Background: Cyclosporine A has been shown to detrimentally affect post-transplantation vascular tone. Tacrolimus (FK506), an immunosuppressant whose mechanism of action is similar to that of cyclosporine A, is
more potent in vitro and has a reportedly high level of safety. The effects of tacrolimus on hepatic vasculature and metabolism in isolated, dually perfused (through both the hepatic artery and porta) rat liver under normal conditions and again in association with a state of hypoperfusion followed
by reperfusion, imitating the liver’s clinical state during organ transplant, were investigated.
Material/Methods: Three groups were perfused normally with Krebs-Henseleit solution and three groups were hypoperfused (75% fl ow reduction) for two hours. Saline, tacrolimus 4 ng/ml, or tacrolimus 40 ng/ml was injected in three normally perfused and three hypoperfused liver groups to determine drug
effects under normal conditions and in low-fl ow-refl ow state. Non-radioactive microspheres were later administered to all livers via the artery to assess microcirculatory patency.
Results: Tacrolimus did not affect the normally perfused livers. Liver hypoperfusion without treatment (saline injection) caused wet-dry weight ratio increase, abnormal increases in hepatic artery pressure and resistance values, and non-physiologically low oxygen extraction during reperfusion.
Hypoperfusion + tacrolimus 4 or 40 ng/ml yielded values closer to those of the normally perfused livers. Finally, more microspheres were trapped in the hypoperfused+saline-treated liver circulation than in the normally perfused or hypoperfused+tacrolimus 4 or 40 ng/ml livers.
Conclusions: Tacrolimus appears to be nontoxic in the isolated liver and to mitigate microcirculatory derangement associated with low-fl ow-refl ow states.

Keywords: Immunosuppressive Agents - pharmacology, Liver - physiopathology, Liver Transplantation, Perfusion, Reperfusion Injury - prevention & control, Tacrolimus - pharmacology