Effect of hypoxia on tyrosine and tryptophan hydroxylation in unanaesthetized rat brain

Abstract

T he T yrosine and tryptophan hydroxylase enzymes have been proposed as rate‐limiting steps in the biosynthesis of catecholamines and 5‐hydroxytryptamine (5‐HT), respectively; thus under normal physiological conditions the rate of amine synthesis appears to be controlled by the activity of these hydroxylase enzymes (see U denfriend , 1966; L ovenberg , J equier and S joerdsma , 1968). Subtle changes in neuronal activity may result not in changes in the levels of the amine neurotransmitters, but rather in alteration in their production and metabolism without measurable change in their levels. Previous studies of the effect of hypoxia on monoamines have dealt with amine levels, but there have been no studies of the effect of lowered oxygen on the synthesis of these substances.