Effect of benserazide on the levels of pineal 5-hydroxytryptamine, melatonin synthesising enzymes and serum melatonin.

The effect of benserazide, an aromatic L-amino acid decarboxylase inhibitor, has been investigated on pineal 5-hydroxytryptamine content, melatonin synthesising enzyme activities and serum melatonin concn. Increasing doses of benserazide caused increasing reductions in the pineal content of 5-hydroxytryptamine. Dark phase serum melatonin concns were also greatly reduced. The drug abolished the diurnal rhythm of hydroxyindole-O-methyltransferase by increasing the light period activities and decreasing the night levels of this enzyme. Pineal N-acetyltransferase was unaffected. It is concluded that benserazide probably inhibits melatonin synthesis by preventing the formation of the substrate, 5-hydroxytryptamine.