The effect of yohimbine on the turnover of brain catecholamines and serotonin.

Yohimbine moderately increased the depletion of brain dopamine (DA) after alpha-methyl-p-tyrosine (AMT) only when the two drugs were given at the same time; the baseline concentration of brain homovanillic acid (HVA) and its accumulation after probenecid were strongly increased by yohimbine. Yohimbine markedly decreased the concentration of brain noradrenaline (NA), both when given alone and before or at the same time as AMT; when it was given at an increasing interval after AMT, the effect became progressively smaller. The baseline concentration of brain 3-methyoxy-4-hydroxyphenylethyleneglycol sulphate and its accumulation after probenecid were increased by yohimbine; this effect was not as marked as that on HVA and was proportional to the quantity of NA depleted in the Amt method. The accumulation of brain k-hydroxyindoleacetic acid after probenecid was decreased by yohimbine pretreatment.