Effects of Bupivacaine on Strips of Rat Thoracic Aortic Rings

Abstract

Background: Local anesthetics depress smooth muscle contractions in the intact bowel and in strips of isolated intestine, and also relax bronchial smooth muscle. Following systemic absorption, local anesthetics act on the cardiovascular system. Their primary site of action is the myocardium, where decreases in electrical excitability, conduction rates, and contraction force occur. In addition, most local anesthetics cause arteriolar dilation. Methods: The ability of bupivacaine to elicit a direct relaxant effect on vascular smooth muscle was studied using isolated rat thoracic aortic rings contracted by phenylephrine (PE). Each thoracic aorta ring was suspended on wire supports in a 20 ml tissue bath under 2 g of resting tension. All tissues were bathed in Tris Tyrode solution at and 100% oxygen was supplied. Results: 1. Bupivacaine ( M) inhibited PE induced contractions of aortic rings significantly (P M) was reversed by L-NAME pretreatment. 3. Relaxation of aortic rings by bupivacaine ( M) was not recovered by methylene blue. 4. Indomethacine enhanced the contraction of aortic rings by bupivacaine ( M). 5. Bupivacaine ( M) inhibited both the influx of extracellular and intracellular release. 6. Relaxation of aortic rings by bupivacaine M was recovered by tetraethylammonium. Conclusions: From the results obtained, it is concluded that the relaxation effects of bupivacaine are related with endothelium dependent, and that cyclooxygenase and not guanylate cyclase participates in this relaxation. Bupivacaine inhibited both intracellular calcium release and extracelluar calcium influx. In addition, the potassium channel was also found to be related to this relaxation effect.