Effect of L-dopa administration on islet monoamine oxidase activity and glucose-induced insulin release in the mouse

Pancreas. 1991 Sep;6(5):522-7. doi: 10.1097/00006676-199109000-00004.


Previous studies have shown that the amine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) is rapidly converted to its corresponding amine, dopamine, in islet beta-cells. In the present investigation, we studied the effect of acute L-DOPA administration on islet monoamine oxidase (MAO) activity and on glucose-induced insulin secretory response in mice. It was observed that at 2 min after intravenous L-DOPA administration, there was a marked increase (+35%) in islet MAO activity, with serotonin as substrate. At 7 min, MAO activity towards dopamine was enhanced by 32% and that towards serotonin and phenylethylamine (PEA) was decreased by 23 and 25%, respectively. The inhibitor of L-aromatic amino acid decarboxylase, benserazide, abolished L-DOPA-induced changes of MAO activity, suggesting that the formed dopamine, and not L-DOPA itself, was responsible for the observed effects. At 60 min, no effect by L-DOPA administration on islet MAO activity was noticed. L-DOPA (125 or 250 mumol/kg), given together with glucose, induced a decrease in glucose-induced insulin response. L-DOPA (125 mumol/kg), given 7 min before glucose, totally suppressed glucose-induced insulin response. This inhibition was eliminated through pretreatment with benserazide. Enhancement of glucose-stimulated insulin response, after deposition of horseradish peroxidase (HRP) in beta-cell vacuolar system, was suppressed by L-DOPA. We conclude that acute L-DOPA-induced dopamine accumulation in pancreatic islets is accompanied by rapid changes in MAO activity, concomitant with an inhibitory effect on glucose-stimulated insulin response. Increased hydrogen peroxide production, following increased MAO activity, may possibly augment the inhibitory effect of dopamine accumulation on insulin release.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Benserazide / pharmacology
  • Female
  • Glucose / pharmacology*
  • Injections, Intravenous
  • Insulin / metabolism*
  • Islets of Langerhans / enzymology*
  • Islets of Langerhans / metabolism
  • Levodopa / administration & dosage
  • Levodopa / pharmacology*
  • Mice
  • Monoamine Oxidase / metabolism*
  • Pancreas / drug effects
  • Pancreas / enzymology
  • Pancreas / metabolism


  • Insulin
  • Levodopa
  • Benserazide
  • Monoamine Oxidase
  • Glucose