Cytochemical localization of Na+, K+-ATPase in the rat hepatocyte.

The enzyme Na+,5+-ATPase was cytochemically localized in the rat hepatocyte by a modification of the Ernst potassium-dependent nitrophenyl phosphatase technique. Measurement of nitrophenol release from 50-micrometer liver slices confirmed the presence of ouabain-inhibitable nitrophenyl phosphatase activity that increased over the 30-min incubation period. Electron micrographs demonstrated that sinusoidal and lateral membrane reaction product deposition was K+-dependent, Mg++-dependent, inhibited by ouabain but not by alkaline phosphatase inhibitors, and was localized to the cytoplasmic side of the membrane. In contrast, canalicular reaction product was K+-independent, Mg++-dependent, inhibited by alkaline phosphatase inhibitors but not by ouabain, and was localized to the luminal side of the membrane. These findings indicate that Na+,K+-ATPase is localized to the sinusoidal and lateral portions of the rat hepatocyte plasma membrane and is not detectable on the bile canaliculus where alkaline phosphatase is confined. This basolateral localization of Na+,K+-ATPase is similar to that found in epithelia where secretion is also directed across the apical membrane.

Hepatic adenosine triphosphate-dependent Ca2+ transport is mediated by distinct carriers on rat basolateral and canalicular membranes.

To characterize and localize hepatic plasma membrane ATP-dependent Ca2+ transport and Na+/Ca2+ exchange, studies were performed using highly purified rat basolateral and canalicular membrane vesicles. ATP-dependent Ca2+ transport activity was present in vesicles from both domains, insensitive to azide, oligomycin, oxalate, calmodulin, and calmidazolium, and virtually abolished at pH 6.8. However, basolateral and canalicular transport differed significantly. While basolateral transport was markedly stimulated by 1 mM Mg2+, canalicular transport was Mg2+ independent. Basolateral transport was similar at pH 7.4 and 8.0 but canalicular activity was stimulated fourfold at pH 8.0. Both Ca2+ Km [1.4 +/- 0.1 (SE).10(-8) vs. 4.8 +/- 0.7.10(-8) M] and Vmax (3.6 +/- 0.1 vs. 9.0 +/- 0.6 nmol mg-1 protein min-1) were lower in basolateral than in canalicular vesicles. Basolateral transport was somewhat more nucleotide specific (for ATP) and sensitive to vanadate (IC50 130 vs. 500 microM, respectively) than was canalicular transport. Na+/Ca2+ exchange activity was not detected in membranes from either domain. These studies suggest that hepatic ATP-dependent Ca2+ transport is mediated by domain-specific carriers on the basolateral and canalicular membranes.

Direct determination of the driving forces for taurocholate uptake into rat liver plasma membrane vesicles.

To determine directly the driving forces for bile acid entry into the hepatocyte, the uptake of [3H]taurocholic acid into rat liver plasma membrane vesicles was studied. The membrane preparation contained predominantly right-side-out vesicles, and was highly enriched in plasma membrane marker enzymes. The uptake of taurocholate at equilibrium was inversely related to medium osmolarity, indicating transport into an osmotically sensitive space. In the presence of an inwardly directed sodium gradient (NaCl or sodium gluconate), the initial rate of uptake was rapid and taurocholate was transiently accumulated at a concentration twice that at equilibrium (overshoot). Other inwardly directed cation gradients (K+, Li+, choline+) or the presence of sodium in the absence of a gradient (Na+ equilibrated) resulted in a slower initial uptake rate and did not sustain an overshoot. Bile acids inhibited sodium-dependent taurocholate uptake, whereas bromsulphthalein inhibited both sodium-dependent and sodium-independent uptake and D-glucose had no effect on uptake. Uptake was temperature dependent, with maximal overshoots occurring at 25 degrees C. Imposition of a proton gradient across the vesicle (pHo less than pHi) in the absence of a sodium gradient failed to enhance taurocholate uptake, indicating that double ion exchange (Na+-H+, OH- -anion) is unlikely. Creation of a negative intravesicular potential by altering accompanying anions or by valinomycin-induced K+-diffusion potentials did not enhance taurocholate uptake, suggesting an electroneutral transport mechanism. The kinetics of taurocholate uptake demonstrated saturability with a Michaelis constant at 52 microM and maximum velocity of 4.5 nmol X mg-1 X protein X min-1. These studies provide definitive evidence for a sodium gradient-dependent, carrier-mediated, electrically neutral transport mechanism for hepatic taurocholate uptake. These findings are consistent with a model for bile secretion in which the basolateral enzyme Na+,K+-ATPase provides the driving force for "uphill" bile acid transport by establishing a trans-membrane sodium gradient.

The transmembrane pH gradient drives uphill folate transport in rabbit jejunum. Direct evidence for folate/hydroxyl exchange in brush border membrane vesicles.

In rabbit jejunal, but not ileal brush border membrane vesicles, an outwardly directed OH- gradient (pH 7.7 inside, pH 5.5 outside) markedly stimulated the initial velocity of folate (0.1 microM) uptake compared with uptake in the absence of a pH gradient. Under pH gradient conditions, folate was transiently accumulated at a concentration four times that found at equilibrium (over-shoot), implying uphill transport of the vitamin. Equilibrium folate uptake was inversely proportional to medium osmolality, suggesting uptake into an osmotically sensitive space. pH gradient-stimulated folate uptake was markedly reduced by inhibitors of anion exchange (4,4'-diisothiocyano-2,2'-disulfonic acid stilbene; 4-acetamido-4-isothiocyanostilbene-2,2'-disulfonic acid; furosemide), and was saturable (folate Km = 0.19 +/- 0.02 microM; Vmax = 12.8 +/- 0.4 pmol X mg protein-1 X min-1). Imposition of an inside-positive electrical potential did not stimulate folate uptake, suggesting that stimulation by a pH gradient was not due to an induced electrical potential. In contrast, an inwardly directed Na+ or K+ gradient did not stimulate folate uptake. These findings provide evidence for a carrier on the jejunal brush border membrane that mediates folate/OH- exchange (or H+/folate co-transport), and are consonant with the known presence of an outwardly directed OH- gradient in vivo (brush border acid microclimate), an acidic pH optimum for intestinal folate uptake, and the primary role of the jejunum in folate absorption.

Binding of unconjugated and conjugated sulfobromophthalein to rat liver plasma membrane fractions in vitro.

As part of a study of the mechanism whereby organic anionic dyes such as sulfobromophthalein and bilirubin enter hepatocytes, the binding of [35S]sulfobromophthalein and of its glutathione conjugate to two rat liver plasma membrane fractions were studied in vitro. Both fractions reversibly and saturably bound conjugated and unconjugated sulfobromophthalein. Three classes of binding site were necessary to account for the observed sulfobromophthalein binding, their maximal binding capacities being 3.5 . 10(-11), 1.6 . 10(-7) and 5.4 . 10(-7) mol/mg membrane protein. The corresponding association constants were 5.5 . 10(7), 1.5 . 10(5) and 1.3 . 10(3) M-1. Binding of the glutathione conjugate could be accounted for by two classes of binding site only, their association constants being 2.0 . 10(8) and 1.9 . 10(3) M-1 and their maximal binding capacities 5.0 . 10(-11) and 2.2 . 10(-7) mol/mg protein, respectively. Conjugated and unconjugated sulfobromophthalein mutually competed for binding, KI being 7.8 . 10(-7) and 5.5 . 10(-5) M for conjugated and unconjugated sulfobromophthalein, respectively. Similarly, bilirubin and indocyanine green, but not taurocholate, competitively inhibited sulfobromophthalein binding. Treatment with trypsin and phospholipases reduced, while treatment with neuraminidase did not affect binding. Neither changes in pH nor substitution of other cations for Na+ in the incubation mixture significantly affected sulfobromophthalein binding. Heating the membranes increased binding. This was due to an increase in maximal binding capacity of the low-affinity, high-capacity sites. The description of saturable binding sites on hepatocellular surface membranes, the affinity of one of the sites exceeding the reported affinities for albumin and ligandin, supports the hypothesis that a membrane-located membrane carrier is responsible for hepatic uptake and biliary excretion of organic anionic dyes. Based on the studies with enzyme treatments, it is speculated that this carrier is a phospholipid-dependent, integral membrane protein.

Fulminant hepatic failure: a rare but often lethal coma syndrome.

Fulminant hepatic failure is an extremely rare coma syndrome resulting from massive necrosis of liver cells. A wide variety of etiologic agents have been identified, including viruses, drugs, and other toxic agents. Treatment focuses on reducing the ammonia load presented to the liver and on preventing or controlling complications, including sepsis, bleeding, cerebral edema, renal failure, and respiratory failure. With further research and identification of the specific toxins or metabolic derangements underlying the pathophysiology of this syndrome, more effective therapeutic measures may be devised.

Enhancement of Na+-dependent bile acid uptake by albumin: direct demonstration in rat basolateral liver plasma membrane vesicles.

The effects of albumin on taurocholate uptake by rat basolateral liver plasma membrane vesicles were examined. With this system direct effects on carrier-mediated Na+-dependent bile acid uptake may be distinguished from nonspecific alterations in carrier-independent diffusion. Bovine serum albumin increased both the initial velocity and peak uptake of taurocholate in the presence of an Na+ gradient but did not enhance Na+-independent bile acid uptake. The effects of albumin were strikingly dependent on albumin concentration. Maximal enhancement of bile acid uptake was observed at albumin concentrations of 0.125 g/dl (18 microM) to 0.25 g/dl (37 microM), which are similar to reported values for the Kd for albumin binding to the plasma membrane. At high albumin concentrations (2.5 g/dl, 367 microM), uptake was reduced but to a lesser extent than the expected fall in free bile acid concentration. Kinetic studies showed that albumin (0.5 g/dl, 74 microM) reduced the taurocholate Km from 36.5 to 16.1 microM but did not affect Vmax, suggesting that albumin binding may increase the affinity of the bile acid receptor for taurocholate. Bovine gamma-globulin, chicken ovalbumin, and human transferrin did not enhance taurocholate uptake. Control experiments demonstrated that the mechanism of the albumin effect was not dependent on residual albumin-bound calcium and did not involve alteration of the underlying driving forces for bile acid uptake (Na+ gradient). These studies have "unmasked" an enhancing effect on taurocholate uptake by low concentrations of albumin that would not have been readily detected at higher concentrations.

A new method for the rapid isolation of basolateral plasma membrane vesicles from rat liver. Characterization, validation, and bile acid transport studies.

Basolateral plasma membrane vesicles were prepared from rat liver by a new technique using self-generating Percoll gradients. The method is rapid (total spin time of 2.5 h) and protein yields were high (0.64 mg/g of liver). Transmission electron microscopy studies and measurements of marker enzyme activities indicated that the preparation was highly enriched in basolateral membranes and substantially free of contamination by canalicular membranes or subcellular organelles. High total recoveries for protein yield and marker enzyme activities during the fractionation procedure indicated that enzymatic activity was neither lost (inactivation) nor increased (activation). Thus, the pattern of marker enzyme activities found in the membrane preparation truly reflected substantial enrichment in membranes from the basolateral surface. Analysis of freeze-fracture electron micrographs suggested that approximately 75% of the vesicles were oriented "right-side-out." In order to assess the functional properties of the vesicles, the uptake of [3H]taurocholate was studied. In the presence of a Na+ gradient, taurocholate uptake was markedly stimulated and the bile acid was transiently accumulated at a concentration 1.5- to 2-fold higher than that at equilibrium ("overshoot"). In the absence of a gradient but in the presence of equimolar Na+ inside and outside of the vesicle, taurocholate uptake was faster than in the absence of Na+. These findings support a direct co-transport mechanism for the uptake of taurocholate and Na+. Kinetic studies demonstrated that Na+-dependent taurocholate uptake was saturable with a Km of 36.5 microM and a Vmax of 5.36 nmol mg-1 protein min-1. The high yield, enzymatic profile and retention of transport properties suggest that this membrane preparation is well suited for studies of basolateral transport.

Kinetic and energetic aspects of the inhibition of taurocholate uptake by Na+-dependent amino acids: studies in rat liver plasma membrane vesicles.

The kinetic and energetic aspects of the inhibition of taurocholate uptake by the Na+-dependent amino acid L-alanine were studied in rat basolateral liver plasma membrane vesicles. In the presence of an inwardly directed Na+ gradient, alanine (5 mM) reduced the initial velocity of taurocholate uptake to 60% of control and virtually abolished the overshoot. In the presence of a K+ gradient, the slow rate of Na+-independent taurocholate uptake was similar in the presence or absence of the amino acid. Inhibition of Na+-dependent taurocholate uptake increased nonlinearly with alanine concentration (half-maximal inhibition at approximately 1 mM) and plateaued at 5-10 mM. Kinetic studies showed that alanine significantly reduced the Vmax for taurocholate uptake from 6.32 +/- 0.22 to 3.68 +/- 0.21 nmol X mg prot-1 X min-1 but did not significantly affect taurocholate Km (38.4 +/- 3.6 vs. 29.0 +/- 4.9 microM). In contrast, the Na+-independent amino acid 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid did not affect either the initial velocity or peak uptake of taurocholate. The effects of alanine on the driving forces for bile acid uptake were directly assessed by measuring vesicle uptake of 22Na. At early time points, 22Na uptake was faster in the presence of alanine than under control conditions. These findings provide further evidence that Na+-dependent amino acids noncompetitively inhibit Na+-dependent bile acid uptake in association with accelerated dissipation of the transmembrane Na+ gradient and extend previous observations of this phenomenon made in isolated rat hepatocytes [Am. J. Physiol. 245 (Gastrointest. Liver Physiol. 8): G399-G403, 1983].

Hydroxyl/bile acid exchange. A new mechanism for the uphill transport of cholate by basolateral liver plasma membrane vesicles.

In order to characterize the driving forces for the concentrative uptake of unconjugated bile acids by the hepatocyte, the effects of pH gradients on the uptake of [3H]cholate by rat basolateral liver plasma membrane vesicles were studied. In the presence of an outwardly directed hydroxyl gradient (pH 6.0 outside and pH 7.5 inside the vesicle), cholate uptake was markedly stimulated and the bile acid was transiently accumulated at a concentration 1.5- to 2-fold higher than at equilibrium ("overshoot"). In the absence of a pH gradient (pH 6.0 or 7.5 both inside and outside the vesicle), uptake was relatively slower and no overshoot was seen. Reductions in the magnitude of the transmembrane pH gradient were associated with slower initial uptake rates and smaller overshoots. Cholate uptake under pH gradient conditions was inhibited by furosemide and bumetanide but not by 4, 4'-diisothiocyano-2,2'-disulfonic stilbene (SITS), 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (DIDS), or probenecid. In the absence of a pH gradient, an inside-positive valinomycin-induced K+ diffusion potential caused a slight increase in cholate uptake which was insensitive to furosemide. Moreover, in the presence of an outwardly directed hydroxyl gradient, uphill cholate transport was observed even under voltage clamped conditions. These findings suggest that pH gradient-driven cholate uptake was not due to associated electrical potentials. Despite an identical pKa to that of cholate, an outwardly directed hydroxyl gradient did not drive uphill transport of three other unconjugated bile acids (deoxycholate, chenodeoxycholate, ursodeoxycholate), suggesting that a non-ionic diffusion mechanism cannot account for uphill cholate transport. In canalicular vesicles, although cholate uptake was relatively faster in the presence of a pH gradient than in the absence of a gradient, peak uptake was only slightly above that found at equilibrium under voltage clamped conditions. These findings suggest a specific carrier on the basolateral membrane of the hepatocyte which mediates hydroxyl/cholate exchange (or H+-cholate co-transport). A model for uphill cholate transport is discussed in which the Na+ pump would ultimately drive Na+/H+ exchange which in turn would drive hydroxyl/cholate exchange.

Anion specificity of the jejunal folate carrier: effects of reduced folate analogues on folate uptake and efflux.

We previously reported that 3H-folate uptake by rabbit jejunal brush-border membrane (BBM) vesicles was markedly stimulated by an outwardly directed OH- gradient (pHin 7.7, pHout 5.5), inhibited by anion exchange inhibitors (DIDS, SITS, furosemide), and saturable (folate Km = 0.19 microM) suggesting carrier-mediated folate/OH- exchange (or H+/folate cotransport). In the present study, the anion specificity of this transport process was examined. Under conditions of an outwardly directed OH- gradient, DIDS-sensitive folate uptake was cis inhibited (greater than 90%) by reduced folate analogues: dihydrofolate (IC50 = 0.40 microM), folinic acid (IC50 = 0.50 microM), 5-methyltetrahydrofolate (IC50 = 0.53 microM), and (+)amethopterin (IC50 = 0.93 microM). In contrast, 10 microM (-)amethopterin had only a modest effect on folate uptake (18% inhibition) suggesting stereospecificity of the folate/OH- exchanger. The nonpteridine compounds which are transported by the folate carrier in L1210 leukemic cells (phthalate, thiamine pyrophosphate, and PO4(-3] did not inhibit jejunal folate uptake. Furthermore, folate uptake was not inhibited by SO4(-2) (4 mM) or oxalate (4 mM) thereby distinguishing this carrier from the previously described intestinal SO4(-2)/OH- and oxalate/Cl- exchangers. After BBM vesicles were loaded with 3H-folate, the initial velocity of 3H-folate efflux was stimulated by unlabeled folate in the efflux medium. The transstimulation of 3H-folate efflux by unlabeled folate was furosemide (or DIDS) inhibitable and temperature sensitive. Half-maximal stimulation of furosemide-sensitive 3H-folate efflux was observed with 0.25 +/- 0.05 microM unlabeled folate, a concentration similar to the Km for folate uptake. These data suggest that folate-stimulated 3H-folate efflux is mediated by the folate/OH- exchanger.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino acid inhibition of bile acid uptake by isolated rat hepatocytes: relationship to dissipation of transmembrane Na+ gradient.

The effects of amino acids on bile acid uptake were studied in isolated rat hepatocytes. The Na+-dependent amino acid L-alanine inhibited [14C]taurocholate uptake in a nonlinear fashion (IC50, approximately 7 mM). Kinetic studies showed that alanine (30 mM) reduced the Vmax for taurocholate uptake from 1.7 +/- 0.1 to 1.1 +/- 0.1 nmol . mg protein-1 . min-1 but did not significantly affect taurocholate Km (42 +/- 7 vs. 35 +/- 7 microM). Taurocholate uptake was also inhibited by alpha-methylaminoisobutyric acid (which shares a common Na+-dependent transport pathway with alanine but is not metabolized) and by L-glutamine (undergoes Na+-dependent hepatic uptake via a carrier distinct from that for alanine). In contrast, the Na+-independent amino acid 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid had no effect on hepatocyte bile acid uptake. Alanine induced a twofold elevation of intracellular sodium concentration as determined by the steady-state uptake of 22Na. These findings suggest that Na+-dependent amino acids noncompetitively inhibit hepatocyte taurocholate uptake by dissipating the transmembrane Na+ gradient and thereby reduce the driving forces for Na+-coupled bile acid entry. Dissipation of the Na+ gradient by substrates that undergo Na+-dependent hepatic transport may represent a novel mechanism of bile secretory failure.

Taurocholate transport by basolateral plasma membrane vesicles isolated from developing rat liver.

Taurocholate transport was characterized in basolateral plasma membrane vesicles prepared from the livers of 14-day-old Sprague-Dawley rats using a self-generating Percoll gradient method. Liver plasma membrane protein yield, intravesicular volume, and enrichments of various marker enzymes were similar to those obtained for vesicles from adult rat liver. The basolateral marker enzyme Na+-K+-ATPase was enriched 26-fold in the suckling rat basolateral membrane fraction while the bile canalicular marker enzymes alkaline phosphatase and Mg2+-ATPase were enriched only 3- and 5-fold, respectively. The activities of marker enzymes for endoplasmic reticulum, mitochondria, or lysosomes were not enriched compared with homogenate. In the presence of an inwardly directed 100 mM Na+ gradient, vesicle accumulation of taurocholate transiently reached a concentration 1.5- to 2-fold higher than that at equilibrium ("overshoot") in suckling and adult membrane vesicles, but the initial rate of taurocholate entry and peak intravesicular accumulation were markedly decreased in suckling compared with adult membrane vesicles. In the presence of an inwardly directed 100 mM K+ gradient, the rate of uptake was slower, and no overshoot occurred in either suckling or adult rat vesicles. The decreased rate of Na+-coupled taurocholate uptake by membrane vesicles from suckling rat liver could not be explained on the basis of more rapid dissipation of the transmembrane Na+ gradient. Kinetic studies demonstrated saturable, Na+-dependent taurocholate uptake for both suckling and adult vesicles. However, the Vmax for taurocholate uptake in suckling rat vesicles was less than half of the adult rate (2.46 +/- 0.13 vs. 5.25 +/- 0.22 nmol X mg prot-1 X min-1, respectively, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino acids are potent inhibitors of bile acid uptake by liver plasma membrane vesicles isolated from suckling rats.

We studied the effects of amino acids which undergo Na+-coupled cotransport on taurocholate uptake by basolateral liver plasma membrane vesicles prepared from 14-day-old rats. At concentrations similar to the total concentration of Na-dependent amino acids measured in portal blood, the Na+-dependent amino acids, L-alanine and L-glutamine, reduced the initial velocity of Na+-dependent taurocholate uptake and impaired uphill transport of the bile acid. In contrast, the Na+-independent amino acid, 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid, did not affect taurocholate uptake. The inhibitory effect of Na+-dependent amino acids on taurocholate uptake was dose dependent. Taurocholate uptake was electroneutral and the inhibition of bile acid uptake by L-glutamine was not affected by the electrical potential. In the absence of a sodium gradient, but with equal intravesicular and extravesicular sodium concentrations, L-glutamine did not inhibit bile acid uptake. With an inwardly directed Na+ gradient, 22Na+ uptake (8 s) was 27% higher in the presence of L-glutamine (5 mM) than without L-glutamine. Kinetic analysis showed that L-glutamine (5 mM) decreased the maximum velocity of Na+-dependent taurocholate uptake to 59% of control (1.62 +/- 0.20 versus 2.73 +/- 0.30 nmol . mg-1 protein . min-1; p less than 0.002), but had no effect on the taurocholate Km (91.7 +/- 26.4 versus 97.1 +/- 25.4 microM). We conclude that physiologic concentrations of Na+-dependent amino acids markedly inhibit taurocholate uptake by membrane vesicles from 14-day rat livers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticosteroid therapy in alcoholic hepatitis. A prospective, double-blind randomized study.

In a prospective, randomized, double-blind study of prednisolone therapy of acute alcoholic hepatitis, 39% of the total group of 28 patients died. Mortality and cumulative survival were similar in steroid- and placebo-treated patients. After 14 days of therapy, the serum albumin concentration and white blood count were significantly higher in the steroid group, but all other parameters were similar. An increased risk of fungal infection appeared to be associated with steroid therapy.

Taurocholate transport and Na+-K+-ATPase activity in fetal and neonatal rat liver plasma membrane vesicles.

The ontogenesis of Na+-K+-ATPase activity and Na+-taurocholate cotransport was studied in basolateral plasma membrane vesicles from fetal and neonatal rat liver. Membrane vesicles from each age group were 30-fold enriched in the basolateral marker enzyme Na+-K+-ATPase, 4- to 7-fold enriched in the bile canalicular membrane marker enzymes alkaline phosphatase and Mg2+ ATPase, and not significantly enriched in activities of marker enzymes for intracellular organelles. Na+-K+-ATPase activity was significantly lower in basolateral membranes from late fetal (day 21-22) and neonatal (day 1) rat liver. Kinetic analysis of Na+-K+-ATPase activity at various concentrations of ATP revealed that the maximum velocity of enzyme reaction (Vmax) for Na+-K+-ATPase was 70 and 90% of adult activity in the fetus and the neonate, respectively. The ATP Km was significantly lower in the neonate than the adult, suggesting a higher affinity of the neonatal enzyme for ATP. In contrast to the early maturation of Na+-K+-ATPase, transport of taurocholate was markedly lower in both fetal and neonatal vesicles compared with the adult. Taurocholate uptake on day 19 of gestation did not differ in the presence of a Na+ or K+ gradient, and uphill transport, as indicated by an overshoot, did not occur. On day 20 taurocholate uptake was stimulated by a Na+ compared with a K+ gradient, and accumulation of isotope above equilibrium was demonstrated. Na+-dependent transport of taurocholate by late fetal (day 22) and neonatal vesicles was saturable but the Vmax at each age was significantly lower and the apparent Km higher in developing compared with adult membrane vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Early idiopathic hemochromatosis with absent stainable bone marrow iron stores.

Early idiopathic hemochromatosis was diagnosed in a 52-year-old woman during the course of a hospitalization for another disorder. Quantitative studies revealed massive hepatic parenchymal siderosis and absent stainable marrow iron. Additionally, intestinal absorption and hepatic sequestration of radiolabeled iron were elevated. These studies in a patient with very early hemochromatosis, before organ damage, complement observations previously made in patients with advanced disease and provide further support for the concept that this disorder may result from impaired reticuloendothelial handling of iron.

Effect of splenectomy of hepatic bilirubin clearance in patients with hereditary spherocytosis. Implications for the diagnosis of Gilbert's syndrome.

BRT and CBR were determined from studies of radiobilirubin kinetics in 14 patients undergoing splenectomy for hereditary spherocytosis. Studies were conducted both before and after the operation in order to assess the effects of the postsplenectomy fall in BRT on CBR. Splenectomy led to a doubling of the RBC-t1/2 from 13.0 +/- 1.7 (S.E.) days to 26.1 +/- 1.5 and a fall in BRT from 15.9 +/- 4.4 mg/kg/day to 4.3 +/- 0.9. In seven patients (group A) initially normal values for CBR were unaltered by surgery. In the remaining seven (group B), low preoperative values for CBR, suggestive of Gilbert's syndrome, uniformly improved after splenectomy, becoming normal in five patients. Nevertheless, family studies and reduced values for UDPGT activity supported the initial impression of concomitant Gilbert's syndrome in group B. These studies suggest the existence of a latent state for Gilbert's syndrome that, in some patients, may be unmasked by a hemolytic stress. As such, they have important implications for both pedigree analysis and incidence studies of this condition.

A model of fulminant hepatic failure in the rabbit.

A highly reproducible model of fulminant hepatic failure was developed by administering intravenously the selective hepatotoxin galactosamine hydrochloride (4.25 mmoles per kg) to genetically uniform rabbits. The great majority of rabbits died between 21 and 44 hr after injection following a period of coma which lasted 2.6 hr on average. Serum biochemical tests and liver histology reflected massive hepatic injury. Changes in plasma ammonia and amino acid concentrations, in coagulation parameters, and in the electroencephalogram were similar to those found in human fulminant hepatic failure. This model appears promising for future studies of the pathogenesis and treatment of fulminant hepatic failure.