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The uptake of riboflavin was studied in everted sacs of rat intestine using [14C]riboflavin and [3H]polyethylene glycol to define the mechanism of mucosal membrane transport. Three-minute incubations were used throughout. Initial studies indicated the presence of saturable uptake in duodenum, jejunum and ileum. Studies in jejunum at low riboflavin concentrations demonstrated saturable uptake [Km = 0.154-0.177 mumol/L, Vmax = 19.6-25.8 pmol/(100 mg dry tissue.min)]. In contrast, uptake was linear with respect to higher concentrations of vitamin (10-50 mumol/L). Uptake at low (0.1 mumol/L) but not high (20 mumol/L) riboflavin concentrations was inhibited by 50 mumol/L lumiflavin, anoxia, 5 mmol/L indoacetamide, Na(+)-free buffer and low temperature (Q10 = 1.64). Conclusions are as follows: 1) Saturable uptake of riboflavin occurs throughout the rat small intestine; 2) uptake by the jejunal mucosa is competitively inhibited and is consistent with a transport carrier located in the brush border membrane; 3) saturable uptake is energy-dependent and may be directly or indirectly driven by a Na+ gradient; and 4) riboflavin is also taken up by rat intestinal mucosa by a nonsaturable, energy-independent mechanism consistent with simple, passive diffusion.

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The first step in the intestinal absorption of phosphorylated forms of vitamin B6 is intraluminal hydrolysis mediated by alkaline phosphatase. The present studies were performed to evaluate the effect of amino acids and oligopeptides, the products of protein digestion, on the hydrolysis of pyridoxal 5'-phosphate. Models utilized rats and included a cell-free in vitro system and the in vivo, single-pass, perfused jejunal segment. In vitro all amino acids and oligopeptides tested significantly inhibited pyridoxal 5'-phosphate decay (hydrolysis). The degree of inhibition of decay was dependent on the particular compound used, the concentration of that compound, and the pH of the medium. Similar effects for L-lysine concentration and perfusate pH were demonstrated in perfused segments in vivo; by contrast, L-lysine had no effect on pyridoxine uptake. These studies demonstrate that intraluminal hydrolysis of phosphorylated vitamin B6 may be modulated by yet other intraluminal constituents and conditions.

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Phosphatase-mediated hydrolysis is the first step in the intestinal absorption of pyridoxal 5'-phosphate (PLP). Studies presented here evaluated the effects of PLP-protein binding and pH on intestinal hydrolysis in the rat. Models included in vitro PLP decay and in vivo PLP disappearance from perfused jejunal segments. Pyridoxal 5'-phosphate binding to albumin was pH-, PLP concentration-, and albumin concentration-dependent. Binding occurred at higher pH levels (5-7.4) and markedly inhibited hydrolysis of 2 microM PLP both in vitro and in vivo. At low pH (3-4), alkaline phosphatase was still active with PLP as substrate; binding of PLP to albumin was negligible; and PLP hydrolysis was unaffected by even a high concentration of albumin. The pH required to prevent binding and thus in turn prevent inhibition of hydrolysis was a function of albumin concentration: the higher the concentration, the lower the pH necessary. The present studies suggest an important role for the low pH values resulting from gastric acid secretion in the normal absorption of dietary PLP, and raise questions about the implications of widespread use of acid-lowering therapeutic modalities on vitamin B6 nutritional status.

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The effect of ethanol on intestinal hydrolysis of pyridoxal 5'-phosphate (PLP), the first step in PLP absorption, was evaluated in the rat. Models included PLP decay during in vitro incubation and PLP luminal disappearance during in vivo perfusion of jejunal segments. Ethanol inhibited PLP in vitro decay (pH = 7.4 and 3.0) and in vivo disappearance (pH = 7.4) in a concentration-dependent manner (1-4% w/v). At pH = 7.4, 4% w/v ethanol inhibited in vitro PLP decay by 48% (p less than 0.001) and in vivo PLP disappearance by 55% (p less than 0.001). This inhibition was reproduced in vitro with other alcohols but not with osmotic controls, paralleled in vitro changes in phosphatase activity in the presence of ethanol, and was completely reversed in vivo after ethanol was removed from the perfusing solution. The inhibition of intestinal PLP hydrolysis may possibly be one of the mechanisms by which a high percentage of alcoholics become biochemically vitamin B6 deficient.

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Hepatitis occurring in patients with congenital X-linked or common variable hypogammaglobulinemia has been reported to follow a usual pattern of rapid progression from acute hepatitis to either chronic active hepatitis or death. This article describes a 21-year-old black man with congenital X-linked hypogammaglobulinemia who has been known to be a hepatitis B-associated antigen carrier during a 9-year follow up period. Liver enzyme studies are normal. His immunologic studies demonstrate no impairment of cellular immunity. His brother, who has the same disease and lives in the same household, has remained negative for hepatitis B-associated antigen. This patient demonstrates that not all hypogammaglobulinemia patients invariably have a severe clinical course with hepatitis.

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The present studies utilized the in vivo single-pass, luminally perfused intestinal segment model in rats to evaluate pyridoxine (PN) uptake under conditions that permitted prolonged exposure of mucosa to relatively constant PN concentrations. Perfusates contained [14C]PN, unlabeled PN, and [3H]polyethylene glycol in buffer. Uptake was constant for 1 h and correlated with water absorption. Uptake of 0.2 microM PN was highest in the duodenum, intermediate in the jejunum, and lowest in the ileum. When expressed as uptake/micromolar PN, uptake of 1 mM compared to 0.2 microM PN was decreased by 37.5% in duodenum (P less than 0.001) and 14.4% in jejunum (P less than 0.05); uptake/micromolar PN were similar in ileum. In duodenum saturable uptake was apparent for 2-100 microM PN and was not explainable by a membrane carrier, presence of bile or lumen-plasma concentration gradients. Conclusions were: 1) uptake of PN by in vivo perfused intestinal segments decreases from proximal to distal; 2) the greater uptake proximally was associated with a saturable component of uptake that was greatest in duodenum, less, but significant, in proximal jejunum and absent in distal ileum and 3) saturation of uptake in the rat proximal small intestine was compatible with a role for mucosal metabolism of absorbed PN in the enhancement of uptake of PN at low luminal concentrations.

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Fever, lymphadenopathy, exfoliative dermatitis, and evidence of drug-induced liver injury developed in a 16-year-old girl three weeks after beginning therapy with phenytoin and phenobarbital. This clinical syndrome can be caused by either of these structurally related drugs but has been more frequently attributed to phenytoin. In vitro studies disclosed marked reactivity of this patient's lymphocytes to concentrations of both drugs, which encompassed their measured serum levels. The demonstration of dual reactivity raises concerns about continuing administration of phenobarbital during an apparent phenytoin-induced reaction. Whether this potential risk is greater than the risk of stopping all anticonvulsant medications in a patient with a seizure disorder is not known and remains to be established.

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The effects of acute ethanol exposure and chronic ethanol ingestion on jejunal mucosal uptake of 2 microM pyridoxine X HCl (PN) was studied in rats. Experimental models included in vitro everted sacs and in vivo perfused segments. The presence of 4% w/v but not 1% w/v ethanol (mucosal side) acutely enhanced PN uptake by 30 to 76%. Ethanol removal rapidly returned uptake rates to base-line. Histological evidence of mucosal injury in perfused segments paralleled observed changes in PN uptake. After chronic ethanol ingestion (1 yr), PN uptake from media without added ethanol was not statistically different from control values. Conclusions are: 1) acutely, enhancement of PN mucosal uptake by ethanol in rat jejunum is associated with the presence of a high ethanol concentration, is rapidly reversible, and correlates with histological evidence of mucosal injury; and 2) chronic ingestion of ethanol appears to have no further effect on PN uptake in the rat.

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The physiology of the liver involves metabolism, excretion, and body defense. Within the context of metabolism, the liver is the site of a multitude of biochemical reactions essential to the human organism; included are synthesis, degradation, interconversion, storage, and biotransformation. A working knowledge of the relationship between structure and function and of hepatic processes under normal conditions is essential for understanding the derangements observed in clinical diseases affecting the liver. Our overview of hepatic physiology highlights some of these facets of normal hepatic anatomy and function of special relevance to the physician confronting liver dysfunction and its varied clinical consequences.

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The relative effects of perfusate alkaline phosphatase activity and net water absorption on 2 microM pyridoxal 5'-phosphate (PLP) luminal disappearance from rat jejunum were studied in a single-pass, in vivo perfused intestinal segment model. Perfusate consisted of unlabeled PLP in buffer (pH = 7.4). Net water flux was monitored by inclusion of [3H]polyethylene glycol. PLP was measured by the [14C]tyrosine apodecarboxylase assay. Single and multiple regression analysis of results during perfusion of 2 microM PLP in Krebs bicarbonate buffer demonstrated no correlation between perfusate alkaline phosphatase activity and net water absorption and significant correlations between PLP luminal disappearance and both perfusate alkaline phosphatase activity and net water absorption. Correlation for the latter was improved when disappearance results were corrected for variations in perfusate alkaline phosphatase activity. When perfusate buffers were selected to yield divergent rates of net water absorption, the one associated with greater net water absorption was also associated with greater PLP disappearance. That this could not be explained by changes in perfusate alkaline phosphatase activity was demonstrated both by assessment of the rate of decay of PLP added in vitro to exited perfusate incubated at 37 degrees C and by measurement of alkaline phosphatase activity under conditions defined by the buffers using a modified spectrophotometric assay. Conclusions were: (1) In vivo PLP luminal disappearance correlates significantly with both perfusate alkaline phosphatase activity and net water absorption; (2) these two factors appear to act as independent variables; and (3) future studies on PLP intestinal absorption will need to take both of these variables into account in the interpretation of results.

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The disappearance of pyridoxal 5'-phosphate (PLP) from the lumen of in vivo perfused segments of rat jejunum was evaluated utilizing a single-pass technique. Net water flux was monitored by [14C] dextran, a nonabsorbable volume marker. Unlabeled PLP was measured by the tyrosine apodecarboxylase assay. PLP disappearance was linear with respect to PLP concentration at concentrations below 300 micrometers but was saturable at high concentrations (3 micrometers). PLP disappearance was significantly inhibited by 1 micrometer pyridoxamine 5'-phosphate and 5 micrometers and 10 micrometers l-phenylalanine but not by 1 micrometer pyridoxamine. Both in vivo disappearance (during perfusion) and in vitro PLP decay (exiting perfusate used as medium) correlated with the measured alkaline phosphatase activity of exiting perfusate under low-phosphate (1.1 micrometer) conditions. In contrast, in vivo PLP disappearance was not correlated with perfusate alkaline phosphatase activity under high-phosphate (80 micrometer) conditions. When exiting perfusate was ultracentrifuged at 105,000 x g for 1 hour, only 35% of the initial alkaline phosphatase activity remained in the supernatant. Conclusions were: 1) PLP disappearance from the lumen of an in vivo perfused segment of rat jejunum is saturable and inhibited by l-phenylalanine; 2) PLP disappearance appears in part to be a function of intraluminal alkaline phosphatase; and 3) A major portion of the alkaline phosphatase activity measured in the exiting perfusate represents membrane-bound enzyme.

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Over a 2-yr period, 3 patients with metastatic liver disease presented with a clinical course compatible with fulminant hepatic failure. The course was characterized by abdominal pain, jaundice, rapidly deteriorating mental status, high-serum enzyme values (SGOT, LDH, alkaline phosphatase), prolonged prothrombin times, and death within 1-12 days after hospitalization. At autopsy a similar histologic picture was present in each: extensive infiltration and replacement of liver by tumor and widespread infarction of remaining parenchyma. To place these 3 cases into a proper perspective, they were compared with 3 similar, previously reported cases (1 primary and 2 metastatic); and a retrospective autopsy review of metastatic liver disease occurring over a 4-yr period was performed. Fulminant hepatic failure due to extensive parenchymal infarction appears to represent an uncommon, but distinct entity in the overall spectrum of metastatic liver disease.

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A patient with congenital x-linked agammaglobulinemia, who had two separate episodes of an apparent bacterial purulent hepatic triaditis in the absence of any known local predisposing factors, is presented. These episodes may reflect the increased susceptibility of an immunodeficient patient to bacterial infections. This case demonstrates the need to consider hepatic involvement in the work-up of fevers of undetermined origin in immunodeficient patients, even in the absence of any radiologic or sonographic evidence of mechanical biliary tract obstruction.

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The effect of vitamin B6 deficiency on the uptake and metabolism of pyridoxine x HCl by rat jejunum was studied in vitro utilizing everted sacs. Rats were studied in three grops: control, B6-replenished, and B6-deficient. Plasma and jejunal tissue pyridoxal phosphate levels in deficient rats were profoundly depressed compared to control and replenished groups. Uptake and phosphorylation rates for pyridoxine x HCl were similar among the three groups. Jejunal pyridoxal phosphate levels were unchanged after incubation of sacs from control and replenished rats for 30 min in 2 and 20 micro M pyridoxine x HCl under low phosphate (1.1 mM) conditions. Jejunal pyridoxal phosphate significantly increased, however, during similar 30-min incubations in sacs of deficient rats under low phosphate conditions and in control sacs under high phosphate (80 mM) conditions. Conclusions are 1) in vitro uptake and phosphorylatin remain intact during vitamin B6 deficiency; 2) jejunal pyridoxal phosphate is maintained at a constant level in sacs from control and replenished rats in spite of ongoing uptake and phosphorylation of pyridoxine; 3) jejunal pyridoxal phosphate significantly increases during incubationin sacs from vitamin B6-deficient rats; and 4) absorbed pyridoxine can serve directly as the source for this increase.

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The luminal disappearance of unlabeled pyridoxal-5'-phosphate (PLP) was studied in vivo in rat jejunum utilizing a perfused segment model. The PLP was measured by a tyrosine decarboxylase assay. [14C]Dextran was used as a nonabsorbable marker to calculate net water absorption. Initial studies validated the use of [14C]dextran as a nonabsorbable marker and established proper conditions of segment perfusion and sample collection for the measurement of PLP luminal disappearance. Subsequent studies demonstrated significant (67.2%) but incomplete inhibition of PLP disappearance by 80 mM phosphate. When nonperfused PLP in 1.1 mM phosphate buffer or perfused PLP in 80 mM phosphate buffer were incubated in vitro for 15 minutes at 37 degrees in a water bath, only negligible changes in PLP concentration were noted. However, when perfused PLP in 1.1 mM phosphate buffer was similarly incubated in vitro, there was a rapid decay in PLP concentration. L-Phenylalanine (5 mM) significantly inhibited this in vitro decay. Conclusions derived from these studies are: 1) The model used is a valid means of studying in vivo luminal disappearance of PLP in the rat jejunum; 2) a major portion of the disappearance seems to involve hydrolysis by alkaline phosphatase; 3) a significant portion of this hydrolysis occurs intraluminally; and 4) a second mechanism of PLP disappearance, which is nonphosphatase-mediated, also appears operative and may represent absorption of the intact, phosphorylated vitamin.

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The absorption and phosphorylation of 3H-pyridoxine . HCl were studied in vivo in isolated loops of rat jejunum. Uptake was rapid and linear over the concentration range of 0.2-1 mM; tissue content of absorbed vitamin was saturable and consisted primarily of phosphorylated forms of vitamin B6. Phosphorylation was saturable with a Km of 11.6 micronM and a Vmax of 1.65 nmol/5 min/g wet tissue. Inhibition of phosphorylation changed neither the t 1/2 of 3H-pyridoxine . HCl disappearance from the lumen nor the calculated uptake after either 5-min or 30-min absorption periods. Inhibition of phosphorylation, however, significantly decreased the t 1/2 for transmural absorption and significantly increased the calculated transmural absorption after a 5-min absorption period. These studies indicate that (a) pyridoxine absorption, over the concentration range tested, is nonsaturable and consistent with passive diffusion; (b) jejunal phosphorylation of pyridoxine occurs in vivo, is saturable, and results in saturation of tissue content of the absorbed vitamin; and (c) phosphorylation has no significant effect on the uptake of pyridoxine but significantly delays the transmural absorption of a finite amount of the vitamin.

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The phosphorylation and dephosphorylation of absorbed vitamin was studied in rat jejunal everted sacs during in vitro uptake of [3H]pyridoxine.HCl. Kinetic studies during 4-min incubations demonstrated that phosphorylation was saturable (Km, 13.3 micron; Vmax, 0.906 nmol/4 min/g wet tissue) and was significantly inhibited by both structural and metabolic inhibitors. Longer incubations (30-min) demonstrated similar saturation and inhibition of net phosphorylation. Dephosphorylation of the phosphate esters formed by the phosphorylation step also occurred, as demonstrated by pulse-chase experiments. Disappearance of these phosphates was initially rapid, approximated first order kinetics, and apparently was mediated by a phosphatase. Whereas phosphorylation did not appear to affect initial uptake rates for [3H]pyridoxine.HCl by the jejunum, net phosphorylation after more prolonged incubations qualitatively paralleled accumulation of total absorbed vitamin in tissue over the same time. The primary effect of phosphorylation during jejunal uptake of pyridoxine by rat jejunum was to increase the accumulation of absorbed pyridoxine in tissue during prolonged incubations. Dephosphorylation had the net effect of limiting the magnitude of that accumulation.

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Blood-pressure and pulse-rate changes were evaluated prospectively in 50 patients undergoing uncomplicated liver biopsies and retrospectively in 4 patients who, since 1973, had recognized postbiopsy hemorrhage requiring transfusion. In uncomplicated biopsies a wide range of variations in vital signs was encountered between "baseline" and "before" controls and between controls and postbiopsy measurements. To place the changes in perspective, percentile scales were developed for percent maximum deviation from control for systolic blood pressure, diastolic blood pressure, and pulse rate. Analysis of changes in patients with significant hemorrhage revealed; (1) marked changes in vital signs in the early (2-hr) postbiopsy period; (2) the association of early hypertensive changes with pain followed by later evidence of hemorrhage in two of the four patients; (3) the lesser helpfulness of pulse change (1 of 4 bleeders) as compared to blood pressure change (4 of 4 patients).

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