Organ and species differences in microsomal activation of methyldopa.

The covalent binding of 3H-methyldopa to microsomal protein in the presence of NADHP and oxygen was studied in various microsomal preparations. Rat and mouse liver microsomes showed high binding, hamster and guinea pig liver microsomes gave intermediate values, whereas no binding was seen with rabbit liver microsomes. No activation of methyldopa was detected with kidney microsomes. Lung microsomes from rats, guinea pigs, and rabbits were quite active with respect to methyldopa binding, and the reactions were totally blocked by superoxide dismutase. There was no sex difference in the binding of methyldopa in liver microsomes from adult rats. No methyldopa activation could be detected in fetal liver microsomes, whereas a rapid increase in activity to above adult levels occurred during the first 2 days after birth.