Intra-arterial thiopentone is directly toxic to vascular endothelium.

Ear artery segments removed from urethane-anaesthetized rabbits were mounted, perfused with Krebs solution, and pressurized before constriction with extraluminal noradrenaline. Vessel diameter was measured using a diode array mounted above the artery. After the degree of dilatation in response to intraluminal acetylcholine and glyceryl trinitrate was measured, vessels were perfused for 120 s with solutions of either 2.5-10% thiopentone or isotonic sodium carbonate in saline of matched pH. Administration of thiopentone solutions in all concentrations resulted in destruction of endothelial cells. The dilatation of vessels to glyceryl trinitrate and their myogenic reactivity was unaltered. Isotonic solutions of sodium carbonate (pH 10.6) had no effect on either endothelial cell function or direct vasodilatation. These data show that administration of thiopentone removes arterial endothelial cells, while vascular smooth muscle function is essentially unaltered.