Inhibition of beta-1 receptor but not vagotomy can abolish the L-NAME evoked bradycardia in anesthetized rat.
We reported previously that the nitric oxide synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) decreases cardiac output. Several studies have shown that inhibition of nitric oxide synthesis decreases the heart rate. In the present study, we investigated the effect of a single bolus administration of L-NAME on blood pressure and heart rate monitored for one hour in anesthetized rats and the influence of vagotomy and beta1-receptor blocker metoprolol on the L-NAME induced bradycardia. After L-NAME treatment, the blood pressure rose immediately after the injection of the drug (peak response in the third minute: +24%, p<0.001) and fell to the control level in the 20th minute. The heart rate decreased immediately after L-NAME administration, the lowest value being reached in the 10th minute (-14%, p<0.001). However, bradycardia was sustained even after the blood pressure had returned to the control level. Bilateral vagotomy failed to influence the negative chronotropic effect of L-NAME, but bradycardia was completely abolished by metoprolol pretreatment. We concluded that the bradycardia evoked by L-NAME is mainly due to the withdrawal of sympathetic tone upon the heart rate. However, the cause of sustained bradycardia after normalization of blood pressure cannot be elucidated.
Vág
J
J
Semmelweis University, Department of Conservative Dentistry, Budapest, Hungary. vag@konfog.sote.hu
Hably
Cs
C
Bartha
J
J
D058671:Adrenergic beta-1 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000139:chemically induced* / Q000188:drug therapy; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D014628:Vagotomy
D058671:Adrenergic beta-1 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D004791:Enzyme Inhibitors; D008790:Metoprolol; D019331:NG-Nitroarginine Methyl Ester