Impairment of smooth muscle function of rat thoracic aorta in an endothelium-independent manner by long-term administration of N(G)-nitro-L-arginine methyl ester.
In this study, we aimed to elucidate whether the daily hypertensive dose of long-term N(G)-nitro-l-arginine methyl ester (l-NAME) treatment, could make a difference between endothelial and smooth muscle functions in rat thoracic aorta. We test the hypothesis that high-dose, long-term l-NAME treatment has a depressive effect on vascular smooth muscle contractile activity which is not related with nitric oxide (NO) synthesis inhibition. After 14 days of treatment, isometric tension and (45)Ca(2+) influx were measured in aortic tissues isolated from l-NAME(10) and l-NAME(100) hypertensive (10 and 100 mg/kg/day, systolic blood pressures 167 +/- 7 and 172 +/- 10 mmHg, respectively) and control normotensive rats (132 +/- 7 mmHg). In l-NAME(10)- and l-NAME(100)-treated rats, acetylcholine-induced relaxation in aortic rings was suppressed with no significant difference between the treatments. l-NAME(100) (but not l-NAME(10)) treatment, significantly inhibited contractile responses to phenylephrine, angiotensin II, and K(+) (80 mm) in endothelium-intact tissues. The effect of l-NAME(100) on phenylephrine-induced contractile responses was not observed after 3 days of treatment. In endothelium-denuded aortic tissues of l-NAME(100) (but not l-NAME(10))-treated rats, phenylephrine (1 x 10(-6) m)- and K(+) (80 mm)-induced contractions and (45)Ca(2+) influxes were significantly reduced. In Ca(2+)-free medium (0.1 mm EDTA), on the contrary, the transient contractions obtained by either phenylephrine (1 x 10(-6) m) or caffeine (1 x 10(-2) m), or the sustained contractions induced by 12-o-tetradecanoylphorbol-13-acetate (1 x 10(-6) m; a protein kinase C activator) in endothelium-denuded aortic rings, were not modified by both l-NAME treatments. These results indicate that in aortic rings from l-NAME hypertensive rats, low and high doses, long-term l-NAME administration may be associated with equivalent inhibition in NO-dependent vasodilator tone (corresponding to equivalent hypertension values); whereas only high-dose, long-term l-NAME administration produces an endothelium-independent decrease in vasocontrictor activity, at least partly explained by a reduction in extracellular Ca(2+) influx.
López
Ruth M
RM
Sección de Estudios de Posgrado e Investigación, Escuela Superior de Medicina, Instituto Politécnico Nacional, Plan de San Luis y Diaz Mirón, Col. Casco de Santo Tomás, CP 11340, México, D.F., México.
Ortíz
Cindy S
CS
Ruíz
Antonio
A
Vélez
Juan M
JM
Castillo
Carlos
C
Castillo
Enrique F
EF
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002132:Calcium Radioisotopes; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology*; D006973:Hypertension / Q000139:chemically induced / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000008:administration & dosage / Q000494:pharmacology*; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D002132:Calcium Radioisotopes; D016861:Cyclooxygenase Inhibitors; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009569:Nitric Oxide; D011188:Potassium; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester