Angiotensin II monoclonal antibody: blood pressure effects in normotensive and spontaneously hypertensive rats

Pharmacologic profiles of KRH-594, a novel nonpeptide angiotensin II-receptor antagonist

We studied pharmacologic profiles of KRH-594, dipotassium (Z)-2-[[5-ethyl-3-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl-1,3,4 -thiadiazolin-2-ylidene]aminocarbonyl]-1-cyclopentenecarb oxylate, a novel angiotensin II (AII)-receptor antagonist. KRH-594 potently displaced specific binding of [125I]-AII from AT1 receptor with a Ki of 0.39 nM in rat liver membranes, but not from AT2 receptor in bovine cerebellar membranes (Ki > 10 microM). KRH-594 exhibited no affinity for 21 other receptors and two enzymes [50% inhibitory concentration (IC50) > 10 microM], demonstrating its high specificity toward AT1 receptors. In isolated rabbit aorta, KRH-594 caused nonparallel shifts to the right of the dose-response curve to AII and decreased the maximal response with a pK(B) of 10.4. We evaluated the in vivo efficacy and the duration of action in freely moving rats under nonfasting conditions. In normotensive rats, orally administered KRH-594 inhibited AII-induced pressor responses with a 50% inhibitory dose (ID50) of 0.39 mg/kg. In spontaneously hypertensive rats (SHRs), both KRH-594 (1 mg/kg p.o.) and losartan (10 mg/kg p.o.) exerted similar blood pressure-reducing effects, and their effects were still significant at 24 h after drug administration. We concluded that KRH-594 is a specific and efficacious AT1 antagonist that may find its use in the treatment of human hypertension.

Mapping of angiotensin II receptor subtypes in peripheral tissues of spontaneously hypertensive rats by in vitro autoradiography

1. The regulation of angiotensin II (AII) receptor subtypes was studied in peripheral tissues of 20 week old male spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats. 2. AII receptor binding was determined by a quantitative in vitro autoradiography using [125I]-[Sar1,Ile8]AII as a ligand on the kidney, adrenal gland, thoracic aorta and heart. CV-11974, a specific AT1 receptor antagonist, and CGP42112B, a specific AT2 antagonist, were used in competition with [125I]-[Sar1,Ile8]AII to differentiate AT1 and AT2 receptor binding. 3. The relative abundance of each subtype was very similar between SHR and WKY rats. In both strains of rats, the adrenal cortex contained predominantly AT1 receptors, while AT2 receptors predominated in the adrenal medulla. The kidney contained exclusively AT1 receptors over glomeruli, proximal tubules and outer medulla. AT1 receptors were predominant in the thoracic aorta and heart. 4. As for relative receptor density, important differences were observed between SHR and WKY rats. In SHR, the adrenal cortex, outer medulla of the kidney, and heart displayed higher AT1 receptor density than WKY rats. 5. These results indicate that the expression of AT1 receptors is differently regulated in some important targets of AII in SHR, and suggest that the altered regulation of AT1 receptor presented in this study should be relevant to the pathophysiological features of SHR.

Opposing actions of angiotensin-(1-7) and angiotensin II in the brain of transgenic hypertensive rats

Lack of specific antagonists to the amino-terminal heptapeptide angiotensin-(1-7) [Ang-(1-7)] prompted us to evaluate the central effects of delivering a specific affinity-purified Ang-(1-7) antibody on the blood pressure and heart rate of 12-week-old conscious homozygous female rats (n = 12) expressing the mouse submandibular Ren-2d gene [(mRen-2d)27] in their genome. Another group of transgenic hypertensive and strain-matched Sprague-Dawley controls were injected with a specific Ang II monoclonal antibody (KAA8). Cerebroventricular administration of the affinity-purified Ang-(1-7) antibody in conscious transgenic hypertensive rats caused significant dose-related elevations in blood pressure associated with tachycardia. The hypertensive response was augmented in transgenic rats studied 7 to 10 days after cessation of lisinopril therapy. Neutralization of Ang II with the Ang II antibody caused a hemodynamic response opposite to that obtained with the Ang-(1-7) antibody. All doses of the Ang II antibody produced hypotension and bradycardia. The magnitude of the depressor response was significantly augmented in transgenic rats weaned off lisinopril therapy. In contrast, central administration of either the Ang-(1-7) or Ang II antibodies had no effect on normotensive rats. Central injections of an affinity-purified IgG fraction were ineffective in both control and transgene-positive rats. These data suggest that in the brain of transgenic hypertensive rats, Ang-(1-7) opposes the action of Ang II on the central mechanism or mechanisms that contribute to the maintenance of this model of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations of cardiac alpha- and beta-adrenoceptors and inotropic responsiveness in hypertensive transgenic rats harbouring the mouse renin gene (TGR(mREN2)27)

In the present study, we investigated the alpha- and beta-adrenoceptor-mediated effects on myocardial force of contraction (using phenylephrine in the presence of propranolol and isoprenaline) and receptor densities (binding studies using [3H]-prazosin and [125I]-iodocyanopindolol) in hypertensive transgenic rats (TGR(mREN2)27) and age-matched Sprague-Dawley rats (SP) as controls. In TGR(mREN2)27 the positive inotropic effects of isoprenaline and phenylephrine were reduced, while the effect of Ca2+ was unchanged. The EC50-values did not differ in both groups. A down-regulation of the beta-adrenoceptors was observed in the hypertrophied left ventricles of transgenic rats, which is postulated to be involved in the reduced beta-adrenoceptor-mediated positive inotropic effect. The alpha-adrenoceptor density was increased, which could represent a compensatory mechanism for the impaired effectiveness of the beta-adrenergic pathway. However, since the effect of alpha-adrenoceptor agonist is not enhanced but even reduced, an uncoupling of alpha-adrenoceptors from post receptor events could play a role in the observed effects.

Ciprokiren (Ro 44-9375). A renin inhibitor with increasing effects on chronic treatment

The present study characterizes the new transition-state renin inhibitor ciprokiren (Ro 44-9375) in squirrel monkeys. Arterial blood pressure was monitored by telemetry in freely moving, chronically instrumented conscious animals. In vitro at pH 7.4, ciprokiren inhibited human renin in buffer and human plasma with an IC50 of 0.07 and 0.65 nmol/L, respectively. It was equipotent against primate plasma renin and also inhibited plasma renin from dog and guinea pig in the nanomolar range (IC50, 29 and 65 nmol/L, respectively). After acute oral administration it reduced arterial blood pressure dose dependently in normotensive sodium-depleted and cyclosporin-induced hypertensive squirrel monkeys, starting with the minimal oral dose of 3 micrograms/kg. Daily oral doses of 1 microgram/kg showed a progressive blood pressure decrease, with a maximal response reached after 1 week. The drug could also be applied transdermally with similar hemodynamic effects without any decrease of plasma renin activity or plasma immunoreactive angiotensin II. Thus, ciprokiren is characterized in squirrel monkeys as a renin inhibitor with high in vivo potency that might act mainly in the tissular compartment.

Angiotensin II receptor blockade: an innovative approach to cardiovascular pharmacotherapy

Through the multiple actions of angiotensin II (AII), the renin-angiotensin system (RAS) participates in cardiovascular homeostasis. Angiotensin II acts by binding to specific membrane-bound receptors, which are coupled to one of several signal transduction pathways. These AII receptors exhibit heterogeneity, represented by AT1 and AT2 receptor subtypes. The AT1 receptor mediates the major cardiovascular action of the RAS. This receptor has been cloned from multiple species, disclosing features consistent with a transmembrane, G-protein-linked receptor. Further AII receptor heterogeneity is evident by the cloning of isotypes of the AT1 receptor. Blocking the interaction of AII with its receptor is the most direct site to inhibit the actions of the RAS. Many AII receptor antagonists, including peptide analogs of AII and antibodies directed against AII, possess unfavorable properties that have limited their clinical utility. The discovery and further development of imidazole compounds with AII antagonist properties and favorable characteristics, however, has promise for clinical utility. The leader in this field is a selective AT1 receptor antagonist losartan (previously known as DuP 753 or MK-954). Losartan was demonstrated to be an effective antagonist of many AII-induced actions and an effective antihypertensive agent in many animal models of hypertension (HTN). Losartan also demonstrated secondary benefits in preventing stroke, treating congestive heart failure (CHF), and delaying the progression of renal disease in animal models. Clinical studies confirm the AII antagonist action of losartan and suggest that losartan will be effective in the treatment of essential HTN. AII antagonism is likely to provide useful treatment in essential HTN and CHF, conditions in which the RAS is known to play a major role. The utility of AII antagonism may extend beyond that of HTN and CHF, as suggested by the potential usefulness of angiotensin-converting enzyme (ACE) inhibition in the treatment or prevention of many other diseases. The key advantage AII antagonists provide over ACE inhibitors is that they may avoid unwanted side effects, related to bradykinin potentiation with the latter drugs. The AII antagonists will help determine the role of the RAS in physiologic regulation and in the pathophysiology of various disease states.

Prolonged angiotensin II antagonism in spontaneously hypertensive rats. Hemodynamic and biochemical consequences

The present study examines the effects of prolonged angiotensin II antagonism in spontaneously hypertensive rats by using an angiotensin II receptor antagonist (DuP 753) that is devoid of agonistic properties and selective for the subtype 1 of the angiotensin II (AT1) receptor. The antihypertensive effects of DuP 753 and its effects on circulating parameters of the renin-angiotensin system were compared with those of a converting enzyme inhibitor (benazeprilat). To minimize any influence of differences in the pharmacokinetic properties of the two blockers, administration was by continuous intravenous infusion. The experiments were performed in conscious, freely moving rats with continuous 24-hour monitoring of blood pressure. DuP 753 (10 or 30 mg/kg/day) lowered mean arterial pressure to the same extent as benazeprilat (3 or 10 mg/kg/day) during a 48-hour period. The antihypertensive effect was sustained when the treatment was extended to 7 days (DuP 753, 10 mg/kg/day; benazeprilat, 3 mg/kg/day). Neither of the compounds affected the baseline or diurnal rhythm of heart rate. Plasma concentrations of renin and angiotensin II were increased sevenfold and 10-fold, respectively, in the rats treated with DuP 753. In rats treated with benazeprilat, plasma renin concentration increased threefold, whereas angiotensin II was unchanged. Heart weights were significantly reduced to a similar extent by DuP 753 and benazeprilat. Both compounds also induced a smaller but significant decrease in blood pressure in Wistar-Kyoto rats. Our results indicate that the antihypertensive effects of converting enzyme inhibitors in spontaneously hypertensive rats are mainly due to the blockade of the renin-angiotensin system. In this rat model, angiotensin II appears to play an important role in the maintenance of hypertension that is mediated via the AT1 receptor.