Effect of uremic plasma on mouse liver delta-aminolevulinic acid synthetase activity

delta-Aminolevulinic acid (delta-ALA) synthetase in mouse liver homogenate was significantly (p less than 0.001) higher in the presence of uremic compared with normal plasma, the ratio of the two values being 1.36 +/- 0.24 in 30 paired experiments. This effect does not seem to be due to increased concentrations of urea or creatinine nor to any possible dialyzable substances. Its relationship to the retention of an inducing factor or decreased production of erythropoietin in uremic patients is discussed. A possible inhibitory effect of erythropoietin on liver delta-ALA synthetase is suggested.