Changes in plasma free and sulfoconjugated catecholamines during the perioperative period of cardiac surgery: effect of continuous infusion of dopamine.

In order to elucidate the pharmacological properties of the formation of sulfoconjugated catecholamines (CAs) in human plasma, we investigated the changes in the plasma levels of free and sulfoconjugated CA during the continuous infusion of dopamine (DA; 4-6 microg/kg/min for 24 h, followed by 3-4 microg/kg/min for 48 h) in patients who had undergone cardiac surgery. The plasma level of free DA increased immediately after the start of the infusion and reached a plateau within 1 h at a level of about 2000 times the basal value. In the control patients who had received non-cardiac surgery without DA infusion, plasma-free DA increased only 5-fold after their operation. The plasma level of DA sulfate increased linearly for 24 h, to 48-fold of the basal value by DA infusion, whereas it showed only a 2-fold increase in the control patients. After 24 h, due to reduction of the infused DA dose, the level of free DA gradually decreased, whereas the level of DA sulfate remained elevated. The plasma levels of free adrenaline (Ad) and noradrenaline (NA) also increased during the DA infusion, but their levels reached a plateau within 1-2 h. Sulfoconjugated Ad and NA increased progressively until the tapering off of DA infusion. In the control patients, both free and conjugated Ad and NA showed transient increases over 12 h after surgery. These results suggest that sulfoconjugation plays a role in regulating the plasma levels of excess free CA, thereby modifying the cardiovascular effects of circulating CA. Measurement of the increase in plasma conjugated CA may be useful as an index of the increase in free CA in plasma due to the administration of an exogenous form or release of endogenous CA from the tissues.