[Staging of pancreatic ductal adenocarcinoma using dynamic MR imaging]

Single breath-hold gradient echo images were obtained before and immediately after bolus intravenous administration of Gd-DTPA (dynamic MR imaging) in the study of the pancreas. Of 37 patients with pathologically proved pancreatic ductal adenocarcinoma, seventeen patients who underwent both dynamic MR imaging studies and curative surgery were included in this study. Correlations between histologic findings in the resected specimens and MR images were analyzed as to tumor extension and staging according to the General Rules for the Study of Pancreatic Cancer (4th Edition) published by the Japan Pancreas Society. In comparison with conventional MR images, dynamic MR imaging improved the detectability of pancreatic carcinoma and delineation of the vasculature by clarifying the margin of the tumor and the vessels. Nonenhanced T1-weighted imaging is the best sequence to estimate peripancreatic tumor extension, because the contrast between the tumor and peripancreatic fat deteriorates with the use of contrast material. There is a tendency to overestimate vascular invasion on MR images, the reason for which is considered to be the contractive nature of fibrotic change induced by pancreatic carcinoma. The diagnostic efficacy of lymph node metastasis remains insufficient on MR images because some cases show no enlargement of lymph nodes in spite of the existence of pathological metastasis. Our results suggest that dynamic MR imaging has the advantage of improving the conspicuity of the tumor and the vasculature.

Analysis of biliary drainage in the caudate lobe of the liver: comparison of three-dimensional CT cholangiography and rotating cine cholangiography

PURPOSE

To evaluate the bile duct anatomy of the caudate lobe without disease involvement with use of three-dimensional (3D) cholangiography and to compare the usefulness of this technique with that of rotating cine cholangiography.

MATERIALS AND METHODS

In 12 patients with obstructive jaundice but without lesions at the hepatic hilum who underwent percutaneous transhepatic biliary drainage, serial examination was performed with cine cholangiography and helical computed tomography (CT). From helical CT scans, 3D cholangiograms were reconstructed. Cine and 3D cholangiograms were evaluated and compared simultaneously.

RESULTS

In the 12 patients, 40 branches of the caudate lobe were detected with 3D cholangiography (mean, 3.3 branches per patient), while 31 were detected with cine cholangiography (mean, 2.6 branches per patient). The difference in detection rate was significant (P < .01). Nine (23%) of 40 branches were detected with 3D cholangiography alone, and all 31 branches detected with cine cholangiography were also detected with 3D cholangiography.

CONCLUSION

3D cholangiography was superior to cine cholangiography in assessment of bile duct anatomy of the caudate lobe of the liver because 3D cholangiography eliminated the overlap of different branches of the bile duct.

Gastric mucosal injury induced by local ischemia-reperfusion in rats. Role of endogenous endothelin-1 and free radical

We investigated the role of an endogenous vasoconstrictor peptide endothelin-1 (ET-1) and free radicals in local gastric ischemia-reperfusion injury in rats. Local gastric ischemia was induced by clamping the left gastric artery for 15 min and reperfusion was done for 10-30 min in the presence of 150 mM exogenous HCl intragastrically. Local gastric ischemia and reperfusion resulted in significant macroscopic and microscopic gastric mucosal damage together with elevation of gastric tissue ET-1 concentration. Gastric tissue ET-1 was found to increase after 15 min of ischemia alone and also with 30 min of reperfusion. A novel nonpeptide endothelin receptor antagonist, bosentan, or a combination of radical scavengers (superoxide dismutase, catalase, and deferoxamine) both attenuated gastric mucosal injury. However, the greater protection observed with bosentan than with radical scavengers might reflect a preferential role of endothelin-1 in this type of injury.

Bosentan, a novel synthetic mixed-type endothelin receptor antagonist, attenuates acute gastric mucosal lesions induced by indomethacin and HCl in the rat: role of endogenous endothelin-1

Endothelin-1 has been reported to be responsible for gastric mucosal damage in various experimental models. We evaluated the role of endogenous endothelin-1 in the pathogenesis of gastric mucosal damage induced by indomethacin and HCl in the rat. Rats were given indomethacin (25 mg/kg) subcutaneously, and 15 min later, 0.2N HCl intragastrically. Gastric mucosal damage, gastric endogenous endothelin-1, and gastric mucosal hemodynamics were measured. The effects of bosentan, a mixed endothelin receptor antagonist, on gastric mucosal integrity and hemodynamics were assessed. Gastric endogenous endothelin-1 was significantly elevated at 20 min, gastric mucosal blood flow began to decrease significantly at 25 min, and gastric damage occupied 52.2% of the total glandular mucosa at 135 min after injection of indomethacin. Intragastric pretreatment with bosentan (5, 10, 30, and 60 mg/kg) significantly attenuated gastric damage, to 26.1%, 7.7%, 3.6%, and 1.6%, respectively, of the total glandular mucosa. Bosentan (60 mg/kg) prevented the initial decrease of blood flow and, even at 135 min, improved blood flow and hemoglobin oxygen saturation significantly. We suggest that indomethacin-induced endogenous endothelin-1 diminishes gastric mucosal blood flow and tissue oxygenation and ultimately causes gastric damage. Endogenous endothelin-1 may play an important role in the pathogenesis of the acute gastric mucosal lesions induced by indomethacin and HCl.

Effects of haloperidol and cocaine pretreatments on brain distribution and kinetics of [11C]methamphetamine in methamphetamine sensitized dog: application of PET to drug pharmacokinetic study

Repeated administration of methamphetamine (MAP) causes behavioral sensitization in animals. We previously reported that the maximum accumulation level of [11C]MAP in the MAP-sensitized dog brain was 1.4 times higher than that in the control. In behavioral studies, haloperidol (a dopamine D2 receptor antagonist) prevents MAP-induced behavioral sensitization, and cocaine (a dopamine reuptake blocker) has the cross-behavioral sensitization with MAP. In the present study, to elucidate the relation between the MAP-induced behavioral sensitization and the pharmacokinetics of MAP, we investigated the effects of haloperidol and cocaine pretreatments on brain regional distribution and kinetics of [11C]MAP using positron emission tomography (PET). A significant increase of [11C]MAP uptake into the sensitized dog brain was prevented by haloperidol and cocaine pretreatments. These pharmacokinetic changes were not due to the changes in the rate of MAP metabolism. These results suggest haloperidol and cocaine can change the cerebral pharmacokinetic profile of MAP in the behavioral-sensitized dog. The variations of MAP-accumulation may affect the development or expression of MAP-induced behavioral sensitization.

Assessment of cancer recurrence in residual tumors after fractionated radiotherapy: a comparison of fluorodeoxyglucose, L-methionine and thymidine

This study evaluates the midterm follow-up of tumor and normal tissue uptake of deoxyglucose, thymidine and methionine after fractionated radiotherapy to assess cancer recurrence in residual tumors.

METHODS

AH109A tumor-burdened rats were treated with one to eight doses of 5Gy 60Co radiation. Tissue distribution study with 18F-FDG, 3H-thymidine and 14C-methionine, double-tracer autoradiography with 18F-FDG and 14C-methionine, and single-tracer autoradiography with 14C-labeled deoxyglucose, thymidine and methionine were performed 6 days after the end of therapy.

RESULTS

Dose response study shows a significant decrease of tumor uptake of all tracers after two and more doses, even in the case of later recurrence. Whereas 3H-Thd and 14C-Met tumor uptake was similar to that of normal muscle, 18F-FDG tumor uptake remains higher than that of muscle, even in the case of complete tumor cure. The irradiated muscle shows a higher 18F-FDG uptake than the nonirradiated muscle. Autoradiography after eight doses (100% tumor cure) reveals elevated 14C-DG tumor uptake to be ascribable to nonmalignant cellular elements, in particular to a macrophage layer at the rim of necrotic areas. Autoradiography after four and six doses (33% and 57% tumor cure) shows the highest methionine and thymidine uptake in viable cancer cells, whereas deoxyglucose uptake did not differ between viable cancer cells and macrophages.

CONCLUSION

To detect and differentiate viable cancer cells in a residual tumor mass after radiotherapy, PET using 11C-methionine or 11C-thymidine may have some advantages over 18F-FDG, especially if the residual tumor includes larger areas of necrosis.

Brain 6-[18F]fluorodopa metabolism in early and late onset of Parkinson's disease studied by positron emission tomography

We measured 6-[18F]fluorodopa (FDOPA) uptake in the caudate nucleus and the putamen of 20 patients with early and late onset of Parkinson's disease (EOPD and LOPD) and 20 normal control subjects using positron emission tomography. The mean influx rate constant values (Ki) were significantly reduced in the caudate nucleus and the putamen of the patients with EOPD and LOPD compared with age-matched control groups (p < 0.01), respectively. There were significant negative correlations between Ki values in the caudate nucleus (r = -0.67, p = 0.0024) and the putamen (r = -0.67, p = 0.0014), and duration of disease in the LOPD group compared with the EOPD group. Similar negative relationships between Ki values and clinical stages by Hoehn and Yahr and degrees of main clinical symptoms (bradykinesia, tremor and rigidity) were more markedly seen in the LOPD group than in the EOPD group. The present results suggest that the function of presynaptic dopaminergic terminals correlates well with clinical disease severity and degrees of main symptoms in the LOPD group, but not in the EOPD group. We speculate that compensatory up-regulatory function in the postsynaptic dopaminergic receptors may modify disease severity and the degrees of main clinical symptoms of EOPD.

Positron emission tomography study of the alterations in brain distribution of [11C]methamphetamine in methamphetamine-sensitized dog

We newly prepared a MAP-sensitized dog by repeated MAP treatment and studied the brain distribution of [11C]MAP in the normal and the MAP-sensitized dog using PET. The maximal level of accumulation of [11C]MAP in the sensitized dog brain was 1.4 times higher than that in the control. No difference was found in the metabolism of MAP between the two conditions. The significant increase of [11C]MAP in the MAP-sensitized brain indicates that subchronic MAP administration causes some functional change in the uptake site of MAP. The pharmacokinetic change may, in part, account for behavioral sensitization.

Re-evaluation of myocardial FDG uptake in hyperglycemia

Myocardial [18F] fluorodeoxyglucose (FDG) uptake depends on several metabolic variables in vivo. The effect of different levels of experimentally induced hyperglycemia on myocardial FDG uptake was examined.

METHODS

FDG uptake was studied in young Donryu rats 1 hr after intravenous injection under various pretreatments that increased serum glucose levels. Serum samples were analyzed for glucose, insulin and free fatty acids. Myocardial distribution of FDG was examined with autoradiography.

RESULTS

Administration of glucose (n = 42), triiodothyronine (n = 7), epinephrine (n = 7), dehydroascorbic acid (n = 5) and 4 mg streptozotocin (Szt, n = 10) increased glucose levels to 120-200 mg/dl. Dexamethasone (Dex, n = 34) and 6 mg Szt (n = 6) increased glucose levels to 200-450 mg/dl. Myocardial FDG uptake increased proportionately with increases in serum glucose level up to 200 mg/dl. In severe hyperglycemia (serum glucose: 200-450 mg/dl), however, the FDG uptake decreased and did not correlate with blood glucose level. A study of fractional FDG uptake calibrated by the arterial FDG curve confirmed the same results. Heterogeneous distribution of FDG was observed in the myocardium, both in fasting and in severe hyperglycemic conditions. The pattern of FDG uptake by skeletal muscles was similar to that of the myocardium, although the uptake was lower than that in the myocardium. Changes in insulin and free fatty acids levels could not explain the FDG uptake pattern in severe hyperglycemia. Blood FDG uptake level remained constant regardless of glucose level.

CONCLUSION

Hyperglycemia induced a biphasic pattern of myocardial FDG uptake, common with skeletal muscles. The understanding of myocardial FDG uptake characteristics and their dependence on blood glucose is helpful in interpreting myocardial FDG-PET images.

PET study of cerebral glucose metabolism and fluorodopa uptake in patients with corticobasal degeneration

We measured cerebral glucose utilization and fluorodopa metabolism in the brain of patients with corticobasal degeneration using position emission tomography. The clinical pictures are distinctive, comprising features referable to both cerebral cortical and basal ganglionic dysfunctions. Brain images of glucose metabolism can demonstrate specific abnormalities with a marked asymmetry in the parietal cortex (the primary motor and sensory cortex and the lateral parietal cortex), the thalamus, the caudate nucleus and the putamen of the dominantly affected hemisphere related to clinical symptoms in six patients. [18F]dopa uptake also reduced in an asymmetric pattern, both the caudate nucleus and the putamen in four patients. This unique combination study measuring both cerebral glucose utilization and fluorodopa metabolism in the nigrostriatal system can provide efficient information about the dysfunctions which are correlated with individual clinical symptoms.

Direct determination of plasma endothelin-I by chemiluminescence enzyme immunoassay

A highly sensitive sandwich-type chemiluminescence enzyme immunoassay for plasma endothelin-I (ET-1), involving no extraction steps, has been developed. Two populations of polyclonal antibodies were used in the present study: One is specific to the C-terminus of the endothelin family of peptides; the other, a Fab' fragment against the N-terminal core region of ET-1, is coupled with horseradish peroxidase (HRP). Labeled HRP activity was measured by using an enhanced chemiluminescence reaction of luminol/hydrogen peroxide. The assay was sensitive enough to detect 0.5 ng/L (0.05 pg/well) of plasma ET-1 and had no significant cross-reactivities with other related peptides, including endothelin-3 and the endothelin precursor peptide, big ET-1. Reliability of the assay was confirmed by comparison with an extraction-based procedure and a commercial kit.

Direct determination of plasma endothelin-I by chemiluminescence enzyme immunoassay

A highly sensitive sandwich-type chemiluminescence enzyme immunoassay for plasma endothelin-I (ET-1), involving no extraction steps, has been developed. Two populations of polyclonal antibodies were used in the present study: One is specific to the C-terminus of the endothelin family of peptides; the other, a Fab' fragment against the N-terminal core region of ET-1, is coupled with horseradish peroxidase (HRP). Labeled HRP activity was measured by using an enhanced chemiluminescence reaction of luminol/hydrogen peroxide. The assay was sensitive enough to detect 0.5 ng/L (0.05 pg/well) of plasma ET-1 and had no significant cross-reactivities with other related peptides, including endothelin-3 and the endothelin precursor peptide, big ET-1. Reliability of the assay was confirmed by comparison with an extraction-based procedure and a commercial kit.

[Development of simple on-line [oxygen-15]water infuser]

A [15O]water production and infusion system was newly developed for blood flow study with positron emission tomography. The system utilizes a electrostatic cooling unit to liquify [15O]vapor in a coiled plastic tube. Labeled [15O]water is collected into an infusion syringe by a wash of the trapping tube with saline. The system is simple and efficient; the recovery rate of [15O]water is over 90% at 10 degrees C of cooling temperature.

Biological evaluation of 5-methyl-branched-chain omega-[18F]fluorofatty acid: a potential myocardial imaging tracer for positron emission tomography

5-Methyl-17-[18F]fluoroheptadecanoic acid (5-MFHA) has been proposed as a new myocardial imaging tracer for positron emission tomography (PET), containing methyl-branching at the odd-numbered position, except the 3-position. To compare the site of methyl-branching of fatty acids on the contribution to myocardial imaging, the biological evaluation of 5-MFHA-using accumulation studies, metabolic studies, and PET studies of the heart muscle-was investigated. In the comparative biodistribution studies for 16-[18F]fluoropalmitic acid (FPA), 3-methyl-17-[18F]fluoroheptadecanoic acid (3-MFHA) and 5-MFHA, the initial myocardial uptake of 5-MFHA (2.64 [%dose/g tissue]) was relatively high between those of FPA and 3-MFHA (3.45 and 1.58, respectively), and the washout from myocardium of 5-MFHA was midway between those of FPA and 3-MFHA. In the lipid analysis studies, 5-MFHA was mainly metabolized to triglycerides in the myocardium, and its metabolic pattern was similar to that of straight-chain fatty acids (FPA). In the PET studies using 5-MFHA in canines, good myocardial images were obtained for up to 30 min after injection.

Analysis of plasma metabolites during human PET-studies with three receptor ligands, [11C]YM-09151-2, [11C]doxepin and [11C]pyrilamine

Carbon-11 labeled metabolites in human plasma were analyzed by high-performance liquid chromatography during positron emission tomography (PET) studies using the dopamine D2 ligand [11C]YM-09151-2 as well as the histamine H1 ligands [11C]doxepin and [11C]pyrilamine. For all the three tracers, blood clearance of the radioactivity was extremely rapid after an i.v. injection. The plasma protein-binding of [11C]YM-09151-2 and [11C]doxepin had protective effects upon the metabolic alteration of the ligands, whereas [11C]pyrilamine was free from the protein-binding and immediately degraded. The degradation of [11C]doxepin was more rapid in epileptic patients on medication than in normal subjects. These results indicate that analysis of metabolites in the plasma is necessary to determine the accurate arterial input function for quantitative PET measurement.

Positron emission tomographic study of central histamine H1-receptor occupancy in human subjects treated with epinastine, a second-generation antihistamine

Histamine H1-receptor occupancy in the human brain was measured in healthy young volunteers by positron emission tomography (PET) using [11C]doxepin. d-Chlorpheniramine, a selective and classical antihistamine, occupied 76.8 +/- 4.2% of the averaged values of available histamine H1 receptors in the frontal cortex after its administration in a single oral dose of 2 mg. Epinastine, a non-sedative antihistamine, occupied 13.2 +/- 18.5% of the available H1 receptors in the human frontal cortex after its administration in a single oral dose of 20 mg. There was significant correlation between H1 receptor occupancy by epinastine and its plasma concentration in each subject. PET data on the human brain were essentially compatible with those on H1-receptor occupancy in the guinea pig brain as determined by an in vivo binding technique, although for the same H1-receptor occupancy, the dose was less in humans than in guinea pigs. Our PET studies demonstrated that receptor occupancy by a second-generation H1 antagonist, epinastine, was less than 20% of the total H1 receptors, and that the low receptor occupancy was closely related to the low incidence of central side effects.

Stable and general-purpose chemiluminescent detection system for horseradish peroxidase employing a thiazole compound enhancer and some additives

A stable and highly sensitive chemiluminescent detection system for horseradish peroxidase (HRP)/luminol/hydrogen peroxide using a newly designed thiazole compound enhancer has been established. Some additives for the chemiluminescent reaction were explored to overcome some defects of the reaction such as rapid decay and high background of light emission. Recrystallization of luminol and the addition of several detergents into the reacting solution were effective to increase specific light emissions. The addition of skim milk into the reacting solution reduced the background. Consequently, skim milk combined with a detergent increased the signal to noise ratio about 20 times compared with the reactions in the absence of both additives. The optimal concentration of enhancer and the addition of egg albumin stabilized the emission. In the new method, 6x 10(-18) mol of HRP was detectable. This would be the most sensitive enhanced chemiluminescent detection system for HRP. Furthermore, we could detect picogram per milliliter (10(-17) mol) concentrations of a trace component in biological materials such as endothelin-1 by employing this reaction.

Histamine H1 receptor occupancy in human brains after single oral doses of histamine H1 antagonists measured by positron emission tomography

1. Histamine H1 receptor occupancy in the human brain was measured in 20 healthy young men by positron emission tomography (PET) using [11C]-doxepin. 2. (+)-Chlorpheniramine, a selective and classical antihistamine, occupied 76.8 +/- 4.2% of the averaged values of available histamine H1 receptors in the frontal cortex after its administration in a single oral dose of 2 mg. Intravenous administration of 5 mg (+)-chlorpheniramine almost completely abolished the binding of [11C]-doxepin to H1 receptors (H1 receptor occupancy: 98.2 +/- 1.2%). 3. Terfenadine, a nonsedative antihistamine, occupied 17.2 +/- 14.2% of the available H1 receptors in the human frontal cortex after its administration in a single oral dose of 60 mg. 4. There was no correlation between H1 receptor occupancy by terfenadine and the plasma concentration of the active acid metabolite of terfenadine in each subject. 5. PET data on human brain were essentially compatible with those on H1 receptor occupancy in guinea-pig brain determined by in vivo binding techniques, although for the same H1 receptor occupancy the dose was less in human subjects than in guinea-pigs. 6. The PET studies demonstrated the usefulness of measuring H1 receptor occupancy with classical and second-generation antihistamines in human brain to estimate their unwanted side effects such as sedation and drowsiness quantitatively.

Positron emission tomography (PET) study of the alterations in brain distribution of [11C]methamphetamine in methamphetamine sensitized dog

[11C]Methamphetamine ([11C]MAP) was synthesized by an automated on-line [11C]methylation system for positron emission tomography (PET) study. We newly produced a MAP sensitized dog by repeated MAP treatment and studied the brain distribution of [11C]MAP in the normal and the MAP sensitized dog. The maximal level of accumulation of [11C]MAP in the sensitized dog brain was 1.4 times higher than that in the control. No difference was found in the metabolism of MAP between the two conditions. The significant increase of [11C]MAP in the MAP sensitized brain indicates that subchronic MAP administration causes some functional change in uptake site of MAP.

Methionine uptake by tumor tissue: a microautoradiographic comparison with FDG

L-methyl-11C-methionine (11C-Met) and 2-deoxy-2-18F-fluoro-D-glucose (18F-FDG) are used for tumor diagnosis and treatment evaluation by PET. In order to examine the role of these tracers in cancer imaging, intratumoral properties of 14C-Met were studied and compared to those of 18F-FDG.

METHODS

The distribution of 14C-Met in various cellular elements of two different mouse malignant tumor tissues, MH134 and FM3A, was analyzed serially using microautoradiography within a period of 120 min after injection of the tracer.

RESULTS

Carbon-14-Met and 18F-FDG showed different distributions in tumor tissue. Carbon-14-Met uptake by the tumor was mostly by viable cancer cells. The uptake by macrophages and other cellular components was low. The uptake was higher in the highly proliferative tumor but did not reflect protein synthesis. The rapid and slow growing tumors demonstrated that 14C-Met uptake ratio was lower than that of 18F-FDG, reflecting de novo DNA synthesis ratio.

CONCLUSION

Carbon-14-Met uptake represents the presence of viable cancer cells. Carbon-11-Met may be suitable for treatment evaluation of individual tumors but not growth rates of different tumors. Fluorine-18-FDG reflects tumor-host immune system reaction and is an excellent tool for pretreatment evaluation of tumors and determination of tumor proliferative activity.

Linearized method: A new approach for kinetic analysis of central dopamine D(2) receptor specific binding

We proposed a new method (;linearized method') to analyze neuroleptic ligand-receptor specific binding in a human brain using positron emission tomography (PET). We derived the linear equation to solve four rate constants, k(3), k(4), k(5), k(6) from PET data. This method does not demand a radioactivity curve in plasma as an input function to the brain, and can perform fast calculations in order to determine rate constants. We also tested the nonlinearized method including nonlinear equations which is a conventional analysis using plasma radioactivity corrected for ligand metabolites as an input function. We applied these methods to evaluate dopamine D(2) receptor specific binding of [(11)C] YM-09151-2. The value of B(max)/K(d)=k(3)/k (4) obtained by the linearized method was 5.72+/-3.1 which was consistent with the value of 5.78+/-3.4 obtained by the nonlinearized method.

[A case of hepatocellular carcinoma with lumbar bone metastasis with high uptake of 18F-fluorodeoxygalactose in PET]

18F-fluorodeoxygalactose (18FDGal) is a tracer for the evaluation of galactose metabolism in the tissue. PET with 18FDGal was performed in a hepatoma (HCC) patient with lumbar bone metastasis. The image at 45 min after i.v. injection of 18FDGal demonstrated very high uptake by the bone metastasis with tumor-to-surrounding normal tissue ratio of 36. The tumor uptake expressed by differential absorption ratio was much higher than that in the cirrhotic liver and kidney. The result indicated that the HCC maintained high activity of galactose metabolism and rises the potential of this tracer for detecting extrahepatic metastases of HCC using PET.

Assessment of dopamine metabolism in brain of patients with dementia by means of 18F-fluorodopa and PET

By means of positron emission tomography (PET) and 18F-fluorodopa (FDOPA), a study was initiated to analyze the cerebral dopamine (DA) metabolism of 32 subjects including those with AD/SDAT and vascular dementia (VD, multi-infarct type). A semiautomated irregular ROI drawing routine to identify the striatum was developed that interactively defined the PET threshold pixels referring to the count histograms and location of the corresponding pixels. A comparative study by five examiners showed significant improvement in the area size definition and count linearity particularly for low contrast objects. The graphical plot was employed to calculate the FDOPA influx rate (Ki) for the ROI data with cerebellar radioactivity as an input function. The striatal Ki value was found to be relatively stable and did not show signs of a significant age-related change. The vascular patients had smaller Ki to the striatum than the aged control. Although the mean Ki of AD/SDAT was almost compatible with that of age-matched normals, their Ki was more scattered with higher and lower Ki cases. The multiple regression analysis revealed that the Ki could be predicted by age and the mini-mental state (MMS) performance (r2 = 0.590, p < 0.01 for AD/SDAT, r2 = 0.401, and p < 0.05 for VD). MMS was found to be a more dominant factor than age. We conclude that dopamine metabolism became disturbed as dementia became progressively severe.

Binding characteristics of a histamine H3-receptor antagonist, [3H]S-methylthioperamide: comparison with [3H](R)alpha-methylhistamine binding to rat tissues

The release and synthesis of neuronal histamine are regulated by histaminergic autoreceptors named as histamine H3 receptors. The development of radiolabeled histamine H3 antagonists is needed to characterize the binding of antagonists to these receptors. Here we describe the binding characteristics of a new histamine H3-receptor antagonist, [3H]S-methylthioperamide (SMT), to rat tissues, and compare its binding with that of [3H](R)alpha-methylhistamine ((R)alpha MH), a selective histamine H3-receptor agonist. The binding of [3H]SMT to the membranes of rat forebrain was found to be stereoselective, saturable, reversible and temperature-dependent. Saturation binding experiments indicated a single class of high affinity sites for [3H]SMT in forebrain membranes (KD = 2.1 nM, Bmax = 24.3 pmol/g of tissue at 4 degrees C). The Bmax was approximately 3 times that of [3H](R)alpha MH binding to rat forebrain membranes (KD = 2.5 nM, Bmax = 7.3 pmol/g of tissue at 25 degrees C). Autoradiographic images of [3H]SMT binding in the brain were essentially the same as those of [3H](R)alpha MH. [3H]SMT also bound appreciably to peripheral tissues (the liver, adrenal, stomach, ileum, kidney, lung and bladder), whereas the [3H](R)alpha MH bindings to these peripheral tissues were negligible. These results indicate that [3H]SMT binds to H3 receptors primarily in the central nervous system, and that it also has high affinity toward non-H3 receptors, probably hemoproteins, in peripheral tissues.