RESUMO
The characteristics of an ideal intravenous anesthetic agent include stability in solution, rapid onset of action, minimal effect on the cardiovascular and respiratory systems, short elimination half life, and minimal side effects. Using this criteria, the ultra-short acting barbiturate, thiopental has long been considered the gold standard of intravenous agents used for induction of anesthesia. In normovolemic subjects, thiopental produces a transient decrease in blood pressure, and increase in heart rate. In practice, thiopental is administered high dose(30 mg/kg IV) for brain protection, rarely. We tried to confirm the direct vascular effects of thiopental and its mechanism on the rabbit abdominal aorta in vitro. The rabbit abdominal aorta were precontracted with norepinephrine(10(-7) M) in 5 ml tissue bath and 10(-5), 10(-4), and 10(-3) M thiopental was administrated in cumulative manner. Ten minutes later, changes of the vascular tones were obtained. For confirming the relaxing mechanism induced by thiopental, experiment was performed by indomethacin, methylene blue and LNAME pretreatment, and endothelium removed, respectively. The results were as follows 1) Thiopental at 10(-5), and 10(-4) M produced no signifcant changes, and at 10(-3) M produced signifcant relaxation. 2) There were no significalnt difference in their vascular tones between intact and denuded endothelium group. 3) The vascular tones were not affected by LNAME, methylene blue, and indomethacin pretreatment. These results suggest that thiopental induce vasorelaxation in rabbit abdominal aorta at high concentration(10(-3) M). The vasorelaxation mechanism is not correlated with NO, cyclic GMP, prostacyclin and endothelium.