High protein diets stimulate albumin synthesis at the site of albumin mRNA transcription.

High dietary protein intake directly stimulates albumin synthesis ald albuminuria in rats with Heymann nephritis. Increased albumin synthetic rate might be due to the presence of increased amino acids available for protein synthesis causing more efficient translation of preformed albumin mRNA, or instead might be linked to increased steady state albumin mRNA levels in the liver. Albumin synthesis, hepatic albumin mRNA content, and albumin mRNA relative to beta actin mRNA (as an internal control) (Alb/beta Act), were measured in rats with Heymann nephritis fed either 8.5% protein (LP), or after protein intake was increased to 40% for 4 days (HP). enalapril (E) was used to modulate the proteinuric effect of HP, yielding four experimental groups, LPN (8.5% protein nephrotic, no enalapril), LPE (8.5% protein, enalapril treated), HPN (40% protein nephrotic, no enalapril), and HPE (40% protein, enalapril treated). Dietary protein augmentation increased the rate of albumin synthesis, steady-state albumin mRNA levels, and Alb/beta Act in both HPN and HPE, compared to either LPH or LPE, even though serum albumin concentration was greater in HPE than in either of the groups fed LP. Both albumin mRNA and Alb/beta Act correlated with the rate of albumin synthesis (r = 0.531, P less than 0.05; and 0.553, P less than 0.01 respectively). Nuclear run-on assays were performed using nuclei isolated from the livers of LPN or HPN to determine whether increased albumin mRNA resulted from an increase in the rate of albumin mRNA transcription.(ABSTRACT TRUNCATED AT 250 WORDS)