POEMS syndrome with Guillan-Barre syndrome-like acute onset: a case report and review of neurological progression in 30 cases.

POEMS (polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes) syndrome is a rare cause of demyelinating neuropathy with monoclonal plasma cell proliferation, and POEMS neuropathy is usually chronically progressive. Herein, the authors report a 34-year-old woman with POEMS syndrome presenting as acute polyneuropathy. Within 2 weeks of disease onset, she became unable to walk with electrodiagnostic features of demyelination and was initially diagnosed as having Guillan-Barré syndrome. Other systemic features (oedema and skin changes) developed later, and an elevated serum level of vascular endothelial growth factor led to the diagnosis of POEMS syndrome. She received high-dose chemotherapy with autologous peripheral blood stem cell transplantation, resulting in good recovery. The authors also reviewed patterns and speed of progression of neuropathy in the 30 patients with POEMS syndrome; 22 (73%) of them were unable to walk independently with the median period of 9.5 months from POEMS onset (range 0.5-51 months). Whereas the speed of neuropathy progression varies considerably among patients, some POEMS patients can show acute or subacute polyneuropathy. The early diagnosis and treatment could result in rapid improvement as shown in the present patient.

Neuromuscular transmission is not impaired in axonal Guillain--Barré syndrome.

BACKGROUND: Previous studies have shown that anti-GQ1b antibodies induce massive neuromuscular blocking. If anti-GM1 and -GD1a antibodies have similar effects on the neuromuscular junction (NMJ) in human limb muscles, this may explain selective motor involvement in axonal Guillain--Barré syndrome (GBS). METHODS: Axonal-stimulating single-fibre electromyography was performed in the extensor digitorum communis muscle of 23 patients with GBS, including 13 with the axonal form whose sera had a high titre of serum IgG anti-GM1 or -GD1a antibodies. RESULTS: All patients with axonal or demyelinating GBS showed normal or near-normal jitter, and no blocking. CONCLUSION: In both axonal and demyelinating GBS, neuromuscular transmission is not impaired. Our results failed to support the hypothesis that anti-GM1 or -GD1a antibody affects the NMJ. In GBS, impulse transmission is presumably impaired in the motor nerve terminal axons proximal to the NMJ.

A pilot study investigating the effect of pimobendan on the cardiac rhythm and selected echocardiographic parameters of healthy cats.

INTRODUCTION: The effects of pimobendan on the heart rhythm in cats are unknown. The purpose of this pilot study was to evaluate the effect of pimobendan on the cardiac rhythm and selected echocardiographic parameters of cats. ANIMALS, MATERIALS, AND METHODS: Six clinically healthy cats received each of four medication protocols for 15 days, with a washout period of at least one month between each protocol. The protocols were, pimobendan 0.5 mg/kg twice daily (high dosage group), pimobendan 0.25 mg/kg twice daily (standard dosage group), pimobendan 0.125 mg/kg twice daily (low dosage group), and Biofermin R, one tablet twice daily (placebo group). Twenty-four-hour ambulatory electrocardiogram recordings, blood pressure measurements, and echocardiographic examinations were performed after two weeks of each medication protocol. Electrocardiographic, echocardiographic, and blood pressure parameters were compared between the four groups. RESULTS: The total number of escape/idioventricular/idiojunctional complexes in the high dosage group was significantly higher compared with the placebo, low dosage, and standard dosage groups (p < 0.001). The blood pressure; total number of heart beats per day; and mean, minimum, and maximum heart rates were not significantly different between the groups. The longitudinal strain rate and calculated cardiac output were significantly increased in the high and standard dosage groups. CONCLUSIONS: The administration of pimobendan, especially at high doses, was associated with increased numbers of escape/idioventricular/idiojunctional complexes in some cats and echocardiographic parameters. Further studies are warranted to investigate both the mechanism underlying the observed changes and what, if any, clinical implications these changes might have in cats with heart disease.

Physicochemical property changes of amino acid residues that accompany missense mutations in SCN1A affect epilepsy phenotype severity.

BACKGROUND: Several different missense mutations in the voltage-gated sodium channel subunit gene SCN1A have been identified in epileptic patients with benign phenotype and patients with severe phenotype. However, the reason why similar missense mutations in SCN1A result in different phenotypes has not yet been fully clarified. OBJECTIVE: To clarify the phenotype-genotype relationship in SCN1A, a meta-analysis was performed to quantitatively determine the effect of amino acid substitutions in SCN1A on epilepsy severity phenotype using physicochemical property indices of the amino acid, and to discuss in the context of the molecular evolution of the proteins. METHODS: PubMed was searched for articles and information was extracted on localisation and types of SCN1A missense mutations in patients with benign and severe epileptic syndromes; detailed information was also extracted. RESULTS: Meta-analysis quantitatively revealed that the physicochemical properties of several amino acids significantly affected epilepsy phenotype severity. It showed that missense mutations that decreased protein hydrophobicity were significantly associated with severe epilepsy phenotypes. It also showed that the phenotype severity of SCN1A missense mutations in the transmembrane domains of SCN1A (128/155; 82.6%) could be predicted with high sensitivity and positive predictive values using the physicochemical property changes, indicating the possibility of phenotype prediction for entirely new missense mutations using analytical methods. CONCLUSIONS: The results show that changes in the physicochemical properties of amino acids affected both the phenotype and clinical symptoms of patients with SCN1A missense mutations. This meta-analysis study provides new insights into SCN1A gene functions and a new strategy for genetic diagnosis, genetic counselling and epilepsy treatment.

Structural characterization of Tn916-like element in Streptococcus parauberis serotype II strains isolated from diseased Japanese flounder.

AIMS: To screen for the existence and determine the structure of Tn916-like element in Streptococcus parauberis serotype II strains isolated from cultured Japanese flounder in western Japan. METHODS AND RESULTS: In this study, the structure of Tn916-like element and the flanking regions were characterized by polymerase chain reaction (PCR) and inverse PCR, followed by cloning and sequencing. The Tn916-like element is 18 031 bp in length and composed of 22 ORFs. Southern blot hybridization analysis showed that the HincII-digested internal structures of Tn916-like elements yielded two patterns among S. parauberis serotype II strains. The flanking sequences were identical with the corresponding region of S. parauberis serotype I strain except for the addition of 6-bp coupling sequence (ATCATA) being adjacent to the upstream of the element. CONCLUSION: The Tn916-like element exhibited high homology (more than 99%) with Tn916 observed in other streptococci and enterococci and was integrated in the same site of chromosome for all of the tested S. parauberis serotype II strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The results indicate that the Tn916-like element encoding tet(M) gene is present in all of the tested S. parauberis serotype II strains, which are disseminated in the flounder-culturing areas in western Japan.

Thalidomide reduces serum VEGF levels and improves peripheral neuropathy in POEMS syndrome.

BACKGROUND: Polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes (POEMS) syndrome is a rare multi-system disorder associated with plasma-cell dyscrasia. Several case series and reports have suggested that high-dose chemotherapy with autologous peripheral blood stem-cell transplantation is efficacious treatment, but this transplantation is not indicated for elderly patients and patients with renal failure. OBJECTIVE: To investigate the effects of thalidomide treatment for POEMS syndrome. METHODS: Nine patients, who were not indicated for high-dose chemotherapy, were treated with thalidomide. Neurological disability scores, nerve conduction studies and serum levels of vascular endothelial growth factor (VEGF) were prospectively examined. VEGF levels were measured by an enzyme-linked immunosorbent assay. RESULTS: During follow-up periods of 8-23 months (mean, 15 months), all patients showed substantial clinical improvement (n = 6) or stabilisation of symptoms (n = 3). Serum VEGF levels decreased in all patients and were normalised in five patients. Nerve conduction velocities in the median nerve increased in seven patients. There were no serious adverse effects, including thalidomide neuropathy. CONCLUSION: Thalidomide treatment should be further studied as a treatment for POEMS syndrome, particularly for patients who are not indicated for transplantation therapy.

Anomalous electronic structure of ionic liquids determined by soft x-ray emission spectroscopy: contributions from the cations and anions to the occupied electronic structure.

Soft x-ray emission spectroscopy was used for elucidating the electronic structure of ionic liquids [C(4)mim](+)PF(6)(-) and [C(4)mim](+)OTf(-), where [C(4)mim](+) stands for methylbutylimidazolium cation and OTf(-) for the trifluoromethanesulfonate anion. Nonresonant spectra measured above N, O, and F 1s edges selectively probed the molecular orbitals (MOs) of the cation and anions. They give a clear evidence that the highest occupied molecular orbital of the [C(4)mim](+) cation contributes to the topmost occupied states of the ionic liquids [C(4)mim](+)PF(6)(-), while both cationic and anionic MOs contribute for the case of [C(4)mim](+)OTf(-). Resonant soft x-ray emission spectra at the N 1s edge of these ionic liquids revealed that the energy gap of [C(4)mim](+)PF(6)(-) is solely determined by the [C(4)mim](+) cation, in contrast to usual ionic crystals. The ionic liquids form a new class of the ionic materials from the viewpoint of the electronic structure.

Inhibition of angiogenic factor production from murine mast cells by an antiallergic agent (epinastine hydrochloride) in vitro.

Angiogenesis is an important event both in the development of allergic inflammatory responses and in the pathophysiology of tissue remodeling in allergic diseases. In the present study, therefore, we examined the influence of antihistamines on angiogenesis through the choice of epinastine hydrochloride (EP) and murine mast cells in vitro. Mast cells (5 x 10(5) cells/mL) presensitized with murine IgE specific for ovalbumin (OVA) were stimulated with 10 ng/mL OVA in the presence of various concentrations of EP for 4 hours. The levels of angiogenesis factors, keratinocyte-derived chemokine (KC), tumor necrosis factor-alpha (TNF), and vascular endothelial growth factor (VEGF) in culture supernatants, were examined by ELISA. We also examined mRNA expression for the angiogenesis factors by RT-PCR. EP significantly inhibited the production of KC, TNF, and VEGF induced by IgE-dependent mechanism at more than 25 ng/mL. Semiquantitative analysis using RT-PCR showed that EP also significantly reduced mRNA expressions for KC, TNF, and VEGF. These results strongly suggest that EP suppresses angiogenesis factor production through the inhibition of mRNA expression in mast cells and results in favorable modification of clinical conditions of allergic diseases.

Evaluation of plasma C-terminal atrial natriuretic peptide in healthy cats and cats with heart disease.

BACKGROUND: The clinical implications of evaluating C-terminal atrial natriuretic peptide (ANP) concentration in cats are still controversial. HYPOTHESIS: The objective of this study was to investigate the relationship between plasma C-terminal ANP concentration and left atrial pressure (LAP) in healthy cats with volume overload (study 1), and to compare plasma C-terminal ANP in normal cats and cats with cardiomyopathy (study 2). ANIMALS: Five healthy adult cats were used in study 1, and clinically healthy cats (n=8) and cats with cardiomyopathy (n=14) were used in study 2. METHODS: In study 1, cats were anesthetized and given acetated Ringer's solution (100 mL/kg/h for 60 minute) via the cephalic vein. Hemodynamic measurements and blood samples, collected from the jugular vein, were performed at 10-min intervals. In study 2, blood samples from normal cats and cats with cardiomyopathy were collected from the cephalic vein. The plasma C-terminal ANP concentration was determined by radioimmunoassay for human alpha-ANP. RESULTS: In study 1, volume overload significantly increased the C-terminal ANP concentration and LAP from baseline. The C-terminal ANP concentration was strongly correlated with the mean LAP. In study 2, age, E wave velocity, and the ratios of the left atrium to aorta were significantly higher in the cats with cardiomyopathy compared with the normal cats. The C-terminal ANP concentration was significantly higher in the cats with cardiomyopathy compared with the normal cats. CONCLUSIONS AND CLINICAL IMPORTANCE: Our results suggest that the measurement of plasma C-terminal ANP in cats may provide additional information for the diagnosis of heart disease.

RCA/IAEA third external dosimetry intercomparisons in East Asia region.

Several intercomparison exercises were organised by the International Atomic Energy Agency (IAEA) on the determination of operational quantities at the regional or interregional basis. In East Asia region, a third phase of the intercomparison finished in mid 2004. It was organised within the frame of the Regional Cooperation Agreement (RCA) as a follow-up to previous exercises carried out during 1990-1992 and 1995-1996. The results of this intercomparison for the determination of operational quantities were satisfactory for all Member States. The laboratories demonstrated a good performance in quantities tested. The purpose of this paper is to present the results of the RCA/IAEA intercomparison and the future of RCA activities in support of assessment of occupational exposure by organising intercomparison runs.

Partial purification of a growth factor synthesized by a rat hepatoma cell line established in serum-free medium.

A rat hepatoma cell line was established from primary culture using RPMI 1640 without supplements. Hepatomas were induced in rats by 0.06% 3'-methyl-4-dimethylaminoazobenzene. An established cell line, FF101, has been maintained as a monolayer for longer than 34 months and subcultured for 42 passages. The population-doubling time was 78 h. The modal chromosome number was 66. FF101 was transplantable, and morphological examination of the transplanted tumors revealed a mixed type of hepatocellular and cholangiocellular carcinoma. FF101 retained the ability to express tyrosine aminotransferase and glucose-6-phosphatase. Also, FF101 synthesized alpha-fetoprotein. FF101-conditioned medium stimulated DNA synthesis and proliferation of several cell lines such as AH66, K562, and BALB/c3T3. The growth-promoting activity of FF101-conditioned medium was abolished by protease, dithiothreitol, acidic treatment, and heating. Gel filtration of conditioned medium on Sephacryl S-200 disclosed the growth-promoting activity at the molecular size of approximately 60,000 Da, and the isoelectric point (pI) was between 5.5 and 6.5. These results suggest that FF101 synthesizes a novel growth factor which has little specificity in both species and organs.

Increased histone acetylation and deacetylation in rat ascites hepatoma cells.

Rates of histone acetylation and deacetylation in nuclei from fetal, adult, and two kinds of neoplastic rat hepatocytes were examined. Histone acetylation in isolated nuclei was measured in the presence of 6 mM sodium n-butyrate, a potent inhibitor of deacetylase, and in the absence of the inhibitor. The deacetylase activity was estimated from the difference between the rates with or without the inhibitor. Both histone acetylation and deacetylation in nuclei from hepatoma cells (AH 66 cells) occurred two times faster than those of nuclei from fetal and adult livers regardless of alpha-fetoprotein production. This increased acetylation and deacetylation in hepatoma cells may be ascribed to either the increased activities of the enzymes or the increased accessibility of histone to the enzymes in the chromatin. Autoradiographic analysis of acetylated histones showed that all of the internal histones of the nucleosomes were acetylated and that apparent difference was found in the pattern of acetylated fractions between hepatoma nuclei and normal liver cell nuclei.

Characterization of glutamate transport system in hydrophobic protein (H protein) of Bacillus subtilis.

Hydrophobic protein (H protein) was isolated from membrane fractions of Bacillus subtilis and constituted into artificial membrane vesicles with lipid of B. substilis. Glutamate was accumulated into the vesicle when a Na+ gradient across the membrane was imposed. The maximum effect of Na+ on the transport was achieved at a concentration of about 40 mM, while the apparent Km for Na+ was approximately 8 mM. On the other hand, Km for glutamate in the presence of 50 mM Na+ was about 8 micro M. Increasing the concentration of Na+ resulted in a decrease in Km for glutamate, maximum velocity was not affected. The transport was sensitive to monensin (Na+ ionophore). Glutamate was also accumulated when pH gradient (interior alkaline) across the membrane was imposed or a membrane potential was induced with K+-diffusion potential. The pH gradient-driven glutamate transport was sensitive to carbonylcyanide m-chlorophenylhydrazone and the apparent Km for glutamate was approximately 25 microM. These results indicate that two kinds of glutamate transport system were present in H protein: one is Na+ dependent and the other is H+ dependent.

Selective block of calcium current by lanthanum in single bullfrog atrial cells.

A single suction microelectrode voltage-clamp technique was used to study the actions of lanthanum ions (La3+) on ionic currents in single cells isolated from bullfrog right atrium. La3+, added as LaCl3, blocked the "slow" inward Ca2+ current (ICa) in a dose-dependent fashion; 10(-5) M produced complete inhibition. This effect was best fitted by a dose-response curve that was calculated assuming 1:1 binding of La3+ to a site having a dissociation constant of 7.5 x 10(-7) M. La3+ block was reversed (to 90% of control ICa) following washout and, in the presence of 10(-5) M La3+, was antagonized by raising the Ca2+ concentration from 2.5 to 7.5 mM (ICa recovered to 56% of the control). However, the latter effect took approximately 1 h to develop. Concentrations of La3+ that reduced ICa by 12-67%, 0.1-1.5 x 10(-6) M, had no measurable effect upon the voltage dependence of steady state ICa inactivation, which suggest that at these concentrations there are no significant surface-charge effects of La3+ on this gating mechanism. Three additional findings indicate that doses of La3+ that blocked ICa failed to produce nonspecific effects: (a) 10(-5) M La3+ had no measurable effect on the time-independent inwardly rectifying current, IK1; (b) the same concentration had no effect on the kinetics, amplitude, or voltage dependence of a time- and voltage-dependent K+ current, IK; and (c) 10(-4) M La3+ did not alter the size of the tetrodotoxin-sensitive inward Na+ current, INa, or the voltage dependence of its steady state inactivation. Higher concentrations (0.5-1.0 mM) reduced both IK1 and IK, and shifted the steady state activation curve for IK toward more positive potentials, presumably by reducing the external surface potential. Our results suggest that at a concentration of less than or equal to 10(-5) M, La3+ inhibits ICa selectively by direct blockade of Ca channels rather than by altering the external surface potential. At higher concentrations, La3+ exhibits nonspecific effects, including neutralization of negative external surface charge and inhibition of other time- and voltage-dependent ionic currents.

A time- and voltage-dependent K+ current in single cardiac cells from bullfrog atrium.

Individual myocytes were isolated from bullfrog atrium by enzymatic and mechanical dispersion, and a one-microelectrode voltage clamp was used to record the slow outward K+ currents. In normal [K+]o (2.5 mM), the slow outward current tails reverse between -95 and -100 mV. This finding, and the observed 51-mV shift of Erev/10-fold change in [K+]o, strongly suggest that the "delayed rectifier" in bullfrog atrial cells is a K+ current. This current, IK, plays an important role in initiating repolarization, and it is distinct from the quasi-instantaneous, inwardly rectifying background current, IK. In atrial cells, IK does not exhibit inactivation, and very long depolarizing clamp steps (20 s) can be applied without producing extracellular K+ accumulation. The possibility of [K+]o accumulation contributing to these slow outward current changes was assessed by (a) comparing reversal potentials measured after short (2 s) and very long (15 s) activating prepulses, and (b) studying the kinetics of IK at various holding potentials and after systematically altering [K+]o. In the absence of [K+]o accumulation, the steady state activation curve (n infinity) and fully activated current-voltage (I-V) relation can be obtained directly. The threshold of the n infinity curve is near -50 mV, and it approaches a maximum at +20 mV; the half-activation point is approximately -16 mV. The fully activated I-V curve of IK is approximately linear in the range -40 to +30 mV. Semilog plots of the current tails show that each tail is a single-exponential function, which suggests that only one Hodgkin-Huxley conductance underlies this slow outward current. Quantitative analysis of the time course of onset of IK and of the corresponding envelope of tails demonstrate that the activation variable, n, must be raised to the second power to fit the sigmoid onset accurately. The voltage dependence of the kinetics of IK was studied by recording and curve-fitting activating and deactivating (tail) currents. The resulting 1/tau n curve is U-shaped and somewhat asymmetric; IK exhibits strong voltage dependence in the diastolic range of potentials. Changes in the [Ca2+]o in the superfusing Ringer's, and/or addition of La3+ to block the transmembrane Ca2+ current, show that the time course and magnitude of IK are not significantly modulated by transmembrane Ca2+ movements, i.e., by ICa. These experimentally measured voltage- and time-dependent descriptors of IK strongly suggest an important functional role for IK in atrial tissue: it initiates repolarization and can be an important determinant of rate-induced changes in action potential duration.

A 718-kb DNA sequence of the Escherichia coli K-12 genome corresponding to the 12.7-28.0 min region on the linkage map.

The 718,122 base pair sequence of the Escherichia coli K-12 genome corresponding to the region from 12.7 to 28.0 minutes on the genetic map is described. This region contains at least 681 potential open reading frames, of which 277 (41%) have been previously identified, 147 (22%) are homologous to other known genes, 139 (20%) are identical or similar to the hypothetical genes registered in databases, and the remaining 118 (17%) do not show a significant similarity to any other gene. In this region, we assigned a cluster of cit genes encoding multienzyme citrate lyase, two clusters of fimbrial genes and a set of lysogenic phage genes encoding integrase, excisionase and repressor in the e14 genetic element. In addition, a new valine tRNA gene, designated valZ, and a family of long directly repeated sequences, LDR-A, -B and -C, were found.

Measurement of NADPH-ferrihemoprotein reductase content in sections of liver.

We developed a method for measuring the content of NADPH-ferrihemoprotein reductase in sections of liver. First, reductase in sections of rat liver was detected with the indirect immunoperoxidase reaction. Subsequently, specific absorbances were measured in the stained sections by microphotometry. Then, the resulting specific absorbances were converted into the reductase content in the sections using an apparent extinction coefficient obtained from a nitrocellulose binding assay. The average of the reductase content in hepatocytes in periportal, intermediate, and perivenous zones thus measured was consistent with the value in liver homogenates estimated by enzyme-linked immunosorbent assay. Therefore, the present method gave accurate measurement of the reductase content in the sections. Perivenous hepatocytes contained 1.5 times as much reductase (1.15 nmol/g liver, mean for five animals) as that in periportal hepatocytes (0.74 nmol/g liver). The reductase content in hepatocytes in the intermediate zone (0.93 nmol/g liver) was intermediate between values of the periportal and perivenous hepatocytes.

Glucagon receptors in endothelial and Kupffer cells of mouse liver.

To determine whether hepatic sinusoidal cells contain glucagon receptors and, if so, to study the significance of the receptors in the cells, binding of [125I]-glucagon to nonparenchymal cells (mainly endothelial cells and Kupffer cells) isolated from mouse liver was examined by quantitative autoradiography and biochemical methods. Furthermore, the pathway of intracellular transport of colloidal gold-labeled glucagon (AuG) was examined in vivo. Autoradiographic and biochemical results demonstrated many glucagon receptors in both endothelial cells and Kupffer cells, and more receptors being present in endothelial cells than in Kupffer cells. In vivo, endothelial cells internalized AuG particles into coated vesicles via coated pits and transported the particles to endosomes, lysosomes, and abluminal plasma membrane. Therefore, receptor-mediated transcytosis of AuG occurs in endothelial cells. The number of particles present on the abluminal plasma membrane was constant if the amount of injected AuG increased. Therefore, the magnitude of receptor-mediated transcytosis of AuG appears to be regulated by endothelial cells. Kupffer cells internalized the ligand into cytoplasmic tubular structures via plasma membrane invaginations and transported the ligand exclusively to endosomes and lysosomes, suggesting that the ligand is degraded by Kupffer cells.

Microphotometric analysis of cytochrome P-450 in periportal, midzonal, and perivenular hepatocytes of mice treated with phenobarbital.

To obtain detailed information on the increase of cytochrome P-450 (P-450) content in periportal, midzonal, and perivenular hepatocytes after phenobarbital (PB) administration, and to study the mechanism of increased P-450 in the endoplasmic reticulum (ER), we estimated microphotometrically the P-450 content and morphometrically the area of ER in hepatocytes of three zones from mice injected with 35, 50, 100, or 150 mg/kg of PB for 3 days. The amount of P-450 per unit cytoplasmic volume and the number of P-450 molecules per unit ER area (P-450 number) were increased by injection of 50, 100, or 150 mg/kg, and the ER area per unit cytoplasmic volume was increased by injection of 100 or 150 mg/kg, in hepatocytes from all three zones. Thus, the amount of P-450 in hepatocytes appeared in general to increase multiplicatively by simultaneous increases in both the P-450 number and the ER area. Furthermore, we could recognize two general types of relationship in the P-450 number and ER area between the patterns of change and the increasing doses: (a) increase in the P-450 number without ER proliferation (active type) in periportal and perivenular hepatocytes after injection of low doses; and (b) increase in ER proliferation without increase in the P-450 number (passive type) in hepatocytes of all three zones after injection of high doses.

A new microphotometric method for measurement of cytochrome P-450 in sections of liver.

We developed a new microphotometric method for measuring the amounts of cytochrome P-450 (P-450) in fresh frozen sections of liver. Four serial frozen sections cut from the liver were separately incubated in 50 mM Tris-HCl buffer (pH 8.0) alone, in buffer containing sodium dithionite, in buffer saturated with carbon monoxide (CO), and in buffer saturated with CO and containing sodium dithionite. The difference between absorbance at 450 nm and that at 490 nm was measured in these sections with a simple microphotometer system. This method yielded precise amounts of P-450 in sections by measuring the true extinction of P-450 and by minimizing the effect of contaminating hemoproteins. Livers of adult rats contained large amounts of P-450, which was greater in perivenular hepatocytes than in periportal hepatocytes. In livers of newborn rats, however, small amounts of the enzyme were distributed evenly throughout the lobule.