Search

Hepatic retention of cysteinyl leukotrienes is a consequence of impaired bile secretion and may be involved in the pathogenesis of intrahepatic cholestasis. In order to assess the mechanisms of altered biliary leukotriene elimination, we studied the secretion and metabolic pattern of leukotriene C4 (LTC4) in bile early in the alterations of bile formation by xenobiotics. To this end, rats were pretreated with alpha-naphthylisothiocyanate (ANIT), ethionine (ETH), or estradiol valerate (EV) at doses which did not increase serum marker enzymes of cholestasis. Bile secretion was assessed in perfused livers isolated from the treated rats. In all models, the access of [14C]sucrose into bile was increased, indicating increased permeability of the bile tract. Biliary recovery of radioactivity infused as [3H]LTC4 was decreased by ANIT and ETH while 3H-efflux into the perfusate was increased concomitantly. The secretion rate of 3H-radioactivity into bile was correlated with that of [14C]taurocholate infused at the same time. After pretreatment with ANIT (but not in the other models) the venous efflux of [3H]LTC4-ANIT pretreatment was increased [14C]sucrose clearance into bile associated with greatly enhanced biliary access of [32P]phosphate. Thus, altered charge selectivity of the paracellular pathway appears to be a prerequisite for reflux of cholephilic anions. HPLC analysis of [3H]LTC4-derived radioactivity in bile revealed that in all models of altered bile secretion the relative amount of LTD4 in bile was elevated. These results demonstrate differential changes in hepatobiliary transport and metabolism of LTC4 in developing cholestasis. ANIT inhibits leukotriene secretion by increasing paracellular permeability with loss of charge selectivity. In contrast, ETH treatment inhibits transcellular transport while treatment with EV only results in enhanced LTC4 metabolism.

Hepatic cell injury was studied in an in vitro system using rat liver slices incubated in two stages. During the first 2 hr slices were exposed to 10 mM paracetamol, this was absent during the subsequent 4 hr of incubation. Cell damage was quantified at the end by measuring leakage of lactic dehydrogenase, increase in water content and potassium loss. Treatment of slices with 20 mM fructose in the second period of incubation prevented paracetamol-induced damage. The effect of fructose was not modified by the continued presence of paracetamol in the second incubation period. The inhibition of glycolysis either with 1 mM NaF or 10 microM iodoacetate blocked the effect of fructose. The protective effect afforded by fructose was not duplicated by the addition of lactate. All these findings strongly suggest an increase in intracellular ATP levels as the most probable explanation for the protective effect of fructose, and point to fructose as a potentially useful therapeutic tool for protection of the liver late in paracetamol intoxication.

A number of sex-related differences in the metabolism of drugs, steroids and xenobiotics have been reported in studies on rats. Generally, male rats tend to metabolize these compounds more efficiently than females. In the studies presented here, male and female rats were fasted for 24-48 hr, and the effects of fasting on total hepatic microsomal cytochrome P-450 were examined. Hepatic cytochrome P-450, as determined by CO difference spectra, was increased significantly as a percentage of control in microsomes from fasted female rats when compared to fasted male rats. Cytochrome P-450 concentration increased from 0.57 +/- 0.07 nmole/mg protein to 0.99 +/- 0.08 nmole/mg protein following a 24-hr fast. In male rats, cytochrome P-450 levels were essentially unaffected by the 24-hr fast. Cytochrome b5 concentration was not altered by fasting. When female rats were fasted for 24 hr and refed, cytochrome P-450 levels were not significantly different from cytochrome P-450 levels in continuously fed animals. Treatment of fasted female rats with the protein synthesis inhibitor ethionine, or the RNA synthesis inhibitor actinomycin D, prevented the induction of cytochrome P-450 in the fasting animal. Cytochrome P-450 concentration in fed animals was not affected significantly by either inhibitor. Induction of cytochrome P-450 by phenobarbital (PB) and 3-methylcholanthrene (MC) under fed and fasted conditions was also investigated in male and female rats. Xenobiotic-induced cytochrome P-450 concentration was significantly higher in fasted female hepatic microsomes when compared to microsomes from fed female rats. Fasting did not significantly affect xenobiotic-induced cytochrome P-450 in male rats. Our results suggest that fasting in female rats results in an increase in cytochrome P-450 which is dependent upon synthesis of RNA and protein.

Studies on alkaline phosphatase were conducted in albino rats exposed to n-octane or n-nonane for 2 and 7 days; there was an increase in alkaline phosphatase activity of liver, spleen and bone marrow. Increase in spleen alkaline phosphatase activity persisted up to 42 days after single dose of n-octane or n-nonane. Pretreatment with protein synthesis inhibitors, cycloheximide or ethionine removed this observed increase of alkaline phosphatase activity in liver and spleen.