Tryptophan hydroxylase and 5-HTP-decar☐ylase activity in cockroach brain and the effects of p-chlorophenylalanine and 3-hydroxybenzylhydrazine (NSD-1015)

Abstract

The activities of two enzymes of the serotonin biosynthetic pathway, namely tryptophan hydroxylase (TPH) and 5-hydroxytryptophan-decar☐ylase (5-HTP-D), were determined in the cockroach, Periplaneta americana, brain using radiometric techniques, significant levels of both enzymes were found, p-Chlorophenylalanine (PCPA) inhibited brain TPH activity strongly both in vitro and in vivo. In vitro, 10 mM PCPA reduced the TPH activity by 76% and in vivo either 15 μg/g or 30 μ/g of PCPA inhibited brain TPH activity by 80–85%. The activity of 5-HTP-D enzyme was inhibited significantly in vivo by 3-hydroxybenzylhydrazine, commonly known as NSD-1015. A recovery in the activity of 5-HTP-D enzyme was observed 12 h after 50 μg/g of NSD-1015 but 100 μ/g caused an inhibition lasting for the 24 h period studied.