The effect of ageing on the biliary excretion of ouabain in the rat

Abstract

Following the intravenous injection of 3H ouabain, plasma concentration and biliary excretion of ouabain were examined in male Wistar rats of 3, 6, 16, 18 and 24 months of age. Plasma concentration of ouabain in the first 10 min after injection showed distinct age differences, with the higher concentrations in older animals. But after 10 min, this age related difference in plasma concentration lessened. Concomitantly, the biliary excretion rate of ouabain decreased as age advanced, especially in the first 10 min. On the other hand, the 40 min cumulative excretion rate showed a smaller difference between young and old rats. Four days' pretreatment with spironolactone for 16 month old rats markedly accelerated the plasma clearance and biliary excretion of ouabain to the point they approached the levels of 6 month old rats or younger. Changes in the bile flow rate was suggested as one cause of this age dependent decrease and its recovery with spironolactone pretreatment. Other possible regulating mechanisms are also suggested.