Conjugated catecholamines and their measurement: some pharmacokinetic aspects

Comparison of the methods of determination of conjugated catecholamines shows that, despite their variable absolute values, the relative proportions of the free and conjugated dopamine, norepinephrine and epinephrine are close (mean of 97.3% of dopamine, 73% of norepinephrine and 84% of epinephrine being conjugated) and these proportions remain similar whether acid or sulphatase hydrolysis is used. Thus, the variability is due rather to the methods of catecholamine determination than to the mode of hydrolysis of conjugated catecholamines. The measurement of dopamine sulphate, which is preferable to non-specific measurements, is a useful tool in detecting individual differences of sulpho-conjugation in subjects who sulphoconjugate dopamine with a delay and are thus more prone to experience, prior to dopamine sulphoconjugation, cardiovascular and other actions of dopamine not seen in subjects who sulphoconjugate dopamine immediately.