Role of monoamine oxidase-B in medroxyprogesterone acetate (17-acetoxy-6 alpha-methyl-4-pregnene-3, 20-dione) induced changes in brain dopamine levels of rats

The effect of medroxyprogesterone acetate (MPA) on brain monoamine levels and monoamine oxidase (MAO) activity was studied in adult, healthy, non-pregnant female rats. MpA was injected in a single dose of 100 mg/kg i.m. Dopamine (DA), noradrenaline (NA), 5-hydroxytryptamine (5-HT) levels and MAO activity were estimated fluorometrically in rat brian. No change in DA, NA, 5-HT or MAO activity was observed after 7 days of MPA treatment while a significant decrease in DA levels along with a significant increase in MAO activity was observed after 21 days of MPA treatment. However, there was no change in NA and 5-HT levels after 21 days of MPA administration. The selective reduction of DA by MPA could be due to an increase in MAO-B activity. MPA does not appear to increase MAO-A activity because neither of the specific substrates (NA and 5-HT) of MAO-A was found to be decreased inspite of the increase in MAO activity as estimated by the kynuramine method. These findings suggest the importance of MAO-B also in DA metabolism in rat brain.