Differential effects of oral losartan and enalapril on local venous and systemic pressor responses to angiotensin I and II in healthy men

Pd(II)-catalyzed, controllable C-H mono-/diarylation of aryl tetrazoles: concise synthesis of Losartan

A palladium(II)-catalyzed C-H arylation directed by tetrazole, a metabolically stable surrogate for the carboxylic acid group in drug design, has been developed. Excellent mono-/di-selectivity was achieved through adjustment of the protecting site on the tetrazole ring. The synthetic utility of this new transformation was demonstrated in the concise total synthesis of Losartan.

Statin treatment in hypercholesterolemic men does not attenuate angiotensin II-induced venoconstriction

Experimental studies suggested that statins attenuate vascular AT1 receptor responsiveness. Moreover, the augmented excessive pressor response to systemic angiotensin II infusions in hypercholesterolemic patients was normalized with statin treatment. In 12 hypercholesterolemic patients, we tested the hypothesis that statin treatment attenuates angiotensin II-mediated vasoconstriction in hand veins assessed by a linear variable differential transducer. Subjects ingested daily doses of either atorvastatin (40 mg) or positive control irbesartan (150 mg) for 30 days in a randomized and cross-over fashion. Ang II-induced venoconstriction at minute 4 averaged 59%±10% before and 28%±9% after irbesartan (mean ± SEM; P<0.05) compared to 65%±11% before and 73%±11% after 30 days of atorvastatin treatment. Plasma angiotensin levels increased significantly after irbesartan treatment (Ang II: 17±22 before vs 52±40 pg/mL after [p = 0.048]; Ang-(1-7): 18±10 before vs 37±14 pg/mL after [p = 0.002]) compared to atorvastatin treatment (Ang II: 9±4 vs 11±10 pg/mL [p = 0.40]; Ang-(1-7): 24±9 vs 32±8 pg/mL [p = 0.023]). Our study suggests that statin treatment does not elicit major changes in angiotensin II-mediated venoconstriction or in circulating angiotensin II levels whereas angiotensin-(1-7) levels increased modestly. The discrepancy between local vascular and systemic angiotensin II responses might suggest that statin treatment interferes with blood pressure buffering reflexes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00154024.

Comparison of inhibitory effects of irbesartan and atorvastatin treatment on the renin angiotensin system (RAS) in veins: a randomized double-blind crossover trial in healthy subjects

Experimental studies point to an interplay between hypercholesterolemia and hypertension, acting through the renin angiotensin system. In a crossover study design with 8 healthy subjects, the authors tested the hypothesis that statin treatment exerts renin angiotensin system-modulating effects in veins by down-regulation of AT1-receptors, resulting in reduced Angiotensin II (Ang II)-induced venoconstriction and by increasing the pleiotropic Ang II-metabolite Ang-(1-7). Irbesartan was used as positive control. Ang II-induced venoconstriction was 49% +/- 9% before and 64% +/- 10% after 30 days of atorvastatin treatment compared to 50% +/- 8% before and 15% +/- 9% after irbesartan (P = .004). Plasma angiotensin levels significantly increased only after irbesartan treatment (Ang II: 35 +/- 4 vs 329 +/- 101 pg/mL [P = .02]; Ang-(1-7): 10 +/- 3 vs 35 +/- 6 pg/mL [P = .01]) compared to atorvastatin treatment (Ang II: 26 +/- 5 vs 31 +/- 4 pg/mL [P = ns]; Ang-(1-7): 9 +/- 2 vs 11 +/- 3 pg/mL [P = ns]). The data indicate that atorvastatin does not inhibit Ang II-induced venoconstriction in vivo and point toward a supportive role of Ang-(1-7) in contributing to the antihypertensive and beneficial vascular effects of irbesartan.

Losartan in cardiovascular disease

Hypertension is a major risk factor for the development of cardiovascular disease. Numerous placebo-controlled trials have demonstrated that treatment of hypertension results in substantial reduction of hypertension-related vascular events. The benefit of specific therapies beyond their effect on blood pressure is well established. Losartan is an orally-active, selective, nonpeptide, angiotensin II type 1-receptor antagonist (ARB), and it was the first in this class to be marketed. Several large-scale clinical trials have demonstrated that losartan and other ARBs have benefits in preventing cardiovascular disease. The Losartan Intervention For End point reduction in hypertension (LIFE) study demonstrated improved outcomes with losartan as compared with atenolol-based therapies in hypertensive patients with left ventricular hypertrophy, mainly because of stroke prevention. The Reduction of End points in Non-insulin-dependent diabetes mellitus with the Angiotensin II Antagonist Losartan (RENAAL) study demonstrated that losartan prevented the progression of diabetic nephropathy. In this review, evidence from these and other clinical trials with losartan shall be discussed. The pharmacodynamic and pharmacokinetic properties of losartan are described to explain its mechanisms of action. Among the ARB class, losartan possesses certain unique properties, which may enhance its cardiovascular protective effects. These include an increase of urinary uric acid excretion and antiatherothrombotic properties. Potential future roles for losartan and other ARBs shall be discussed, in addition to emphasizing areas in which evidence is currently lacking or indecisive, including head-to-head comparisons of ARBs and the effects of combining an ARB with angiotensin-converting-enzyme inhibitors.

Left ventricular hypertrophy with exercise and ACE gene insertion/deletion polymorphism: a randomized controlled trial with losartan

BACKGROUND

Local cardiac renin-angiotensin systems may regulate left ventricular (LV) hypertrophic responses. The absence (deletion [D]) of a 287-bp marker in the ACE gene is associated with greater myocardial ACE levels and exercise-related LV growth than is its presence (insertion [I]), an effect potentially mediated through either increased activity of the cellular growth factor angiotensin II on the angiotensin type 1 (AT(1)) receptor or increased degradation of growth-inhibiting kinins. We sought to confirm ACE genotype-associated exertional LV growth and to clarify the role of the AT(1) receptor in this association.

METHODS AND RESULTS

One hundred forty-one British Army recruits homozygous for the ACE gene (79 DD and 62 II) were randomized to receive losartan (25 mg/d, a subhypotensive dose inhibiting tissue AT(1) receptors) or placebo throughout a 10-week physical training program. LV mass, determined by cardiac magnetic resonance, increased with training (8.4 g, P:<0.0001 overall; 12.1 versus 4.8 g for DD versus II genotype in the placebo limb, P:=0.022). LV growth was similar in the losartan arm: 11.0 versus 3.7 g for DD versus II genotypes (P:=0.034). When indexed to lean body mass, LV growth in the II subjects was abolished, whereas it remained in the DD subjects (-0.022 versus 0.131 g/kg, respectively; P:=0.0009).

CONCLUSIONS

ACE genotype dependence of exercise-induced LV hypertrophy is confirmed. Additionally, LV growth in DD (unlike II) subjects is in excess of the increase in lean body mass. These effects are not influenced by AT(1) receptor antagonism with the use of losartan (25 mg/d). The 2.4-fold greater LV growth in DD men may be due to the effects of angiotensin II on other receptors (eg, angiotensin type 4) or lower degradation of growth-inhibitory kinins.

Effect of losartan on angiotensin II-mediated endothelin and prostanoid excretion in humans

Angiotensin II (Ang II) stimulates renal prostanoid and vascular endothelin-1 (ET-1) release. Most known Ang II effects are mediated by AT1 receptors. Our aim was to determine whether AT1 receptor activation mediates Ang II-evoked renal prostanoid and ET-1 release. Eleven healthy men were randomized in a crossover, double-blind fashion to receive 100 mg/day of losartan or matching placebo, for 8 days. Blood and urine were sampled before and after a 2-h infusion of Ang II at a rate previously determined to increase mean arterial pressure (MAP) by 25 to 30 mm Hg in each subject. After a 14-day washout, subjects received the alternate treatment. Pretreatment with losartan had little effect on baseline MAP, but increased plasma renin activity, and virtually eliminated the pressor response to Ang II infusion. Angiotensin II significantly increased prostanoid excretion after placebo; the prostanoid response to Ang II was even greater after losartan. Plasma ET-1 was not altered by Ang II infusion, with or without losartan. In contrast, urine ET-1 excretion rate decreased to 40% of baseline after Ang II but not after losartan pretreatment; losartan alone had no effect. We conclude that Ang II decreases renal ET-1 synthesis and release through the AT1 receptor. In contrast, Angiotensin II-mediated renal prostanoid synthesis does not require activation of AT1 receptors. These findings indicate that AT1 receptor antagonists could provide renal protection through indirect mechanisms.

Practical considerations of the pharmacology of angiotensin receptor blockers

A review of the drug class of angiotensin receptor blockers (ARBs) as well as the ARBs currently available by prescription in the United States is presented. The importance of angiotensin II production by non-angiotensin-converting enzyme (non-ACE) pathways, particularly human chymase, is discussed. Emphasis is placed on the mechanism of action of ARBs and the different binding kinetics of these agents. Although all ARBs, as a group, block the AT1 receptor, they may differ in the pharmacological characteristics of their binding and be classified as either surmountable or insurmountable antagonists. Mechanisms of surmountable and insurmountable antagonism as well as possible benefits of these blocking characteristics are discussed in relation to the various ARBs. The cardiovascular effects of activation of the two main subtypes of angiotensin receptors (AT1 and AT2) are presented. In addition to their treatment of hypertension, ACE inhibitors are recognized as being effective in the management of heart failure, left ventricular hypertrophy, recurrent myocardial infarctions, and renal disease. ARBs are currently indicated only for the treatment of hypertension; however, in vitro and in vivo pharmacological studies as well as preliminary clinical data suggest that ARBs, like ACE inhibitors, may also provide effective protection against end-organ damage in these conditions.

Inhibition of angiotensin-converting enzyme in human hand veins

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

Angiotensin II antagonism and plasma radioreceptor-kinetics of candesartan in man

AIMS

The pharmacodynamic properties of the angiotensin II antagonist candesartan in humans were assessed from the rightward shifts of angiotensin II dose-effect curves (Schild regression technique). The pharmacokinetic characteristics were determined by radioreceptor assay (r.r.a.) and h.p.l.c.

METHODS

Twelve healthy male volunteers received single oral doses of 4, 8 and 16 mg candesartan cilexetil and placebo. Plasma was obtained for h.p.l.c. and r.r.a. (receptors: rat lung; radioligand: [125I-Sar1Ile8]-angiotensin II). Before and up to 24 h post dosing angiotensin II was infused in ascending dose steps until blood pressure (systolic and/or diastolic) increased by +25 mmHg. Individual angiotensin II dose-effect curves were fitted according to an Emax model and dose ratios (DR) calculated from the antagonist induced rightward shifts.

RESULTS

Candesartan, the active metabolite of candesartan cilexetil, declined from peak concentrations at about 4 h with a t1/2 of about 6 h. A linear relation (slope 1) between h.p.l.c. and r.r.a. data revealed that there is no other active metabolite. DR at 6-9 h post dosing reached a maximum of about 30 and at 24 h still amounted to 4-7, indicating the persistence of a relevant antagonistic effect in vivo. The apparent Ki-doses (derived from Schild regression plots) indicated a high potency (1.9 mg at 24 h) and slow decline of effect. Between plasma concentrations and antagonistic effect a counterclockwise hysteresis was visible.

CONCLUSIONS

A longer persistence of the antagonistic effect at the receptor site than expected by the presence in plasma indicates a slow off-rate of candesartan cilexetil from in vivo receptors. This provides an additional rationale for the observed 24 h therapeutic activity of candesartan cilexetil.

Venoconstriction by angiotensin II in the human forearm is inhibited by losartan but not by nicardipine

Arterial constriction by angiotensin II (Ang II) in the human forearm is inhibited by the infusion of the AT1-receptor antagonist losartan. We investigated venous constriction by Ang II in the forearm of 19 healthy subjects (23 +/- 1 years) and the inhibitory effects of losartan. Furthermore, we investigated, in both the arterial and venous systems, whether the constrictor effects of Ang II are calcium influx dependent by determining the influence of nicardipine. Arterial forearm blood flow (FBF) and maximal venous outflow (MVO) were measured by venous-occlusion plethysmography. Sodium nitroprusside (5-12.5 ng/kg/min) was infused to predilate the forearm vasculature. Ang II (0.1, 1, and 10 ng/kg/min) was infused before and during losartan (0.3 and 3 microg/kg/min) or nicardipine (0.05 and 0.15 microg/kg/min), respectively. Ang II decreased FBF (Emax-FBF) by 79 +/- 4% and MVO (Emax-MVO) by 28 +/- 3% (p < 0.05). Nicardipine at 0.05 and 0.15 microg/kg/min reduced Emax-FBF from -79 +/- 4% to -48 +/- 4% and -6 +/- 2%, respectively (p < 0.05). Losartan in both doses completely inhibited Emax-MVO (p < 0.05), whereas nicardipine did not influence the venoconstriction by Ang II (p > 0.05). In conclusion, Ang II causes a constriction of both arteries and veins in the human forearm, which may be inhibited by losartan. The arterial constriction appears to be caused by an AT1-receptor-mediated calcium influx via L-type calcium channels. In contrast, the venoconstrictor effect of Ang II proved insensitive to the calcium antagonist nicardipine.

Losartan, an orally active angiotensin (AT1) receptor antagonist: a review of its efficacy and safety in essential hypertension

Losartan potassium, an angiotensin II receptor antagonist, is the first of a new class of agents to be introduced for the treatment of hypertension. In this review, we describe the clinical pharmacology of losartan, including its pharmacokinetics in healthy, male volunteers and special patient groups, such as the elderly, patients with liver disease and patients with renal impairment. We also review its pharmacodynamics, including safety and tolerability; specificity of action; and the effect of salt depletion. We then review the studies examining clinical efficacy and safety in hypertension.

Endogenous angiotensin II does not contribute to sympathetic venoconstriction in dorsal hand veins of healthy humans

BACKGROUND

Sympathetically mediated venoconstriction is augmented by exogenously administered angiotensin II. This study was designed to assess whether endogenous angiotensin II influences sympathetically mediated venous tone.

METHODS

Responses of dorsal hand veins to local intravenous administration of subsystemic doses of losartan, an angiotensin II type-1 receptor antagonist, were assessed with use of a well-validated displacement technique in eight healthy male volunteers. In a four-phase study, responses to local infusions of angiotensin II (4 to 64 ng/min) and norepinephrine (1 to 128 ng/min) or to sympathetic venoconstriction produced by a single deep breath were compared in the presence of either saline placebo or 30 microg/min losartan. Each phase of the study was conducted on a separate day, in random order, and each phase was separated by at least 1 week.

RESULTS

Angiotensin II (p = 0.03) and norepinephrine (p < 0.001) caused dose-dependent venoconstriction. Losartan attenuated the venoconstriction induced by angiotensin II (p = 0.048) but had no effect on the responses to norepinephrine or the venoconstriction induced by a single deep breath.

CONCLUSIONS

In contrast to exogenously administered angiotensin II, basal endogenous angiotensin II does not influence sympathetically mediated venoconstriction in healthy humans. However, endogenous angiotensin II may have a role in circumstances of renin-angiotensin system activation, such as salt depletion.

Losartan potassium: a review of its pharmacology, clinical efficacy and tolerability in the management of hypertension

Losartan potassium is an orally active, nonpeptide angiotensin II (AII) receptor antagonist. It is the first of a new class of drugs to be introduced for clinical use in hypertension. This novel agent binds competitively and selectively to the AII subtype 1 (AT(1)) receptor, thereby blocking AII-induced physiological effects. An active metabolite, E3174, contributes substantially to its antihypertensive effect, which persists throughout 24 hours after once-daily administration. In patients with mild to moderate hypertension, losartan potassium 50 to 100mg once daily as monotherapy lowers blood pressure to a similar degree to enalapril, atenolol and felodipine extended release (ER). Losartan potassium combined with hydrochlorothiazide reduces blood pressure further than either drug given separately. About one-third of patients with severe hypertension have responded to the combination product. Losartan potassium appears to be effective in elderly patients. Losartan potassium is very well tolerated. In clinical trials, dizziness was the only drug-related event reported more frequently with losartan potassium monotherapy than with placebo. First-dose hypotension is uncommon. An aspect of the drug's tolerability profile which may prove to be particularly advantageous is that it is associated with a similar incidence of cough to placebo in patients with a history of ACE inhibitor-related cough. Additionally, clinically relevant adverse metabolic effects or laboratory abnormalities have not been documented during losartan potassium therapy and renal function is preserved in patients with or without renal insufficiency. The adverse effect profile of the losartan potassium-hydrochlorothiazide combination resembles those for losartan potassium monotherapy and placebo. Long term tolerability data are limited (<2 years) but support the very good tolerability profile in shorter studies. Elements of the drug's profile yet to be assessed or reported fully in the literature include long term efficacy; potential to favourably influence cardiovascular and renovascular systems (and ultimately mortality) in patients with hypertension and, lastly, cost effectiveness and influence on quality of life. In summary, losartan potassium is the first AT(1)+ receptor antagonist to become available for the management of hypertension and, as such, it is an important new antihypertensive agent. Pending long term data as outlined above, it is likely to find initial use in patients with mild to severe hypertension who are unresponsive to, or intolerant of their current therapy. However, with its novel mechanism of action, good efficacy and favourable tolerability profile, losartan potassium is well placed to claim a prominent position in the management of patients with essential hypertension in the future.