Plasma free, sulfo- and glucuro-conjugated catecholamines in uremic patients

Plasma free, sulfo- and glucuro-conjugated catecholamines in uremic patients. The metabolism of catecholamines (CA) in non-selected patients with chronic renal failure and under hemodialysis (CRFh) was studied by measuring the concentration of plasma free, sulfo- and glucuroconjugated CA, dopamine (DA), norepinephrine (NE), and epinephrine (EPI). Our data demonstrate a statistically significant increase of free DA and free NE concentration in CRFh, while that of free EPI was not different from controls. However a careful scrutiny of 35 individual data suggests that sub-groups of patients with either high normal or low plasma–free NE concentration could exist; this likely heterogeneity could be a good explanation for conflicting conclusions provided by previous reports. Suspecting that conjugated CA might be altered in CRFh, plasma sulfo- and glucuro-conjugated DA, NE and EPI were also measured. We have found a predictable and highly significant increase of sulfo-conjugated CA; plasma concentration of glucuro-conjugated DA and NE in CRFh was not different from controls, while that of glucuro-conjugated EPI was significantly increased. The physiological meaning, if any, of these new observations on conjugated CA cannot be assessed at the moment. The effects of hemodialysis were also investigated. Measurements on the arterial and on the venous line showed highly significant differences for tyrosine, free and sulfo-conjugated CA, and a lack of difference for glucuro-conjugated CA. Thus tyrosine, free and sulfo-conjugated CA were eliminated by the artificial kidney, but not glucuro-conjugated amines. Furthermore, the hemodialysis–induced losses of tyrosine were about 200-fold greater than those of CA, suggesting that hemodialysis is likely to have a double series of effects on CA metabolism by reducing: a) their circulating level, and b) the amount of tyrosine available, and thus the amount of CA synthesized. Hemodialysis during a two hour period of time was associated with no change in arterial concentration of tyrosine and free CA, while that of DA sulfate and NE sulfate was significantly decreased; an interpretation is tentatively proposed