Impaired relaxation to acetylcholine in 2K-1C hypertensive rat aortas involves changes in membrane hyperpolarization instead of an abnormal contribution of endothelial factors

• Published in: General pharmacology Vol. 34; no. 6; pp. 379 - 389
• Main Authors: Callera, G.E., Varanda, W.A., Bendhack, L.M.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.06.2000; Elsevier
• Subjects: 2K-1C rats; Acetylcholine - pharmacology; Animals; Aorta; Aorta - drug effects; Arterial hypertension. Arterial hypotension; Biological and medical sciences; Biological Factors - physiology; Blood and lymphatic vessels; Cardiology. Vascular system; Clinical manifestations. Epidemiology. Investigative techniques. Etiology; Cyclic GMP - metabolism; Disease Models, Animal; EDHF; Endothelial factors; Endothelium, Vascular - drug effects; Hypertension, Renal - physiopathology; Hypertension, Renovascular - physiopathology; Indomethacin - pharmacology; Male; Medical sciences; Membrane potential; Membrane Potentials - drug effects; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle Relaxation - drug effects; Muscle, Smooth, Vascular - drug effects; Nitric oxide; Phenylephrine - pharmacology; Rats; Rats, Wistar; Stimulation, Chemical; Vasodilator Agents - pharmacology; Aorta; Membrane potential; EDHF; Nitric oxide; Endothelial factors; 2K-1C rats; Hypertension; Pathophysiology; Rat; Rodentia; Electrophysiology; Cardiovascular disease; 3',5'-GMP; Smooth muscle; In vitro; Vasodilation; Endothelium; Muscular relaxation; Vertebrata; Mammalia; Animal; Neurotransmitter; Acetylcholine; Hyperpolarization
• ISSN: 0306-3623; 1879-0011
• DOI: 10.1016/S0306-3623(01)00075-1

The contribution of endothelial factors and mechanisms underlying decreased acetylcholine-induced relaxation and endothelial inhibitory action on phenylephrine-induced contraction were evaluated in aortas of two-kidney, one-clip hypertensive (2K-1C) and normotensive (2K) rats. Relaxation induced by acetylcholine in 2K-1C precontracted by phenylephrine was lower [Maximum Effect (ME): 71.33±3.36%; p D 2: 7.050±0.03] than in 2K (ME: 95.26±1.59%; p D 2: 7.31±0.07). This response was abolished by N G-nitro- l-arginine (L-NNA) in 2K-1C, but was only reduced in 2K (ME: 29.21±9.28%). Indomethacin had no effect in 2K-1C, and slightly attenuated acetylcholine-induced relaxation in 2K. The combination of L-NNA and indomethacin almost abolished acetylcholine-induced relaxation in 2K-1C, while in 2K, the inhibition (ME: 56.61±8.95%) was lower than the effect of L-NNA alone. During the KCl-induced precontraction, 2K and 2K-1C aortas showed similar acetylcholine-induced relaxation (43.50±5.64% vs. 41.60±4.36%), which was abolished by L-NNA. The levels of cGMP produced in response to acetylcholine were not different between 2K and 2K-1C. The sensitivity to sodium nitroprusside was lower in phenylephrine-precontracted aortas from 2K-1C than 2K, as showed by the p D 2 values (7.72±0.20 vs. 8.59±0.17), and this difference was abolished in aortas precontracted by KCl. The membrane potential was less negative in 2K-1C than in 2K (−41.57±1.19 vs. −51.00±1.13 mV) and hyperpolarization induced by acetylcholine was lower in 2K-1C than in 2K aortas (6.00±0.66 vs. 13.27±1.61 mV). Phenylephrine-induced contraction in aortas with endothelium was similar in both groups, and increased by the endothelium removal. This increase was lower in 2K-1C (from 1.32±0.06 to 1.90±0.21 g) than 2K (from 1.49±0.07 to 2.83±0.18 g). L-NNA and the endothelium removal had similar effect in 2K-1C (1.85±0.18 g) and were lower in 2K (2.18±0.20 g). Indomethacin decreased phenylephrine-induced contraction only in 2K. In conclusion, our major finding was a selective defect in smooth muscle membrane hyperpolarization, which could explain the decreased relaxation to acetylcholine and the attenuated inhibitory effect of endothelium on the contractile function in 2K-1C aortas.