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Desensitization of the pulmonary adenylyl cyclase system

A cause of airway hyperresponsiveness in congestive heart failure?¹

^a Department of Cardiology, Angiology and Pulmonary Medicine, Heidelberg University, Heidelberg, Germany

View larger version (12K): [in a new window]   Figure 1 Development of myocardial hypertrophy and heart failure after aortic banding. Organ wet weights are shown relative to body weight (BW). (A) Progressive left ventricular (LV) hypertrophy occurs early after aortic banding (closed squares) as compared with sham-operated rats (open squares). (B) Right ventricular (RV) weight increases in animals with banded aorta as left heart failure develops. (C) Twenty-eight days after aortic banding, lung wet weight is increased significantly, indicating congestive heart failure (CHF). Mean ± SEM. *p 0.05; **p 0.0005 (two-tailed t test).

View larger version (22K): [in a new window]   Figure 2 Radioligand binding assay for beta-adrenergic receptors in lung membrane preparations from rats with CHF after aortic banding and from control animals was performed using [125I]iodocyanopindolol (A). Saturation isotherms established by the least-squares method are from single data referring to CHF and control animals 28 days after aortic banding. Nonspecific binding (bottom) was determined as the residual binding in the presence of 10 µmol/liter alprenolol. (B) Density (Bmax) and affinity (KD) of pulmonary adrenergic receptors from rats at 3 days (n = 6), 7 days (n = 11) and 28 days (n = 12) after aortic banding (hatched bars) are compared with respective controls (n = 5, 9 and 10, respectively) (open bars). Mean ± SEM; *p 0.001 (two-way ANOVA). KD values (shown in numbers) were not significantly different. (C) Ratio of adrenergic receptor subtypes as determined by two-site competition curves obtained with the beta1-selective receptor antagonist bisoprolol (Biso) and the beta2-selective antagonist ICI 118,551 (ICI). No differences in the beta1-/beta2-subtype ratio of 20:80 were observed between lungs from rats with CHF (after 28 days; n = 3) and from sham-operated control animals (n = 3).

View larger version (17K): [in a new window]   Figure 3 Linear regression analysis (±95% CI) of pulmonary beta-adrenergic receptor density (Bmax) and parameters of left ventricular failure in rats with CHF 28 days after aortic banding. For comparison, sham-operated control are also shown. (A) Left ventricular end diastolic pressure: r = 0.62 (n = 9; p 0.05). (B) Lung wet weight: r = 0.71 (n = 12; p 0.05).

View larger version (50K): [in a new window]   Figure 4 Absence of regulation of Gs and Gi proteins in pulmonary membrane preparations from rats with CHF (hatched bars) and controls (open bars) (n = 3). The G protein subunits were detected by specific antibodies and visualized by a chemoluminescence technique (see Methods). Values derived from the densitometric analysis (AUC, area under the curve) are shown as percent of controls. Insets depict respective lanes from representative experiments running at 40 kDa.

View larger version (35K): [in a new window]   Figure 5 Adenylyl cyclase activity in rat pulmonary membrane preparations was determined in lungs from animals with CHF 28 days after aortic banding (n = 7; hatched bars) and sham-operated controls (n = 7; open bars). Enzyme activity was measured under basal conditions and during stimulation with isoproterenol (Iso, 0.1 mmol/liter), sodium fluoride (NaF, 10 mmol/liter) or forskolin (Fors, 0.1 mmol/liter). Total lung membrane protein concentration was unchanged after aortic banding (see Results section). Mean ± SEM. *p 0.05 (two-tailed t test).

View larger version (22K): [in a new window]   Figure 6 Concentration response curves obtained with isoproterenol (10 pmol/liter to 10 µmol/liter) in tracheal strips from rats with CHF (n = 8) and control animals (n = 8). Tracheal strips were precontracted with carbachol (1 µmol/liter). Relaxant responses are plotted as a percentage of the maximal relaxation achieved with isoproterenol (A; NS) and of the maximal relaxation obtained with papaverin (B; p 0.0001 by two-way ANOVA). Curves were fitted using the least-squares method. Data points are mean ± SEM.

View larger version (40K): [in a new window]   Figure 7 Cumulative relaxation of tracheal strips obtained with isoproterenol (Iso, 10 µmol/liter, n = 12), forskolin (Fors, 1 mmol/liter; n = 12) and papaverin (Pap, 0.1 mmol/liter; n = 8) successively added to the organ bath after precontraction with carbachol (1 µmol/liter). Values are plotted as percentage of maximal contraction obtained with carbachol. Mean ± SEM. *p 0.05 (two-tailed t test).