Abstract

The accumulation of H-catecholamines in brain was measured in rats given i. p. H³-tyrosine (H³-TYR). In animals injected at the same time of day, brain H³-TYR reached a peak within 10 minutes of injection and remained at this level for at least 120 minutes. Brain H³-catecholamine content was highest 60 minutes after injection. However, H³-catecholamine content corrected for the specific activity of H³-TYR during the accumulation period attained its peak within 10 minutes of the injection and remained at this level for the next two hours; this suggests that the newly synthesized catecholamine equilibrates rapidly with one of several brain pools. Animals maintained under light for 12 hr/day received H³-TYR at the middle or end of the daily light or dark period and were killed after 3 or 60 minutes. The accumulation of H³-catecholamine was significantly higher in the middle of the light period than in the dark period when correction was made for fluctuations in the specific activity of tyrosine.