AJP - Gastrointestinal and Liver Physiology, Vol 254, Issue 2 232-G241, Copyright © 1988 by American Physiological Society

ARTICLES

Ursodeoxycholic acid choleresis: relationship to biliary HCO-3 and effects of Na+-H+ exchange inhibitors

E. L. Renner, J. R. Lake, E. J. Cragoe Jr, R. W. Van Dyke and B. F. Scharschmidt
Department of Medicine, University of California School of Medicine, San Francisco 94143.

We have recently shown that substitution of Li+ for perfusate Na+ eliminates the HCO3(-)-rich choleresis produced by ursodeoxycholic acid (UDCA) in isolated perfused rat liver and that the increase in bile flow produced by both UDCA and taurocholic acid is partially inhibited by 1 mM amiloride. Although these findings are consistent with a role for Na+-H+ exchange in the choleresis produced by these bile acids, both Li+ substitution and amiloride affect other cellular processes, including Na+-K+-ATPase activity. We have now further explored both the relationship between UDCA-stimulated bile flow and biliary HCO3- secretion and the possible role of Na+-H+ exchange in this process by comparing the effects of amiloride with two of its more potent and presumably more specific analogues, 5-(N,N-dimethyl)amiloride hydrochloride (DMA) and 5-(N-ethyl-N-isopropyl)amiloride (EIA). In the absence of inhibitor, UDCA increased biliary HCO3- concentration ([HCO3-]) up to an apparent maximum of 60-70 mM, and bile flow and biliary HCO3- output appeared to be linearly related over a sixfold range of bile flow rates. Amiloride, DMA, and EIA each produced a concentration-dependent inhibition of UDCA-stimulated bile flow and biliary HCO3- output with an apparent rank order potency (EIA greater than DMA greater than amiloride) similar to that reported for inhibition of Na+-H+ exchange in other systems. None of the inhibitors significantly altered biliary UDCA output or the relationship between UDCA-induced bile flow and either biliary [HCO3-] or biliary HCO3- output. Effects of these inhibitors did not appear attributable either to nonspecific toxicity, as reflected by hepatic release of lactate dehydrogenase or K+, or to inhibition of hepatic Na+-K+-ATPase, measured as Na+-dependent uptake of 86Rb. In contrast to their effects on UDCA choleresis, these inhibitors had little or no effect on basal bile flow, biliary [HCO3-], and biliary HCO3- output. These findings indicate that UDCA-induced but not basal bile formation is closely coupled to biliary HCO3- concentration and output, and they provide additional evidence that UDCA choleresis requires an intact Na+-H+ exchange mechanism.