Endothelium-Derived Hyperpolarizing Factor (EDHF) Mediates Acetylsalicylic Acid (Aspirin) Vasodilation of Pregnant Rat Mesenteric Arteries

Abstract

Acetylsalicylic acid (aspirin) exhibits a broad range of activities, including analgesic, antipyretic, and antiplatelet properties. Recent clinical studies also recommend aspirin prophylaxis in women with a high risk of pre-eclampsia, a major complication of pregnancy characterized by hypertension. We investigated the effect of aspirin on mesenteric resistance arteries and found outdiscovered the molecular mechanism underlying this action. Aspirin (10^-12-10^-6 M) was tested on pregnant rat mesenteric resistance arteries by a pressurized arteriography. Aspirin was investigated in the presence of several inhibitors of: (a) nitric oxide synthase (L-NAME 2 × 10^-4 M); (b) cyclooxygenase (Indomethacin, 10^-5 M); (c) Ca²⁺-activated K⁺ channels (Kca): small conductance (SKca, Apamin, 10^-7 M), intermediate conductance (IKca, TRAM34, 10^-5 M), and big conductance (BKca, paxilline, 10^-5 M); and (d) endothelial-derived hyperpolarizing factor (high KCl, 80 mM). Aspirin caused a concentration-dependent vasodilation. Aspirin-vasodilation was abolished by removal of endothelium or by high KCl. Furthermore, preincubation with either apamin plus TRAM-34 or paxillin significantly attenuated aspirin vasodilation (p < 0.05). For the first time, we showed that aspirin induced endothelium-dependent vasodilation in mesenteric resistance arteries through the endothelial-derived hyperpolarizing factor (EDHF) and calcium-activated potassium channels. By activating this molecular mechanism, aspirin may lower peripheral vascular resistance and be beneficial in pregnancies complicated by hypertension.

Keywords: calcium-activated potassium channels; endothelial cells; hypertension; pre-eclampsia; relaxation; smooth muscle cells.

Figure 1

Acetylsalicylic acid vasodilation on mesenteric arteries. Acetylsalicylic acid (ASA) and its vehicle ethanol (ETOH) were tested on phenylephrine preconstricted mesenteric arteries isolated from gravid rats. Data are reported as mean ± SEM, n = number of experiments, *** p < 0.001 (two-way ANOVA).

Figure 2

Acetylsalicylic acid effect on entire and denuded mesenteric arteries. Acetylsalicylic acid was tested on phenylephrine preconstricted mesenteric arteries entire (Control) and without endothelium (Denuded) isolated from gravid rats. Data are reported as mean ± SEM, n = number of experiments. *** p < 0.001 (two-way ANOVA).

Figure 3

Effect of acetylsalicylic acid in the presence of nitric oxide synthase and cyclooxygenase inhibitors. Acetylsalicylic acid was tested on phenylephrine preconstricted mesenteric arteries isolated from gravid rats in the absence (Control) and in the presence of inhibitors of either nitric oxide synthase (L-NAME, 2 × 10⁻⁴ M), or cyclooxygenase (Indom., 10⁻⁵ M). Data are reported as mean ± SEM, n = number of experiments.

Figure 4

Effect of acetylsalicylic acid on preconstricted arteries. Acetylsalicylic acid was tested on mesenteric arteries isolated from gravid rats, preconstricted with phenylephrine (Control) or with high KCl (80 mM), which induces depolarization (Depol). Data are reported as mean ± SEM, n = number of experiments, *** p < 0.001 (two-way ANOVA).

Figure 5

Effect of acetylsalicylic acid in the presence of calcium-activated potassium channel inhibitors. Acetylsalicylic acid was tested on phenylephrine preconstricted mesenteric arteries isolated from gravid rats in the absence (Control) or in the presence of both calcium-activated potassium channel small (Sk_Ca,) and intermediate (IK_Ca) inhibitors Apamin (10⁻⁷ M) and TRAM-34 (10⁻⁵ M), respectively. Data are reported as mean ± SEM, n = number of experiments, * p < 0.05 (two-way ANOVA).

Figure 6

Effect of acetylsalicylic acid in the presence of BKca channel inhibitor. Acetylsalicylic acid was tested on mesenteric arteries isolated from gravid rats in the absence (Control) or in the presence of big potassium channel (BKca) inhibitor (paxillin, 10⁻⁵ M). Data are reported as mean ± SEM, n = number of experiments, * p < 0.05 (two-way ANOVA).