This study investigated the effects of thiopental on endothelium-dependent relaxation (EDR), and especially the effects on nitric oxide- and prostacyclin-independent EDR. Fresh porcine coronary artery rings (4 mm long), were consecutively tested with and without 20 microg/ml thiopental in Krebs-Henseleit solution. Indomethacin (10 micromol/l) was used in all experiments to eliminate prostacyclin effects. Prostaglandin F(2alpha) (10 micromol/l) was used to induce contractions and bradykinin (10(-10) - 10(-5) M) was used to induce EDR. Experiments were also carried out using 300 micromol/l N-nitro-L-arginine to block nitric oxide production and to assess the influence of thiopental on nitric oxide- and prostacyclin-independent EDR. Thiopental induced statistically significant increases in EDR at concentrations of 10(-6) - 10(-5) M bradykinin. Following nitric oxide production block, thiopental significantly reduced the relaxation response at concentrations of 10(-8) - 10(-5) M bradykinin. At a clinically relevant concentration of 20 microg/ml thiopental, a significant increase in EDR and a significant reduction in nitric oxide- and prostacyclin-independent relaxation was observed in porcine epicardial coronary arteries.