PLASMA ERYTHROCYTE RELATIONSHIP OF CATECHOLAMINES IN HUMAN BLOOD

The equilibrating process of catecholamines (CAs) between plasma and r ed blood cells (RBC) was studied by measuring their erythrocyte/plasma concentration gradient (E/P ratio); ratio of E/P > 1 for a given amin e was considered the consequence of its accumulation in or on RBC. We studied in vitro human blood obtained from 9 polycythemic patients fro m whom blood was drawn in control conditions and in response to loadin g with exogenous CAs. Preliminary study showed a lack of difference in results obtained in these patients from those in 9 healthy volunteers and confirmed that RBC accumulate dopamine (DA) and epinephrine (EPI) but not norepinephrine (NE). When a moderate amount of exogenous CAs was added, plasma and RBC concentrations were increased, with a delay between the two compartments indicated by a decrease in the E/P ratio of DA and EPI. When a large amount of exogenous CAs was added, their R BC concentrations were in direct proportion to their plasma concentrat ions. Thus, the kinetics of CA equilibration between plasma and RBC ap pears to be dependent on their chemical structure (DA is more easily a ccumulated than NE) and their plasma concentrations. Physiologically, the E/P ratio of DA was significantly greater than 1, suggesting that RBC maintained their capacity to accumulate DA even when DA plasma con centration was very high. Additional studies demonstrated that accumul ation of CAs in or on RBC is a reversible process, inhibited by cold t emperature and increased when blood pO2 is drastically reduced. Whethe r the erythrocyte accumulation has any role in clearing CAs from plasm a is not clear at the moment; further studies must be designed to inve stigate whether RBC have a catabolic role in CA metabolism or behave a s physical reservoir only.