Abstract

Protein has been found in urine in all relevant studies. Why are there proteins in urine? If they act as nutrients, should all proteins be reabsorbed into blood during starvation to maintain homeostasis of internal environment? Are they toxic? If they are toxic or are discarded for regulation of body's own cellular functions, they still must be released into urine even after starvation. Does kidney need proteins to maintain urine flow? If proteins are necessary to maintain urine flow, at least some of them should remain in urine after starvation. In this study, five Sprague Dawley rats were starved continuously for 7 days. The quantity, composition, and posttranslational modification of the urine proteome was studied before and after starvation. After 7-day starvation, urinary protein concentration had no significant changes, even though serum protein concentration decreased for about 10%. Only five and thirteen urinary proteins were significantly changed in the 4- and 7-day starvation groups respectively, compared with before starvation group. These findings indicate there were still proteins even after starvation which supports those urinary proteins may be necessary for kidney to maintain urine flow or be toxic and discarded for the regulation of cellular functions. It seems that removing proteins in urine is important for the survival of the animals.

Keywords

uinary proteins, homeostasis, toxic, kidney, medical sciences, glucose, lipid, starvation, posttranslational, proteins, kidney, concentration, starvation, cellular