of age were significantly higher than those observed 

 on the other experimental diets. Exceedingly high 

 values were observed for rats 300 to 400 days of 

 age. Elevated serum cholesterol values were seen 

 before there was evidence of kidney damage, and 

 showed no relation to the amount of liver fat. 

 The addition of cholesterol to the SPE diet already 

 high in cholesterol appeared to exert little influ- 

 ence on the serum level of this sterol, indicating 

 that a saturation level had been reached with 

 the diet containing 25 percent egg. Dietary 

 cholesterol alone was not responsible for the high 

 serum cholesterol levels in SPE rats; the values 

 for rats fed the exceedingly high cholesterol- 

 containing diet YlOO were significantly lower than 

 those with SPE diet. In the levels fed, there 

 was no evidence that supplementation with 

 choline, vitamin B 6 , vitamin Bi 2 , or ascorbic 

 acid exerted a significant influence on the cholesterol 

 levels found in moribund rats fed SPE diet. A 

 serum cholesterol level of 160 mg./lOO ml. appeared 

 to be the upper limit for serum levels associated 

 with normal kidneys in stock or SP 8 HVO rats; 

 the upper limit for rats fed SPE diet was 250 

 mg./lOO ml. 



Serum protein components 



Rats maintaining weight on stock, SP 8 

 HVO, and SPE diets. — In table 71 are sum- 

 marized data from electrophoretic analysis of 

 blood serum from rats maintaining weight on 

 stock, SP 8 HVO, and SPE diets. The data 

 reported are for fasted rats. The results are 

 reported as percentage of total protein; no data 

 were available for total serum protein. Values 

 for albumin and alphaj globulin have been com- 

 bined because of difficulty encountered in obtain- 

 ing a clear-cut separation of these components 

 for some of the serum samples analyzed. The 

 presence of one or more components with an 

 electrophoretic mobility faster than that of 

 albumin (PA) was of particular interest. Because 

 of the influence of this prealbumin component 

 on the relative percentage of the other serum 

 proteins, data for serum samples with no PA 

 present are reported separately from those with 



The usual serum protein components with a 

 normal distribution were found in the serum of 

 rats less than 300 days old that were maintaining 

 their weight on the stock diet. In rats over 300 

 days of age, serum proteins contained smaller 

 concentrations of albumin and alphas globulin 

 and higher concentrations of the other components 

 than those in the younger rats. In some rats 

 small amounts of a fast-moving component were 

 found, generally represented by a diffuse band 

 rather than by a clear-cut peak or peaks. The 

 highest value observed for this fast-moving 

 component was 2.4 percent of the total serum 

 proteins. 

 _ The results with SP 8 HVO diet were in general 

 similar to those with stock diet except for the 



83 



greater proportion of rats with PA in their sera. 

 This component was present in the sera from 

 some of the rats that were less than 300 days old, 

 and was found in 67 percent of the animals more 

 than 300 days old. Some relatively high con- 

 centrations of this component were found in sera 

 from the oldest group of rats. The relative con- 

 centration of alpha 2 globulin also tended to in- 

 crease with age. 



On SPE diet, the fast-moving component was 

 present at all ages, generally showing a more 

 distinct separation, and evidence of more than 

 one fast-moving component was frequently ob- 

 tained. Between 300 and 400 days, the propor- 

 tion of animals with sera containing PA was large 

 and the amounts of PA tended to be high. This 

 component was absent from all but one of the 

 sera from rats 400 to 499 days old but again was 

 seen in a high percentage of the rats 500 days old. 

 The significance of this decrease in PA in the 

 400- to 499-day-old group was not apparent but 

 may be related to the ability of these rats to 

 survive the critical 300- to 399-day period. The 

 relative concentration of the other protein com- 

 ponents varied and showed no consistent trend 

 with age. The concentration of gamma globulin 

 in the sera of SPE rats tended to be low whether 

 or not PA was present. 



Rats losing weight on stock, SP 8 HVO, and 

 SPE diets. — In table 72 are summarized data for 

 rats that were losing weight on these same diets. 

 The data available for moribund or sick rats fed 

 stock diet were limited in number and were for 

 older rats. Except for a higher concentration of 

 PA, the results were similar to those obtained for 

 rats of comparable age that were maintaining 

 weight on this diet. 



The relative concentration of albumin and 

 alphai globulin tended to be lower in rats that 

 were losing weight than in those maintaining 

 weight on SP 8 HVO diet, and difficulty was 

 encountered, in the older rats, in obtaining a 

 separation of these components from alpha 2 globu- 

 lin. PA was absent from the sera of rats under 

 300 days old and was low when present in the 

 sera of rats over 600 days of age. Of interest was 

 the exceedingly high PA value of 41.8 percent in 

 one rat with a liver tumor. This value has been 

 excluded from the results in table 72. 



On SPE diet, large amounts of PA were found 

 in the sera of moribund rats of all age groups 300 

 days and over, including the 400- to 499-day-old 

 animals. There were too few data to assess 

 accurately the influence of the extent of weight 

 loss on the serum proteins, but it may be of 

 significance that the three rats over 300 days old 

 showing no PA had all lost over 100 grams. 



Serum cholesterol, kidney size, and damage 

 in relation to PA. — In table 73 are summarized 

 data on cholesterol levels and kidney size and dam- 

 age as related to increasing amounts of the fast- 

 moving component in the sera of rats fed SP 8 

 HVO and SPE diets. On SP 8 HVO diet, when 



