Developmental Characteristics of Phenylethanolamine and Octopamine in the Rat Brain

Phenylethanolamine and octopamine have been detected in the developing rat brain. Maximum concentration of these amines occurs early in development (16‐17 days of gestation). At this developmental stage, the brain concentration of these amines is higher than that of norepinephrine. There is a sharp decline in the phenylethanolamine and octopamine concentrations on day 18 of gestation to approximately those of the adult. This decrease coincides with an increase in‐monoamine oxidase activity of fetal brain, with an increase in the activities of tyrosine hydroxylase and dopamine‐β‐hydroxylase, and with the appearance of a saturable active uptake mechanism for norepinephrine. The administration of iproniazid, a monoamine oxidase inhibitor, to pregnant rats produced an increase in phenylethanolamine, octopamine and norepinephrine concentrations in the fetal rat brain at 16 days of gestation. p‐Chlorophenylalanine, an inhibitor of phenylalanine hydroxylase, decreased fetal brain norepinephrine; this drug increased brain levels of phenylethanolamine and octopamine. The combined administration of iproniazid, p‐chlorophenylalanine and phenylalanine to pregnant rats resulted in increased concentrations of octopamine and in a several‐fold increase of phenylethanolamine levels; norepinephrine concentrations were sharply reduced. The possible significance of these findings in relation to pathological conditions such as phenylketonuria is discussed.