Introduction: In the field of organ preservation, various solutions exist according to the composition of electrolytes, buffers  antioxydants and energy precursors. Insulin was recommended and added to University of Wisconsin preservation solution with the aim of stimulating glycolysis during preservation (1). Nevertheless, previous studies have shown that insulin exacerbates the ischemic injury in rat liver transplantation (2,3).  The value of insulin in preservation solution therefore remains unclear. The aim of this study was to determined the effect of insulin at two concentrations on preservation of an ex vivo glucose-free perfused rat liver. 
Materials and methods:  After University Animal Care Committee approval, female Wistar rats were fasted for 16 hours. After they were anesthetized, the portal vein was cannulated, the liver removed and perfused at a flow rate of 5 ml/min in a closed ex vivo system with HBSS supplemented with HEPES and O2.  The animals were divided into three groups (n = 5 in each group): control group; insulin groups in which livers were perfused with HBSS medium containing respectively 35 or 70 IU/L.   The experiment consists of perfusion for 135 min.  Glucose, lactate, potassium, and enzymes were analyzed in perfusate samples at different time-points. The proportion of glycogen in hepatocytes and energy charge (EC= [ATP]+1:2[ADP]/ [ATP]+[ADP]+[AMP])  were  determined in tissue biopsies at 0 and 135 min.  Mean  SD.  ANOVA  and Chi 2 tests. 
Results: Variables at 135 min are displayed in Table 1.  The concentrations of potassium and enzymes were lower in both insulin groups (P < 0.01).  
Variable 	Control	Insulin 35 IU/L	Insulin 70I U/L	P-value
Glucose (mg/dl)	7.50 ± 1.91	11.20 ± 7.33	25.40 ± 18.09	0.092
Lactate (mmol/L)	0.38 ± 0.17	0.46 ± 0.19	1.06 ± 0.96	0.14
Potassium (mEq/L)	8.88 ± 1.34	8.28 ± 0.57	5.38 ± 1.31	<0.001
GOT (IU/L)	687.75 ± 787.02	324.80 ± 234.69	57.00 ± 51.49	0.007
GPT (UI/L)	413.75 ± 354.37	219.60 ± 213.81	23.60 ± 39.35	0.002
LDH (UI/L)	4,065.3 ± 4533.1	2,421.8 ± 1839.6	277.80 ± 290.87	0.004
Glycogène (%)	7.58 ± 1.43	10.47 ± 4.77	21.22 ± 27.80	0.19
Energetic charge	0.10 ± 0.04	0.15 ± 0.04	0.17 ± 0.08	0.69

Discussion: Results of the present experiment show that insulin minimizes rat liver injury during ex vivo perfusion. In essence, insulin accelerates glycolysis, a source of ATP, and simulates glycogen synthesis (1). We observed a dose-effect of insulin on the release of potassium and enzymes, as well as for metabolic variables. In the present experimental conditions, we observed a slight but not significant increased in EC and glycogen concentration in hepatocytes. Such findings seem to indicate that livers perfused with insulin in a glucose-free buffer solution were metabolically more active at the end of the preservation period. 
References : 1. Biguzas et al. Transplantation 1990;49:1051-5; 2. Yu et al Transplantation 1990;49:1060-6; 3.  Li et al. Transplantation 2003;76:44-9.

Insulin minimises cell injury in an ex vivo perfused rat liver model