Methods: Sixteen Wistar albino type male rats were used. The thoracic aortas were removed carefully and were transferred to petri dishes containing Krebs solution. Aortic rings of approximately 5 mm in length were prepared and placed in the organ bath. Contraction and relaxation forces of the aortic rings were recorded. Contraction response was obtained by applying 10^-5M phenylephrine to aortic rings. Subsequently, cumulative doses of levosimendan (10^-8M-10^-4M) was applied to eight aortic rings and cumulative doses of dobutamine (10^-8M-10^-3M) was applied to the other eight aortic rings and dose-response curves were recorded. The EC₅₀ and pD2 values were calculated by the computer program named Graph Pad Prisim 4.0. The Mann-Whitney U-test was performed for statistical analysis.

Results: The relaxation response of the aortic rings with levosimendan 10-4M administration was %92.33 while the relaxation response with dobutamine 10-4M administration was %82.48. It did not show a significant difference between both relaxation responses (p=0.059). The EC₅₀ value was calculated as 6.605x10^-6M for dobutamine and 5.093x10^-5M for levosimendan. The pD2 value was found to be 5.2±0.4 for levosimendan and 4.3±0.2 for dobutamine.

Conclusion: Levosimendan and dobutamine molecules in vitro rat aortic rings have similar vasorelaxant effects.