EndotheHum Dependent Relaxation of Isolated Rat Aorta to Samorin (lsometamidium Chloride)

Abstract

Relaxation responses to samorin (Isometamidiumchloride) were.tested on rat aortic rings pre-contracted with 10· 7 M noradrenaline (NA) and SOmMpotassium chloride (IcCI). . Samorin (10-8 to IO-4M) relaxedaortic ringspre-contracted With10·7Mnoradrenaline concentration - dependently but had no effect on' KCI contracted rings. A mean relaxation of 69.7 ± 8.8% was achieved at a concentration 064 x iO,sM samorin with ECsoof 10.9 ± 2.39 x 10~. . This relaxation response was significantly attenuated by removal of endothelium. since endothelium denuded ring showed a mean relaxation of 35 ± 8.5% at the same concentration of 4 x lO, s M samorin with ECso of 37.4 ± 13.7, x 10-6 M (P<O.OS). Moreover. endothelium intact rings which were pretreated with 1O~ methylene blue showed a significant attenuated relaxation to 4 x 10' s samorin with a mean relaxation of 18.3 ± 2.8%and an ECsoof80 ± 14x 10-6 M(P<O.OS). The results therefore suggest that samorin-induced relaxation of rat aortic smooth muscle occurs by endothelium dependent mechanism which is probably mediated throu8h the release of endothelium - derived relaxing factor(EDRF)