PubMed1979
The effects of various injectable anaesthetics and relaxants on the pressure-diameter relations of isolated segments of the rat tail artery were investigated in vitro. The wall of this vessel contains about 75% smooth muscle fibres. Measurements were made before and after the induction of a virtually maximum constriction of the vascular segments which was produced by 1 mg/ml noradrenaline. When added to pure Tyrode's solution all the agents used did not markedly influence the pressure-diameter curves. However, the noradrenaline-induced constriction of the vessels was inhibited to varying degrees. This effect was most evident after thiopentone which caused the diameter to increase by 50%. After pentobarbitone, the increase in diameter was found to be less pronounced (15%). Administration of methohexitone was followed by lesser relaxation of the arterial smooth muscle resulting in a maximum increase in diameter of 7%. After alphathesin (CT 1341) and propanidid, the arterial segments dilated about 20%, after etomidate and 4-hydroxybutyrate about 10%. The muscle relaxants suxamethonium and d-tubocurarine induced dilations of 10 to 15%, alcuronium and pancuronium, however, of less than 5%. The results presented here concur with those of experiments in vivo in which the influence of narcotics and relaxants on the peripheral resistance was studied. This indicates that the dilatation of peripheral resistance vessels seen after the administration of such agents is not exclusively caused by a neurally mediated inhibition of the vascular tone. The direct action of these substances on the vascular smooth muscle may often contribute to their complex haemodynamic effects.