Maintenance of the functional state of isolated rat liver by hypothermic perfusion with an erythrocyte-free medium.

Isolated rat liver was studied before, during, and after hypothermic perfusion at 5 C for 24, 48, or 72 hr with an acellular perfusate consisting of 7% bovine serum albumin in Kreb-Ringer buffer containing glucose, penicillin, and streptomycin. Bile production ceased at 5 C but resumed when the temperature was raised to 35 C. The rate of flow and the total amount produced was unaffected by 24 hr of hypothermia but decreased when the cooling period was extended to 48 and 72 hr. The data of other workers was used to show a correlation between bile flow and oxygen consumption by the liver. Cooling also caused the release of potassium into the perfusate but it was quickly reaccumulated after rewarming; however, the extent and rate of reaccumulation decreased as the cooling period increased, as did the ability of the livers to retain the ion. Urea synthesis did not cease after cooling and after rewarming, the rate of synthesis increased as the period of hypothermia was lengthened. The maximum concentration of urea in the perfusate was found when rewarmed livers had produced 200 mumol of urea but at this point, control livers had produced 280 mumol. The concentration of glucose in the perfusate of livers maintained at 35 C showed peaks at 2 and 9 to 10 hr after the start of perfusion. After cooling for 24 hr these peaks arose at 2 and 7 hr after rewarming, but with 48 hr of hypothermia, these peaks were higher and appeared at 2 and 4 hr. When the cooling period was extended to 72 hr, only a single peak was seen 2 hr after rewarming. These results suggest that rat liver can be cooled to 5 C for 24 hr with little effect on its functional characteristics but a marked decline becomes apparent when the cooling period is extended beyond 24 hr. None of the livers studied was transplanted after perfusion and it remains to be seen how the functional tests conducted in vitro correlate with the ability of the livers to support life.