EFFECT OF EXTRACELLULAR VOLUME EXPANSION ON ERYTHROCYTE CATION-TRANSPORT IN CIRRHOTIC RATS

Erythrocyte intracellular Na+ and K+, and ouabain- and bumetanideinhib itable Na+ efflux and Rb-86 uptake have been measured in control and c irrhotic rats with or without extracellular volume expansion (EVE, sal ine, 3% body wt., 3h). Non-expanded, cirrhotic rats showed a lower Na excretion (UNaV) than controls. After EVE, control rats showed a sign ificantly higher UNaV (90%) and urinary flow (40%), than non-expanded controls. In cirrhotics, the increases in urinary flow (10%) and UNaV (17%) were not significant. No differences in intracellular Na+ and K levels between control and cirrhotic rats were observed. In controls none of these values changed with volume expansion, but in cirrhotic r ats intracellular Na+ was significantly higher in expanded than in non -expanded rats. No differences in Rb-86 uptake between nonexpanded con trol and cirrhotic rats were observed. In controls EVE induced a decre ase of pump-mediated Rb-86 influx, but in cirrhotic rats, total and pu mp-mediated Rb-86 influxes were lower in expanded than in non-expanded animals. By contrast, EVE induced a decrease in ouabain-inhibitable R b-86 uptake. In conclusion, in spite of the limitations imposed by con sidering the erythrocyte as representative of the renal cells, these r esults do not support an alteration in the response of the ouabain-inh ibitable sodium pump as responsible for the lack of natriuretic respon se to extracellular volume expansion in cirrhotic rats. However, modif ication of the cotransport system in cirrhosis could play some role in this impaired response.