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Liver uroporphyrinogen synthetase activity was measured in 45 mice, divided in three groups. The mice of the 1st group served as controls, those of the 2nd starved for 24 hours, while those of the 3rd were injected intraperitoneally with phenobarbital. The enzymic activity was found significantly (p less than 0.001) lower in the animals of the 2nd group (17.49 +/- 2.25 nmol/g/h) and higher in those of the 3rd (25.82 +/- 3.73 nmol/g/h) as compared to the controls (20.89 +/- 2.11 nmol/g/h). If these effects also exist in the human it could be suggested that starvation may be doubly harmful for the patients with acute intermittent porphyria by aggravating both their enzymic disorders. On the contrary, in the case of phenobarbital its undesired effect on porphyria may be moderated by a simultaneous induction of the uroporphyrinogen synthetase.

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.