significant changes in the vessel structure suggests that ACE activity might be one of the mechanisms that trigger neointima formation in the rat.

Cardiac growth during high and low dose perindopril treatment in spontaneously hypertensive rats

1. The effect of high and low dose angiotensin converting enzyme (ACE) inhibition and the contribution of bradykinin potentiation in this treatment on left and right ventricle weights and wall volume was investigated in immature spontaneously hypertensive rats (SHR). 2. Male SHR were treated from 7 to 11 weeks of age with perindopril (an ACE inhibitor) at a low dose of 0.1 mg/kg per day or a high dose of 1 mg/kg per day. Half the animals were also treated with a bradykinin receptor antagonist, HOE 140 (500 micrograms/kg per day). 3. After 4 weeks of treatment, hearts were arrested in diastole and perfusion fixed. The right and left ventricle plus septum were weighed, cut into 1 mm slices and volume was determined using the Cavalieri principle. 4. Low dose perindopril treatment did not significantly affect blood pressure in the SHR. High dose perindopril treatment maintained blood pressure at a level similar to Wistar-Kyoto (WKY) rats. 5. Growth of the right ventricle was not influenced by ACE inhibition. However, high dose treatment significantly lowered the left ventricle plus septum volume:bodyweight ratio (LV + S VOL:BWT) compared with control SHR (2.85 +/- 0.02 vs 3.36 +/- 0.08 mm3/g, respectively) to a level similar to the normotensive WKY rats (2.80 +/- 0.11 mm3/g). Similarly, low dose treatment significantly lowered the LV + S VOL:BWT ratio (2.89 +/- 0.09 mm3/g). HOE 140 treatment did not reverse the effect of ACE inhibition. Similar effects were observed on left ventricular weights. 6. ACE inhibition, independent of its blood pressure lowering effect, prevents the development of left ventricular hypertrophy in the SHR but does not influence growth of the right ventricle. This effect of ACE inhibition does not appear to be mediated by bradykinin potentiation.

Effects of trandolapril and verapamil on glucose transport in insulin-resistant rat skeletal muscle

We have used an animal model of insulin resistance-the obese Zucker (fa/fa) rat-to test whether oral administration of the non-sulfhydryl-containing angiotensin-converting enzyme (ACE) inhibitor, trandolapril, alone or in combination with the Ca2+-channel blocker, verapamil, can induce a beneficial effect on insulin-stimulated glucose transport and metabolism in skeletal muscle. Insulin-stimulated 2-deoxyglucose (2-DG) uptake in the isolated epitrochlearis muscle was less than 50% as great in obese animals compared with lean (Fa/-) controls (P < .05), but was significantly improved in the obese group by both short-term (6 hours, +33%) and long-term (14 days,+70%) oral treatment with trandolapril. Verapamil treatment alone did not alter insulin-stimulated 2-DG uptake in muscle, but simultaneous administration of verapamil and trandolapril resulted in the most pronounced effect on insulin-stimulated 2-DG uptake (+106%). Long-term treatment with trandolapril alone and in combination with verapamil significantly increased muscle glycogen (+26% to 27%), glucose transporter GLUT-4 protein (+27% to 31%), and hexokinase activity (+21% to 49%), and decreased plasma insulin levels (-23% to -29%). Muscle citrate synthase activity was enhanced only when trandolapril and verapamil were administered in combination (+24%). We conclude that the long-acting, non-sulfhydryl-containing ACE inhibitor, trandolapril, alone and in combination with the Ca2+-channel blocker, verapamil, can significantly improve insulin-stimulated glucose transport activity in skeletal muscle of the insulin-resistant obese Zucker rat, and that this improvement is associated with favorable adaptive responses in GLUT-4 protein levels, glycogen storage, and activities of relevant intracellular enzymes of glucose catabolism.

Pharmacokinetics of remikiren, a potent orally active inhibitor of human renin, in rat, dog and primates

1. An hplc method with fluorescence derivatization was developed for the quantification of remikiren in plasma (limit of quantification 2 ng/ml). This was used to determine the pharmacokinetics in various species of primate, in which the compound is a potent inhibitor of renin, as well as in the rat and dog in which it is less active. 2. After intravenous administration the mean residence time was < or = 1.5 h in all species, and the plasma clearance approached the corresponding hepatic blood flows. 3. Studies in the bile-duct cannulated rat and dog demonstrated that the high clearance was due to a combination of rapid metabolism, plus biliary and renal excretion of intact drug. 4. Consistent with the high hepatic clearance, oral bioavailability was low ( < or = 6%) in each species. However, all of the species tested absorbed a small proportion of an oral dose extremely rapidly, to give peak concentrations generally within 5 min of administration. 5. 'Simultaneous' collection of blood samples from the hepatic portal vein and aorta of rat confirmed that shortly after oral dosing the intact drug did cross the liver; however, the later collections contained predominantly more polar metabolites. 6. The rapid absorption of intact remikiren is consistent with the transient blockade of plasma renin activity, previously observed in primates after oral administration. However, the high clearance appears inconsistent with the subsequent prolonged decrease in blood pressure, suggesting that the latter effect is mediated through a 'tissue' compartment.

Distribution of remikiren, a potent orally active inhibitor of human renin, in laboratory animals

1. Whole-body autoradiography was used to compare the distribution of remikiren in the squirrel monkey, in which the compound is a potent inhibitor of renin, with the rat and the guinea-pig in which it is less active. 2. Following intravenous administration, drug-related material was rapidly and extensively taken up by the tissues of all three species. Consistent with rapid biliary elimination, high levels of radioactivity were found in the bile duct/gall bladder/intestinal contents. Of the remaining organs, the kidney consistently showed the highest concentrations of drug-related material. 3. Radio-hplc analysis of the kidney samples demonstrated that the majority of the retained material was present as intact remikiren, even at 24 h after administration. A similar degree of retention by the kidney was also found after oral dosing. 4. Uptake of remikiren by the kidney may act as a reservoir for the drug, resulting in the prolonged duration of pharmacological activity, which, despite the high plasma clearance of the drug, has previously been observed in primates.

Role of kinins in the renal response to enalaprilat in normotensive and hypertensive rats

This study examined the role of endogenous kinins in the alteration of renal hemodynamics induced by low-dose converting enzyme inhibition in hydropenic normotensive rats and in the nonclipped kidney of hydropenic two-kidney, one clip hypertensive rats. Infusion of a bradykinin B2 receptor antagonist (D-Arg0,[Hyp3,Thi5,8,D-Phe7]-bradykinin, 1 or 10 micrograms.kg-1.min-1) did not alter renal function of normotensive rats. In a second series of experiments, infusion of enalaprilat at 0.1 mg.kg-1.h-1 increased renal blood flow (P < .01) and decreased renal vascular resistance (P < .01). The superimposition of the kinin antagonist at 1 micrograms.kg.min-1 during the enalaprilat infusion decreased renal blood flow to a value similar to the preenalaprilat baseline and significantly different from the mean of the two enalaprilat periods before and after the addition of the kinin antagonist--the "mean effect of enalaprilat." The decrease in renal blood flow induced by the kinin antagonist was associated with an increase in renal vascular resistance above the mean effect of enalaprilat (P < .025). In two-kidney, one clip hypertensive rats, systemic infusion of enalaprilat augmented the hemodynamics of the nonclipped kidney by a degree similar to that in normotensive rats. In contrast to normotensive rats, superimposition of the kinin antagonist did not alter the enalaprilat-induced change in blood flow or vascular resistance of the nonclipped kidney. The results of this study suggest that endogenous kinins contribute to the increased renal function induced by low-dose converting enzyme inhibition in hydropenic normotensive rats but appear to contribute less to the enalaprilat-induced alterations of renal function in the nonclipped kidney of two-kidney, one clip hypertensive rats.

Cardiovascular hypertrophy: role of angiotensin II and bradykinin

Angiotensin II can raise blood pressure rapidly by inducing direct vasoconstriction and by activating the sympathetic nervous system via central and peripheral mechanisms. In addition, this peptide may act as a growth factor to cause vascular and cardiac hypertrophy (CVH). The structural changes caused by hypertension can therefore be amplified by angiotensin II. Blockade of angiotensin II generation with angiotensin-converting enzyme (ACE) inhibitors appears to be particularly effective in preventing the development of cardiovascular hypertrophy. This beneficial effect might be related to some extent to local accumulation of bradykinin. ACE is one of the enzymes physiologically involved in bradykinin degradation. Treatment of hypertensive rats with a selective bradykinin antagonist can attenuate the blood pressure-lowering effect of ACE inhibition and render less effective the prevention of intimal thickening after endothelial removal from the rat carotid artery. Bradykinin is a vasodilator that acts by increasing the release of endothelium-derived factors such as nitric oxide and prostacyclin, which may have antiproliferative activity. However, blockade of the renin-angiotensin system with an angiotensin II subtype 1-receptor antagonist is also effective in preventing cardiac hypertrophy and neointimal proliferation after endothelial injury. Therefore, the exact contribution of bradykinin to the beneficial effects of ACE inhibition on cardiovascular hypertrophy remains to be further explored.

Renal circulation and blockade of the renin-angiotensin system. Is angiotensin-converting enzyme inhibition the last word?

The mechanism by which angiotensin-converting enzyme (ACE) inhibition influences renal perfusion and function has assumed growing importance as alternatives for blocking the system have emerged. Neither renin inhibitors nor angiotensin II (Ang II) antagonists are likely to trigger responses similar to ACE inhibitor-induced involvement of kinins, prostaglandins, or nitric oxide. Several observations suggest species variation in the contribution of these pathways to the renal response to ACE inhibition. In humans, recent investigation suggests that virtually all of the renal response is due to a fall in Ang II formation. Perhaps most persuasive is the surprising observation that the renal hemodynamic response to renin inhibitors exceeds by more than 50% the response to ACE inhibition in healthy humans. To the extent that kinins or prostaglandins contribute to the renal response to ACE inhibition, one would anticipate a smaller response to renin inhibition. Possible explanations include an unanticipated additional action of renin inhibitors, better tissue penetration of these highly lipophilic agents, or more effective blockade of Ang II formation through an action at the rate-limiting step or non-ACE-dependent Ang II generation. Substantial evidence favors the latter two possibilities. Whatever the explanation, these observations raise the intriguing possibility that the undoubted therapeutic efficacy of ACE inhibition in renal injury, documented most rigorously for type I diabetes mellitus, might be exceeded with the newer classes of agent.

The role of platelets in essential hypertension

Recent research is helping us understand the complex interactions that occur between platelets and their environment. The several intracellular events that occur during platelet activation are being identified as ar their effects on other platelets, the endothelium and coagulation factors. Heightened platelet activation is seen early in essential hypertension and probably plays an important role in the initiation and progression of atherosclerosis and the disorders associated with it. This review identifies some of the changes in platelet structure and function in essential hypertension and their role in the pathogenesis of hypertensive vascular disease.

Antihypertensive effect of sour milk and peptides isolated from it that are inhibitors to angiotensin I-converting enzyme

This study reports the antihypertensive effect of orally administered doses of either Calpis sour milk or peptides (Val-Pro-Pro and Ile-Pro-Pro), which are inhibitors to angiotensin I-converting enzyme, isolated from the sour milk using strain SHR spontaneously hypertensive rats. Single oral administration of the sour milk (5 ml/kg of BW), corresponding inhibitory units of the peptides Val-Pro-Pro (.6 mg/kg of BW), or Ile-Pro-Pro (.3 mg/kg of BW) significantly decreased the systolic blood pressure from 6 to 8 h after administration. Blood pressure returned to the initial level at 24 h after administration. Antihypertensive activity of these two tripeptides was dose-dependent up to 5 mg/kg of BW. Conversely, the sour milk (25 ml/kg of BW) and mixed tripeptides (10 mg each of Val-Pro-Pro and Ile-Pro-Pro/kg of BW) did not change the systolic blood pressure of the normotensive strain WKY Wistar-Kyoto rats.

Prevention by blockade of angiotensin subtype1-receptors of the development of genetic hypertension but not its heritability

1. We determined whether early inhibition of angiotensin II subtype1 (AT1) receptors by the newly synthesized nonpeptidic antagonist, A-81988, can attenuate the development of hypertension in spontaneously hypertensive rats (SHR) and if the altered blood pressure phenotype can be passed on to the subsequent generation, not exposed to the antagonist. 2. Pairs of SHR were mated while drinking tap water or A-81988 in tap water, and the progeny was maintained on the parental regimen until 14 weeks of age. At this stage, A-81988-treated rats showed lower systolic blood pressure and body weight values (136 +/- 5 versus 185 +/- 4 mmHg and 247 +/- 4 versus 283 +/- 4 g in controls, P < 0.01); while heart rate was similar. In addition, mean blood pressure was reduced (101 +/- 7 versus 170 +/- 7 mmHg in controls, P < 0.01), and the pressor responses to intravenous or intracerebroventricular angiotensin II were inhibited by 27 and 59%, respectively. Heart/body weight ratio was smaller in A-81988-treated rats (3.2 +/- 0.1 versus 3.8 +/- 0.1 in controls, P < 0.01). 3. The antihypertensive and antihypertrophic effect of A-81988 persisted in rats removed from therapy for 7 weeks (systolic blood pressure: 173 +/- 4 versus 220 +/- 4 mmHg, heart/body weight ratio: 3.4 +/- 0.1 versus 4.1 +/- 0.1 in controls at 21 weeks of age, P < 0.01 for both comparisons), whereas the cardiovascular hypertensive phenotype was fully expressed in the subsequent generation that was maintained without treatment. 4. These results indicate that chronic blockade of angiotensin AT1-receptors attenuates the development of hypertension in SHR but it does not prevent the transmission of hypertension to the following generation. Thus, heritability of the SHR's hypertensive trait is not affected by pharmacological manipulation of the cardiovascular phenotype.

Angiotensin-converting enzyme activity and contractile effects of angiotensin I and II in human uteroplacental arteries

OBJECTIVE

Our purpose was to study local angiotensin-converting enzyme activity and the mechanical effects of angiotensin I and II in human uteroplacental arteries.

STUDY DESIGN

Angiotensin-converting enzyme activity was measured by a simple radioimmunoassay with tritiated benzoyl-glycyl-glycyl-glycine as substrate in isolated human intramyometrial arteries from nonpregnant (n = 8) and term pregnant women (n = 8) and placental (n = 8) stem villous arteries. Moreover, in these vessels the mechanical effects of angiotensin I and II were investigated in organ bath experiments. Endothelium-intact and endothelium-denuded arteries were used, and the integrity of the endothelium was examined by histologic studies.

RESULTS

The activity of angiotensin-converting enzyme ranked the intramyometrial arteries from pregnant women >> intramyometrial arteries from nonpregnant women > fetal stem villous arteries. Angiotensin-converting enzyme activity was unaffected by removal of the endothelium. Angiotensin II 10(-5) mol/L produced contractile responses in the intramyometrial arteries without significant differences between arteries from nonpregnant and pregnant women. In fetal stem villous arteries the effects of angiotensin II 10(-5) mol/L were less pronounced. As for angiotensin II, the contractile responses to angiotensin I 10(-5) mol/L showed marked development of tachyphylaxis. In the endothelium-denuded preparations the contractile responses to angiotensin I 10(-5) mol/L were significantly enhanced in intramyometrial arteries from nonpregnant women but remained unchanged in intramyometrial arteries from pregnant women and in fetal stem villous arteries. In all preparations pretreatment with captopril or perindopril (10(-5) mol/L) markedly reduced angiotensin-converting enzyme activity, whereas no effects were observed on the contractile responses to angiotensin I. Saralasin 10(-5) mol/L completely abolished the contractile responses to angiotensin I and II.

CONCLUSION

Local angiotensin-converting enzyme activity in human intramyometrial arteries seems to be markedly increased during pregnancy and shows marked differences between maternal and fetal uteroplacental arteries. High concentrations of angiotensin I may imply direct effects on the angiotensin II receptor independent of the local angiotensin-converting enzyme activity.

Renal vascular responses to renin inhibition with zankiren in men

Renin inhibition represents an alternative to angiotensin-converting enzyme (ACE) inhibition for pharmacologic interruption of the renin-angiotensin system. In addition to inhibiting the formation of angiotensin II, ACE inhibitors also inhibit the degradation of kinin and result in accumulation of powerful renal vasodilator prostaglandins and bradykinin. We were therefore surprised by the large renal vasodilator response achieved with the renin inhibitor enalkiren, because substrate-specific renin inhibitors reduce the formation of angiotensin II without affecting other vasodilator mechanisms. To determine whether previous findings were reflective of the renin inhibitor class, we studied 12 healthy men on a sodium-restricted diet, each of whom received two or three escalating oral doses of zankiren, a new agent. Plasma renin activity decreased with the smallest dose (5 mg), and this effect was sustained. The increase in renal plasma flow was clearly related to dose (r = 0.86, F = 9.67), reaching a maximum of 134 +/- 26 ml/min/1.73 m2 at 250 mg, the highest dose. Renin inhibition exerts a remarkable renal vasodilator action, perhaps reflecting the lipophilicity of the agents developed to date, an action that may have clinical implications for the prevention of renal injury in patients at risk.

Early blockade of bradykinin B2-receptors alters the adult cardiovascular phenotype in rats

We evaluated whether long-term inhibition of bradykinin B2-receptors by the long-acting antagonist Hoe 140 (D-Arg,[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin) affects the blood pressure of normotensive rats. Neither Hoe 140 (at 75 nmol/d for 8 weeks) nor its vehicle altered systolic pressure of adult rats on a normal or high sodium intake. In further experiments, pairs of Hoe 140-treated rats were mated and their offspring maintained on Hoe 140 and a normal sodium diet. Controls were given vehicle instead of Hoe 140. At 9 weeks of age, rats given Hoe 140 during prenatal and postnatal phases of life showed greater systolic pressures, heart rates, and body weights than controls (122 +/- 1 versus 113 +/- 1 mm Hg, 444 +/- 6 versus 395 +/- 8 beats per minute, 258 +/- 7 versus 213 +/- 3 g, respectively, P < .01), whereas urinary creatinine excretion was reduced (1.13 +/- 0.05 versus 1.36 +/- 0.04 mumol/100 g body wt in controls, P < .05). The difference in blood pressure (confirmed by direct intra-arterial measurement) persisted after 20 days of dietary sodium loading, whereas it was nullified by sodium restriction. In additional experiments, the offspring of untreated rats received Hoe 140 or vehicle from 2 days to 11 weeks of age. At this stage, systolic pressure and body weight were significantly greater in Hoe 140-treated rats compared with controls, and heart rate was similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of captopril on glucose transport activity in skeletal muscle of obese Zucker rats

This study tested whether the angiotensin-converting enzyme (ACE) inhibitor captopril can modify the glucose transport system in insulin-resistant skeletal muscle. Obese Zucker (fa/fa) rats (approximately 300 g)--a model of insulin resistance--were administered by gavage either a single dose (50 mg/kg body weight) or repeated doses (50 mg/kg/d for 14 consecutive days) of captopril. Corresponding groups of age-matched, vehicle-treated lean (Fa/-) littermates (approximately 170 g) were also studied. Glucose transport activity in the epitrochlearis muscle was assessed by in vitro 2-deoxyglucose (2-DG) uptake. The increase in 2-DG uptake due to insulin (2 mU/mL) in muscles from vehicle-treated obese rats was less than 50% (P < .05) of the increase observed in muscles from lean rats. Short-term captopril treatment improved insulin-stimulable 2-DG uptake in muscles from obese rats by 46% (P < .05), and this enhanced insulin action due to captopril was completely abolished by pretreatment with the bradykinin antagonist HOE 140 (100 micrograms/kg). Long-term treatment with captopril produced a 60% improvement in insulin-stimulated 2-DG uptake (P < .05). Contraction-stimulated 2-DG uptake was significantly impaired (-31%, P < .05) in the obese rat, but was not altered by long-term captopril treatment. These findings indicate that both short- and long-term treatments with captopril significantly improve insulin-stimulated glucose transport activity in skeletal muscle of the obese Zucker rat, and that this improvement involves bradykinin metabolism. These data therefore support the hypothesis that captopril-induced improvements in glucose disposal result in part from an enhancement of the skeletal muscle glucose transport system.

A bradykinin-potentiating peptide (peptide K12) isolated from the venom of Egyptian scorpion Buthus occitanus

A nontoxic peptide with bradykinin-potentiating activity was isolated from the dialyzed venom of the scorpion Buthus occitanus by reverse-phase high performance liquid chromatography (RP-HPLC). The pharmacological activity of the peptide was bioassayed by its ability to potentiate added bradykinin (BK) on the isolated guinea pig ileum as well as the isolated rat uterus for contraction. Moreover, the peptide potentiates in vivo the depressor effect of BK on arterial blood pressure in the normotensive anesthetized rat. Chemical characterization of the peptide was also performed. The amino acid composition of the peptide showed 21 amino acid residues per molecule including three proline residues. The amino acid sequence of the purified peptide was confirmed by mass spectrometry. Either N- or C-terminal ends were free. The sequence does not show a homology with bradykinin-potentiating peptides isolated from either scorpion or snake venoms. Furthermore, we did not find a significant sequence homology between the sequence of the isolated peptide and any of proteins or peptides in GenPro or NBRF data banks. The peptide also inhibited angiotensin-converting enzyme (ACE), and could not serve as substrate for the enzyme. It could be concluded that the mechanism of bradykinin-potentiating peptide (BPP) activity may be due to ACE inhibition.

Effects of bradykinin B2 receptor antagonism on the hypotensive effects of ACE inhibition

1. The aim of this study was to determine the participation of endogenous bradykinin (BK) in the antihypertensive effects of the angiotensin converting enzyme inhibitor (ACEI), perindoprilat, in the spontaneously hypertensive rat (SHR) on different salt diets. 2. Conscious SHRs receiving either a low or a high NaCl diet were used in order to evaluate the respective roles of angiotensin II suppression and bradykinin stimulation in the acute hypotensive effects of perindoprilat. Two different B2 receptor antagonists (B 4146 and Hoe 140) were used after bolus administration of 7 mg kg-1 of the ACEI, perindoprilat. In separate animals, Hoe 140 was administered before the injection of perindoprilat. In other experiments, the effects of Hoe 140 on the hypotensive effects of the calcium antagonist, nicardipine, were tested. 3. The different NaCl diets had no effect on baseline blood pressure. Hoe 140 injection before ACE inhibition did not modify blood pressure. Perindoprilat caused more marked hypotension in the low salt-fed rats than in the high salt animals (P < 0.01). Administration of Hoe 140 or B4146 after perindoprilat significantly reduced the antihypertensive effects of perindoprilat in the different groups, but this effect was more pronounced in high salt-fed rats. However, in SHRs receiving Hoe 140 before perindoprilat, the antihypertensive effect of perindoprilat was completely abolished in both high or low salt diet rats. In separate experiments we confirmed that Hoe 140 did not affect the hypotensive efficacy of the calcium antagonist, nicardipine. 4. Our study shows that inhibition of endogenous bradykinin degradation participates in the acute antihypertensive effects of perindoprilat in SHRs. The role of bradykinin is more pronounced following exposure to a high salt diet i.e., when the renin-angiotensin system is suppressed. Blockade of bradykinin B2 receptors by Hoe 140 before administration of perindoprilat completely abolished the hypotensive effect of perindoprilat suggesting an increased role of bradykinin in the onset of hypotensive action of ACE inhibitors. However, the exact mechanism of this interaction remains unclear.

Major role of the renin angiotensin system in the neointima formation after vascular injury in guinea pigs

ACE inhibition has been shown to prevent neointima formation after vascular injury. However, it is not known if this effect is due to a specific inhibition of the renin angiotensin system or to another mechanism such as the accumulation of bradykinin. In order to answer this question we compared the effects of maximal effective doses of cilazapril, an angiotensin converting enzyme (ACE) inhibitor, and ciprokiren, a new renin inhibitor, in guinea pigs. Vascular injury was induced by endothelial denudation of the right carotid artery of guinea pigs treated either by saline (control group), cilazapril (30 mg/kg/day) or ciprokiren (24 mg/kg/day). Twelve days after the ballooning, the guinea pigs were sacrificed, the carotid arteries were perfused fixed and neointima formation was evaluated by quantitative morphometry. Both, ciprokiren and cilazapril prevented neointima formation to the same extent (inhibition by 42 and 49%, respectively, p < 0.05). These results suggest that, in guinea pigs, renin inhibition prevents neointima formation to a similar extent as ACE inhibition. Therefore, ACE inhibitors seem to act in this model by inhibiting the renin angiotensin system and not by other effects such as accumulation of bradykinin.

Cytosolic Ca2+ transients in endothelium-dependent relaxation of pig coronary artery, and effects of captopril

To determine the mechanism of endothelium-dependent relaxation by bradykinin, we simultaneously measured changes in cytosolic calcium concentrations ([Ca2+]i) and force of fura-2-loaded strips of porcine coronary artery. We also examined effects of captopril, an angiotensin converting enzyme inhibitor, on bradykinin-induced relaxation. Bradykinin, in a concentration-dependent manner (10(-10) to 10(-7) M), decreased both [Ca2+]i and force to resting levels, during 10(-5) M prostaglandin F2 alpha-induced contractions, only when endothelium was intact. Treatment with 10(-5) M captopril enhanced the bradykinin-induced decreases in [Ca2+]i and force and shifted the concentration-response curve to the left. During 118 mM K+ depolarization, bradykinin induced a greater relaxation than that expected from the reduction in [Ca2+]i. Captopril had no effects on the relationship between reduction in [Ca2+]i and relaxation induced by bradykinin. Bradykinin relaxes porcine coronary artery in an endothelium-dependent manner, by decreasing [Ca2+]i and also by controlling the Ca2+ sensitivity of the contractile apparatus of smooth muscle. Captopril enhanced the bradykinin-induced relaxation, with no apparent direct effect on Ca2+ sensitivity of the contractile apparatus.

Human small intestinal angiotensin-converting enzyme: intracellular transport, secretion and glycosylation

Human intestinal angiotensin-converting enzyme (ACE) exists in the brush-border membrane as a monomeric protein of apparent molecular mass 184 kDa. It is associated with the membrane via a hydrophobic segment and has a transmembrane orientation [Naim (1992) Biochem. J. 286, 451-457]. In addition to the membrane-bound form (ACEm), hydrophilic forms of ACE (ACEsec) can be identified in biosynthetically labelled intestinal cells. Thus the culture medium of biosynthetically labelled human biopsy samples contains an ACE molecule which has an apparent molecular mass similar to that of its membrane-bound counterpart. The secreted ACEsec forms follow a precursor/product relationship with the mature ACE molecule. The effect of the monomeric structure of ACE in its intracellular transport and secretion was investigated by pulse-chase experiments on human biopsy samples labelled with [35S]methionine. The results reveal 2-3-fold slower transport of ACE from the endoplasmic reticulum (ER) to the Golgi as compared with the homodimeric proteins dipeptidylpeptidase IV and aminopeptidase N. Further, the transport kinetics of ACE are comparable with those of human sucrase-isomaltase and human maltase-glucoamylase, two brush-border disaccharidases that do not form homodimers in the ER of human small-intestinal cells. These findings strongly suggest that homodimerization of brush-border proteins may influence the rate of transport of these proteins from the ER to the Golgi. The effect of glycosylation on the transport and secretion of ACE was investigated by utilizing several inhibitors of glycan processing. Here, secretion of ACE molecules continued to take place, albeit to a considerably lesser extent. In fact, approx. 2-fold less ACE molecules were secreted in the presence of inhibitors of ER glucosidases I and II and cis-Golgi mannosidase-I, suggesting that carbohydrate processing is important in the attainment of a transport-competent conformation.

Effect of chloride and diamide on serum angiotensin I-converting enzyme activity from eight mammalian species

1. The effect of chloride on serum angiotensin I-converting enzyme (ACE) activity was characterized in eight mammalian species: dog, guinea pig, hamster, human, mouse, rabbit, rat, and sheep. 2. Optimum chloride concentrations varied from 300 mM for rabbit to 1700 mM for hamster. 3. The increments with these optimum concentrations with respect to 100 mM chloride concentration were from 1.4-fold in rabbit to 7.9-fold in hamster and dog. 4. There was no correlation between serum chloride concentration or serum ACE activity and optimum chloride concentration. 5. Serum ACE increased only in humans with diamide pretreatment suggesting the presence of endogenous inhibitors.

Effect of a short-term captopril treatment on serum and tissue angiotensin I-converting enzyme activity from four mammalian species. Differences using diamide in the in vitro assay

1. Angiotensin I-converting enzyme (ACE) activity was determined in serum and nine tissues from control and captopril-treated rats, mice, guinea pigs and rabbits. 2. ACE activity was determined with and without sample pretreatment with diamide (total and basal activity, respectively). 3. A very different pattern of response to captopril was observed among the different species. 4. There was no relationship between serum ACE activity and the response to captopril. 5. There were important differences in the determinations of total or basal ACE activities. 6. Endogenous ACE inhibitors were found in some tissues from mouse and rabbit.

Monocrotaline pyrrole-induced changes in angiotensin-converting enzyme activity of cultured pulmonary artery endothelial cells

1. Changes in the structural and functional integrity of endothelium have been recognized as relatively early features of delayed and progressive pulmonary vascular injury caused by the pyrrolizidine alkaloid, monocrotaline (MCT). Although a number of investigators have evaluated angiotensin-converting enzyme (ACE) activity in the lungs of rats treated with MCT, the exact nature of changes in activity of this enzyme and the role they may play in MCT pneumotoxicity remain controversial. 2. We examined the direct effects of monocrotaline pyrrole (MCTP), a toxic metabolite of MCT, on cultured endothelial cell ACE activity. Post-confluent monolayers of porcine or bovine pulmonary artery endothelial cells (PECs or BECs, respectively) were treated with a single administration of MCTP at time 0; then they were examined for their ability to degrade the synthetic peptide, [3H]-benzoyl-Phe-Ala-Pro. 3. In PECs, which are relatively insensitive to the direct cytolytic effects of MCTP, monolayer ACE activity was unchanged initially but gradually decreased within 4 days after treatment with a high concentration of MCTP (150 microM). This decrease was transient, and PEC monolayer ACE activity returned to the control value by 10 days post treatment. 4. BEC monolayer ACE activity was also unchanged initially but rapidly declined within 4 days after MCTP treatment and remained depressed throughout the post treatment period. BECs were quite sensitive to the cytolytic effects of MCTP and the decline in ACE activity occurred coincident with the decrease in monolayer cellularity and appearance of marked cytotoxicity. 5. We conclude that high concentrations of MCTP decrease endothelial ACE activity. The decline in ACE activity is delayed and the magnitude and duration of the decrease corresponds to the degree ofMCTP-induced cytotoxicity. This suggests that altered endothelial ACE activity is unlikely to be a direct effect of MCTP on the enzyme but may reflect the delayed cell injury which results from exposure to this compound.

Comparative effects of three different potent renin inhibitors in primates

The goal of the present study was to compare the effects of three potent reference renin inhibitors (remikiren, CGP 38560A, and enalkiren) in sodium-depleted normotensive squirrel monkeys. In these monkeys, arterial pressure was measured in the conscious state with a telemetry system. Oral and intravenous maximal effective doses of the three renin inhibitors were compared in parallel groups of monkeys. In additional experiments, remikiren was given on top of either CGP 38560A or enalkiren in the same animals. Finally, the three drugs were compared with the angiotensin converting enzyme inhibitor cilazapril. The effects of the three drugs on the plasma components of the renin-angiotensin system (plasma renin activity, immunoreactive renin, and immunoreactive angiotensin II concentrations) were also measured. Our results show that remikiren was as effective as cilazapril and markedly more effective than CGP 38560A or enalkiren in reducing arterial pressure in our monkey model. Interestingly, these differences in arterial pressure could not be explained by differences of in vitro potency or different biochemical changes of the plasma components of the renin-angiotensin system, because the inhibitors all reduced immunoreactive angiotensin II to similarly low levels. One possible explanation is that, in our model, remikiren in contrast to CGP 38560A and enalkiren is able to inhibit renin in a functionally important extraplasmatic compartment.

Differential effects of captopril on regional haemodynamic responses to angiotensin I and bradykinin in conscious rats

1. Conscious, Long Evans rats were chronically instrumented with pulsed Doppler flow probes and intravascular catheters to allow regional haemodynamic (coeliac, mesenteric and hindquarters vascular beds) responses to i.v. bradykinin to be assessed in the absence and presence of captopril and of ganglion blockade (with mecamylamine). 2. Bradykinin (3 nmol kg-1, i.v. bolus) had no effect on mean arterial blood pressure, although it caused hyperaemic vasodilatation in the coeliac, mesenteric and hindquarters vascular beds. Following administration of captopril at a dose (28 nmol kg-1) which had no effect on responses to angiotensin I, the hypotensive and coeliac and mesenteric vasodilator responses to bradykinin were enhanced. However, there was a temporal dissociation between these events indicating that changes in cardiac output must have been contributing to the changes in mean arterial blood pressure. 3. Captopril at a higher dose (280 nmol kg-1) caused reversible inhibition of the pressor and coeliac and mesenteric vasoconstrictor effects of angiotensin I, but the inhibition of the mesenteric vascular responses was significantly less than that of the coeliac vascular responses. Under the same conditions, the mesenteric vasodilator effects of bradykinin were less enhanced than the coeliac vasodilator effects, consistent with greater inhibition of angiotensin-converting enzyme (i.e., kininase II) in the coeliac than in the mesenteric vascular bed. But, since the hypotensive action of bradykinin was markedly enhanced in these circumstances, the possibility existed that baroreflex responses influenced the haemodynamic effects of bradykinin. However, assessment of the haemodynamic changes following bradykinin administration(bolus or infusion) in the presence of ganglion blockade showed that only the hindquarters vasodilator response to bradykinin was enhanced, while the coeliac and mesenteric vasodilator responses were diminished. Thus, additional factors must have been influencing the latter responses.4. The results show that inhibition of angiotensin-converting enzyme (kininase II) can have differential effects on the regional haemodynamic responses to angiotensin I and bradykinin. The results provide a striking illustration of our previous assertion that the measurement of arterial blood pressure alone cannot provide sufficient information to allow interpretation either of the effects of vasoactive substances,or of the influence of drugs thereupon.

Enhancement by captopril of bradykinin-induced calcium transients in cultured endothelial cells of the bovine aorta

Using microscopic fluorometry and fura-2-loaded cultured bovine aortic endothelial cells, we determined the effects of captopril, an angiotensin converting enzyme (ACE) inhibitor, on bradykinin-induced Ca2+ transients in endothelial cells. In the presence of extracellular Ca2+, 10(-9) M bradykinin induced an early rise in the transients followed by sustained elevations of cytosolic calcium concentration ([Ca2+]i). Bradykinin concentration-dependently increased [Ca2+]i (EC50 6.7 x 10(-9) M). Captopril, 10(-5) M, enhanced and prolonged the bradykinin-induced Ca2+ transients and shifted the concentration-response curve to the left (EC50 8.5 x 10(-10) M). In porcine coronary aterial strips with intact endothelium, cumulative applications of bradykinin induced an endothelium-dependent relaxation during prostaglandin F2 alpha-induced contraction (EC50 = 2.0 x 10(-9) M). Treatment with 10(-5) M captopril enhanced the bradykinin-induced relaxation and shifted the concentration-response curve to the left (EC50 = 7.6 x 10(-10) M). Thus, captopril enhances the bradykinin-induced relaxation by mechanisms mainly dependent on the endothelium, namely the inhibition of ACE.

Regulatory functions of the coronary endothelium

In this brief review three functions of the coronary endothelium are surveyed: (a) its barrier and exchange function, (b) the prevention of coagulation and platelet aggregation, and (c) its role in vasoregulation. Impairment of these functions can occur in ischemia, hypertension, arteriosclerosis and inflammation.

Bovine angiotensin converting enzyme cDNA cloning and regulation. Increased expression during endothelial cell growth arrest

Angiotensin converting enzyme (ACE) is a zinc-containing dipeptidase that converts angiotensin I to angiotensin II, a powerful vasoconstrictor and smooth muscle growth factor. ACE activity has been shown to be dynamically regulated by hormones, ACE inhibitors, and endothelial cell growth state. To study how ACE expression is regulated, we isolated and sequenced the bovine ACE gene using both ACE-specific cDNA and genomic clones. Bovine ACE cDNA encodes a single polypeptide of 1,306 residues with a molecular mass of 150 kd. Bovine ACE is approximately 80% homologous to that of other species. It contains two homologous domains of equal size. Alignment of ACE sequences from bovine, human, mouse, and rabbit reveals that during evolution both domains have been highly conserved. We used the bovine ACE cDNA to study regulation of ACE gene expression during density-dependent growth arrest. As endothelial cells became growth-arrested (6 days after confluence), there was a 12-fold increase in ACE activity and a 90% decrease in DNA synthesis. Immunocytochemically detectable ACE markedly increased in growth-arrested cells. The increase in ACE was due to increased ACE gene expression, as assayed by RNase protection, which showed a 20-fold increase in ACE-specific mRNA. The present study shows that bovine ACE is highly regulated by endothelial cell growth state at the level of protein and mRNA expression. Such dynamic regulation may have important consequences for angiotensin II production during endothelial cell proliferation after arterial injury.

Effect of long-term captopril therapy on left ventricular remodeling and function during healing of canine myocardial infarction

To determine whether the long-term reduction of preload and afterload by captopril during healing after acute anterior myocardial infarction might attenuate left ventricular remodeling and improve function, 30 chronically instrumented dogs with infarction produced by left anterior descending coronary artery ligation were randomized 2 days later to oral therapy with placebo (n = 15) or captopril, 50 mg twice daily (n = 15), for 6 weeks. Serial hemodynamic as well as topographic and functional variables (two-dimensional echocardiography) were measured over 6 weeks. Scar topography (planimetry), occluded bed size (coronary arteriography) and collagen (hydroxyproline) content were measured at 6 weeks. Between 2 days and 6 weeks, captopril decreased (p less than 0.001) mean arterial pressure and mean left atrial pressure more than did placebo, but it did not influence heart rate. Infarct scar mass, transmurality and collagen content at 6 weeks were similar in the two groups but scars showed less (p less than 0.001) thinning and expansion with captopril than with placebo. Echocardiograms showed similar infarct expansion and thinning in the two groups at 2 days but less aneurysm with captopril at 6 weeks. Between 2 days and 6 weeks, expansion index (infarct-/noninfarct-containing segment length) decreased (p less than 0.001) with captopril but increased (p less than 0.001) with placebo. Also, thinning ratio (infarct/normal wall thickness) decreased (p less than 0.001) with placebo but did not change (p = NS) with captopril. By 6 weeks, left ventricular asynergy and volumes showed a greater decrease (p less than 0.01) and global ejection fraction a greater increase (p less than 0.05) with captopril.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of renin-angiotensin system blockade in guinea pigs

The goal of the present study was to compare the hemodynamic and biochemical effects of the renin inhibitor Ro 42-5892, the angiotensin converting enzyme inhibitor cilazapril, and the angiotensin II receptor blocker EXP132, the aldehyde derivative of DuP 753. The three drugs were evaluated in guinea pigs, previously treated with furosemide, using their maximal effective doses. Cilazapril decreased arterial blood pressure more than Ro 42-5892 and EXP132. In contrast, Ro 42-5892 and EXP132 had similar effects. The larger decrease of arterial pressure induced by cilazapril was not due to a larger decrease of angiotensin II in plasma and was not influenced by cyclooxygenase inhibition with indomethacin or by bradykinin antagonism with Hoe 140. After binephrectomy, most of the blood pressure-lowering effect of Ro 42-5892 disappeared. In contrast, cilazapril was still markedly effective, pointing to extrarenal effects. We conclude that in furosemide-treated guinea pigs, as opposed to previously published animal models, the decrease of arterial pressure induced by angiotensin converting enzyme inhibitors may be partly due to extrarenal effects not related to the renin-angiotensin system.

Blood pressure control by the renin-angiotensin system in normotensive subjects. Assessment by angiotensin converting enzyme and renin inhibition

BACKGROUND

The participation of the renin-angiotensin system in the control of blood pressure in normal, sodium-replete subjects is not clear. The use of a specific inhibitor of human renin should allow a better delineation of the importance of this system.

METHODS AND RESULTS

Blood pressure responses were measured 1 hour after randomized, double-blind administration of the renin inhibitor Ro 42-5892 (600 mg p.o.) or the angiotensin converting enzyme inhibitor captopril (50 mg p.o.) in 20 healthy men on an ad libitum sodium diet. Effective inhibition of the renin-angiotensin system by either compound was indicated by increases of immunoreactive renin associated with an increase of angiotensin I production rate of 67.8 +/- 33.6% after captopril and a decrease of 79.5 +/- 16.4% after Ro 42-5892. Furthermore, Ro 42-5892 decreased plasma renin activity by 64%. Whereas intra-arterial diastolic (60 +/- 5.1 to 51.4 +/- 7.2 mm Hg, p less than 0.01) and mean arterial (77.7 +/- 6.0 to 71.4 +/- 8.5 mm Hg, p less than 0.001) pressures decreased after captopril, they remained unchanged after Ro 42-5892. Captopril, but not Ro 42-5892, increased forearm blood flow (2.4 +/- 0.8 versus 1.9 +/- 0.8 ml/min/100 ml, p less than 0.01) and significantly enhanced the increase of forearm blood flow to brachial artery infusions of bradykinin (0.15, 1.5, 5, 15, and 50 ng/min/100 ml; 5 minutes each) from 744 +/- 632% to 1,383 +/- 514% (p less than 0.01). Furthermore, repeat bradykinin infusions resulted in further decreases of blood pressure (from mean pressure of 71.4 +/- 8.5 to 63.2 +/- 7.6 mm Hg, p less than 0.01) only after captopril. Changes of blood pressure after captopril were unrelated to baseline plasma renin activity but correlated with captopril-induced enhancement of vasodilation to bradykinin (r = 0.68, p less than 0.05).

CONCLUSIONS

The lack of blood pressure effects of renin inhibition in contrast to angiotensin converting enzyme inhibition suggests that the renin-angiotensin system does not contribute significantly to blood pressure control in normotensive, sodium-replete subjects. The hypotensive activity of angiotensin converting enzyme inhibitors may result from additional hormonal effects, for example, inhibition of bradykinin degradation and/or subsequent increases of vasodilating prostaglandins or endothelium-derived relaxing factor(s).

A lack of effect of captopril on platelet aggregation in patients with congestive heart failure

We have studied the acute and chronic effects of an ACE inhibitor (captopril) on platelet function and the renin-angiotensin system in patients with congestive heart failure. Plasma concentrations of angiotensin II fell significantly after a single dose of captopril (25 mg) and during long-term treatment with captopril (2 weeks, 75 mg/day). Plasma renin activity increased significantly after both the single and repeated doses. Captopril did not affect ADP-induced platelet aggregation or concentrations. It seems unlikely that circulating angiotensin II affects ADP-induced platelet aggregation in patients with congestive heart failure.

Tissue and plasma angiotensin converting enzyme and the response to ACE inhibitor drugs

1. There is a body of circumstantial and direct evidence supporting the existence and functional importance of a tissue based RAS at a variety of sites. 2. The relation between circulatory and tissue based systems is complex. The relative importance of the two in determining haemodynamic effects is unknown. 3. Despite the wide range of ACE inhibitors already available, it remains unclear whether there are genuine differences related to tissue specificity. 4. Pathological states such as chronic cardiac failure need to be explored with regard to the contribution of tissue based ACE activities in generating acute and chronic haemodynamic responses to ACE inhibitors. 5. The role of tissue vs plasma ACE activity may be clarified by study of the relation between drug concentration and haemodynamic effect, provided that the temporal dissociation is examined and linked to circulating and tissue based changes in ACE activity, angiotensin peptides and sympathetic hormones.

Transcription of testicular angiotensin-converting enzyme (ACE) is initiated within the 12th intron of the somatic ACE gene

Angiotensin-converting enzyme (ACE) is a zinc-containing dipeptidyl carboxypeptidase that catalyzes the conversion of angiotensin I to the potent vasoconstrictor angiotensin II. By analyzing cDNA and genomic DNA, we have constructed a consensus sequence encoding the testis isozyme of mouse ACE. Testis ACE cDNA contains 2,435 base pairs and encodes a protein of 732 amino acids. The N-terminal 66 amino acids are unique to the testis isozyme, while the remaining 666 are identical to the carboxyl half of mouse somatic ACE. The overall conservation of amino acid sequence between the testis isozymes of the mouse, rabbit, and human is 78 to 84%. The conservation of amino acids for the N-terminal domain uniquely expressed within the testis is 63 to 67% between these species. Primer extension and RNase protection experiments show that RNA transcription of the testis ACE isozyme begins 16 or 17 bases upstream from the translation start site. A sequence element resembling a TATA box is found 25 bases 5' of the transcription start site. To create its unique isozyme of ACE, the testis begins mRNA transcription in the middle of the exonic-intronic structure of somatic ACE, within a sequence treated as an intron by somatic tissues. Testis ACE is not the result of alternative RNA splicing but seems due to the start of transcription at a unique site within the ACE gene.

Transcription of testicular angiotensin-converting enzyme (ACE) is initiated within the 12th intron of the somatic ACE gene

Angiotensin-converting enzyme (ACE) is a zinc-containing dipeptidyl carboxypeptidase that catalyzes the conversion of angiotensin I to the potent vasoconstrictor angiotensin II. By analyzing cDNA and genomic DNA, we have constructed a consensus sequence encoding the testis isozyme of mouse ACE. Testis ACE cDNA contains 2,435 base pairs and encodes a protein of 732 amino acids. The N-terminal 66 amino acids are unique to the testis isozyme, while the remaining 666 are identical to the carboxyl half of mouse somatic ACE. The overall conservation of amino acid sequence between the testis isozymes of the mouse, rabbit, and human is 78 to 84%. The conservation of amino acids for the N-terminal domain uniquely expressed within the testis is 63 to 67% between these species. Primer extension and RNase protection experiments show that RNA transcription of the testis ACE isozyme begins 16 or 17 bases upstream from the translation start site. A sequence element resembling a TATA box is found 25 bases 5' of the transcription start site. To create its unique isozyme of ACE, the testis begins mRNA transcription in the middle of the exonic-intronic structure of somatic ACE, within a sequence treated as an intron by somatic tissues. Testis ACE is not the result of alternative RNA splicing but seems due to the start of transcription at a unique site within the ACE gene.

Genomic DNA 5' to the mouse and human angiotensin-converting enzyme genes contains two distinct regions of conserved sequence

Genomic DNA 5' to the mouse and human genes encoding angiotensin-converting enzyme has been isolated and analyzed. A sequence comparison identifies two discrete regions of genomic DNA that are highly conserved. One region, found immediately 5' to the mouse and human ACE genes, is a GC rich segment that contains a "TATA box" and several potential Spl binding sites. The second conserved region is found further 5' and contains several potential regulatory cis elements including a possible glucocorticoid responsive element. These two regions of genomic DNA may influence the rate of mRNA transcription from the angiotensin-converting enzyme gene.

A deeply recessed active site in angiotensin-converting enzyme is indicated from the binding characteristics of biotin-spacer-inhibitor reagents

Two biotinylated derivatives of the angiotensin-converting enzyme (ACE) inhibitor, lisinopril, were synthesized. Compounds BL11 (epsilon-biotinamidocaproyl-lisinopril) and BL19 (epsilon-biotinamidocaproyl-beta-alanyl-beta-alanyl-lisinopril) have, respectively, 11 and 19 atoms of spacing structure between the biotin and the inhibitor moieties. Both compounds were found to be potent inhibitors of mouse kidney ACE, but they lost this ability in the presence of streptavidin in free solution. However, BL19 (but not BL11), when complexed to ACE, retained enough residual binding strength for streptavidin to allow the complex to be specifically removed from solution by streptavidin-agarose beads. It was thus possible to employ BL19 for the affinity isolation of ACE from crude mixtures. These results indicate that the bound determinant of lisinopril must lie at least 11 A below the outer surface of the ACE molecule.

Perindopril. A review of its pharmacokinetics and clinical pharmacology

Perindopril is an orally active, non-thiol angiotensin-converting enzyme (ACE) inhibitor, which in doses of 4 to 8mg is effective in the control of essential hypertension. As monotherapy it is as effective as once-daily atenolol and possibly more effective than twice-daily captopril. A synergistic response has been noted when perindopril is combined with a thiazide diuretic. Maximal pharmacodynamic effects (ACE inhibition, increase in plasma renin activity and angiotensin I, reduction in aldosterone and angiotensin II and blood pressure) are seen 4 to 6 hours after dosing, with substantial effects still present at 24 hours. Perindopril is a prodrug which requires de-esterification to perindoprilat for useful ACE inhibition. Maximal plasma perindoprilat concentrations are reached 2 to 6 hours after oral administration of perindopril, and 70% of the active metabolite is cleared by the kidneys. The other major metabolite of perindopril is an inactive glucuronide. Ageing is associated with increased serum perindoprilat concentrations, which are probably caused by a combination of enhanced conversion to the active metabolite and diminished renal clearance. Compensated cirrhosis does not appear to have an independent effect. There is little published experience of the use of perindopril in patients with cardiac failure or other cardiac disease, but preliminary evidence would support the general value of this class of agent as adjunctive therapy.

Angiotensin converting enzyme inhibitor potentiated the vasorelaxant response of atrial natriuretic peptide in toad aortic rings

1. The vasorelaxant effect of synthetic atrial natriuretic peptide (ANP) on the vascular response to angiotensin II (A II) and norepinephrine (NE) in aortic rings from Bufo arenarum toad was studied. 2. Pretreatment with ANP partially inhibited the vascular response to A II and NE. 3. Angiotensin converting enzyme inhibitor (ACEI) treatment partially inhibited the contractile response of angiotensin I (A I) and did not affect the A II response. 4. The inhibitory effect of ANP on vascular response to A II and NE were potentiated by pretreatment with ACEI. 5. Results suggest that the angiotensin converting enzyme present in the vascular wall from Bufo arenarum toad may be involved in the metabolism of ANP.