Bioluminescence assays for bile acids in the detection and follow-up of experimental liver injury

Release of Ca2+ from the endoplasmic reticulum is not the mechanism for bile acid-induced cholestasis and hepatotoxicity in the intact rat liver

The hypothesis that monohydroxy bile acids exert their cholestatic and hepatotoxic effects via a sustained elevation of cytosolic [Ca2+] was tested in the isolated perfused rat liver. Infusion of the specific inhibitor of microsomal Ca2+ sequestration, 2,5-di(tert-butyl)-1,4-benzohydroquinone (tBuBHQ) (25 microM for 10 min) produced efflux of Ca2+ from the liver and a sustained (20 min) increase in cytosolic [Ca2+] as indicated by the threefold increase in hepatic glucose output. Release of the endoplasmic reticular Ca2+ pool was demonstrated by the complete abolition of vasopressin- and phenylephrine-induced Ca2+ exchange between the liver and perfusate. Despite the profound perturbation of intracellular Ca2+ homeostasis produced by tBuBHQ, there was no decrease in bile flow and no evidence of hepatocellular injury (for 60 min), as indicated by lactate dehydrogenase release. In contrast, lithocholic acid (25 microM for 10 or 30 min) or taurolithocholic acid (5 microM for 10 or 30 min) produced an 80-90% inhibition of bile flow and a progressive increase in perfusate lactate dehydrogenase activity. During and after bile acid infusion, there was no change in Ca2+ fluxes between liver and perfusate, no stimulation of glucose output from the liver, and hormone-stimulated Ca2+ responses were preserved. It is concluded that the mechanisms for bile acid-induced cholestasis and hepatotoxicity in the intact liver are not attributable to changes in intracellular Ca2+ homeostasis, and especially not to prolonged release or depletion of Ca2+ sequestered in the endoplasmic reticulum.

D-Galactosamine hepatotoxicity is associated with endotoxin sensitivity and mediated by lymphoreticular cells in mice

Two strains of mice (C57BL/10ScN and C3H/HeJ) that carry the same mutant lipopolysaccharide gene (Lpsd) which makes them resistant to the toxic effects of endotoxin (LPS) are also partially resistant to the hepatotoxic effects of D-galactosamine. As measured by serum alanine aminotransferase, the degree of liver injury induced by D-galactosamine in the LPS-resistant strains is only 10%-30% that of closely related strains of LPS-sensitive mice. Similarly, histopathologic changes are less pronounced in the endotoxin-resistant strains than in LPS-susceptible mice. By transferring spleen cells from LPS-susceptible strains to lethally irradiated, LPS-resistant mice, we established that susceptibility to D-galactosamine is mediated by lymphoreticular cells. Radiation-resistant spleen cells transferred D-galactosamine sensitivity, suggesting a role for macrophages. We did not exclude the possibility that lymphocytes can also transfer the response to D-galactosamine. These results establish that in mice, D-galactosamine sensitivity is associated with endotoxin sensitivity and that the former is mediated by lymphoreticular cells, not by hepatocytes.