oxadiazoles and Hypertension--Renovascular

Activation of angiotensin (ANG) II type 1 receptors (AT1R) promotes vasoconstriction, inflammation, and renal dysfunction. In this study, we addressed the ability of azilsartan (AZL), a new AT1R antagonist, to modulate levels of plasma ANG-(1-7) and renal epoxyeicosatrienoic acids (EETs) and 20-hydroxyeicosatetraenoic acid (20-HETE).. Sprague-Dawley rats were infused with ANG II (125 ng/min) or vehicle (VEH). AZL (3 mg/kg/day) or VEH was administered starting 1 day prior to ANG II or VEH infusion. On day 10, plasma was obtained for measurement of ANG-(1-7) and kidneys for isolation of microvessels for EET and 20-HETE determination and histological evaluation.. Mean 24-hour blood pressure (BP) was not different between VEH and AZL treatment groups, whereas the BP elevation with ANG II infusion (121 ± 5 mm Hg) was completely normalized with AZL cotreatment (86 ± 3 mm Hg). The ANG II-induced renal damage was attenuated and cardiac hypertrophy prevented with AZL cotreatment. Plasma ANG-(1-7) levels (pg/ml) were increased with AZL treatment (219 ± 22) and AZL + ANG II infusion (264 ± 93) compared to VEH controls (74.62 ± 8). AZL treatment increased the ratio of EETs to their dihydroxyeicosatrienoic acid (DHET) metabolites and reduced 20-HETE levels.. Treatment with AZL completely antagonized the elevation of BP induced by ANG II, prevented cardiac hypertrophy, attenuated renal damage, and increased ANG-(1-7) and EET/DHET ratio while diminishing 20-HETE levels. Increased ANG-(1-7) and EETs levels may emerge as novel therapeutic mechanisms contributing to the antihypertensive and antihypertrophic actions of AZL treatment and their relative role compared to AT1R blockade may depend on the etiology of the hypertension.

Topics: Angiotensin I; Animals; Benzimidazoles; Blood Pressure; Disease Models, Animal; Hydroxyeicosatetraenoic Acids; Hypertension; Hypertension, Renovascular; Male; Oxadiazoles; Peptide Fragments; Rats; Rats, Sprague-Dawley; Vasoconstriction

Acetylcholine induced relaxation in a concentration-dependent way in isolated phenylephrine-contracted carotid artery rings from normotensive two-kidney (2K) and hypertensive two-kidney one-clip (2K-1C) rats. In the presence of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NOARG, 100 micromol/l), the relaxation stimulated with acetylcholine was blocked in 2K arteries. However, in 2K-1C arteries, the relaxation was only partially inhibited. Indomethacin (3 micromol/l) had no effect in both groups. In 2K arteries, the combination of L-NOARG and indomethacin had similar effects to L-NOARG alone. On the other hand, in 2K-1C arteries, indomethacin further inhibited the maximum effect induced by acetylcholine. Endothelium-dependent relaxation induced by acetylcholine was markedly reduced in 2K arteries contracted with 90 mmol/l KCl, and it was abolished in 2K-1C arteries. The remaining response to acetylcholine in 2K arteries was blocked by L-NOARG. Thus, in addition to NO, a relaxing factor sensitive to extracellular K+ changes in the membrane potential contributes to endothelium-dependent relaxation in 2K-1C rat carotid artery. On the other hand, in arteries from 2K rats, only NO is involved in the relaxation induced by acetylcholine. The combination of 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 3 micromol/l), indomethacin (3 micromol/l) and L-NOARG (100 micromol/l) reduced the relaxation induced by acetylcholine in arteries from 2K-1C rats contracted with phenylephrine. On the other hand, in 2K arteries, the relaxation induced by acetylcholine was abolished. The combination of ODQ and K+ channel blockers charybdotoxin (100 nmol/l), apamin (500 nmol/l) and 4-aminopyridine (1 micromol/l) abolished the relaxation induced by acetylcholine in 2K and 2K-1C carotid arteries. These data indicate that the endothelium-derived relaxing factors that contribute to relaxation induced by acetylcholine are different in 2K and 2K-1C arteries. In 2K arteries, the only factor is NO, which involves the activation of K+ channels and the cGMP pathway. However, in 2K-1C arteries, the relaxation induced by acetylcholine is dependent on NO in addition to another factor, which is insensitive to indomethacin, but also activates the K+ channels and the cGMP pathway, presumably by membrane hyperpolarization through endothelium-derived hyperpolarizing factor.

Topics: Acetylcholine; Animals; Biological Factors; Carotid Arteries; Cyclic GMP; Cyclooxygenase Inhibitors; Enzyme Inhibitors; Epoprostenol; Hemoglobins; Hypertension, Renovascular; Indomethacin; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nerve Tissue Proteins; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitroarginine; Oxadiazoles; Potassium Channel Blockers; Potassium Chloride; Quinoxalines; Rats; Rats, Wistar; Vasodilator Agents

Several functional and biochemical characteristics of hypertrophied hearts isolated from rats with renovascular hypertension provide indirect evidence that cellular Ca2+ dynamics during myocardial contraction-relaxation are altered. In this study, intracellular Ca2+ concentration ([Ca2+]i) dynamics were examined in paced left ventricular (LV) myocytes isolated from rats with hypertension (HYP) induced by partial occlusion of the left renal artery and from normotensive rats (Sham). Characteristic myocardial changes produced by renovascular hypertension included a 40% increase in LV weight and a 3.6-fold increase in the fractional expression of the beta-heavy chain of myosin in isolated LV myocytes. In periods of mechanical quiescence between contractions, basal [Ca2+]i values were similar in Sham and HYP LV myocytes. During a contraction-relaxation cycle in HYP myocytes, peak [Ca2+]i, +d[Ca2+]i/dt, and -d[Ca2+]i/dt were reduced, whereas the time required for [Ca2+]i to rise from a basal value to a peak value (time-to-peak [Ca2+]i) was unaffected. In both Sham and HYP myocytes, the fall in [Ca2+]i from peak to basal values could be approximated by a monoexponential rate constant, kf. Values for kf were significantly smaller in HYP than in Sham myocytes. After treatment with 4 microM isoproterenol, peak [Ca2+]i, +[Ca2+]i/dt, -d[Ca2+]i/dt, and kf increased in both Sham and HYP myocytes. In contrast, basal [Ca2+]i and time-to-peak [Ca2+]i did not change. Thus, despite recent reports of inefficiencies of beta-adrenergic receptor coupling, there was no evidence of blunted beta-adrenergic responsiveness in HYP myocytes with respect to [Ca2+]i dynamics during contraction-relaxation. Finally, no Sham vs. HYP differences in the number of specific [3H]-PN200-110 binding sites per cell in quiescent, rod-shaped myocytes were detected, but a significant reduction in [3H]-PN200-110 binding sites in an enriched sarcolemmal membrane fraction isolated from HYP animals was observed. These observations are suggestive of a reduction in slow, Ca2+ channel surface density in HYP myocytes. The results of this study clearly indicate that [Ca2+]i dynamics during contraction-relaxation in single left ventricular myocytes are affected by residence in a chronic setting of renovascular hypertension. In addition, the prolonged [Ca2+]i removal phase observed in HYP myocytes can be restored toward normal by beta-adrenergic agonists.

Topics: Analysis of Variance; Animals; Calcium; Calcium Channel Blockers; Cardiomegaly; Cells, Cultured; Fura-2; Heart Ventricles; Hypertension, Renovascular; Isoproterenol; Isradipine; Kinetics; Male; Myocardium; Myosins; Oxadiazoles; Rats; Rats, Inbred Strains; Reference Values; Sarcolemma; Spectrometry, Fluorescence