In order to study
cation transport in vivo we have measured the changes in plasma and intra-erythrocytic
rubidium concentrations following an oral load of
rubidium chloride. The changes in plasma
rubidium concentration are related to the distribution of
rubidium to all the body tissues and the changes in intra-erythrocytic
rubidium concentrations provide an example of
rubidium uptake by one particular tissue. In eight healthy volunteers pretreatment with a loading dose of
digoxin (20 micrograms/kg) enhanced the rise in plasma
rubidium concentrations and attenuated the rise in intra-erythrocytic
rubidium concentrations after the oral load of
rubidium chloride. Ten patients with
chronic renal failure, compared with a well-matched control group, were found to have changes similar to, but more marked than, those caused by
digoxin, i.e. a much greater rise in plasma
rubidium concentrations and a much smaller rise in intra-erythrocytic
rubidium concentrations, after the oral load of
rubidium chloride. These findings are consistent with wide-spread reduction in Na+, K+-
ATPase activity in subjects who have taken a loading dose of
digoxin and patients with
chronic renal failure. They are, therefore, consistent with the findings of previous studies in vitro and show that it is possible to demonstrate changes in
cation transport in vivo.