Mechanisms for defects in muscle protein metabolism in rats with chronic uremia. Influence of metabolic acidosis.

Chronic renal failure (CRF) is associated with metabolic acidosis and abnormal muscle protein metabolism. As we have shown that acidosis by itself stimulates muscle protein degradation by a glucocorticoid-dependent mechanism, we assessed the contribution of acidosis to changes in muscle protein turnover in CRF. A stable model of uremia was achieved in partially nephrectomized rats (plasma urea nitrogen, 100-120 mg/dl, blood bicarbonate less than 21 meq/liter). CRF rats excreted 22% more nitrogen than pair-fed controls (P less than 0.005), so muscle protein synthesis and degradation were measured in perfused hindquarters. CRF rats had a 90% increase in net protein degradation (P less than 0.001); this was corrected by dietary bicarbonate. Correction of acidosis did not reduce the elevated corticosterone excretion rate of CRF rats, nor did it improve a second defect in muscle protein turnover, a 34% lower rate of insulin-stimulated protein synthesis. Thus, abnormal nitrogen production in CRF is due to accelerated muscle proteolysis caused by acidosis and an acidosis-independent inhibition of insulin-stimulated muscle protein synthesis.