Absorption and Excretion of an Oral Dose of Tritiated Vitamin K1 in Man

S ummary . The radioactivity in the plasma, urine and faeces has been determined in three studies carried out in two normal men after an oral dose of tritiated vitamin K₁ (50–100 μCi). Radioactivity in the plasma was detected by 30 min, reached a peak at 2–4 hr and then declined relatively rapidly. A low level of radioactivity persisted in the plasma for at least 96 hr. Most of the radioactivity in the plasma at the peak time was in the form of vitamin K₁ as shown by thin-layer chromatography; the remaining plasma radioactivity was due to water-soluble material.
Examination of serum taken at the time of peak absorption showed that most of the radioactivity could be floated to the top in the ultracentrifuge (in a medium of density 1.21) and appeared in the void volume on gel filtration (Sephadex G-200): The results suggest that absorbed vitamin K₁ in plasma becomes associated with chylomicra mainly but that some may also be associated with other lipoproteins. Faecal excretion of radioactivity was maximal in the first 2 days and appeared to be essentially complete after 5 days; the total faecal radioactivity accounted for about 52% of the ingested dose of labelled vitamin K₁, and about 18% of the dose was recovered as unchanged vitamin K₁. The faecal results suggest that at least half of the ingested dose was absorbed. Excretion of radioactivity in the urine was greatest in the first 24 hr and 8–19% of the administered dose of labelled vitamin K₁ was recovered from the urine after 3 days. The urinary radioactivity was present in water-soluble and chloroform-soluble forms.     

Effect of Warfarin Anticoagulation on Vitamin-K1 Metabolism in Man

S ummary . Three normal men were injected intravenously with 1 mg [1',2'-³H₂]-vitamin K₁ before and after treatment with therapeutic doses of warfarin for 8–10 days. Warfarin treatment caused a delayed clearance of lipid-soluble radioactivity from the plasma. This was found to be due to the accumulation in the plasma of a metabolite with the properties of vitamin K₁ oxide as shown by thin-layer chromatography: the rate of clearance of vitamin K₁ from the plasma was not affected. Under warfarin treatment there was about a two-fold increase in the urinary excretion of radioactivity.     

Biliary Iron Excretion in Rats following Pyridoxal Isonicotinoyl Hydrazone

S ummary Biliary excretion of iron after administration of pyridoxal isonicotinoyl hydrazone (PIH), a recently identified effective iron-chelating agent, was investigated in rats. PIH administered both intraperitoneally and orally was shown to increase significantly ⁵⁹Fe excretion into bile of rats which had previously been injected with ⁵⁹Fe-transferrin to label hepatic parenchymal cells. ⁵⁹Fe-PIH appears in bile as early as 15 min after chelator administration and the peak of ⁵⁹Fe-radioactivity in bile is seen 1–5 h following intraperitoneal PIH injection. PIH, administered intraperitoneally, 125–250 mg/kg, increased 24 h biliary radioiron excretion about 35 times and in addition increased urinary and faecal iron excretion. When PIH was given immediately before ⁵⁹Fe-transferrin, 24 h cumulative biliary ⁵⁹Fe excretion was even higher. PIH was also demonstrated to increase biliary excretion of radioiron released from ⁵⁹Fe-haemoglobin catabolysed in reticuloendothelial cells. The effect of PIH was confirmed by estimation of biliary iron concentration using the method of atomic absorption spectrophotometry. Repeated PIH administration to rats decreased ⁵⁹Fe radioactivity in liver and kidney and increased urinary and faecal iron excretion.     

Potential role of vitamin K2 as a chemopreventive agent against hepatocellular carcinoma

Vitamin K, a cofactor necessary for the production of several antihemorrhagic factors, can inhibit the growth of various types of cells derived from neoplasms. In hepatoma cells, vitamin K₂ causes cell-cycle arrest and apoptosis. Vitamin K₂ is widely used in Japan to treat osteoporosis. The safety, relatively low cost and ease of use of vitamin K₂ have led to good compliance with treatment. The result of preliminary clinical trials in patients with chronic liver diseases are intriguing and suggest that vitamin K₂ might reduce the risk of hepatocellular carcinoma (HCC) in patients with liver cirrhosis as well as prevent disease recurrence after curative therapy in patients with HCC. This article reviews the potential role of vitamin K₂ as a chemopreventive agent against HCC and discusses future directions for clinical trials.     

Evidence for Rapid Loss of Newly Synthesized Haemoglobin S Molecules in Sickle Cell Anaemia and Sickle Cell Trait

The present study indicates that newly completed haemoglobin S molecules rather than free β^S-chains are preferentially bound to the reticulocyte stroma of individuals with sickle cell trait and sickle cell anaemia. Reticulocytes from individuals with HbAA, AS and SS were incubated with [³H]leucine from 1.25 min to 120 min. Unlike the stroma-free haemolysates, the stroma of all individuals contained an excess of labelled β-chains relative to α-chains after short incubation times. In haemoglobin AA and AS individuals, the stromal β^A radioactivity was 1–2% of the total cellular β^A radioactivity. In haemoglobin AS and SS individuals, the stromal β^S radioactivity was 3–5% and 10–20% of the total cellular β^S radioactivity, respectively. All of the stroma β-chain radioactivity was associated with completed haemoglobin molecules. Because of the unlabelled free α-chain pool found in reticulocytes, after short incubation times newly completed haemoglobin molecules have predominantly labelled β-chains and unlabelled α-chains. These findings suggest that part of the discrepancy between the stroma and stroma-free haemolysate α/β radioactivities seen in HbAS and HbSS individuals may result from normal labelling kinetics.
A pulse chase experiment performed on an individual with HbSS revealed that completed HbS molecules, in addition to being associated with the stroma, were lost from the cell.     

The Contribution of Vitamin K2 (Menaquinones) Produced by the Intestinal Microflora to Human Nutritional Requirements for Vitamin K

Background: Coagulopathy manifest by elevation of the prothrombin time (PT) in patients receiving broad spectrum antimicrobials indirectly suggests a role for intestinal microflora synthesized menaquinone (MK) in the maintenance of normal coagulation. Nonetheless, no direct evidence is available to support this contention. Objective: Our objective was therefore to provide evidence that bacterially produced MK may be absorbed by the distal small bowel of humans. Methods: Using a cell harvester, Staphylococcus aureus (ATCC 29213) was grown in 12-L batches, harvested, and extracted by high performance liquid chromatography (HPLC) to obtain 8 mg of pure MK. Four normal volunteers were placed on a diet severely restricted in vitamin K, (median 32–40 U/day), and were given warfarin to maintain an International Normalized Ratio of approximately 2.0. On the 10th day of warfarin administration, nasoileal intubation was performed and 1.5 mg of MK was delivered into the ileum. PI, factor VII, II and serum vitamin K₁ levels were monitored throughout the study. Results: Mean serum vitamin K₁ levels were reduced to 30% of the prediet value at the time of MK administration. Within 24 h of ileal MK administration, there was a significant (p < 0.05) increase in the factor VII level of 0.28 ± 0.10 U/ml (mean ± SEM) and a significant decrease of 2.5 (± 0.1) s in the PT, whereas in the control phase (during which no MK was administered), there were no significant changes in the PT or factor VII at corresponding time intervals. Conclusion: These data provide direct evidence for the absorption of vitamin K₂ from the distal small bowel, supporting a definite role for bacterially synthesized vitamin K₂ in contributing to the human nutritional requirements of this vitamin.     

Studies of the Kinetics of Purified Conjugated Bilirubin-3H in the Rat

Radio-labeled conjugated bilirubin was purified from rat bile by affinity chromatography. Following the intravenous injection of tracer does of this material, the initial fractional plasma disappearance rate of conjugated bilirubin-³H in the normal Sprague-Dawley rat was found to be approximately 50% faster than that for unconjugated bilirubin-³H (0.51 ± 0.04 [SE] vs. 0.35 ± 0.02 min.⁻¹; P > .001). Hepatic recovery studies in the rat indicated that, over the first four minutes after injection, disappearance of cholephilic anions from plasma is accounted for almost entirely by hepatic uptake. Hence, these studies demonstrate that hepatic uptake of conjugated bilirubin is substantially faster than that of unconjugated bilirubin. Net hepatic clearance of conjugated bilirubin in normal rates was three-fold greater than that of unconjugated bilirubin (0.94 ± 0.16 vs. 0.30 ± 0.03 ml ./min./100gm. body weight; P > .001), presumably reflecting both the more rapid hepatic uptake and the ability of the formar pigment to by-pass the conjugation step. Hepatic uptake of conjugated bilirubin was shown to be inhibited by uncojugated bilirubin, sulfobromophthalein and indocyanine green but not by glycocholate. These observations cannot be explained by simple diffusion and suggest that the hepatic uptake mechanism for conjugated bilirubin is the same as that for the unconjugated pigment.     

Turnover of Ethyl-Linoleate in Rat Plasma and Its Distribution in Various Organs

The fate of [¹⁴C]ethyl-linoleate (EthLin) after its intravenous administration was investigated in pentobarbital-anesthetized rats. The disappearance of [¹⁴C]EthLin from the plasma was very rapid and followed quite closely a biexponential function of time. Fitting of the experimental data to a two-compartmental mammillary model revealed that the labeled compounds are eliminated from the plasma with a half-life of <1 min during the early time following the intravenous injection and that a large portion of the EthLin is hydrolyzed instantly to linoleic acid and ethanol. About 9–11 % of the plasma [¹⁴C]EthLin or its breakdown products are irreversibly cleared from the plasma compartment each minute. Most of the ¹⁴C-labeled compounds that originated in the plasma were recovered in the rat liver and lungs and to a lesser extent in the heart, spleen, and kidneys. Two hr after the [¹⁴C]EthLin administration, -2.5–5.5% of the total radioactivity in the various organs was still associated with EthLin. Such accumulations, although relatively small, indicate that fatty acid ethyl esters (FAEEs) may be taken up from the plasma. Thus, some of the FAEEs that are formed in certain organs may spillover to the circulating blood where much of it would be hydrolyzed to free fatty acids, but reuptake from the plasma may still account, to some extent, to FAEE-induced damage in chronic alcohol abusers.     

A Vitamin B12 Binder with Transcobalamin I Characteristics Synthesized and Released by Human Granulocytes in Vitro

S ummary . In-vitro synthesis and release of a vitamin-B₁₂ binding protein by peripheral leucocytes derived from healthy subjects and patients with chronic myeloid leukaemia (CML), acute promyelocytic leukaemia (APL) and acute myeloblastic leukaemia (AML) were investigated.
Myeloid cells, incubated in a nutrient medium containing [³H]leucine, incorporated labelled amino-acid into the vitamin-B₁₂ binding protein with an increase of the unsaturated vitamin-B₁₂ binding capacity (UBBC) of the cells.
The increase in the UBBC of the medium was due to the presence of the newly produced leucocyte binder which was released into the medium by the cells during incubation. On chromatography the newly synthesized binder was similar to transcobalamin I.
The incorporation of [³H]leucine into the leucocyte binder by mature granulo-cytes and undifferentiated myeloblasts was very limited and reached a maximum after 60 min of incubation. Cells from CML and APL patients showed a higher rate of incorporation of the labelled amino-acid which reached a plateau after 40 hr. The increase in the UBBC of the leucocyte binder was paralleled by the incorporation of [³H]leucine.
The percentage of immature myeloid cells in the incubation mixture (promyelocytes to stab forms) was correlated with both the incorporation of [³H]leucine and with the increase in UBBC.     

Patient Variation in Pernicious Anaemia, as Shown in a Clinical Trial of Cyanocobalamin, Hydroxocobalamin and Cyanocobalamin–Zinc Tannate

Cyanocobalamin, hydroxocobalamin and cyanocobalamin-zinc tannate were given in turn, as a single dose equivalent to 500 μg. of vitamin B₁₂, to twelve patients who had untreated Addisonian pemicious anaemia. The order in which the drugs were given to each patient was determined by a series of random numbers. Following the first injection, frequent measurements were made of serum vitamin B₁₂ activity until this was reduced to 100 pg./ml. Then the second drug was given with the same follow-up, and ultimately the third drug.
In every case, serum concentrations of vitamin B₁₂ greater than 140 and 100 pg./ml. persisted after hydroxocobalamin and cyanocobalamin-zinc tannate for twice as long as after cyanocobalamin. However, differences between patients were very great, such that the entire trial with the three drugs was completed in 11 months in one case but lasted more than 4 years in another. Variation between patients makes it impossible to anticipate the duration of effect of a single injection of one of these drugs in any patient.
Studies were made of clearance from injection sites using radioisotopically labelled drugs. Cyanocobalamin and hydroxocobalamin were both cleared with a half-time of 30–100 minutes, whereas that of cyanocobalamin-zinc tannate was 48–130 hours.
Urinary excretion of radioactivity was measured in parallel with microbiological assay of urinary vitamin B₁₂. Good agreement was found between the two methods in almost all cases tested. Following injections of cyanocobalamin and hydroxocobalamin most of the excretion occurred in the first 24 hours; with hydroxocobalamin the excretion was less than with cyanocobalamin. The urinary excretion following injection of the zinc tannate complex was very much less than with the other two drugs and most of the excretion occurred after the first 24 hours.     

Uptake of Vitamin B12 by Phytohaemagglutinin-Transformed Lymphocytes

Phytohaemagglutinin (PHA)-transformed lymphocytes have been used as a model cell system to study the uptake of radioactive vitamin B₁₂ by haemopoietic cells. Both mature granulocytes and PHA-transformed lymphocytes took up more vitamin B₁₂ than mature, non-transformed lymphocytes. Uptake of vitamin B₁₂ by PHA-stimulated lymphocytes was greatest at 48–72 hr of culture, i.e. at about the time or just before the time of peak DNA synthesis.
Vitamin B₁₂ deficient lymphocytes took up significantly less vitamin B₁₂ than normal lymphocytes. Folate deficient lymphocytes took up an average of about 50% more vitamin B₁₂ than normal but the difference was not statistically significant for the numbers tested. Vitamin B₁₂ uptake by PHA-stimulated lymphocytes was related to their rate of RNA synthesis (measured by ³H-uridine uptake) and was closely related to active cytoplasmic protein synthesis since it was rapidly inhibited by puromycin and cycloheximide.     

Absorption of Vitamin B12 by the Guinea-Pig

The gastrointestinal distribution and subcellular localization of radioactivity in the ileum of the guinea-pig was determined 2 hr after oral feeding of physiological doses of cyano-, methyl- and 5' desoxyadenosyl-cobalamin. The gastrointestinal distribution of the three analogues was similar although the uptake of methyl- and adenosylcobalamin by the ileum was less than that of cyanocobalamin. All three analogues were significantly localized in the mitochondrial fraction of the ileal mucosa during absorption.
Guinea-pigs were injected with sodium fluoroacetate, a drug which is thought to interfere with the conversion of cyano- to adenosylcobalamin. Large doses of the drug caused a marked delay in gastrointestinal transit. The subcellular distribution of radioactivity in the ileum was similar in the control group and those pretreated with a small dose (5μg/100 g) of fluoroacetate.
It is concluded that the mitochondrial localization of vitamin B₁₂ during absorption by the ileum plays a fundamental role in the transport of the vitamin but that interconversion of cyano- to adenosylcobalamin is not the reason for this localization.     

Plasma Clearance of 125I-labelled Haemopexin in Normal and Haem-loaded Rabbits

S ummary . Plasma clearance of ¹²⁵I-labelled rabbit haemopexin has been studied in six normal control rabbits and in a test group of rabbits haem-loaded with 25 mg of haem.
Following intravenous injection, equilibration of ¹²⁵I-haemopexin between intravascular and extravascular compartments appeared to be complete within 24 hr and the decline in plasma activity then became constant in rate. The plasma activity curve was resolved into two exponential functions of time and from the data, fractional catabolic rate, intravascular:extravascular distribution of haemopexin and total haem binding capacity were calculated.
Control group. Mean plasma half-clearance time of haemopexin was 20.3 hr; fractional catabolic rate was 1.8 (SD 0.19) times the intravascular haemopexin pool per day. Extravascular haemopexin was 0.6 (SD 0.11) times the mass of haemopexin in the intravascular pool.
Test group. 90–95% of injected ¹²⁵I-activity was eliminated from the plasma with a mean half-clearance time of 1.57 hr and was associated with a significant urinary excretion of labelled iodine. Fractional catabolic rate was 5.84 (SD 0.3) times the intravascular haemopexin pool per day and extravascular haemopexin was 3.38 (SD 1.03) times the mass of haemopexin in the intravascular pool.
Haemopexin concentration in normal rabbit plasma was 31–52 mg/100 ml; intravascular plus extravascular haemopexin was 54.5 mg (mean value) and total haem binding capacity of haemopexin was 0.53 mg (mean value).
Intravascular haem rapidly complexed with haemopexin and the data suggested that this complex was promptly eliminated from the plasma and the haemopexin catabolized.     

Biliary excretion of radioactivity after intravenous administration of [3H]25-hydroxyvitamin D3 in man

The biliary excretion of radioactivity after intravenous [3H]25-hydroxyvitamin D3 was studied in nine patients with T-tube bile drainage. The mean +/- SD 24-hr radioactivity excretion in T-tube bile expressed as a percentage of the administered dose was 6.7 +/- 2.9%; after correction for incomplete bile collection, the value obtained was 16.0 +/- 11.1%. Chloroform solubility of biliary radioactivity increased from 27.4 +/- 8.9% to 72.9 +/- 10.1% following incubation with beta-glucuronidase. High-performance liquid chromatographic analysis of chloroform extracts of bile revealed that most of the eluted radioactivity was more polar than [3H]25-hydroxyvitamin D3. No free [3H]25-hydroxyvitamin D3 was demonstrated. Thus in man, most of the biliary radioactivity excreted following [3H]25-hydroxyvitamin D3 is in the form of water-soluble compounds, mainly glucuronides. However, our results suggest that glucuronides of metabolites other than 25-OHD3 are predominantly formed.     

Uptake of Tritiated Folates by Human Bone Marrow Cells in Vitro

S ummary . Using incubation periods up to 4 hr, it was demonstrated that uptake of tritiated pteroylglutamic acid ([³H]PteGlu) by human bone marrow cells in vitro was in the range of six-fold greater than uptake by reticulocytes. Uptake was temperature-dependent, increasing during 4 hr at 37°C but not at 4°C; a similar temperature dependence was found for the uptake of [³H]methyltetrahydrofolate ([³H-CH₃]H₄PteGlu). The pH optimum for [³H]PteGlu uptake was in the range of 7.4. Percentage uptake decreased as concentration of [³H]PteGlu increased. Preincubation with unlabelled PteGlu reduced uptake of subsequently added [³H]PteGlu by twice as much as did preincubation with methotrexate, suggesting that methotrexate may only partly share the uptake mechanism for [³H]PteGlu. [³H]PteGlu uptake was not affected by preincubation with diphenylhydantoin or a sulphydryl inhibitor. Uptake of [³H-CH₃]H₄PteGlu by human bone marrow cells appeared to be approximately twice the uptake of [³H]PteGlu. The findings support the concept of two mechanisms for folate uptake by human reticulocytes and bone marrow cells: an energy-dependent, active carrier mechanism probably of primary physiologic significance, and a seemingly passive diffusion-like mechanism, probably primarily of pharmacologic significance.     

Leucine and Glucose Turnover in Chronic Alcoholics During Early Abstinence and After an Ethanol Load

We studied leucine turnover using a primed infusion of [1-¹⁴C]- l -leucine and glucose turnover using a primed infusion of [6-³H]- d -glucose in five alcoholic patients without liver damage and five age-matched controls. Infusions were maintained for 6 hr, and at the end of the 3rd hour, a 0.8 g/kg iv ethanol load was administered in 20 min. Leucine flux, nonoxidative disposal and oxidation rates, and glucose rate of appearance were calculated during the 3rd and 6th hours of infusion. Ethanol disappearance rate and the percentage completely metabolized to CO₂ and H₂O in 3 hr were also calculated. Compared with controls, alcoholics had significantly higher basal leucine flux (55.6 ± 12 vs. 37.3 ± 9.3 μ m /m²/min) and nonoxidative disposal (48.7 ± 8.7 vs. 31.1 ± 7.5 μ m /m²/min). No differences were observed in basal glucose appearance rates in alcoholics and controls (397.6 ± 115.2 vs. 349.4 ± 120.6 μ m /m²/min). Compared with controls, alcoholics had a higher alcohol disappearance rate (2.72 ± 0.59 vs. 1.84 ± 0.43 m m /kg/min) and percentage of ethanol metabolized to CO₂ and H₂O in 3 hr (40.6 ± 10.2 vs. 22.9 ± 6.9%). After the ethanol load, both leucine turnover and glucose rate of appearance decreased significantly only in alcoholics. There was a positive correlation between the change in leucine flux and ethanol disappearance rate and percentage metabolized to CO₂ and H₂O in alcoholics.     

Regional Differences in the Effects of Chronic Ethanol Administration on [3H]Zolpidem Binding in Rat Brain

A strong association has been observed between [³H]zolpidem binding and the presence of γ-aminobutyric acid (GABA_A) receptor mRNA for α₁-, β₂-, and γ₂-subunits in specific brain regions. This correlates with observed sensitivity of individual neurons to zolpidem and ethanol in these same regions. Previous studies using homogenate binding approaches showed small alterations in [³H] zolpidem binding levels after chronic ethanol exposure. This study was undertaken to ascertain if there is regional specificity of the effects of chronic ethanol administration on [³H] zolpidem binding levels. Chronic ethanol administration induced small, but significant alterations in [³H] zolpidem (5 nM) binding in the Inferior colliculus, substantia nigra, and the medial septum. [³H]Zolpidem binding was increased in the inferior colliculus and substantia nigra, and decreased in the medial septum. No significant differences in [³H] zolpidem binding were noted in any other brain area analyzed, including the cortex and cerebellum. These findings show that chronic ethanol administration has small effects on [³H] zolpidem binding, although they occur in a site-specific and bidirectional manner. Moreover, there is no correlation between changes in [³H] zolpidem binding and alterations In GABA_A receptor subunit expression.     

In vivo uptake of chylomicron [3H]retinyl ester by rat liver: evidence for retinol transfer from parenchymal to nonparenchymal cells.

We have studied hepatic uptake of chylomicron retinyl ester. Chylomicrons were obtained from intestinal lymph of rats that were given retinol in groundnut oil by intraduodenal injection. When lymph was injected intravenously into normal rats, the radioactivity was cleared from blood with t1/2 approximately equal to 10 min. Retinyl ester was taken up initially by the liver, which, after 30 min, contained 80-90% of the radioactivity injected. Initially, most of the radioactivity was in hepatocytes, but after 30 min it disappeared from these cells and reappeared in nonparenchymal liver cells. After 2 hr these cells contained more radioactivity than the hepatocytes. When lymph was injected into vitamin A-deficient rats or rats given vitamin A in the form of retinoic acid, the plasma clearance and initial hepatic uptake of radioactivity were similar to that found in control animals. However, the nonparenchymal cells in these animals did not accumulate radioactivity. The current data suggest that vitamin A (in chylomicron remnants) is taken up initially by hepatocytes and then is released from these cells and delivered mainly to nonparenchymal liver cells in normal animals. In vitamin A-deficient rats, the vitamin is transferred from the hepatocytes to extrahepatic tissues.     

New Kinetic Role for Serum Ferritin in Iron Metabolism

S ummary . The role of the iron in serum ferritin was investigated with regard to iron kinetics. Serum (or plasma) was fractionated on a sucrose gradient by ultra-centrifugation to separate iron in ferritin from other iron-containing components in serum. After injection of heat-treated [⁵⁹Fe]RBC in rats, detectable labelling of the serum ferritin fraction was brief, between 20 and 40 min. The labelling of other iron components in the serum was maximal between 1 and 2 hr. No labelling of the serum ferritin fraction was detected after intravenous administration of [⁵⁹Fe]-transferrin in man and in the rat, or after [⁵⁹Fe]haemoglobin-haptoglobin or oral [⁵⁹Fe²⁺]citrate in the rat. These results indicate that iron in serum ferritin originates in part from the degradation of haemoglobin in senescent red cells and that this labelled ferritin is cleared from the serum rapidly.
In normal rats, [⁵⁹Fe]ferritin, purified from rat liver and injected intravenously, disappeared from the serum at an exponential rate with a half-disappearance time (HDT) of 4 min. After 1 hr 97% of the label had accumulated in the liver. After a delay of 24 hr, increasing amounts of label appeared in the RBC to an estimated maximum of 70–80% at 5 days. Conditions which increased or decreased rates of synthesis of haemoglobin altered the percentage of [⁵⁹Fe]ferritin incorporated into haemoglobin, but these conditions did not change the rate of removal of [⁵⁹Fe]ferritin from the serum by the liver. These results indicate that the iron in serum ferritin is cleared from the serum much more rapidly than transferrin-bound iron. The data are consistent with the passage through serum ferritin of a major portion of the iron that is released from the degradation of red cell haemoglobin in the RE system.     

Serum 'Uracil+Uridine'Levels Before and After Vitamin B12 Therapy in Pernicious Anaemia

S ummary . The serum 'uracil+uridine'levels, expressed as uracil, have been measured in 10 cases of pernicious anaemia both before and after treatment, and compared with the levels in 97 normal subjects. The mean pre-treatment value (8.82 μmol/l., range 6.0–12.0 μmol/l.) differed significantly from that of the normal controls (15.7 μmol/l., range 5.7–40.5 μmol/1., t = 8.8, P <0.001). This confirms the low serum uracil level previously reported in pernicious anaemia in relapse. The level rose progressively after treatment, reaching a maximum on the fourth day (mean 17.85 μmol/1., range 9.3–23.4 μmol/l.). This was not significantly different from the mean of the normal control group. The difference between the pre- and post-treatment levels was significant on days 3, 4 and 5 ( P <0.005, P <0.001 and P <0.005 respectively) and the rise preceded the reticulocyte response by 24 h. A further case was treated with physiological doses of vitamin B₁₂ (2 μg daily for 6 d) and a similar rise in the serum uracil level noted.
These results are not explained by any of the known functions of vitamin B₁₂. They are, however, similar to the changes in the serum methionine levels previously reported in pernicious anaemia. The latter were readily explained by the known action of vitamin B₁₂ on ' de novo 'methionine synthesis and it is suggested that the synthesis of uracil, like that of methionine, might be influenced by vitamin B₁₂ in man.