Using adrenal dopamine as indicator we have previously obtained evidence that 
quinpirole and several other agonists on dopamine D2-like receptors acutely 
stimulate the synthesis of adrenal catecholamines. In the present study we 
measured the effect of quinpirole and dopamine on the hydroxylation of tyrosine 
in the adrenals, using the method of DOPA (3,4-dihydroxyphenylalanine) 
accumulation following the administration of the inhibitor of aromatic L-amino 
acid decarboxylase NSD 1015 (3-hydroxybenzylhydrazyne). In view of the large 
amounts of catecholamines in the adrenal tissue samples, this necessitated a 
modification of the method for analysing DOPA. Both quinpirole and dopamine 
significantly enhanced the rate of DOPA accumulation in the adrenals, indicating 
stimulation of adrenal tyrosine hydroxylase. The effect of dopamine was blocked 
by domperidone, a dopamine D2 receptor antagonist that penetrates poorly into 
the central nervous system. Thus the effect of dopamine, which itself penetrates 
poorly into the central nervous system, was presumably mediated peripherally. 
Similarly epinine, i.e. the N-methyl derivative of dopamine, appeared to enhance 
adrenal catecholamine synthesis, as indicated by an elevated adrenal dopamine 
level. The data support the view that stimulation of peripherally located 
dopamine D2-like receptors can enhance the rate of adrenal catecholamine 
synthesis by stimulating the activity of tyrosine hydroxylase.