Early and Late Effects of High- Versus Low-Dose Angiotensin Receptor Blockade on Renal Function and Outcomes in Patients With Chronic Heart Failure
Matthew C. KiernanDouglas GregoryMark J. SarnakPatrick RossignolJoseph M. MassaroRobb D. KociolFaı̈ez ZannadMarvin A. Konstam
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Delayed recovery of hypertension after single dose losartan in angiotensin II-infused conscious rats
Objective In a conscious unrestrained rat model, it takes approximately 1 week for angiotensin II to increase blood pressure to maximum levels. We investigated the time required for hypertension to fully recover after acute angiotensin II receptor blockade in this angiotensin II dependent hypertensive model. Design Conscious unrestrained rats (n = 8) infused with 10 ng/kg per min angiotensin II for 21 days received losartan (10 mg/kg) on day 17 of angiotensin II infusion. Mean arterial pressure (MAP) and heart rate were monitored continuously. The acute pressor response to 50 ng/kg per min angiotensin II was monitored for 2 h on days 15, 17, 18, 19 and 20 of angiotensin II infusion. Plasma renin concentration (PRC) was measured daily. Results Angiotensin II increased MAP acutely by 26 ± 2 mmHg and by a further 23 ± 4 mmHg between days 4 and 8. Losartan acutely reduced MAP by 75 ± 2 mmHg; 24 h later MAP had partially recovered but remained suppressed by 47 ± 3 mmHg. MAP had not fully recovered 4 days later. Some 2 h after losartan, the acute pressor response to angiotensin II had fallen from 24 ± 2 mmHg to zero. This recovered to 13 ± 5 and 28 ± 2 mmHg 24 and 48 h post losartan. After losartan PRC rose from 0.1 ± 0.05 to above 1 ng/ml per h for less than 24 h. Conclusion A single dose of losartan reverses both the fast and slow pressor effects of continuous angiotensin II infusions. While losartan is metabolized, the fast vasoconstrictor effect recovers quickly but the slow pressor effect takes almost a week to build up again to maximum levels. Since the slow pressor effect is mediated via the AT1 receptor, any means of blocking the renin–angiotensin system is likely to keep blood pressure below maximum hypertensive levels for several days after the drug has disappeared from the circulation.
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Candesartan is a new angiotensin II type 1 (AT 1 ) receptor blocker that produces more effective 24-h blood pressure lowering than losartan in hypertensive patients. In in vitro tissue preparations, candesartan displays insurmountable antagonism of the responses to angiotensin II. Both irbesartan and EXP-3174, the active metabolite of losartan, have also previously been described in some studies as insurmountable AT 1 -receptor blockers, whereas losartan exhibits surmountable blockade of the AT 1 -receptor. We compared the properties of candesartan, irbesartan, losartan and EXP-3174 in isolated vascular preparations of rat portal vein and rabbit aortic strips. The concentrations of the different AT 1 -receptor antagonists that were effective in these in vitro preparations were also correlated to the non-protein bound plasma concentrations obtained in clinical use. Preparations of the rabbit aorta and the rat portal vein were dissected, mounted on a force-displacement transducer and submerged in oxygenated Krebs' buffer at 37°C. The vessel strips were pre-stretched to a passive force of 5 and 20 mN for portal vein and aorta, respectively. The response to angiotensin II, measured as the mean force development in response to increasing concentrations of angiotensin II, was recorded in the absence and presence of candesartan, 0.003-10 nmol/l, irbesartan, 1-100 nmol/l, losartan, 1-100 nmol/l, and EXP-3174, 0.01-10 nmol/l, for a period of 90 min. In rabbit aortic strips, candesartan caused a non-parallel shift and suppression of the angiotensin II concentration-response curve, with complete suppression of the response to angiotensin II at a dose of candesartan of 1 nmol/l. In contrast, irbesartan, losartan and EXP-3174 all caused a parallel shift of the concentration-response curve. No suppression of the angiotensin II response was seen with losartan, while its active metabolite caused saturable suppression of the maximal response at higher concentrations. For irbesartan, some degree of suppression of the maximal response could not be excluded at the highest concentration studied. Similar concentration-response curves were obtained in rat portal vein. Data on protein binding for the different AT 1 -receptor blockers are variable in the literature. Plasma protein binding for the different AT 1 -receptor blockers was determined (in triplicate) by liquid chromatography with fluorescence detection after equilibrium dialysis (6 h) of cold drug at a concentration of 1500 nmol/l. Protein binding was high (see Table) and, for candesartan, losartan and its active metabolite EXP-3174, in accordance with previously reported levels. For irbesartan, a large discrepancy in protein binding between previously reported and the present experimental data, obtained from two different non-associated laboratories, was found. The higher plasma protein binding for irbesartan found in the present study may explain why high doses of irbesartan seem to be needed for clinical efficacy. It appears unlikely that losartan exerts any significant inhibitory effect at therapeutic plasma levels, and the main AT 1 -blocking effect observed after oral losartan is probably exerted by EXP-3174. It is concluded that AT 1 -receptor blockers differ in their ability to inhibit angiotensin II-mediated vascular contraction, and that the antagonistic characteristics are similar in vessel preparations of different origins and with different degrees of AT 1 -receptor reserve.
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Telmisartan
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We examined the effects of U-97018, an AT, receptor antagonist, on the pressor response to intracere-broventricularly (i.c.v.) administered angiotensin II (AII) in conscious normotensive rats in comparison to losartan, EXP 3174, EXP 655, and saralasin. In an i.c.v. study, U-97018, losartan, and EXP 3174 reduced the pressor response. EXP 655, an AT2 selective antagonist, also inhibited the pressor response to i.c.v. AII. U-97018 combined with EXP 655 did not fully eliminate the pressor response to i.c.v. AII. Moreover, saralasin, a nonselective peptide AH antagonist, also failed to abolish the pressor response to i.c.v. AII. Therefore, both AT1,– and AT2–receptors probably are functional in inhibiting the pressor response to i.c.v. All and that a part of the i.c.v. All-induced pressor response occurs through non-AT1–and non-AT2–receptors. In an intravenous (i.v.) study, U-97018, losartan, and EXP 3174 reduced the pressor response to i.c.v. AII. At 10 mg/kg orally (P.O.), which is an antihypertensive dose in spontaneously hypertensive rats (SHR), neither U-97018 nor losartan reduced the pressor response to i.c.v. All even at 180 min after administration. This result indicates that neither U-97018 nor losartan, at the oral antihypertensive dose, reaches the brain in sufficient amount to affect the pressor response to i.c.v. AII.
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Abstract Binding experiments show that ZD 7155 is a potent angiotensin II type 1 receptor antagonist. In this study this novel substance was studied in normotensive and hypertensive rats. The relative potency and duration of the antihypertensive effects of ZD 7155 were compared with those of the reference substance, losartan. The inhibitory effects of both compounds on angiotensin II-induced pressor actions were studied in the conscious normotensive Sprague-Dawley (SD) rat and in the conscious, spontaneously hypertensive rat (SHR). Arterial blood pressure and heart rate (HR) were obtained by direct intraarterial recording. Angiotensin II infusion was administered intravenously in the dose range 53.3 ng—12.8 μg kg−1 min−1 to the conscious rats. ZD 7155 was administered in a bolus dose of 1.082 μmol kg−1 (0.51 mg kg−1) and losartan in bolus doses of 2.165 and 6.495 μmol kg−1 (1.0 and 3.0 mg kg−1). In conscious SD rats, ZD 7155 and losartan behaved as competitive antagonists and the pressor response curve to angiotensin II was shifted to the right. Experiments in conscious SD rats also showed that ZD 7155 was approximately ten times as potent as losartan in suppressing the angiotensin II-induced pressor response (240 ng kg−1; 10 min infusion). In addition, experiments with conscious rats demonstrated that ZD 7155 could suppress the angiotensin II-induced pressor response for approximately 24 h when ZD 7155 was administered intravenously in a 1.082 μmol kg−1 bolus dose and angiotensin II was given at 240 ng kg−1 (in a 10−min infusion). Experiments in conscious SHRs using ZD 7155 (1.082 μmol kg−1) and losartan (6.495 μmol kg−1) as intravenous boluses indicated that both ZD 7155 and the reference compound losartan exhibited a significant antihypertensive effect. These results demonstrate that ZD 7155 is a potent angiotensin II-type 1 antagonist which is approximately ten times as potent as losartan in suppressing the angiotensin II-induced pressor response. Furthermore, ZD 7155 may suppress the angiotensin II-induced pressor response for 24 h and in the SHR ZD 7155 induces a pronounced and persistent antihypertensive effect.
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This study investigated the ability of the selective angiotensin II (AII)-type (AT)1 receptor antagonist losartan to reverse the fast (< 30 sec) pressor effect of AII, and the hypertension produced by chronic (2 weeks) i.v. infusion of AII (AII hypertension). We hypothesized the following: if AII hypertension is caused solely by stimulation of AT1 receptors mediating the fast pressor effect, then the time course of the antihypertensive effect of losartan in AII hypertension should parallel the time course of losartan inhibition of pressor responses to acute, bolus injection of AII. Thus, in one group of rats, pressor responses to bolus injections of AII (10 ng, n = 10) were measured before and subsequently at numerous time points after losartan administration (3 mg.kg-1 i.v.). Other groups of rats received continuous infusions of AII i.v. for 15 days at 2 ng.min-1 (n = 8), 4 ng.min-1 (n = 8) or 10 ng.min-1 (n = 6). On days 2, 7 and 12 of the AII infusion, rats received a bolus injection of losartan (3 mg.kg-1, i.a.). Mean arterial pressure (MAP) was then measured at numerous time points after losartan administration. Within 5 min of administration, losartan caused almost complete inhibition of fast pressor responses to acute injections of AII, and the magnitude of this inhibition did not change for over 24 hr. On the other hand, in AII hypertension, losartan lowered MAP significantly within 5 min only in rats receiving 10 ng.min-1 AII, but in all three groups caused a slower decline in MAP that peaked around 2 hr after losartan injection.(ABSTRACT TRUNCATED AT 250 WORDS)
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Recent data suggest that hypotensive effect of losartan may not be attributed solely to AT1-receptor blockade, but also to excessive AT2 or other receptors stimulation by elevated angiotensin II and its derivative peptides. Therefore in the present study we examined the effect of angiotensin II on mean blood pressure after AT -receptor blockade with losartan. Male Wistar rats were anaesthetised and received injection of either losartan (30 mg/kg, 1 ml/kg, i.v.) or saline (the same volume and route) followed by bolus injection of angiotensin II (100, 300 or 1,000 ng/kg; 1 ml/kg, i.v.) or 1-hour infusion of angiotensin II (200 ng/kg/min; 2.5 ml/kg/h, i.v.). Control animals received saline instead. Angiotensin II, given either as the injection or the infusion, caused an evident increase in mean blood pressure (p ranged from 0.05 to 0.001 depending on the experimental group). Losartan caused a rapid drop in mean blood pressure and blunted the hypertensive effect of angiotensin II (p < 0.01). Moreover, in the losartan-pretreated animals the hypotensive phase was enhanced by the infusion, but not single injection of angiotensin II, which was most evident from the 30 th minute of observation (p < 0.05 vs control). In conclusion, hypotensive effect of losartan may be amplified by simultaneous increase in angiotensin II level, the situation observed during chronic AT1-receptor blockade.
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Losartan (DuP 753) and PD123177 are nonpeptide angiotensin (ANG) receptor ligands for subtypes of ANG II receptors ANG II-1 and ANG II-2, respectively. We examined the effects of losartan and PD123177 on dose – mean arterial pressure (MAP) response curves for ANG II and ANG III in eight groups (n = 6 each) of conscious rats. Saline (0.9% NaCl), losartan (1 × 10 −6 and 9 × 10 −6 mol/kg), and PD123177 (2 × 10 −5 mol/kg) were i.v. bolus injected 15 min before the construction of ANG II dose–response curves in groups I, II, III, and IV, respectively. Groups V–VIII were treated similarly to I–IV except that ANG III was given in place of ANG II. Losartan dose dependently shifted the dose–response curves of ANG II and ANG III to the right with similar dissociation constants (−log K I of 6.6 ± 0.7 and 6.6 ± 0.1 mol/kg, respectively) and no change in the maxima. PD123177 affected neither maximum MAP nor ED 50 values for ANG II or ANG III. Our results show that losartan but not PD123177 is a competitive antagonist of the MAP effects of ANG II and ANG III.Key words: nonpeptide angiotensin receptor antagonist, angiotensin II, angiotensin III, blood pressure, losartan.
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Angiotensin III
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