VPT 321: Veterinary Neuropharmacology (2+1) copy 1

DRUGS THAT AFFECT NORADRENALINE SYNTHESIS

• α - methyl-p- tyrosine: (Metyrosine) It is a structural analogue of tyrosine. On administration it is taken up by the adrenergic neurons and adrenal medulla where it blocks the enzyme tyrosine hydroxylase. This results in failure of synthesis of noradrenaline, adrenaline and dopamine.
• Carbidopa: It is a dopa derivative that inhibits dopa-decarboxylase enzyme peripherally. Central dopamine synthesis is unaffected as it cannot cross blood brain barrier.
• α-methyl dopa
  • It is an analogue of l-dopa, the precursor of dopamine and noradrenaline.
  • α-methyl dopa is taken up by adrenergic neurons, mainly CNS, where it is decarboxylated and then dehydroxylated to from α-methyl noradrenaline is a potent α₂- receptor agonist and thus inhibits sympathetic discharge from the brain, which in turn causes peripheral vasodilation and reduction of total peripheral resistance.
  • It indirectly also causes reduced synthesis of true transmitter i.e., noradrenaline.