Angiotensin-converting enzyme inhibition improves defective angiogenesis in the ischemic limb of spontaneously hypertensive rats.

OBJECTIVES: Natural angiogenesis has been shown to be impaired in spontaneously hypertensive rats (SHR). The purpose of this study was to determine whether pathological angiogenesis in the setting of tissue ischemia is also impaired in SHR, and to what extent it is modified by angiotensin-converting enzyme (ACE) inhibition. METHODS: Ischemia was induced in the hindlimb of SHR by excision of the femoral artery, after which the animals were randomly assigned to receive low-dose perindopril (sub-antihypertensive, 0.2 mg/kg/day), high-dose perindopril (antihypertensive, 2.0 mg/kg/day), or vehicle for 3 weeks. Wistar-Kyoto rats (WKY) with femoral artery excision served as a control group. RESULTS: Tissue ACE activity in SHR was significantly increased compared to WKY (49.4+/-6.2 vs. 34.0+/-14.2 IU/mg, P<0.01). Administration of perindopril significantly reduced ACE activity in SHR (low dose: 12.4+/-2.3; high dose: 11.0+/-2.1 IU/mg, P<0.005). Angiogenesis of the ischemic limb muscles was significantly impaired at 4 weeks in SHR versus WKY as indicated by the lower capillary density in the former (364.5+/-43.0 vs. 463.8+/-63.0/mm(2), P<0.05) as well as the reduced hindlimb perfusion assessed by laser Doppler imaging (0.86+/-0.08 vs. 1.03+/-0.09, P<0.05). Administration of perindopril significantly augmented both the capillary density (low dose: 494.3+/-69.8; high dose: 543.9+/-76.9/mm(2), P<0.005) and the limb perfusion (low dose: 1.06+/-0.15; high dose: 1.05+/-0.12, P<0.05) of the ischemic limb in SHR. CONCLUSIONS: These findings indicate that pathological angiogenesis in the setting of tissue ischemia is impaired in SHR compared with WKY, and that this impairment can be reversed by ACE inhibition. The angiogenic properties of an ACE inhibitor may benefit patients with essential hypertension presenting with lower limb vascular insufficiency.

Potentiation by endothelin-1 of 5-hydroxytryptamine-induced contraction in coronary artery of the pig.

1. In order to elucidate the physiological and potential pathological roles of endothelin-1 (ET-1) in coronary artery contraction and relaxation, we undertook the present study to examine the action of ET-1 itself, and the combined effects of ET-1 with vasoconstrictor agonists such as acetylcholine (ACh), histamine, and 5-hydroxytryptamine (5-HT), all of which have been implicated in the genesis of coronary spasm. 2. Isometric tension and cytosolic Ca2+ concentration ([Ca2+]i) in a ring segment of porcine coronary artery loaded with fura-2 were measured simultaneously. 3. ET-1 contracted the artery in a concentration-dependent manner; and nisoldipine, a Ca2+ channel blocking drug of the 1,4-dihydropyridine type, antagonized the ET-1 action non-competitively. A radio-receptor binding assay also indicated the mutually exclusive binding of ET-1 and (+)-[3H]-PN200-110, a Ca2+ channel ligand, to the membrane fraction of porcine coronary artery. 4. ET-1 (10-100 pM) increased tension and [Ca2+]i in a parallel manner, while at higher concentrations (1-10 nM) it produced further contraction with a small increase in [Ca2+]i. 5. ET-1 (30-100 pM) selectively potentiated the 5-HT-induced contraction 1.5 to 2 times over the control without causing a significant increase in [Ca2+]i, which seems to be qualitatively similar to a tumour promoting phorbol ester, 12-deoxyphorbol 13-isobutylate (DPB). Bay K 8644 (10 nM), on the other hand, potentiated the contraction in response to practically all agonists used and affected a concomitant increase in [Ca2+]i.6. A Ca2+ channel blocking drug such as diltiazem abolished the increase in [Ca2+]i and partially attenuated the mechanical potentiation produced by a small amount of ET-1 in combination with 5-HT.7. The results suggest that ET-1 and 5-HT interact functionally at the cellular or subcellular level and modulate the Ca2 + sensitivity of the contractile elements through the possible activation of protein kinase C.

Pharmacological profile of semotiadil fumarate, a novel calcium antagonist, in rat experimental angina model.

1. The aim of the present study was to determine whether antianginal efficacy of semotiadil fumarate (SD-3211), a structurally novel calcium antagonist, is distinct from those of diltiazem, nifedipine and nisoldipine. 2. First, the duration of the inhibitory effects of semotiadil was compared with that of other Ca2+ antagonists in rat experimental angina evoked by vasopressin. Semotiadil (10 mg kg-1, p.o.) was effective for at least 9 h in the anginal model and those effects of semotiadil were longer-lasting than those of diltiazem (30 mg kg-1, p.o.), nifedipine (10 mg kg-1, p.o.), and nisoldipine (3 mg.kg-1, p.o.). 3. Second, the selectivity of actions of these Ca2+ antagonists for the coronary arteries and myocardium was evaluated in rat isolated perfused hearts. Diltiazem (10(-6) M) reduced cardiac contractility without inhibiting the elevation of perfusion pressure evoked by acetylcholine. Semotiadil (10(-7) M) significantly suppressed cardiac contractility and inhibited the coronary response to acetylcholine. In contrast, nifedipine (3 x 10(-9)-3 x 10(-8) M) and nisoldipine (3 x 10(-10)-10(-8) M) did not reduce cardiac contractility at concentrations which significantly inhibited the increase in perfusion pressure to acetylcholine. 4. The selectivity of semotiadil for coronary artery and myocardium is intermediate between diltiazem and dihydropyridines tested in the present study. 5. These findings suggest that semotiadil has an advantage of diltiazem, nifedipine, and nisoldipine in the treatment of angina with regard to long-lasting action and selectivity for coronary artery and myocardium.

Lack of correlation of hypotensive effects with prevention of cardiac hypertrophy by perindopril after ligation of rat coronary artery.

1. The present study was designed to test the hypothesis that beneficial effects of angiotensin converting enzyme (ACE)inhibitors are independent of a fall in blood pressure in rat experimental heart failure following coronary ligation. 2. The animals were assigned randomly to six groups; sham operation, controls subjected to coronary ligation (control), coronary ligation plus chronic treatment with ACE inhibitors at non- and hypotensive doses; perindopril (0.2 or 2 mg kg-1 day-1) or enalapril (2 or 20 mg kg-1 day-1) for three weeks starting one week after the ligation. 3. Systemic blood pressure was measured every week during the experiments. At the end of the treatments, cardiac function and heart weight (an index of myocardial hypertrophy) were determined. In the other animals, ACE activities in plasma and tissues including heart, kidney, lung and blood vessels were measured. 4. In the controls, cardiac ACE activity, weight of right ventricle and left ventricular end-diastolic pressure (LVEDP) were higher compared to those in the sham-operated animals four weeks after the coronary ligation. However, ACE activities were not changed in plasma, kidney, lung and aorta by ligation of the coronary artery. 5. The chronic treatment with perindopril at a dose of 0.2 mg kg-1 day-1 inhibited the increase in ACE activity in cardiac tissue and suppressed the right ventricular hypertrophy without affecting systemic haemodynamics. In contrast, enalapril at a dose of 20 mg kg-1 day-1, but not 2 mg kg-1 day-1, prevented the development of the right ventricular hypertrophy. Enalapril at 20 mg kg-1 day-1 also lowered systemic blood pressure. 6. There is no significant correlation between systemic blood pressure and right ventricular hypertrophy at the end of the treatment with perindopril (r = 0.06) or enalapril (r = 0.1).7. These findings demonstrate that perindopril, an ACE inhibitor, prevents cardiac hypertrophy without affecting systemic blood pressure in the rat with heart failure after coronary ligation, and suggest that selective augmentation of ACE activity in cardiac tissue is involved in the progression of hypertrophy in this model.

Long-lasting ex vivo inhibition by perindopril of rat vascular response to angiotensin I.

The ex vivo effects of perindopril and enalapril, inhibitors of angiotensin-converting enzyme (ACE), were studied on rat aortae and perfused hearts to clarify the inhibition of vascular response to angiotensin I. The duration of the effects of these inhibitors was also studied. One hour after oral administration of perindopril (0.1-30 mg/kg) or enalapril (0.3-100 mg/kg), the aortae and hearts were isolated for the measurement of isometric force and coronary flow, respectively. In aortae, perindopril and enalapril dose-dependently inhibited the maximal contractions to angiotensin I (1-1000 nM). In isolated perfused hearts, the compounds inhibited the decrease in coronary flow induced by angiotensin I (100 ng). In other experiments, the inhibitory effects of perindopril lasted for 24 h in both aortae (3 mg/kg, p.o.) and hearts (10 mg/kg, p.o.). In contrast, the effects of enalapril disappeared within 6 h in aortae (3 mg/kg, p.o.) and 12 h in hearts (100 mg/kg, p.o.). These results demonstrate that oral administration of ACE inhibitors reduce the ex vivo vascular response to angiotensin I and suggest that perindopril is a longer-lasting inhibitor than enalapril on vascular contraction to locally generated angiotensin II.

Induction of cardiac beta-adrenergic receptor kinase 1 in rat heart failure caused by coronary ligation.

Beta-adrenergic receptor kinase 1 (beta ARK1) participates in the desensitization of beta-adrenergic receptors by uncoupling the signal transduction. The present study was designed to examine whether neurohumoral increase is crucial for the activation of beta ARK1 in heart failure. Four weeks after the ligation of rat coronary artery, LV dP/d t max was reduced, cardiac response to isoproterenol was impaired, and ratio of right ventricular weight to body weight, an index of cardiac hypertrophy, was increased. At the same time, beta ARK1 expression and activity were augmented in the hypertrophied hearts. In addition, plasma norepinephrine content was enhanced in accordance with cardiac hypertrophy, cardiac beta ARK1 expression, LV dP/d t max, and LVEDP. These results of the present study suggest that beta ARK1 is augmented in concert with circulating norepinephrine level and that beta ARK1 may account for, at least in part, the cardiac dysfunction in rat with myocardial infarction.

Synergistic coronary vasoconstriction produced by endothelin-1 in combination with 5-hydroxytryptamine.

The present study was undertaken to examine the action of endothelin-1 (ET-1) per se, or the combined effects of ET-1 with vasoconstrictor agonists such as acetylcholine (ACh), histamine (His), and 5-hydroxytryptamine (5-HT), all of which have been implicated in the genesis of coronary spasm. Isometric tension development and the cytosolic Ca2+ concentration [( Ca2+]i) in a ring segment of porcine coronary artery loaded with fura-2 were measured simultaneously with a mechanoelectric transducer and a fluorometer, respectively. ET-1 (30-100 pM) specifically potentiated the 5-HT-induced contraction without causing a significant increase in [Ca2+]i. This effect of the peptide seems to be qualitatively similar to that produced by the tumor-promoting phorbol ester, DPB. These results suggest that the combined stimulation of ET-1 and 5-HT augments the Ca2+ sensitivity of the contractile elements through the possible activation of protein kinase C.

Inhibitory effect of perindopril, a novel angiotensin-converting enzyme inhibitor, on neointima formation after balloon injury in rats and cholesterol-fed rabbits.

We investigated the effect of perindopril, a novel angiotensin-converting enzyme (ACE) inhibitor, on neointima formation in vessel walls after balloon injury in rats (carotid artery) and cholesterol-fed rabbits (thoracic aorta). Continuous treatment with perindopril significantly reduced neointima formation in both species, as compared with the control group: intima/media (I/M) ratio (rats -62%; p < 0.001; rabbits -25%, p < 0.05); neointima area (rats -65%, p < 0.01; rabbits -24%, p < 0.05). These changes involved reduction of intimal smooth muscle cells (SMC) in rats and of macrophages in rabbits. Furthermore, perindopril also significantly decreased ACE activity in both aortic tissue and serum [11.38 +/- 0.87 vs. 34.93 +/- 6.44 pmol His-Leu (HL)/mg/min (p < 0.01) and 2.79 +/- 0.28 vs. 38.50 +/- 5.41 pmol HL/mg/min (p < 0.001), respectively], aortic contraction evoked by angiotensin I (AI) and mean blood pressure (BP, 84.9 +/- 3.5 vs. 109.3 +/- 3.8 mm Hg, p < 0.001) as compared with control values. These results indicate that perindopril may reduce neointima formation by suppressing the aortic renin-angiotensin system (RAS). These findings indicate that perindopril may be capable of preventing restenotic lesions after angioplasty in humans [corrected].

Evaluation of high through-to-peak ratio of perindopril in SHR.

The present study was designed to evaluate trough-to-peak ratio (T/P) of ACE inhibitors in spontaneously hypertensive rats (SHR) by a continuous monitoring of ambulatory blood pressure for 24 hours with a biotelemetric system. Blood pressure was recorded uninterruptedly with a battery-operated transmitter connected to a sensor catheter. Perindopril (3 mg/kg), trandolapril (1 mg/kg), quinapril (10 mg/kg) and enalapril (6 mg/kg) were given once a day for 7 days. On the first day of the treatment these ACE inhibitors equally decreased blood pressure by 20 mmHg at each peak. The peak and trough blood pressure decreased steadily until day 4, and then they were constant until the end of experiment (day 7). T/P for each inhibitor also increased until day 4, and the ratios in systolic blood pressure at the end of experiments (day 7) were as follows, perindopril: 0.63, trandolapril: 0.62, quinapril: 0.41, enalapril: 0.27. The T/P of perindopril was significantly higher than that of enalapril. The results of the present studies testing four ACE inhibitors are well consistent with those in clinical trials. Thus, the measurement of T/P in SHR would provide a meaningful information for the evaluation of antihypertensive agents like ACE inhibitors.

Role of bradykinin-NO pathway in prevention of cardiac hypertrophy by ACE inhibitor in rat cardiomyocytes.

To examine whether the bradykinin-nitric oxide (NO) pathway directly participates in the antihypertrophic property of angiotensin-converting enzyme (ACE) inhibitors in congestive heart failure, the effects of bradykinin were studied in rat cultured heart cells. Bradykinin (0.1, 1 nM) prevented the phenylephrine-induced increase in protein/DNA content, an index of hypertrophy of heart cells, and amplified the nitrite/nitrate content in the medium. Perindoprilat (1 microM), an ACE inhibitor, also restrained the progression of cardiac hypertrophy and augmented NO release. These effects of perindoprilat were abolished by HOE-140 (kinin B2 antagonist), N omega-nitro-L-arginine (NO synthase inhibitor), and methylene blue (guanylate cyclase inhibitor). Furthermore, there was a significant correlation between protein/DNA content and nitrite/nitrate content. These results indicate that bradykinin inhibits the progression of cardiac hypertrophy due to the increase in NO release and that perindoprilat produces beneficial effects on cardiac hypertrophy by stimulating the bradykinin-NO pathway.