DEVELOPMENTAL-CHANGES IN MONOAMINE-OXIDASE ACTIVITY TOWARDS SEROTONININ CHICK HEART AND LIVER

We have analysed quantitative changes and properties of monoamine oxid ase (MAO) activity against serotonin in heart and liver of chick embry os starting from E6 until hatching (E21). All determinations were carr ied out in the presence of semicarbazide to eliminate any activity due to semicarbazide-sensitive amine oxidase. Starting from E6 serotonin was actively deaminated in both organs. Expressing MAO activity as eit her pmoles of product/mg protein or as pmoles of product/mg tissue, pe ak activity in the heart was observed at E18 and in the liver at E10. In the liver a second activity peak was observed at E21, but only when the activity was expressed as pmoles of product/mg tissue. K-m value from embryonic heart remained constant,while V-max value was higher at E18. K-m value from embryonic liver decreased significantly after E10 and V-max value showed a peak at E10. Values of kinetic parameters su ggested that in the heart at E18 and in the Liver at E10 there was an increase in the number of molecules of enzyme. The inhibition curves o btained by testing various concentrations of clorgyline and deprenyl i ndicated that both in the heart and liver from the various embryonic s tages serotonin, at least under the experimental conditions used, is m ainly degraded by MAO A. MAO activity against serotonin was analized a lso in heart and liver from young adults aged three months acid the re sults were compared with those obtained for embryos.