Reversal of ethinyl estradiol-induced bile secretory failure with Triton WR-1339

The Pathological Mechanisms of Estrogen-Induced Cholestasis: Current Perspectives

Estrogens are steroid hormones with a wide range of biological activities. The excess of estrogens can lead to decreased bile flow, toxic bile acid (BA) accumulation, subsequently causing intrahepatic cholestasis. Estrogen-induced cholestasis (EIC) may have increased incidence during pregnancy, and within women taking oral contraception and postmenopausal hormone replacement therapy, and result in liver injury, preterm birth, meconium-stained amniotic fluid, and intrauterine fetal death in pregnant women. The main pathogenic mechanisms of EIC may include deregulation of BA synthetic or metabolic enzymes, and BA transporters. In addition, impaired cell membrane fluidity, inflammatory responses and change of hepatocyte tight junctions are also involved in the pathogenesis of EIC. In this article, we review the role of estrogens in intrahepatic cholestasis, and outlined the mechanisms of EIC, providing a greater understanding of this disease.

Preeclampsia with abnormal liver function tests is associated with cholestasis in a subgroup of cases

OBJECTIVE

To investigate whether women with preeclampsia and abnormal liver function tests have raised serum bile acids.

DESIGN

Measurement of serum bile acids in serum specimens collected at the John Radcliffe Hospital, Oxford.

SETTING

Imperial College School of Medicine.

SAMPLE

Stored sera from 37 women with preeclampsia and abnormal liver function tests and from 19 controls.

METHODS

Enzymic total bile acid assay.

MAIN OUTCOME MEASURES

Total bile acid levels.

RESULTS

Women with preeclampsia and abnormal liver function tests had higher median bile acid levels than controls (5.7 vs. 3.2, p = 0.01). The reason for the raised median serum bile acid levels in the patient group is that three (8%) women with preeclampsia had markedly raised serum bile acids levels. There were no obvious clinical or biochemical features specific to these patients.

CONCLUSIONS

The pathological mechanisms causing hepatic impairment in some women with preeclampsia may predispose to cholestasis. As some women with preeclampsia and abnormal liver function complain of pruritus, we recommend checking the serum bile acids in this group of women. If these acids are raised the fetal prognosis may be adversely affected.

Fatty acids specifically related to the anisotropic properties of plasma membrane from rat urothelium

Four different luminal surfaces of rat urothelium differing in their fatty acid composition were prepared by dietary induction. In order to induce lipid changes, each of four groups of rat received a basal diet rich in one of the unsaturated n-3, n-6 or n-9 fatty acid families and a commercial (control) diet. The effects of the dietary regime on the fatty acid composition of luminal urothelial membranes and their relation to the mobility of fluorescent probes were studied. In comparison with the control diet membrane, all three fatty acid-rich diets induced a decrease of the percentage amount of saturated fatty acid while that of the unsaturated fatty acids was increased. Accordingly, all three diets increased the unsaturation index in comparison with the control diet. The anisotropy across each membrane fraction was assessed using the n-(9-anthroyloxy) fatty acid fluorescent probes 3-AS, 7-AS and 12-AS, which locate at different depths in the membrane. Two different anisotropy profiles were observed. One profile showed the highest anisotropy at the C7 depth, whereas the other exhibited a continuous decrease of the anisotropy from the surface to the center of the bilayer. The molecular properties (isomerization) of 18:2n-9 fatty acid may account, at least in part, for the observed V-shaped profile (the ascending trend) of the membrane anisotropy values as a function of the respective 18:2n-9 fatty acid contents. Nevertheless, the minimum value of the profile did not correspond to the minimum 18:2n-9 fatty acid content, but rather to the higher amount of docosahexaenoic (22:6n-3) fatty acid. Thus, a modulating role of the 22:6n-3 fatty acid on the rigidifying effect of 18:2n-9 fatty acid is suggested, possibly mediated by relationships between fatty acid composition, saturated and unsaturated chain lengths, and freedom of motion of the phospholipid acyl chains.

Effect of a synthetic androgen on biliary lipid secretion in the female hamster

This study was designed to elucidate the effect of the synthetic androgen, methyltestosterone, on bile flow and biliary lipid secretion in female hamsters. Animals were divided into four groups and fed the following diets: group 1, lithogenic diet for three weeks; group 2, lithogenic diet + 0.05% methyltestosterone for three weeks; group 3, lithogenic diet for six weeks; group 4, lithogenic diet + 0.05% methyltestosterone for six weeks. At the end of each experimental period, the hamsters were operated on to establish external biliary fistulas. During the depletion of the endogenous bile acid pool (for two hours), the basal bile flow of group 4 was significantly smaller than that of group 3. Basal bile acid output was significantly lower in the methyltestosterone-fed groups 2 and 4 than in control groups 1 and 3. In contrast, groups 2 and 4 secreted more cholesterol than groups 1 and 3. Group 4 had a higher ratio of cholesterol output to phospholipid output than group 3. Increasing doses of taurocholate were infused after the bile acid depletion period, and it was found that methyltestosterone did not change the bile acid independent bile flow. The increments in cholesterol or phospholipid output induced per increment of bile acid output (linkage coefficients) were analyzed by linear regression. The methyltestosterone-fed groups (groups 2 and 4) had a higher linkage coefficient of cholesterol output to bile acid output than the control groups (groups 1 and 3). The linkage coefficients of phospholipid output to bile acid output of groups 2 and 4 were also higher compared to groups 1 and 3. The linkage coefficient of cholesterol output to phospholipid output of group 2 was higher than that of group 1. These results suggest that methyltestosterone stimulated the cosecretion mechanism of cholesterol and phospholipid in bile associated with an increasing ratio of cholesterol to phospholipid. In conclusion, the synthetic androgen, methyltestosterone, caused a decrease in basal bile flow and bile acid secretion, and an increase in basal cholesterol secretion and the biliary cholesterol-to-phospholipid ratio. These findings explain, in part, how methyltestosterone intensifies the formation of cholesterol gallstones in female hamsters.

Hepatoprotection in ethinylestradiol-treated rats is provided by tauroursodeoxycholic acid, but not by ursodeoxycholic acid

Ursodeoxycholic acid (UDCA) and tauroursodeoxycholic acid (TUDCA) have been suggested as potential treatments for drug-induced cholestasis. It was therefore decided to study the effects of administration of UDCA or TUDCA on individual serum bile acid concentration, conventional liver tests and associated hepatic ultrastructural changes in ethinylestradiol-treated (EE) rats mg/kg per day). Control rats were treated s.c. with propylene glycol. EE-treated rats were randomly assigned to receive daily i.p. injections of placebo, TUDCA or UDCA. Four rats in each group were treated for 4 consecutive days, and a second four for 14 days. After 4 days of treatment, the serum levels of cholic acid and taurocholic acid were significantly increased in EE-treated rats. None of the conventional liver tests were significantly different among the four groups. After 14 days of treatment the serum levels of cholic acid, chenodeoxycholic acid, glycocholic acid, glycochenodeoxycholic acid, taurocholic acid, taurochenodeoxycholic acid, bilirubin, alkaline phosphatase and gamma glutamyltransferase were significantly raised in EE and EE plus UDCA treated rats. EE plus TUDCA treated rats, however, had no significant changes in these individual serum bile acids or conventional liver tests. The ultrastructure of livers from EE plus TUDCA treated rats was similar to those of controls. On the other hand, EE and EE plus UDCA rats both showed a significant reduction in sinusoidal microvilli. These results show that treatment of rats for 4 days with EE induces significant rises in the serum concentrations of two individual bile acids and that TUDCA protects against this.(ABSTRACT TRUNCATED AT 250 WORDS)

Organic solvents increase membrane fluidity and affect bile flow and K+ transport in rat liver

Following the earlier observation that inhalation of volatile lipid solvents and of narcotic gases causes cholestasis, we studied the effects of various organic solvents on bile flow, plasma membrane fluidity and potassium movement in rat liver. Both in vivo and in the isolated perfused liver, applications of CCl4, CHCl3, dichloromethane, trichloroethylene, halothane, benzene and cyclohexane elicited rapid and sustained but reversible cholestasis. A transient phase of choleresis was observed prior to and after cholestasis, during the increase and fall in liver tissue solvent concentrations, respectively. Tissue concentrations required to produce cholestasis were lower the higher the lipophilicity of the solvent. Membrane fluidity was measured in isolated basolateral liver cell membranes by fluorescence polarization. Fluidity increased with increasing solvent concentration, the increase being associated with either biphasic stimulation and inhibition of membrane enzymes (Na+,K(+)-ATPase, 5'nucleotidase) or with inhibition alone (Mg(2+)-ATPase). In the isolated perfused liver, application of organic solvents caused hepatic uptake of K+ that was followed by K+ release upon withdrawal of the solvent. The magnitude of K+ uptake elicited by the solvent was comparable with the effect of blocking K+ channels with 2 mM Ba2+, but Ba2+ was ineffective in the presence of the solvent. In contrast, application of ouabain caused K+ release in equal amounts in the absence and presence of the solvent, indicating that K+ uptake elicited by the solvent results from inhibition of K+ efflux through K+ channels rather than stimulation of the Na+,K+ pump. The data show that cholestasis elicited by lipid solvents is associated with an increase in membrane fluidity and with disturbance of liver K+ homeostasis. The significance of these observations is discussed with respect to other models of experimental cholestasis.

Ethinylestradiol treatment induces multiple canalicular membrane transport alterations in rat liver

We investigated the effects of 17 alpha-ethinylestradiol treatment of rats on various transport functions in isolated basolateral and canalicular liver plasma membrane vesicles. Both membrane subfractions were purified to a similar degree from control and cholestatic livers. Although moderate membrane lipid alterations were predominantly observed in basolateral vesicles, no change in basolateral Na+/K(+)-ATPase activity was found. Furthermore, while Na(+)-dependent taurocholate uptake was decreased by approximately 40% in basolateral vesicles, the maximal velocity of ATP-dependent taurocholate transport was decreased by 63% in canalicular membranes. In contrast, only minimal changes or no changes at all were observed for electrogenic taurocholate transport in "cholestatic" canalicular membranes and total microsomes, respectively. However, canalicular vesicles from cholestatic livers also exhibited marked reductions in ATP-dependent transport of S-(2,4-dinitrophenyl)glutathione and in Na(+)-dependent uptake of adenosine, while in the same vesicles HCO3-/SO4- exchange and Na+/glycine cotransport activities were markedly stimulated. These data show that in addition to the previously demonstrated sinusoidal transport abnormalities ethinylestradiol-induced cholestasis is also associated with multiple canalicular membrane transport alterations in rat liver. Hence, functional transport alterations at both polar surface domains might ultimately be responsible for the inhibitory effects of estrogens on the organic anion excretory capacity and on bile formation in rat liver.

Ethinylestradiol increases volume and decreases sinusoidal membrane surface in the rat liver: a stereological analysis

Structural alterations of liver parenchyma caused by ethinylestradiol, a synthetic estrogen known to induce cholestasis and to act as a tumor promoter factor, were investigated. Male rats treated with 17 alpha-ethinylestradiol (5 mg/kg body weight for 5 days) were compared with controls (n = 5 each). After perfusion fixation and systematic random sampling, paraffin sections, semithin sections and thin sections were examined observing standard stereological techniques. Ethinylestradiol treatment induced an increase in liver volume by 65% (p less than 0.001), which was caused more by hypertrophy (volume of singular hepatocyte +35%, p less than 0.001) than by hyperplasia (number of hepatocytes +23%, p less than 0.001). A decrease in sinusoidal membrane surface density (-43%, p less than 0.005) associated with a decrease in sinusoidal microvillar volume density (-50%, p less than 0.005) were both compensated for by the increase in liver volume. No canalicular alterations were observed. Thus changes in hepatocytes detectable with stereological techniques affect the sinusoidal pole where decreased sinusoidal membrane surface is associated with or reflects a substantial loss of membrane phospholipids. The increased liver volume may constitute an adaptive response compensating for the relative decrease in sinusoidal membrane surface and displays characteristics comparable to those of preneoplastic hepatocytes.

Effect of ethinylestradiol and epomediol on bile flow and biliary lipid composition in rat

Epomediol (1,3,3-trimethyl-2-oxabicyclo(2.2.2.)octan-6,7-endo,endo-diol) (EPO) is a terpenoid compound shown to reverse 17 alpha-ethinylestradiol (EE)-induced cholestasis in rat. The effect is related to the restoration of normal liver plasma membrane fluidity values. To further characterize the effect of EPO, bile flow and biliary lipid composition were measured in rats treated either with EE or EE associated with EPO. EE significantly reduced the bile flow; this reduction was prevented by concomitant treatment with EPO with an increase in the bile salt secretion rate. EPO alone showed a choleretic effect. The biliary secretion rate of cholesterol was also significantly reduced by EE while being comparable to controls in EE-EPO-treated animals. Phospholipid (PL) biliary excretion was significantly (P less than 0.002) increased by EE either alone or combined with EPO. After EE treatment, the biliary PL composition showed a reduction in phosphatidylcholine (PC) concentration with a parallel increase in lyso-phosphatidylcholine (LPC) when compared to control animals (PC:LPC ratio 5.0 +/- 2.5 vs 26.8 +/- 9.9, mean +/- SD, P less than 0.005). EPO administration to EE-treated rats restored the biliary PC:LPC ratio to control values (27.6 +/- 10.6). EPO alone did not show any appreciable effect as compared to both control and EE-EPO treated animals. As increased concentrations of LPC have been reported to induce an alteration in the function of membrane lipids and membrane-associated proteins, such as regulatory enzymes for bile acid, cholesterol and phospholipid metabolism, these results suggest that the protective effect of EPO in EE-induced cholestasis may be related to the reversal of the alterations in membrane lipid composition and function induced by EE.

S-adenosyl-L-methionine reverses the cholestatic effect of ethinylestradiol in rat hepatocytes by increasing its catabolism

In this study, ethinylestradiol inhibited the uptake of taurocholate by cultured rat hepatocytes, increasing the Km while leaving the Vmax unchanged. S-Adenosyl-L-methionine (SAMe) had no effect on taurocholate uptake or release, but was able to reverse the competitive inhibition induced by ethinylestradiol. S-Adenosyl-L-homocysteine did not reverse this inhibition, which suggests that the methyl group of SAMe affects its activity. Several possible mechanisms for the action of SAMe were investigated. The methylation of cell membrane phospholipids was eliminated as a possible mechanism. The presence of SAMe greatly increased the catabolism of ethinylestradiol by hepatocytes and reduced its covalent binding to hepatocyte macromolecules. In culture supernatants, both highly polar (conjugated) and non-conjugated metabolites could be detected. Moreover, most of the metabolites were methylated. This suggests that SAMe may revert the effects of ethinylestradiol of taurocholate uptake by increasing its catabolic rate by hepatocytes.

Na+/K(+)-ATPase activity and its alpha II subunit gene expression in rat skeletal muscle: influence of diabetes, fasting, and refeeding

We have examined the effects of diabetes, fasting, and refeeding on Na+/K(+)-adenosine triphosphatase (ATPase) activity and its catalytic alpha II subunit gene expression in skeletal muscle. Two hypoinsulinemic states, streptozotocin-induced diabetes and 48-hour fasting caused a significant decrease (P less than .05) in skeletal muscle Na+/K(+)-ATPase activity and a marked increase (P less than .01) in the levels of alpha II subunit mRNA. A decrease in enzyme activity was observed on the 2nd and the 14th day of diabetes, whereas an increase in alpha II mRNA levels was found only on the 14th day. The levels of alpha I mRNA were not affected, while the levels of mRNA of the structural beta subunit were decreased on the 14th day of diabetes. Correction of hyperglycemia with insulin restored enzyme activity and alpha II isoform mRNA levels toward normal in diabetic animals. Refeeding for 48 or 72 hours restored these parameters to normal in skeletal muscle of previously fasting rats. These observations suggest that a decrease in muscle Na+/K(+)-ATPase activity may lead to a compensatory increase in its alpha II subunit gene expression. The levels of insulin and not of glycemia appear to be critical in modulating Na+/K(+)-ATPase activity and gene expression.

Novel high-performance liquid chromatography for determination of membrane phospholipid composition of rat hepatocytes

We have developed a new, quick and efficient method of high-performance liquid chromatography (HPLC) for the isolation and quantitative determination of phospholipids in hepatocyte membranes. A silica gel column was used for the isolation and determination, and an isocratic mixture of acetonitrile, methanol and 85% phosphoric acid (130:5:1.7, v/v/v) was used as a mobile phase. Six kinds of phospholipids, i.e. phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylcholine (PC), lysophosphatidylcholine (LPC) and sphinogomyelin (SPH), in this order, were completely isolated within 45 min. The phospholipid composition of sinusoidal membrane vesicles (SMV) and canalicular membrane vesicles (CMV) obtained from rat liver, as well as of human erythrocyte ghosts were determined by this HPLC method. The level of SPH in CMV was significantly higher than that in SMV, and the level of PC in CMV was significantly lower than that in SMV. These results were considered attributable to the low fluidity of CMV. The phospholipid composition of human erythrocyte membrane was different from that of rat SMV and CMV. The present technique is suitable for quantitative determination of phospholipids in cell membranes.

Role of S-adenosyl-L-methionine in the treatment of intrahepatic cholestasis

Recent studies have established the clinical efficacy of S-adenosyl-L-methionine (SAMe) in the treatment of cholestasis associated with hepatic diseases, pregnancy and the administration of estrogen-containing oral contraceptives. In 4 clinical trials involving a total of 639 patients with cholestasis due to acute or chronic liver disease, SAMe in an intravenous dose of 800 mg/day or an oral regimen of 1.6 g/day for 2 weeks was superior to placebo in relieving the symptom of pruritus and in restoring serum total bilirubin and serum alkaline phosphatase towards normal. The drug is also effective in intrahepatic cholestasis of pregnancy (ICP), with intravenous administration of 800 mg/day for 2 weeks producing a substantial reduction in pruritus and an improvement in abnormal liver function indices. Moreover, SAMe treatment decreases the incidence of premature labour. SAMe appears to be the first safe and effective approach to the treatment of this syndrome, and also protects against the adverse hepatic effects of small doses of estrogen in patients with a history of ICP by normalising liver biochemistry and the oversaturated biliary lipid composition of the gallbladder bile. In animal models, SAMe reverses the pathological liver changes induced by xenobiotics such as taurolithocholate and alpha-naphthyl-isothiocyanate (ANIT) and the antipsychotic chlorpromazine. Several cooperative mechanisms appear to underlie the anticholestatic action of SAMe, the most important being the restoration of normal hepatocyte membrane fluidity and Na+, K+ ATPase activity, through a reversal of the reduction in phospholipid methylation produced by hepatotoxic agents. In addition, SAMe may act by promoting trans-sulphuration pathway reactions and consequently improving the detoxifying capacity of this metabolic system.

Reversal of ethinylestradiol-induced cholestasis by epomediol in rat. The role of liver plasma-membrane fluidity

Epomediol (EPO) is a synthetic terpenoid compound shown to be active in increasing bile flow and some enzymatic activities of liver plasma membranes in the rat. The possible effect of EPO treatment in the ethinyl-estradiol (EE) induced cholestasis in the rat was investigated by measuring the hepatic transport of sulfobromophthalein (BSP) (plasma clearance and biliary secretion) and bile flow. Liver plasma membrane fluidity was also determined by the steady state fluorescence polarization (P) of diphenylhexatriene (DPH). EE administration (5 mg/kg s.c. for 5 days) was followed by a significant, comparable reduction (P less than 0.001) in BSP plasma clearance and biliary excretion and in bile flow. Intraperitoneal administration of EPO (100 mg/kg) to EE-treated rats restored both parameters of BSP transport, as well as bile flow, to control values. Liver plasma membrane fluidity was markedly (P less than 0.01) decreased by EE administration with a concomitant reduction (P less than 0.01) in Na+/K+-ATPase activity. EPO administration significantly increased membrane fluidity to values higher either to cholestatic (P less than 0.05) or control (P less than 0.05) animals. On the contrary, EPO did not influence Na+/K+-ATPase activity in either EE-treated or control animals. These data indicate that EPO fully reverses the impairments of BSP transport and bile flow induced by EE, possibly by reversing the decrease in liver plasma membrane fluidity induced by the synthetic estrogen. On the contrary, the EE-mediated decrease in Na+/K+-ATPase activity was not reversed by EPO.

Thyroid hormones and the hepatic handling of bilirubin. I. Effects of hypothyroidism and hyperthyroidism on the hepatic transport of bilirubin mono- and diconjugates in the Wistar rat

The effects of thyroidectomy and of thyroid hormone administration on the hepatic transport of endogenous bilirubin were investigated in the Wistar R/APfd rat. Hypothyroidism resulted in an enhanced hepatic bilirubin UDP-glucuronosyltransferase activity and in a decreased p-nitrophenol transferase activity. It caused a cholestatic condition with a 50% decrease in bile flow and bile salt excretion, and an increased proportion of conjugated bilirubin in serum. The biliary output of unconjugated and monoconjugated bilirubins decreased in parallel by about 65%, whereas the excretion rate of the diconjugate dropped by only 47%, resulting in an increased di- to monoconjugate ratio in bile. Hyperthyroidism was characterized by a decreased bilirubin and an increased p-nitrophenol transferase activity, and by an augmented bilirubin output in bile. The output of unconjugated and monoconjugated bilirubins increased in parallel by about 50 or 100%, whereas the excretion of the diconjugate increased by only 20 to 50%, depending on the dose of thyroxine administered; this resulted in a decreased di- to monoconjugate ratio in bile. A linear positive relationship was found between bilirubin UDP-glucuronosyltransferase activity and the ratio of bilirubin di- to monoconjugates present in bile or formed by in vitro incubation of liver homogenates at low concentration of bilirubin (10 to 15 microM), indicating that bile pigment composition is mainly determined by the conjugation activity in the liver. The inverse relationship observed between hepatic beta-glucuronidase activity and the ratio of di- to monoconjugates in bile warrants further investigation to analyze whether this enzyme activity also plays a possible role in the changes in bile pigment composition in hypo- and hyperthyroid rats.

Effect of different doses of S-adenosyl-L-methionine (SAMe) on nicotinic acid-induced hyperbilirubinaemia in Gilbert's syndrome

S-adenosyl-L-methionine (SAMe) has been shown to increase hepatocyte membrane fluidity thereby relieving signs of oestrogen-induced cholestasis. S-adenosyl-L-methionine might therefore prove effective in improving the efficiency of the transport of organic anions such as nicotinic acid (NA) and bilirubin which is impaired in Gilbert's syndrome (GS). In this study the effects on the metabolization rate of NA and bilirubin of two dosages of SAMe were evaluated in respect to placebo in ten male inpatients (mean age 24 years, range 16-31) with GS. Each patient received both SAMe (800 and 200 mg/day, respectively) and placebo treatment i.v. over a period of 10 days. The NA test (5.9 mumol/kg b.w. i.v.) was carried out in the same volunteers after each treatment. Unconjugated bilirubin (UCB) levels were significantly lower (p less than 0.01) after 800 mg/day SAMe than after placebo while the lower dosage of SAMe did not affect UCB values. The bilirubin time curve concentration, expressed as area under the curve (AUC), was significantly reduced (p less than 0.01) after 800 mg SAMe in comparison with the values obtained after placebo and 200 mg SAMe. Also plasma NA half-life was significantly reduced (p less than 0.01) by the higher dose of SAMe in respect to placebo and not by the lower dose.

Modulation of Na+-H+ exchange by ethinyl estradiol in rat colonic brush-border membrane vesicles

Prior studies by our laboratory have suggested that a relationship may exist between rat colonic brush-border membrane vesicular fluidity and Na+-H+ exchange. To further explore this possible relationship, in the present studies the effects of ethinyl estradiol (17 alpha-ethinyl-1,3,5-estratriene-3,17-beta-diol) administration subcutaneously (5 mg/kg body wt. per day) for 5 days, on rat colonic brush-border membrane fluidity and Na+-H+ exchange were examined. This treatment regimen has previously been shown to decrease the lipid fluidity of rat hepatic and rabbit small intestinal plasma membranes. In agreement with these prior studies, the present results demonstrate that this agent decreases the lipid fluidity of treated-rat colonic brush-border membranes compared to control membranes, as assessed by steady-state fluorescence polarization techniques using three different fluorophores. An increase in the cholesterol content and cholesterol/phospholipid molar ratio of treated-membranes appear to, at least partially, be responsible for the fluidity differences. Furthermore, examination of the kinetic parameters for amiloride-sensitive sodium-stimulated proton efflux in treated and control membrane vesicles, utilizing the pH-sensitive fluorescent dye, Acridine orange, revealed that ethinyl estradiol administration decreased the Vmax for this exchange mechanism, expressed in arbitrary fluorescence units, by approx. 25% but did not influence its Km for sodium. These data, therefore, lend further support to the contention that alterations in fluidity may modulate Na+-H+ exchange in rat colonic brush-border membrane vesicles.

Drug-induced cholestasis

Intrahepatic cholestasis, defined as arrested bile flow, mimics extrahepatic obstruction in its biochemical, clinical and morphological features. It may be due to hepatocyte lesions of which there are three types, termed canalicular, hepatocanalicular and hepatocellular, respectively; or it may be due to ductal lesions at the level of the cholangiole or portal or septal ducts. Defective bile flow due to hepatic lesions reflects abnormal modification of the ductular bile. Defective formation of canalicular bile may involve bile acid-dependent or independent flow. It appears to result most importantly from defective secretion of bile acid-dependent flow secondary to defective uptake from sinusoidal blood, defective transcellular transport and defective secretion; or from regurgitation of secreted bile via leaky tight junctions. An independent defect in bile acid-independent flow is less clear. Defective flow of bile along the canaliculus may reflect increased viscosity and impaired canalicular contractility secondary to injury of the pericanalicular microfibrillar network. Impaired flow beyond the canaliculus may result from ductal injury. Sites of lesions that contribute to cholestasis include the sinusoidal and canalicular plasma membrane, the pericanalicular network and the tight junction and, less certainly, microtubules and microfilaments and Golgi apparatus. A number of drugs that lead to cholestasis have been found to lead to injury at one or more of these sites. Other agents (alpha-naphthylisothiocyanate, methylenedianiline, contaminated rapeseed oil, paraquat) lead to ductal injury resulting in cholestasis. Reports of inspissated casts in ductules (benoxaprofen jaundice) and injury to the major excretory tree (5-fluorouridine after hepatic artery infusion) have led to other forms of ductal cholestasis. Most instances of drug-induced cholestasis present as acute, transient illness, although important chronic forms also occur. The clinical features include the reflection of the cholestasis (pruritus, jaundice), systemic manifestations and extrahepatic organ involvement. While nearly all classes of medicinal agents include some that can lead to cholestasis, there are differences among the various categories. Phenothiazines and related antipsychotic and 'tranquillizer' drugs characteristically lead to cholestatic hepatic injury. The tricyclic antidepressants may lead to cholestatic or hepatocellular injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Ethynylestradiol alters lipid composition and phosphatidylethanolamine metabolism in red blood cells

Treatment of female rats with ethinylestradiol at a dose of 60 micrograms/rat, daily for 21 days, produced marked changes in red blood cell lipids. Cholesterol was decreased by 22% and total phospholipids were increased by 13%, resulting in a 31% decrease in the cholesterol to phospholipid ratio. The mass distribution of phosphatidylcholine and phosphatidylethanolamine relative to total phospholipids was unchanged. Whereas control red cells incorporated preferentially fatty acids in phosphatidylcholine, ethinylestradiol stimulated their incorporation specifically in phosphatidylethanolamine, where increases occurred with palmitic acid (+75%), oleic acid (+68%) and arachidonic acid (+31%). Incorporation in phosphatidylcholine was unaffected with any of the 3 fatty acids. The stimulation of fatty acid incorporation in phosphatidylethanolamine is likely to reflect an estrogen-dependent increase in turnover rate of fatty acids in this phospholipid. Such alterations in lipid composition and fatty acid incorporation in red cell phospholipids may have significant effects on membrane function.

Effects of ethinyl estradiol on intestinal membrane structure and function in the rabbit

Structural and functional properties of the small intestinal microvillus membrane were evaluated in the rabbit after administration of ethinyl estradiol, a synthetic estrogen with a demonstrated propensity to alter hepatic membrane lipid fluidity, and promote cholestasis. In the jejunum, no estrogen-induced changes in microvillus membrane total lipid, cholesterol or phospholipid content were observed. However, the ileal microvillus membrane in estradiol-treated animals demonstrates significant reductions vs. controls (per mg protein) in total lipid (0.55 milligrams vs. 0.89 milligrams) [corrected] and phospholipid (206.7 micrograms vs. 304.91 micrograms) (p less than 0.001) content, as well as modifications in specific phospholipid species. The increase in the ileal microvillus membrane cholesterol: phospholipid molar ratio (0.65 vs. 0.51, p less than 0.05) was associated with a significant decrease in membrane lipid fluidity reflected by an increase in fluorescence anisotropy measurements utilizing diphenyl hexatriene as the fluorophore (r at 25 degrees C = 0.306 vs. 0.282, p less than 0.05). Thermotropic lipid phase transitions, assessed by Arrhenius plots of both fluorescence data and ileal microvillus membrane p-nitrophenylphosphatase activity demonstrate that phase changes occur between and 24 and 28 degrees C in both treated and untreated groups. Within the temperature range studied (40-10 degrees C) no differences from control were observed in microvillus membrane alkaline phosphatase activity following estrogen treatment. These data therefore indicate that ethinyl estradiol-induced effects on microvillus membrane lipid composition and physical properties occur predominantly in the ileum and appear to be related, in part, to specific alterations in the availability of phospholipid following estrogen treatment.

Effects of ethinyl estradiol on substrate uptake and efflux by isolated rat hepatocytes

Ethinyl estradiol is a well documented, predictable cholestatic agent. The direct effects of this drug on hepatocellular uptake and efflux have been investigated. Uptake of taurocholate and ouabain, which are both actively transported, was inhibited, while uptake of cadmium, which occurs by a combination of facilitated and simple diffusion, was unaffected. The Vmax for taurocholate uptake was not altered by the presence of ethinyl estradiol, whereas the Km was increased, suggesting a reduced affinity of receptor for taurocholate. Efflux of taurocholate from pre-loaded cells remained unchanged in the presence of ethinyl estradiol. The data are not entirely consistent with an interference of Na+,K+-ATP ase by ethinyl estradiol being an important site of action. The observations may help to explain the mechanism of biliary dysfunction induced by ethinyl estradiol.

Effect of dietary cholesterol on biliary cholesterol content and bile flow in the hypothyroid rat

The hypothyroid rat model was used to investigate the effect of dietary-induced hypercholesterolemia on biliary cholesterol content and bile flow. Rats were divided into four dietary groups--diet A: Rat Chow; diet B: Rat Chow plus 0.1% propylthiouracil; diet C: Rat Chow plus 0.1% propylthiouracil, 0.3% taurocholate, 5% lard; diet D: Rat Chow plus 0.1% propylthiouracil, 0.3% taurocholate, 5% lard, and 1% cholesterol. After 6 wk, bile was collected and livers were excised for the preparation of membranes. In cholesterol-fed animals, biliary cholesterol content was increased. However, because of a significant decrease in the rate of bile flow that occurred in these animals, biliary cholesterol output was unchanged from the cholesterol output observed in control animals. Dietary cholesterol also caused a threefold increase in liver membrane cholesterol content and a 64% decrease in the activity of sodium-potassium-stimulated adenosine triphosphatase (Na+,K+-ATPase). In a separate group of animals, microsomes prepared from livers of control rats were incubated with phosphatidylserine liposomes, liposomes containing cholesterol, or buffer. The activity of Na+,K+-ATPase was increased in microsomes incubated with phosphatidylserine liposomes. However, when the cholesterol content of the microsomes was increased twofold by incubating the membranes with liposomes containing cholesterol, the stimulation of Na+,K+-ATPase activity was significantly decreased. The data suggest that in the cholesterol-fed hypothyroid rat, biliary cholesterol content is significantly increased; however, because of a decrease in the rate of bile flow, biliary cholesterol output is not changed. The decrease in bile flow is associated with an accumulation of cholesterol and a decrease in the activity of Na+,K+-ATPase in hepatic membranes.

The effect of drugs on bile flow and composition. An overview

Many drugs are eliminated via the hepatobiliary route, after biotransformation in the liver. Some of them may affect bile flow and/or the hepatic secretion of biliary lipids such as bile acids, cholesterol and phospholipids. Bile acids are the most potent agents which increase bile flow, especially unconjugated bile acids. Other drugs which increase bile flow include phenobarbitone (phenobarbital), theophylline, glucagon and insulin. In contrast, ethacrynic acid, amiloride, ouabain, oestrogens and chlorpromazine are among those agents which decrease bile flow. Biliary bile acid secretion is altered by a variety of drugs, including cheno- and ursodeoxycholic acids (CDCA and UCDA), the bile acid sequestrants cholestyramine and colestipol, and ethinyloestradiol. The composition of bile can also be altered by drug therapy. Thus, clofibrate increases biliary cholesterol secretion, and reduces bile acid concentrations, without altering biliary phospholipid concentrations. However, other clofibrate derivatives may produce changes of a different pattern, suggesting that the risk of developing gallstones may differ for each derivative. Nicotinic acid and d-thyroxine also increase biliary cholesterol saturation, while CDCA and UDCA reduce biliary cholesterol concentration. The potential consequences of drug-induced changes in bile flow and composition extend to the liver, the gallbladder and the intestine. If adverse effects are to be avoided, further study in this often overlooked area is required.

Regulation of bile acid synthesis via direct effects on the microsomal membrane

Rats treated with ethinylestradiol (5 mg kg-1 day-1 for 5 days) secrete de novo synthesized bile acids at a markedly reduced rate (-57%). Administration of the nonionic detergent Triton WR-1339 to estradiol-treated rats rapidly restored the rate of secretion of de novo synthesized bile acids to control levels. In contrast, when Triton was administered to control rats, the secretion rate of bile acids was unaffected. The reduction in bile acid synthesis displayed by estradiol-treated rats was similar to the 50% decrease in the activity of hepatic microsomal 7 alpha-hydroxylase. The activity of 7 alpha-hydroxylase was also restored to control levels by the administration of Triton to estradiol-treated rats. We examined the possibility that estradiol acts directly on the hepatic microsomes. Adding increasing amounts of estradiol to microsomes obtained from control rats resulted in decreasing activities of 7 alpha-hydroxylase. The inhibition by estradiol of 7 alpha-hydroxylase obtained in vitro occurred with amounts of estradiol that were found to accumulate in the liver via in vivo treatment. Double-reciprocal analysis showed that at and below 50 micrograms of estradiol/0.5 mg of protein uncompetitive inhibition was displayed. Additional experiments showed that adding Triton to microsomes obtained from estradiol-treated rats increased the activity of 7 alpha-hydroxylase to control levels. In contrast, Triton did not increase the activity of 7 alpha-hydroxylase when it was added to control microsomes. These data show for the first time that the estrogenic steroid estradiol acts directly on the microsomes and inhibits both the activity of 7 alpha-hydroxylase and the rate of bile acid synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

The release of intralysosomally-stored 125I-Triton WR-1339 and lysosomal enzymes from the isolated perfused rat liver in the presence and absence of cytochalasin B

The effect of in vivo loading of the lysosomotropic agent 125I-Triton WR-1339 on the release of lysosomal enzymes in isolated perfused rat liver has been studied in the presence and absence of the microfilament poison cytochalasin B, as has the release of the 125I-Triton WR-1339 itself. Perfused isolated rat livers released all the enzymes studied (arylsulphatase, beta-galactosidase and lactate dehydrogenase) and, when preloaded, 125I-Triton WR-1339 was also released into the perfusate. The magnitude of the net release (after 5 hr perfusion) was in the order beta-galactosidase = 125I-Triton WR-1339 greater than lactate dehydrogenase greater than arylsulphatase. Preloading of the lysosomes with the detergent appeared to bring about an increase in the release of all the enzymes studied (3.5 X for beta-galactosidase, 2.6 X for arylsulphatase and 1.7 X for lactate dehydrogenase). The addition of the microfilament poison cytochalasin B into the perfusate of non-loaded livers significantly increased the release of the lysosomal enzymes but not that of lactate dehydrogenase. However in the 125I-Triton WR-1339- loaded livers cytochalasin B had no effect on the release of lysosomal enzymes or detergent, but reduced the loss of lactate dehydrogenase by about 50%. This failure of cytochalasin B to potentiate the exocytosis of lysosomal contents in 125I-Triton WR-1339-loaded livers is similar to the effect found previously with 125I-PVP-loaded livers and may be related to the already enhanced loss of lysosomal enzymes apparently caused by the loading.

Effects of iron overload on bile secretion and hepatic porphyrin metabolism in ethinyl estradiol-treated rats

We investigated the effects of ethinyl estradiol (5 mg/kg body wt daily for 5 days, orally) and/or iron sorbitol (50 mg/kg body wt daily for 5 days, i.m.) on bile flow, bile salt independent fraction (BSIF), hepatic delta-aminolevulinate synthase (ALA-S) and uroporphyrinogen decarboxylase (URO-D) in female rats. Ethinyl estradiol administration was associated with a significant decrease of bile flow and BSIF and an increase in URO-D activity in comparison to control values. Iron alone did not modify biliary parameters, but significantly increased the activity of ALA-S. Combined treatment with ethinyl estradiol plus iron partially corrected the reduction of BSIF and restored the activity of ALA-S and URO-D to control levels. Thus iron appears to exert a partially protective effect against ethinyl estradiol-induced cholestasis. No porphyrinogenic effect was observed.

Renal cortical brush-border and basolateral membranes: cholesterol and phospholipid composition and relative turnover

A new procedure for the rapid isolation of renal cortical brush-border and basolateral membranes from the same homogenate is described. Brush-border membranes isolated using Mg2+-EGTA precipitation were enriched 18-fold for leucine aminopeptidase and had a recovery of 32.5%. Basolateral membrane fractions were isolated using a discontinuous sucrose gradient and showed an enrichment of 10.7-fold and recovery of 12.8% using (Na+,K+)-ATPase as a marker enzyme. Lipid analysis using two-dimensional TLC separation of phospholipids and gas liquid chromatography for cholesterol showed marked differences in the lipid composition of the brush-border and basolateral membranes. The brush-border membrane had increased sphingomyelin, phosphatidylserine, ethanolamine plasmalogens, and an increased cholesterol-to-phospholipid and sphingomyelin-to-phosphatidylcholine ratio compared to the basolateral membrane. The relative turnover of total membrane and individual phospholipid species using a double isotope ratio method was carried out. Phospholipids were labeled with either phosphorus 32 and 33 or acetate (3H, 1-14C). The relative turnover of phospholipid species and cholesterol differed strikingly. Phosphatidylcholine showed a high turnover, phosphatidylethanolamine and phosphatidylinositol had intermediate values and sphingomyelin, phosphatidylserine and cholesterol had low relative turnover rates. The order of phospholipid class relative turnover was independent of the labeled precursor used. The brush-border membrane had a significantly reduced relative turnover rate for total membrane phospholipids, sphingomyelin and cholesterol compared to the basolateral membrane. These data show marked differences in the lipid composition and relative turnover rates of the phospholipid species of the brush-border and basolateral membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the dietary fatty acid component on the release of 14C-taurocholate, 14C-bilirubin, alkaline phosphatase, and aspartate transaminase by isolated rat liver cells

Rats were fed liquid diets for 7 days containing either triolein or Liposyn, which is rich in linoleic acid, as fat sources, and liver cell suspensions were prepared following collagenase perfusion. The release from isolated cells of alkaline phosphatase and aspartate transaminase during a 3-hr incubation did not differ. The uptake and release of 14C-taurocholate during a brief incubation was lower but not significantly in Liposyn-fed rats (0.1 greater than p greater than 0.05): the uptake was 9.74 +/- 1.58 vs 16.7 +/- 3.3 nmol/mg protein in triolein-fed rats; the release was 3.17 +/- 0.65 vs 5.35 +/- 1.01 nmol/mg protein in triolein-fed rats. The uptake of 14C-aminolevulinic acid was similar in both groups, but release of 14C-bilirubin during a 30-min incubation was 5,420 +/- 1010 in the Liposyn group vs 12,030 +/- 2,200 dpm/mg protein in the triolein group (p = 0.02). It is concluded that a diet high in linoleic acid decreases bilirubin release in isolated liver cells consistent with the ability of this diet to cause cholestasis in vivo.

Increased cholesteryl ester content in liver of mice fed lipid emulsion diets high in polyunsaturated fats

Mice were fed a liquid diet containing different fat sources for 6 days and several biochemical parameters in the liver were examined. Mice fed diets containing Nutralipid or Liposyn as 45% of total calories had 30.5 +/- 2.5 and 25.8 +/- 3.7 nmol cholesteryl esters per milligram liver protein, respectively, as compared with 13.14 +/- 2.4 for those fed regular mouse food and 13.7 +/- 2.45 for those fed an emulsion containing mostly triolein as fat source. A similar increase in liver cholesteryl esters resulting from estrogen treatment has been proposed as the basis for changes resulting in decreased bile flow in the rat. It is suggested that the high content of polyunsaturated fatty acids in nutrient emulsions might be responsible for cholestasis sometimes observed in patients receiving these preparations. This is further supported by the observation that, as in the case of estrogen treatment, the cholesteryl ester level returned to normal when mice were treated with the detergent Triton WR-1339.

Selectively reduced biliary excretion of cholyldiglycylhistamine but not of cholyltetraglycylhistamine in ethinyl estradiol-treated rats. A possible indicator of increased bile canalicular permeability

A series of bile acid derivatives were synthesized, purified and radiolabelled. These were [125I]cholylglycylhistamine [( 125I]CGH), [125I] cholyldiglycylhistamine [( 125I]CG2H), [125I]cholyltriglycylhistamine [( 125I]CG3H), and [125I]cholyltetraglycylhistamine [( 125I]CG4H). These derivatives were rapidly excreted unchanged into the bile of bile-fistula rats. In normal rats the 30-min cumulative excretion following intravenous administration was only 39.0 +/- 0.7% for [125I]CGH but greater than 80% for the three larger compounds. This marked difference in biliary recovery between CGH and the other larger compounds could be due to a threshold biliary permeability, and we postulated that the critical molecular weight threshold for effective biliary retention of such compounds falls between [125I]CGH (MW 683) and [125I]CG2H (MW 740). Increased permeability, involving a shift to a higher molecular weight threshold would then be anticipated to diminish biliary excretion of [125I]CG2H (MW 740) before exerting a major influence on the biliary excretion of [125I]CG4H (MW 854). We previously reported functional and morphological studies which suggest that ethinyl estradiol (EE) may alter the permeability of bile canalicular tight junctions. In this study we have looked for further evidence of a progressive permeability change in EE-induced cholestasis by observing the biliary excretion of CG2H and CG4H in rats. Treatment with EE (5 mg/kg/day) for 3 days (EE3) or with the injection vehicle propylene glycol for 7 days (C7) reduced biliary excretion to a significant extent when compared to 3-day controls (C3) but had no differential effect on the 30-min recoveries from bile of CG2H and CG4H, respectively: C3 (81.2 +/- 1.8% and 81.7 +/- 2.1%, P = CN): C7 (72.3 +/- 3.0% and 73.5 +/- 3.6%, P = NS): EE3 61.8 +/- 2.5% and 61.9 +/- 2.7%, P = NS). However, treatment with EE for 7 days significantly reduced the biliary recovery of CG2H (46.8 +/- 9%) compared to EE3 rats (P less than 0.0025) but there was no significant change of biliary CG4H recovery (61.0 +/- 2.5%, P = NS) compared with EE3 rats. These results are compatible with our hypothesis that EE-induced cholestasis is associated with a change of biliary permeability which, as it progresses, affects successively larger molecules.

Effect of lithocholic acid on cholesterol synthesis and transport in the rat liver

The cellular origin of cholesterol which accumulates in liver cell plasma membrane fractions enriched in bile canalicular structures after lithocholic acid treatment was determined in vivo. Rats were given [3H]cholesterol followed 16 h later by [2-14C]mevalonic acid, [2-14C]acetic acid or lithocholic acid. Lithocholic acid injection enhanced the de novo synthesis of cholesterol in the microsomes and both compounds were transported to the bile canalicular membranes. However, in vitro studies demonstrated that lithocholic acid is capable of stripping cholesterol from microsomal membranes even in the absence of increased de novo synthesis. This suggests that transfer of cholesterol from subcellular organelles (microsomes) to bile canalicular membranes may be the initial step in the development of lithocholic acid-induced cholestasis.

Hepatic transport of sulfated and nonsulfated bile acids in the rat following relief of bile duct obstruction

The effect of bile duct ligation for 5 days on the hepatic transport of sulfated and nonsulfated bile acids was studied. Tracer doses of radioactive bile acids [3H]taurochenodeoxycholate-3-sulfate [3H]chenodeoxycholate-3-sulfate, [3H]taurochenodeoxycholic acid and [14C]taurocholic acid were injected 90 min after relief of obstruction when the plasma total bile acid concentration had reverted to normal. Plasma clearance and biliary excretion of sulfated bile acids were lower than those of nonsulfated bile acids, particularly in the cholestatic rats (p less than 0.02). For each bile acid, hepatic transport in the cholestatic rats was significantly reduced compared with the control rats. [3H]Chenodeoxycholate-3-sulfate and [3H]taurochenodeoxycholic acid were partially metabolized to [3H]taurochenodeoxycholate-3-sulfate prior to biliary excretion. This data suggests that the hepatic transport system for sulfated bile acids is less efficient and more easily impaired by cholestasis than that for nonsulfated bile acids.

A dietary regimen alters hepatocyte plasma membrane lipid fluidity and ameliorates ethinyl estradiol cholestasis in the rat

A dietary regimen which induces hepatic fatty acyl desaturase activities increases the lipid fluidity of hepatocyte plasma membranes, both in normal rats and in animals treated with ethinyl estradiol to produce cholestasis. In the cholestatic animals the fluidity change is accompanied by a significant increase in bile flow rate of approx. 33%.

Reversal of intrahepatic cholestasis of pregnancy in women after high dose S-adenosyl-L-methionine administration

Previous investigations have indicated that S-adenosyl-L-methionine (SAMe) leads to reversal of estrogen-induced bile flow impairment in rats. This randomized, single-blind clinical trial was performed to determine whether SAMe reverses intrahepatic cholestasis of pregnancy (ICP) which occurs in hypersensitive women associated with increased estrogen levels in late pregnancy. Eighteen women with ICP were randomly divided into three groups of six and treated for 20 days as follows: Group I received 200 mg per day of i.v. SAMe; Group II received 800 mg per day of i.v. SAMe; Group III served as control. At the beginning of the study, clinical and biochemical parameters were similar among groups. After 10 and 20 days of treatment with the higher dose of SAMe, the mean values of serum transaminases, conjugated bilirubin and total bile acids fell significantly in respect to initial levels; opposite results were found in the other two treatment groups. The final values of these selected parameters were lower in the group of subjects treated with 800 mg per day SAMe than in the other two groups of women. Pruritus graded on a 0 to 4+ scale significantly was reduced only in patients treated with the higher dose of SAMe. These results indicate a trend toward remission of ICP in women treated with 800 mg per day SAMe and suggest that SAMe administration may be a new therapeutic modality for ICP.

Cholestasis induced by estradiol-17 beta-D-glucuronide: mechanisms and prevention by sodium taurocholate

Estradiol-17 beta-D-glucuronide (E-17G), a metabolite of natural estrogen, is a potent cholestatic agent in vivo. We, therefore, studied the mechanisms of E-17G cholestasis using in vitro perfused rat liver system. Furthermore, since it has been postulated that sodium taurocholate (TC) may interfere with either uptake or biliary excretion of other steroid agents, we tested whether E-17G cholestasis could be modified by TC administration. During a constant infusion of TC at a physiological rate (0.50 mumole per min), a dose-dependent decrease of bile flow was observed after E-17G addition from 1.5 to 5 X 10(-5) M. E-17G decreased bile acid excretory rate but not bile acid concentration in bile. In separate experiments, TC was infused at different rates (0, 0.25, 0.50, and 0.75 mumole per min) into the perfusate over the entire experimental period, and E-17G was added at 1.75 X 10(-5) M. In this setting, E-17G cholestasis was diminished by increasing TC infusion rate and was prevented by TC at 0.75 mumole per min. Infusion of sodium dehydrocholate (0.75 mumole per min), a nonmicelle-forming bile acid, did not prevent E-17G cholestasis. During E-17G cholestasis, an increased biliary permeability to 14C-sucrose was observed. This effect was also prevented by TC, but not by sodium dehydrocholate which was infused at 0.75 mumole per min. The perfusate disappearance curves of 3H-E-17G at the different TC infusion rates showed no changes in the initial uptake phase, but a profound dose-dependent difference in the excretory phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased tight junction permeability: a possible mechanism of oestrogen cholestasis

Ethinyl oestradiol increased rat biliary permeability for 3H-inulin and 14C-sucrose, and significantly raised serum concentrations of bile acids after 3 and 7 days' treatment (P less than 0.0005) and bilirubin after 7 days (P less than 0.005) but not after 3 days. Following intravenous infusion of bromsulphthalein or phenolphthalein, ethinyl oestradiol-treated rats had elevated plasma concentrations of the three bile constituents, bromsulphthalein (P less than 0.0005 after 3 and 7 days), bromsulphthalein-glutathione conjugate (P less than 0.005 after 3 days; P less than 0.0005 after 7 days) and phenolphthalein glucuronide (P less than 0.005 after 3 days; P less than 0.0005 after 7 days), but the plasma concentration of unconjugated phenolphthalein, which was undetectable in bile, was unchanged. Similar changes followed partial biliary obstruction produced by bile cannula elevation. This pattern suggests that biliary constituents are refluxing from bile to plasma via the paracellular pathway, a concept further supported by structural changes in tight junction morphology in the oestrogen-treated rats. 'Leakiness' of canalicular tight junctions may explain the pathophysiology of oestrogen-induced cholestasis.

Bile secretion and liver microsomal mixed function oxidase system in mice with griseofulvin-induced hepatic protoporphyria

Administration of 2.5% griseofulvin in the diet to male CD1 mice produced protoporphyria and cholestasis. Protoporphyria became evident as early as after 10 days of treatment, whereas cholestasis, expressed in terms of total bile flow reduction, developed only after 45 days of griseofulvin. Bile flow impairment was due both to the length of treatment and to the severity of liver protoporphyria. Griseofulvin administration was also associated with a significant modification of the relative amounts of hepatic microsomal cytochromes P-450 and b5, a loss in concentration/mg of protein of cytochrome P-450 and a concomitant increase of b5. Despite these changes, the activity of aniline hydroxylase expressed per mg of microsomal protein, assessed in vitro, was not modified.

Cholestasis

These discussions are selected from the weekly staff conferences in the Department of Medicine, University of California, San Francisco. Taken from transcriptions, they are prepared by Drs David W. Martin, Jr, Professor of Medicine, and David G. Warnock, Associate Professor of Medicine, under the direction of Dr Lloyd H. Smith, Jr, Professor of Medicine and Chairman of the Department of Medicine. Requests for reprints should be sent to the Department of Medicine, University of California, San Francisco, School of Medicine, San Francisco, CA 94143.

Modulation by S-adenosyl-L-methionine of hepatic Na+,K+-ATPase, membrane fluidity, and bile flow in rats with ethinyl estradiol-induced cholestasis

Structural and functional changes in the surface membranes of hepatocytes play a pivotal role in the induction and reversion of some forms of drug-induced cholestasis. To elucidate the mechanism by which S-adenosyl-L-methionine (SAMe) leads to a partial reversion of bile flow impairment caused by ethinyl estradiol (EE), female Sprague-Dawley rats were given oral doses of EE (5 mg per kg per day, for 3 days) with and without simultaneous administration of SAMe (25 mg per kg, 3 times per day, for 3 days). Na+,K+-ATPase activity and membrane microviscosity as measured by fluorescent polarization were assayed in isolated liver plasma membranes (LPMs). SAMe administration to normal and EE-treated rats resulted in a marked increase in Na+,K+-ATPase activity and LPM fluidity. EE alone did not cause any change in the physicochemical properties of the LPMs. Hepatic Mg2+-ATPase and gamma-glutamyl transpeptidase activities were not affected by SAMe alone but increased when SAMe was given together with EE. These data indicate that the interaction of in vivo administered SAMe with hepatocyte plasmalemma and its effect on lipid fluidity and enzymes of the LPMs showed a high specificity and an inverse relationship between Na+,K+-ATPase activity and fluorescence polarization values. Furthermore, modulation of hepatic Na+,K+-ATPase was associated with SAMe-induced protection against bile flow impairment due to EE; however, it was not the causative factor for EE-induced cholestasis under the experimental conditions. These findings suggest that changes in surface membrane structure and function might account in part for the reversal by SAMe of EE-induced impairment of bile secretory function.

Regulation of bile salt transport in rat liver. Evidence that increased maximum bile salt secretory capacity is due to increased cholic acid receptors

Expansion of the bile salt pool size in rats increases maximum excretory capacity for taurocholate. We examined whether increased bile salt transport is due to recruitment of centrolobular transport units or rather to adaptive changes in the hepatocyte. Daily sodium cholate (100 mg/100 g body wt) was administered orally to rats. This treatment was well tolerated for at least 4 d and produced an 8.2-fold expansion of the bile salt pool. This expanded pool consisted predominently (99%) of cholic and deoxycholic acids. Significantly increased bile salt transport was not observed until 16 h after bile acid loading, and maximum elevations of transport capacity to 2.3-fold of control required approximately 2 d. In contrast, maximum sulfobromophthalein excretion rates increased 2.2-fold as early as 4 h and actually fell to 1.5-fold increase at 4 d. We studied the possibility that this adaptive increase in bile salt secretory transport was due to changes in canalicular surface membrane area, lipid composition, or increased number of putative carriers. Canalicular membrane protein recovery and the specific activities of leucine aminopeptidase, Mg(++)-ATPase and 5'-nucleotidase activities were unaltered by bile salt pool expansion. The content of free and esterified cholesterol and total phospholipids was unchanged in liver surface membrane fractions compared with control values. In contrast, sodium cholate administration selectively increased specific [(14)C]cholic acid binding sites twofold in liver surface membrane fractions. Increased numbers of [(14)C]cholic acid receptors (a) was associated with the time-dependent increase in bile salt transport, and (b) was selective for the taurine conjugate of cholate and (c) was reduced by chenodeoxycholate. Changes in bile acid binding sites 16 h following taurocholate and chenodeoxycholate and the lack of change with glycocholate was associated with comparable changes in bile salt transport. In conclusion, selective bile salts increase bile salt transport in the liver through an adaptive increase in the density of putative bile acid carriers in liver surface membrane.