To determine whether
dietary protein restriction (LPD) causes
protein catabolism in
adriamycin nephrosis, nephrotic and control rats were paired by weight and gavage fed an 8.5%
protein diet for 3 days (protocol 1) or 12 days (protocol 2). Fasting whole body
protein turnover was then measured using a constant infusion of L-[1-14C]
leucine. After 3 days of LPD,
proteinuria decreased slightly and
body weight did not change in either group. In contrast,
leucine oxidation and urinary
urea nitrogen excretion in nephrotic rats decreased by 18% and 37%, respectively (P < or = 0.05). After 12 days of LPD,
weight loss did not differ between groups. In contrast to protocol 1,
proteinuria decreased by 45% in nephrotic rats fed LPD for 12 days, and
leucine oxidation rats increased to the level of control rats. Rates of whole body
protein synthesis (PS) and degradation (PD) did not differ between nephrotic and control rats receiving LPD for 3 or 12 days, but were significantly lower than rates measured in rats fed 22%
protein. We conclude that 1)
proteinuria stimulates
protein conservation even when
dietary protein intake is restricted; 2) the decrease in
amino acid oxidation was dependent on moderate
proteinuria, since prolonged LPD ameliorated
nephrosis and
leucine oxidation rates increased to control levels; and 3) since
weight loss and rates of whole body PS and PD in nephrotic and control animals were indistinguishable, moderate
proteinuria did not increase
protein catabolism.