Histamine H2-receptor antagonism improves conduit artery endothelial function and reduces plasma aldosterone level without lowering arterial blood pressure in angiotensin II–hypertensive mice

Figures

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  Fig. 1. The flowchart displays the inclusion and distribution of animals in the experimental series. Twenty-seven animals were included for blood pressure analysis, 18 for wire myography, and 15 for perfusion myography. The mice that completed the infusion protocol were included in myography (either wire or perfusion). Therefore, animals which were not included in the blood pressure analysis due to technical sampling error (i.e., data not recorded by the software) and animals who were only implanted with a venous catheter could still be included for wire/perfusion myography

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  Fig. 2. The panels show recordings of mean arterial blood pressure (A and B) for 24 days (D1–D24) and heart rate (C and D) responses to AngII infusion as measured via indwelling femoral artery catheter at 100 Hz in 15 i.v. angiotensin II+vehicle (AngII) and 12 ranitidine+angiotensin II (ranitidine/R+AngII)-treated C57BL/6 mice. Blood pressure measurements were averaged for every 12 h. Daytime blood pressures are labeled with D1–D24 (A), whereas nighttime is indicated by ticks on the x-axis in B. Blood pressure was not different in the two series and increased similarly and significantly in AngII (P<0.0001, ANOVA) and ranitidine+AngII- (P<0.0001, ANOVA) treated animals (A and B). Integrated long-term blood pressure responses were statistically similar as indicated by no difference in area under the curve (AUC) in diagrams shown on the right side ((A) daytime P=0.3, B nighttime P=0.8, Student’s t-test) after maximal blood pressure response. Heart rate transiently decreased following AngII-infusion in ranitidine+AngII-treated animals (A) P=0.002, Holm-Sidák’s multiple comparisons test) but not in AngII-treated animals (A) P=0.2, Holm-Sidák’s multiple comparisons test). Heart rate responses…

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  Fig. 3. The panel shows plasma aldosterone concentration in resting unstressed C57Bl/6 mice after 24 days of angiotensin II (AngII) and ranitidine+angiotensin II (ranitidine+AngII) treatment. During angiotensin II infusion, plasma levels of aldosterone were reduced significantly by 50% in ranitidine-treated animals, as compared to the Student’s t-test for unpaired observations (P=0.02). The normality of residuals was evaluated by frequency distribution and quantum-quantum plot. Data are reported as means ± SEM

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  Fig. 4. Panels show diameter changes during responses to acetylcholine in isolated perfused mesenteric arteries from C57Bl/6 mice treated in vivo with infusion of angiotensin II (AngII) or combined ranitidine+angiotensin II (ranitidine+AngII). Ex vivo, arteries were pre-constricted with a sub-maximal dose of U46619. The EC50 of acetylcholine was significantly lower in arteries from ranitidine+angiotensin II–treated animals as compared with arteries from angiotensin II infused animals ((A) EC50 −7.6 ± 0.2 vs −6.6 ± 0.3 log(mol/L), P=0.03 as compared by Student’s t-test). This difference was absent following 1-h incubation with 1 nmol/L aldosterone ((B) EC50 −7.4 ± 0.3 vs −6.8 ± 0.3 log(mol/L), P=0.06 as compared by Student’s t-test). There were no differences in maximal responses for any treatment ((A) difference 11 ± 9%, P=0.6 and (B) 8 ± 10%, P=0.8 as compared by Holm-Sidák’s multiple comparisons test). The protocol for perfusion myography is illustrated in C. The normality of residuals was evaluated by frequency distribution and quantum-quantum plot. Data are reported as means ± SEM

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  Fig. 5. Panels show changes in isometric tension in aortic ring segments isolated from C57Bl/6 mice treated in vivo with angiotensin II (AngII) and combined ranitidine+angiotensin II (ranitidine+AngII). Segments were prestimulated to obtain baseline tension with the thromboxane receptor agonist U46619. Responses to cumulatively increasing concentrations of acetylcholine were tested in parallel in rings that were subjected to ex vivo vehicle, ranitidine and eplerenone. Acetylcholine-induced relaxation was significantly impaired in aortic segments from mice treated in vivo with ranitidine as measured by Emax ((A) 40 ± 4 vs 74 ± 6%, P=0.03, as compared by F-test) but was similar to segments from AngII-treated mice after in vitro 30-min treatment with either mineralocorticoid receptor inhibition by 10 µmol/L eplerenone (65 ± 13 vs 73 ± 5%, P=0.24 (B)) or H2-receptor inhibition by 10 µmol/L ranitidine ((C), 64 ± 8 vs 79 ± 7%, P=0.08, as compared by F-test). An illustration of the myograph protocol is given in D. Four segments from four mice were run in parallel with initially three, later four different conditions: time control, then aldosterone treatment (1 nmol/L, initially also…

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  Fig. 6. Panels show changes in isometric tension in aortic segments ex vivo isolated from C57Bl/6 mice treated in vivo with angiotensin II (AngII) and ranitidine+angiotensin II (ranitidine+AngII). Baseline tension in all segments was achieved by the thromboxane receptor agonist U46619. Responses to cumulatively increasing concentrations of acetylcholine were tested after a 1-h aldosterone treatment period. Some rings incubated additionally with either eplerenone or ranitidine before exposure to acetylcholine. One-hour aldosterone treatment ex vivo abolished the difference in acetylcholine responses (B) as did time (A). No effect was detected by combined eplerenone and aldosterone incubation (C) but combined ranitidine and aldosterone incubation reintroduced the difference in acetylcholine response ((D) 33 ± 6 vs 62 ± 8%, P=0.01 as compared by F-test) as was seen in Figure 5A. Protocol was terminated by examining relaxation in response to the NO donor diethylamine NONOate. Responses were similar in aortic segments from in vivo angiotensin II and ranitidine+angII-treated animals (data not shown) and were not affected by ex vivo addition of eplerenone (E) or ranitidine (F). The normality of…