EFFECTS OF AGE, PHENOBARBITAL, BETA-NAPHTHOFLAVONE AND DEXAMETHASONE ON RAT HEPATIC DELTA-AMINOLEVULINIC-ACID SYNTHASE

delta-Aminolevulinic acid synthase is a key enzyme leading to the synt hesis of cytochrome P-450, a compound of the mixed function oxidase sy stem. Because of this, we have studied the effects of both age and thr ee typical mixed function oxidase system inducers on this enzyme activ ity in male Wistar rats. Our results suggest that delta-aminolevulinic acid synthase activity in intact rats increases up to maturity and th en decreases being, however, higher in the oldest animals than in the youngest. Phenobarbital affects delta-aminolevulinic acid synthase act ivity very characteristically. This activity is high in 4-week-old ani mals and then increases slightly until the twelfth month of life. Phen obarbital enzymic inducibility tends to decrease with age. In the beta -naphthoflavone groups, the profile of delta-aminolevulinic acid synth ase activity looks like that in the control ones. Generally, beta-naph thoflavone is a weaker delta-aminolevulinic acid synthase inducer than phenobarbital, but it seems to induce delta-aminolevulinic acid synth ase like dexamethasone, which, being a physiological inducer of the mi xed function oxidase system, is also an inducer of delta-aminolevulini c acid synthase and this inducibility is closely connected with age.