rats. Of the nonfasting rats approximately 375 

 days old, those fed SPE diet excreted the most 

 protein. Differences in excretion by rats fed SP 

 8 HVO, SPM, or SPB diets were small. Rats 

 fed SPPB diet tended to excrete somewhat more 

 protein, and the excretion of 3 of the 11 rats 

 exceeded 100 mg. 



Wistae rats. — Protein excretion by Wistar rats 

 was low on SP 8 HVO and SPE diets, in marked 

 contrast to the results with BHE rats. For 

 a 7-hour collection period, urinary protein aver- 

 aged 9 mg. for fasted 614-day-old Wistar rats 

 fed SPE diet. No data were available for a 

 comparable age group of BHE rats because of 

 their short survival on this diet. However, by 

 approximately 350 days, BHE rats were excreting 

 87 mg. of protein when urine was collected under 

 comparable conditions. 



Urinary protein and kidney damage. — Most 

 measurements of urinary protein were made con- 

 siderably before the age at which the animals 

 died, and provide little direct evidence to relate 

 extent of protein excretion to kidney damage or 

 age of survival. The low urinary protein from 

 rats less than 200 days old gave little indication 

 of the extent of kidney damage at death or of the 

 lifespan of the animals. The only young rat 

 (180 days) to excrete over 100 mg. of protein had 

 a 5-gram kidney when he died at the relatively 

 early age of 358 days. In rats 350 to 400 days of 

 age, urinary protein appeared to be a fairly good 

 index of kidney damage and expected survival, 

 with lifespan generally decreasing as urinary 

 protein increased. 



Discussion. — The results for BHE and Wistar 

 rats reported in this publication confirm the find- 

 ings of other investigators that some protein may 

 be excreted by animals with kidneys that appear 

 normal in all respects. Urinary protein for BHE 

 rats was considerably greater than that generally 

 reported by other investigators. Gilson (72) 

 found protein ivria to be a usual occurrence in 

 Wistar and Sprague-Dawley-Holtzman strains of 

 rats. The average excretion during fasting was 

 3.0 mg. globulin and 3.3 mg. albumin in 24 hours. 

 Particularly heavy protein precipitates were ob- 

 served in the urine of a group of animals main- 

 tained at a temperature of 4°C. for 3 months. 

 Saxton and Kimball (168) reported appreciable 

 excretion of albumin by rats over 300 days old. 

 Proteinuria was found to increase with age, 

 although there was somewhat reduced frequency 

 of protein excretion in rats over 800 days old. 

 McCay, Maynard, Sperling, and Osgood (121) 

 obtained an average daily protein excretion of 23 

 mg. for rats on a low level of dietary protein and 

 82 mg. for those on a high level. Albumin was 

 found in the urine of mature rats with normal 

 kidneys, but with chronic nephrosis increased 

 amounts were present. There appeared to be a 

 rough correlation between kidney damage and 

 increased protein excretion, although the lifespan 

 of the animals did not appear to be related to the 



latter. Rather (155) suggests that the thresh- 

 old of the kidney to protein may be due to tubu- 

 lar resorption with proteinuria occurring if tubular 

 resorption capacity is exceeded. Using rabbit 

 anti-rat kidney serum to produce nephrotic rats, 

 Drab kin and Marsh (51) observed a marked 

 increase in labeled urinary protein after injection 

 of labeled glycine into the nephrotic animals. 

 Total serum protein decreased and the albumin 

 moiety almost completely disappeared. 



Summary. — Urinary protein excretion in BHE 

 rats tended to increase with age and to be in- 

 fluenced by diet. The extent of the proteinuria 

 observed appeared to parallel the occurrence of 

 degenerative changes in the kidneys of these 

 animals. Protein excretion in the urine was con- 

 siderably greater than has generally been observed 

 and seemed to be related to the shorter lifespan of 

 these rats. 



Protein excretion by Wistar rats was generally 

 small and within the range reported by other 

 investigators. 



Liver 



Rats maintaining weight on stock, SP 8 

 HVO, and SPE diets. — In table 56 are sum- 

 marized data for protein, fat, and ash in livers of 

 rats maintaining weight on stock, SP 8 HVO, or 

 SPE diets, and included are results for per- 

 centage composition and total content. Most of 

 the results recorded are for fasted rats. Limited 

 data were obtained for nonfasted stock rats 300 

 days of age and older and for a group of young rats 

 less than 300 days old fed SPE diet. 



Age appeared to have little influence on the 

 composition of livers from rats fed stock diet when 

 the glycogen content of the livers from nonfasted 

 rats was taken into consideration. Values of 

 76.2 percent for protein, 15.8 percent for fat, and 

 5.0 percent for ash were obtained when the results 

 for nonfasted rats were calculated on a glycogen- 

 free basis. 8 The percentage of protein and of ash 

 in the livers of rats fed SP 8 HVO diet did not differ 

 with age, but the percentage of fat showed a con- 

 sistent tendency to increase. With SPE diet, 

 as with stock diet, the composition of the liver 

 appeared to be uninfluenced by the age of the ani- 

 mal. When the data for nonfasted rats fed this 

 diet were calculated to a glycogen-free basis, 8 

 values for protein, fat, and ash were 55.8, 34.1, 

 and 3.9 percent, respectively — values differing 

 greatly from those on the stock diet. 



Data comparing the content of the livers from 

 fasted and nonfasted rats were limited but seemed 

 to indicate that diet could influence the response of 

 the liver to fasting. As the result of a 17-hour 

 fasting period, the protein, fat, and ash content of 

 the livers of rats fed SP 8 HVO diet were reduced. 

 Both protein and ash content were smaller in the 



8 Assuming a liver glycogen of 8 percent on the dry- 

 weight basis using a value obtained for comparable rats 

 (unpublished data). 



68 



