Decreased cGMP level contributes to increased contraction in arteries from hypertensive rats: role of phosphodiesterase 1

Abstract

Recent evidence suggests that angiotensin II (Ang II) upregulates phosphodiesterase (PDE) 1A expression. We hypothesized that Ang II augmented PDE1 activation, decreasing the bioavailability of cyclic guanosine 3' 5'-monophosphate (cGMP), and contributing to increased vascular contractility. Male Sprague-Dawley rats received mini-osmotic pumps with Ang II (60 ng·min(-1)) or saline for 14 days. Phenylephrine (PE)-induced contractions were increased in aorta (E(max)168% ± 8% vs 136% ± 4%) and small mesenteric arteries (SMA; E(max)170% ± 6% vs 143% ± 3%) from Ang II-infused rats compared to control. PDE1 inhibition with vinpocetine (10 μmol/L) reduced PE-induced contraction in aortas from Ang II rats (E(max)94% ± 12%) but not in controls (154% ± 7%). Vinpocetine decreased the sensitivity to PE in SMA from Ang II rats compared to vehicle (-log of half maximal effective concentration 5.1 ± 0.1 vs 5.9 ± 0.06), but not in controls (6.0 ± 0.03 vs 6.1 ± 0.04). Sildenafil (10 μmol/L), a PDE5 inhibitor, reduced PE-induced maximal contraction similarly in Ang II and control rats. Arteries were contracted with PE (1 μmol/L), and concentration-dependent relaxation to vinpocetine and sildenafil was evaluated. Aortas from Ang II rats displayed increased relaxation to vinpocetine compared to control (E(max)82% ± 12% vs 445 ± 5%). SMA from Ang II rats showed greater sensitivity during vinpocetine-induced relaxation compared to control (-log of half maximal effective concentration 6.1 ± 0.3 vs 5.3 ± 0.1). No differences in sildenafil-induced relaxation were observed. PDE1A and PDE1C expressions in aorta and PDE1A expression in SMA were increased in Ang II rats. cGMP production, which is decreased in arteries from Ang II rats, was restored after PDE1 blockade. We conclude that PDE1 activation reduces cGMP bioavailability in arteries from Ang II, contributing to increased contractile responsiveness.

Figure 1. PDE-1 inhibition decreases vascular contraction in arteries from Ang II hypertensive, but not control, rats

Concentration-response curves to PE were performed in (A) aorta and (B) small-mesenteric arteries from Ang II hypertensive (▲) and control (■) rats, in the absence (open symbols) or in the presence (filled symbols) of vinpocetine (10µM, 30 minutes). Data are mean ± SEM (n=6). Symbols represents the results from two-way ANOVA, and express differences in the E_max. * P<0.05 vs. control. † P<0.05 vs. Ang II.

Figure 2. PDE-5 inhibition decreases vascular contraction similarly in arteries from Ang II hypertensive and control rats

Concentration-response curves to PE were performed in (A) aorta and (B) in small-mesenteric arteries from Ang II hypertensive (▲) and control (■) rats, in the absence (open symbols) or in the presence (filled symbols) of sildenafil (10µM, 30 minutes). Data are mean ± SEM (n=6). Symbols represents the results from two-way ANOVA, and express differences in the E_max. * P<0.05 vs. control. † P<0.05 vs. Ang II+ vehicle.

Figure 3. Ca²⁺-induced vascular contraction is increased in aortas from Ang II hypertensive rats

Concentration-response curves to Ca²⁺ (CaCl₂) were performed in (A) aorta and (B) small-mesenteric arteries from Ang II hypertensive (▲) and control (■) rats, in the absence (open symbols) or in the presence (filled symbols) of vinpocetine (10µM, 30 minutes). Symbols represents the results from two-way ANOVA, and express differences in the E^max. Data are mean ± SEM (n=6). * P<0.05 vs. control. † P<0.05 vs. Ang II. ‡ p<0.05 vs. control + vinpocetine.

Figure 4. Vinpocetine induced-relaxation is increased in arteries from Ang II hypertensive rats

Concentration-response curves to A) vinpocetine, B) sildenafil, C) 8-Bromo cGMP and D) Bay 41-2272 were performed in aortas (continuous trace) contracted with PE (1µM) or small-mesenteric arteries (dashed trace) contracted with U-46619 (1µM), from Ang II hypertensive (▲) and control (■) rats. Data are mean ± SEM (n=6). Symbols represents the results from two-way ANOVA, and express differences in the E^max. * P<0.05 vs. control.

Figure 5. PDE1 vascular expression is increased in arteries from Ang II hypertensive rats

Above, representative western blot images of PDE1A, PDE1B, PDE1c and PDE5. Bellow, corresponding graphs showing the relative expression of PDEs isoforms in (A) aorta and (B) small-mesenteric arteries from Ang II hypertensive (black bars) and control (white bars) rats. Data are mean ± SEM (n=6). * P<0.05 vs. respective control.

Figure 6. PDE-1 inhibition restores cGMP bioavailability in arteries from Ang II hypertensive rats

cGMP production was evaluated in the presence or absence of vinpocetine (10 µM) in (A) aorta and (B) small-mesenteric arteries from Ang II hypertensive (black bars) and control (white bars) rats. Data are mean ± SEM (n=6). * P<0.05 vs. control. † P<0.05 vs. respective vehicle group.