Attempts to measure endogenous levels of dopa and 5-hydroxytryptophan in rat brain.

We have used previously published analytical methods of high sensitivity, developed in our laboratory, in an attempt to detect endogenous dopa and 5-hydroxytryptophan (5-HTP) in normal rat brain. In the brains of rats killed by decapitation we were unable to detect any dopa and found only a few ng/g of 5-HTP. Higher levels were found in the brains of rats killed by exposing their heads to microwaves. The levels of dopa found under these conditions varied considerably between different rat strains, and also between different experiments on the same strain, ranging between 2.5 and 13.8 ng/g. True resting levels may be lower than those observed because the procedure necessitated a short-lasting immobilization stress which increased the dopa (but not 5-HTP) levels. The 5-HTP levels were also variable and ranged between 5 and 25 ng/g. The highest levels of dopa and 5-HTP were found in the Japanese Wistar strain with spontaneous hypertension. Some analytical pitfalls are pointed out.