[Sex differentiated protein pattern in the urine of the rat following castration]

Protein excretion and protein fractions according to their molecular weight (SDS polyacrylamide-gelectrophoresis) were studied in the urine of male and female rats before and after castration. The polyacrylamide-gels were investigated qualitatively as well as quantitatively by densitometry. Male rats excrete considerably more protein in the urine than female rats. The values for the absolute protein quantity in 24-h-urine and the relative proteinuria (mg protein per 24 h and 100 g body weight) are five and three times higher, respectively, in males than in females. After castration proteinuria decreases significantly in both sexes, in males, however, more considerably (by about 75%) than in females (by about 30%), so that there is no significant difference in relative proteinuria between castrated males and females. The electrophoresis method used in this study allows to distinguish at least 10 to 11 protein fractions in the total urinary protein of both sexes within a molecular weight range from about 94.000 d to 14.000 d. Low molecular weight proteins (about 31.000 d to about 14.000 d) represent in both sexes the main part of the urinary protein. Females, however, excrete relatively more high molecular weight proteins (about 94.000 d to 60.000 d; about 25% of total urinary protein) than males (about 15% of total urinary protein). Concerning the relative parts in total urinary protein there are sex differences in all protein fractions, especially, however, in the fraction with a molecular weight of about 19.000 d (males more than 50%, females about 17% of total urinary protein). Castration causes in males more distinct changes in the relative parts of protein fractions in total urinary protein (drastic decrease of the 19.000-d-fraction) than in females. The results can be interpreted among other things in connection with a sex different handling of proteins in the proximal tubule of the rat kidney. The lysosomal catabolism of proteins in the proximal tubule is probably lower in males than in females, thus contributing to a higher proteinuria and a higher excretion especially of low molecular weight proteins in males in comparison with females.