L-dihydroxyphenylalanine: effect on S-adenosylmethionine in brain.

Forty-five minutes after intraperitoneal injection of a single dose (100 milligrams per kilogram) of L-dihydroxyphenylalanine, the concentration of S-adenosylmethionine in rat brain was lowered by 76 percent. As little as 10 milligrams of L-dihydroxyphenylalanine per kilogram decreased content of S-adenosylmethionine in the adrenal medulla by 51 percent, whereas 100 milligrams per kilogram did not significantly depress concentration of S-adenosylmethionine in the liver in this time interval. Concentration of S-adenosylmethionine in the brain varied diurnally; L-dihydroxyphenylalanine lowered this concentration whether administered at the daily peak or at the nadir.