Reevaluation of analytical procedures on quantitation of urinary protein in rats

In this study, the original method (Lowry method) of Lowry et al. (1951), its modified method (Lowry-TCA method) with protein precipitation by trichloroacetic acid (TCA) and the new method (BCA method) with bicinchoninic acid reaction, were reexamined as to whether these three methods were applicable to urinary protein quantitation of rats. Because of the presence of the urinary interfering substances, the quantitations in the Lowry- and BCA methods were found to be overestimated more than 3 times as large as in the Lowry-TCA method. When the urine sample was dialyzed against water and determined by the Lowry- and BCA methods, more than 24 hours were found to be needed in order to completely exclude the interfering substances from the urine. From these findings, the Lowry-TCA method is recommended for quantitation of urinary protein in rats.