Age-Dependent Changes in the Excretion of Urinary Proteins by the Rat

Abstract

The excretion of total urinary proteins (TUP) of rats beginning at weaning and extending to 12 mo. of age was correlated with the output of the sex-dependent .alpha.2u-globulin and albumin. At puberty, 40 days of age, the excretion of TUP corresponded to the output of .alpha.2u-globulin. At this age, .alpha.2u represented 30% of the total while albumin less than 10%. From 100-200 days of age, TUP remained constant while the excretion of albumin steadily increased. After 150-180 days of age, the concentrations of .alpha.2u and albumin in TUP were approximately equal. Thereafter, the excretion of albumin and TUP increased markedly whereas .alpha.2u excretion remained constant. At 373 days of age, albumin represented over 50-60% of the TUP while .alpha.2u was only 6-7%. Female rats which excrete little or no .alpha.2u exhibited a much lower level of proteinuria than the male during the 1st yr. Two phases of proteinuria in the male rat may exist, namely, an early physiologic or .alpha.2u-globulinuric phase and a later albuminuric phase during which increasing quantities of plasma proteins, especially albumin, are lost.