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Comparative effect of proteins, peptides, and amino acid mixtures on recovery from 70% hepatectomy in rats.

The effects of proteins, peptides, and amino acid mixtures on the recovery from 70% hepatectomy were compared in rats. In Experiment 1, the most suitable time for the comparison was studied. Rats weighing 250 g after 70% hepatectomy were fed 20% casein diet. On day 0,1,2,3,4,6,8,11,15 post-operation, 3-5 rats were killed for the observation of recovery. The recovery time, evaluated by daily food intake, body weight gain, liver weight and compositions, and hematologic values was about 10 days. For the comparison of different nitrogen sources, we estimated that the 6th day after the operation when the animals did not fully recover was suitable. In Experiment 2, rats of each group after hepatectomy were fed one of 14 experimental diets containing protein (3 types), peptides (8 types), or amino acid mixture (3 types) for 5 days and killed on the 6th day after the operation. Daily food intake, body weight gain, liver weight and compositions, and hematologic values were measured and pathological examination was also done. The effect of different nitrogen sources were similar on the recovery after 70% hepatectomy with only a few minor exceptions in rats.

3. Liver recovery-On the day of operation, resected liver was weighed (E) . Total liver weight (F) on the day of operation was calculated as 1 .54E. On the 6th day, rats were killed and the liver was weighed (G). The liver recovery was G/F. Statistical analysis: Statistical analysis was done by Student's t-test and Duncan's multiple-range test.
Results. Experiment 1: Table 2 shows the time course of body weight , liver weight, food intake before and after the hepatectomy. Body weight decreased about 45g during the 2 starved days. After the operation, rats' body weight increased as the rate of 10g/day. Before operation, average liver weight was 11 .33 g. After 24h of fast, it became 7.89g. By the operation it became 2.73g, however, it increased to 3.41g in spite of 24h fast. After the operation liver weight increased to 9.39g (about 2g/day) linearly by the 4th day. Then the increasing rate fell to 0 .5 g/day. On day 15 post-operation, liver weight was 14.51g. Food intake increased from 12 to 24g during the first 4days, and remained constant at about 24g throughout the experiment. Table 3 shows the changes in liver composition and hematological values. The percentage of water of liver before operation was 71.5%. It fell to 69.1 and 66.5% on the 1st and 2nd day by fasting and operation. It increased to 73.8% rapidly the next day by the feeding, and maintained at the pre-operation level . Liver protein level rather increased by fasting but decreased 2-4 days after the operation and returned to the pre-operation level on the 8th day. After fasting, liver glycogen reduced to almost zero. It increased slowly and returned to pre-operation level at the 11th day.
Blood sugar reduced from 113 to 57mg/dl by fasting and operation. When feeding was commenced it reverted to the original level on the 11th day after operation. Total protein decreased gradually after the operation until the 4th day . Albumin remained constant (3-4g/dl) throughout the experimental period. GOT and GPT rose from 79 to 199IU, 21 to 77IU, respectively , by the operation. They returned to 69 and 32IU on the 6th day.
Experiment 2: Table 4 shows body weight, food intake, food efficiency ratio (FER), and liver recovery. Growth and FER of casein pep-1 group were lower as compared to those of casein pep-2 and casein amino acid mixture groups . However, all the other diets showed the similar results with a few minor exceptions . Table 5 shows the composition of liver and hematological values . Liver water level was similar in all the groups in each experiment except it was lower in caseinn amino acid group than in others in Experiment 2-C. Protein values were also similar in all the groups; however, the value in the SP group was a little lower than those of the other groups. Liver glycogen and all the hematological values were not significantly different among the dietary groups, except a few minor differences .
Discussion. The recovery of rats after hepatectomy has to be decided from various points. The important indicators are liver weight , body weight, liver glycogen (19), blood glucose (20,21), serum albumin (22,23), GOT, and GPT. The recovery-times to the pre-operation levels were 6days for body weight , GOT, CHAN et al. Table 3. Composition of liver and hematological values (Experiment 1).  and GPT, and 11days for liver weight, liver glycogen, and blood glucose, respectively. Other indicators such as liver water and protein, serum total protein and albumin were rather similar to the pre-operation levels throughout the experi mental period. Therefore we inferred that 10days seemed appropriate for the rats to recover from such stress. The comparative effects of the various diets may be evident during the period of recovery, as the indicators tend to be similar among the dietary groups after total recovery. The recovery ratios on the 6th day post-operation against the pre operation levels were 103% for body weight, 95% for liver weight, 95% for liver protein, 70% for liver glycogen, 115% for serum total protein, 68% for blood glucose, 88% for GOT, and 100% for GPT. From these results of Experiment 1, we estimated the 6th day after the stress to be suitable for the comparison of the recovery among various dietary groups in Experiment 2.
Although many researchers have reported the superiority of peptides to amino acid mixture or proteins in normal and under surgical stress, especially stress of digestive organs, in animals and men, we could not observe such benefit of peptides in our studies (3). In the present experiment we studied 3 types of proteins, 3types of amino acid mixtures, and 8types of peptides produced from these proteins by enzymatic hydrolysis but could not observe any superiority of peptides to protein and amino acids on the recovery of rats from 70% hepatectomy. On the contrary, one of the peptides produced from casein (casein pep-1) was rather inferior to amino acid mixture in the growth and food efficiency ratio. We did histological examination (data not shown) but no difference was observed among the different CHAN et al. nitrogen sources.
Therefore we are inclined to disagree with other workers regarding effective utilization of peptides in comparison to amino acid mixtures and proteins.
From these reports, we may be able to conclude that some specific peptides may be superior to amino acid mixtures or proteins but, in general, relative nutritional value of peptides is similar to other form of nitrogen. Therefore the superiority of peptides should not be claimed without careful evaluations.