Imidazoleacetic Acid, a γ-Aminobutyric Acid Receptor Agonist, Can Be Formed in Rat Brain by Oxidation of Histamine

Abstract: It is generally accepted that in mammalian brain histamine is metabolized solely by histamine methyltransferase (HMT), to form tele -methylhistamine, then oxidized to tele -methylimidazoleacetic acid. However, histamine's oxidative metabolite in the periphery, imidazoleacetic acid (IAA), is also present in brain and CSF, and its levels in brain increase after inhibition of HMT. To reinvestigate if brain has the capacity to oxidize histamine and form IAA, conscious rats were injected with [³H]histamine (10 ng), either into the lateral ventricles or cisterna magna, and decapitated 30 min later. In brains of saline-treated rats, most radioactivity recovered was due to tele -methylhistamine and tele -methylimidazoleacetic acid. However, significant amounts of tritiated IAA and its metabolites, IAA-ribotide and IAA-riboside, were consistently recovered. In rats pretreated with metoprine, an inhibitor of HMT, labeled IAA and its metabolites usually comprised the majority of histamine's tritiated metabolites. [³H]Histamine given intracisternally produced only trace amounts of oxidative metabolites. Formation of IAA, a potent GABA-A agonist with numerous neurochemical and behavioral effects, from minute quantities of histamine in brain indicates a need for reevaluation of histamine's metabolic pathway or pathways in brain and suggests a novel mechanism for interactions between histamine and the GABAergic system.     

Disposition of Histamine, Its Metabolites, and pros-Methylimidazoleacetic Acid in Brain Regions of Rats Chronically Infused with α-Fluoromethylhistidine

Abstract: In mammalian brain, histamine is known to be metabolized solely by histamine methyltransferase (HMT), forming tele -methylhistamine (t-MH), then tele -methylimidazoleacetic acid (t-MIAA). We previously showed that imidazoleacetic acid (IAA), a GABA agonist, and histamine's metabolite in the periphery, is present in brain where its concentration increased after inhibition of HMT. Also, when [³H]histamine was given intracerebroventricularly to rats, a portion was converted to IAA, a process increased by inhibition of HMT. These results indicated that brain has the capacity to oxidize histamine but did not show whether this pathway is operative under physiological conditions. To address this question, rats were infused for >4 weeks with α-fluoromethylhistidine (α-FMHis), an irreversible inhibitor of histamine's synthetic enzyme, l -histidine decarboxylase. Compared with controls (untreated and saline-treated rats), brain levels of histamine, t-MH, and t-MIAA in all regions were markedly reduced in treated rats. As a percentage of controls, depletion of t-MIAA > t-MH > histamine in all regions, and regional depletions of histamine corresponded to its turnover rates in regions of rat brain. In contrast, levels of IAA were unchanged as were levels of pros -methylimidazoleacetic acid, an isomer of t-MIAA unrelated to histamine metabolism. Results suggest that in brains of rats, unlike in the periphery, most IAA may not normally derive from histamine. Because histamine in brain can be converted to IAA under certain conditions, direct oxidation of histamine may be a conditional phenomenon. Our results also support the existence of a very slow turnover pool of brain histamine and use of chronic α-FMHis infusion as a model to probe the histaminergic system in brain.     

Presence of Kynurenic Acid in the Mammalian Brain

Kynurenic acid, a tryptophan metabolite able to antagonize the actions of the excitatory amino acids, has been identified and measured for the first time in the brain of mice, rats, guinea pigs, and humans by using an HPLC method. Its content was 5.8 +/- 0.9 in mouse brain, 17.8 +/- 2.0 in rat brain, 16.2 +/- 1.5 in guinea pig brain, 26.8 +/- 2.9 in rabbit brain, and 150 +/- 30 in human cortex (pmol/g wet wt. mean +/- SE). The regional distribution of this molecule was uneven. In rats, guinea pigs, and rabbits, the brainstem was the area richest in this compound. Tryptophan administration (100-300 mg/kg, i.p.) to rats resulted in a significant increase of the brain content of kynurenic acid. Similarly, 1 h after probenecid administration (200 mg/kg, i.p.), the brain content of kynurenate increased by fourfold, thus suggesting that its turnover rate is relatively fast.     

An aluminum-based rat model for Alzheimer's disease exhibits oxidative damage, inhibition of PP2A activity, hyperphosphorylated tau, and granulovacuolar degeneration

In Alzheimer's disease (AD), oxidative damage leads to the formation of amyloid plaques while low PP2A activity results in hyperphosphorylated tau that polymerizes to form neurofibrillary tangles. We probed these early events, using brain tissue from a rat model for AD that develops memory deterioration and AD-like behaviors in old age after chronically ingesting 1.6 mg aluminum/kg bodyweight/day, equivalent to the high end of the human dietary aluminum range. A control group consumed 0.4 mg aluminum/kg/day. We stained brain sections from the cognitively-damaged rats for evidence of amyloid plaques, neurofibrillary tangles, aluminum, oxidative damage, and hyperphosphorylated tau. PP2A activity levels measured 238.71+/-17.56 pmol P(i)/microg protein and 580.67+/-111.70 pmol P(i)/microg protein (p<0.05) in neocortical/limbic homogenates prepared from cognitively-damaged and control rat brains, respectively. Thus, PP2A activity in cognitively-damaged brains was 41% of control value. Staining results showed: (1) aluminum-loading occurs in some aged rat neurons as in some aged human neurons; (2) aluminum-loading in rat neurons is accompanied by oxidative damage, hyperphosphorylated tau, neuropil threads, and granulovacuolar degeneration; and (3) amyloid plaques and neurofibrillary tangles were absent from all rat brain sections examined. Known species difference can reasonably explain why plaques and tangles are unable to form in brains of genetically-normal rats despite developing the same pathological changes that lead to their formation in human brain. As neuronal aluminum can account for early stages of plaque and tangle formation in an animal model for AD, neuronal aluminum could also initiate plaque and tangle formation in humans with AD.     

Presence of biologically and immunologically active secretin-like substance in the mammalian brain

The present study involves the isolation and characterization of secretin-like immunoreactivity from the brains of pigs, rats and dogs. Secretin-like immunoreactivity was extracted with 0.1 N HCl and subjected to SP-Sephadex ion exchange chromatography and gel filtration on a Sephadex G-50 superfine column. The average amounts of secretin-like immunoreactivity in the extracts of 2 pigs, 7 rats and 6 dog brains were 0.25 ng/g, 2.4 +/- 0.2 ng/g and 0.34 +/- 0.07 ng/g fresh tissue weight, respectively. The secretin-like immunoreactivities in the brain extracts exhibited the same retention coefficient as natural porcine secretin on gel filtration and were eluted in the same salt gradient from the SP-Sephadex column. A partially purified secretin-like immunoreactivity isolated from canine brain exhibited the same bioactivity as natural porcine secretin to stimulate pancreatic volume flow in anesthetized rats (n = 4). These results indicated that secretin-like immunoreactivities from brain extracts possess the same molecular size and charge as natural porcine secretin and the secretin-like immunoreactivity isolated from dog brain is active in stimulating pancreatic secretion in anesthetized rats.     

Comparison of Freeze-Blowing and Funnel-Freezing of Rat Brain for the Measurement of Cerebral Glucose Concentration In Vivo

The efficacy of funnel-freezing of rat brain to inactivate metabolic processes and preserve in vivo tissue glucose concentration was validated by comparing the results obtained by funnel-freezing with those obtained with freeze-blowing of brain. The arterial plasma glucose level was clamped at 9 mM in halothane-anesthetized rats to produce identical glucose levels in brain tissue prior to freeze fixation. In funnel-frozen and freeze-blown brains, tissue glucose concentrations were 2.47 +/- 0.05 and 2.47 +/- 0.06 mumol/g (means +/- SEM), respectively. Lactate levels in funnel-frozen brains were slightly but significantly higher than those in freeze-blown brains, i.e., 1.56 +/- 0.05 mumol/g versus 1.30 +/- 0.05 mumol/g (means +/- SEM; p less than 0.05). Regional analysis in funnel-frozen brains revealed that glucose concentrations in superficial and basal brain areas remained approximately equal at 2.30 +/- 0.1 mumol/g and 2.31 +/- 0.09 mumol/g (means +/- SEM), respectively. Our findings indicate that in the anesthetized rat, funnel-freezing of brain is suitable for the measurement of regional in vivo glucose concentrations.     

Increase in the Content of Quinolinic Acid in Cerebrospinal Fluid and Frontal Cortex of Patients with Hepatic Failure

Abstract: Quinolinic acid (QUIN), an excitotoxic tryptophan metabolite, has been identified and measured in human cerebrospinal fluid (CSF) using a mass-fragmentographic method. Furthermore, its content has been evaluated in frontal cortex obtained at autopsy from the cadavers of patients who died after hepatic coma. During the coma, the concentration of QUIN in the CSF was 152 ± 38 pmol ml^-1. In contrast, the concentration in control patients affected by different pathologies was 22 ± 7 pmol ml^-1. In the frontal cortex of patients who died after episodes of hepatic encephalopathy, the content of QUIN was three times higher than in controls (2.6 ± 0.6 versus 0.80 ± 0.08 nmol/g wet weight). As a result of these investigations we are now able to extend our previous observations on the increase of QUIN in the brains of rats used as experimental models of hepatic encephalopathy to man. QUIN should therefore be added to the list of compounds possibly involved in the pathogenesis and symptomatology of brain disorders associated with liver failure.     

A method for determination of subpicomole concentrations of tetrahydropapaveroline in rat brain by high-performance liquid chromatography with electrochemical detection

A sensitive and selective method for detection of tetrahydropapaveroline (THP) in rat brain has been developed. The procedure employs a multiple-stage separation scheme that selectively isolates THP from rat brain tissue and utilizes the sensitivity and resolution of reversed-phase high-performance liquid chromatography with electrochemical detection to provide an analysis with high specificity for THP. The mean (+/- SD) recovery of THP from rat brain homogenates, fortified at levels ranging from 0.25 to 3.0 pmol per whole brain, was 43.4 +/- 3.5%. The concentration of THP in brains of rats pretreated with L-dopa was 0.44 +/- 0.14 (SD) pmol per gram. The limit of detection of THP was approximately 0.1 pmol (0.03 ng) per gram brain.     

The Significance of Homovanillic Acid and 3,4-Dihydroxyphenylacetic Acid Concentrations in Human Lumbar Cerebrospinal Fluid

The concentrations of the acidic dopamine (DA) catabolites homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) measured in human CSF are supposed to reflect the "turnover" of DA in the brain. The notion of "turnover" is, however, not synonymous with impulse nerve activity in the dopaminergic systems. Significant amounts of DOPAC and HVA could, indeed, be demonstrated in brain structures wherein dopaminergic innervation has not been documented. It must also be noted that DA is not only a neurotransmitter itself, but also a precursor of norepinephrine and epinephrine. Furthermore, in lumbar CSF, levels of biogenic amine catabolites partially reflect metabolism in the spinal cord and may have limited relevance to neurotransmission in the brain. To elucidate these points further, we determined the concentrations of DOPAC and HVA in 22 areas of six human brains and eight levels of six human spinal cords. The data were correlated with the concentration of DA. Quantitative determinations were done using HPLC with electrochemical detection, after solvent and ion-pair extraction. In this study, significant amounts of both DOPAC and HVA were demonstrated in brain structures not previously associated with dopaminergic innervation. The relatively lower DA concentration in these structures suggests that in these regions, the DOPAC and HVA concentrations are unrelated to dopaminergic neurotransmission. The possible role of capillary walls and glial cells in the catabolism of DA must be further evaluated. The demonstration of DOPAC and HVA in the spinal cord is another argument against the hypothesis that CSF levels of HVA and DOPAC reflect closely the activity of the dopaminergic systems in the brain.     

在吲哚乙酸不同位点偶联载体蛋白对其抗体特异性的影响

分别选择吲哚乙醇分子上的Ｃ１位羧基和吲哚环上的Ｎ位作为偶联载体蛋白的位点,用混合酸酐法和甲醛搭桥法分别合成了两种免疫原ＩＡＡ—ＣＯ—ＮＨ一ＨＳＡ和ＩＡＡ－Ｎ－ＢＳＡ,并进而制得了对吲哚乙酸侧链识别能力不同的两种多克隆抗体,分别可特异识别甲酯化ＩＡＡ和游离态ＩＡＡ;用碳化二亚胺法和甲醛搭桥法分别合成ＩＡＡ—ＣＯ—ＮＨ－ＢＳＡｂＩＡＡ—Ｎ—ＯＶＡ两种复合物,以之为包被物,建立了两种ＩＡＡＥＬＩＳＡ。其灵敏度分别为０．３５ｐｍｏｌ和１．８０ｐｐｍｏｌ;检测范围分别为０．７８～８００ｐｍｏｌ和１．９５～２０００ｐｍｏｌ;批内变异系数分别为４．４５％和４．７９％;批间变异系数分别为１．１５％和１．５０％。笔者用这两种ＥＬＩＳＡ检测了兰花气生根和桑树苗样品中ＩＡＡ的含量,发现两种检测结果相当一致。     

5-Hydroxytryptophol in Human Cerebrospinal Fluid: Conjugation, Concentration Gradient, Relationship to 5-Hydroxyindoleacetic Acid, and Influence of Hereditary Factors

The serotonin metabolite 5-hydroxytryptophol was studied in human cerebrospinal fluid. A minor fraction (approximately 13%) was found in conjugated form from which it was liberated by treatment with sulphatase containing beta-glucuronidase activity. A concentration gradient of 5-hydroxytryptophol concentration was shown on lumbar tapping and the concentration in ventricular CSF was about 2.5 times higher than that in lumbar CSF. 5-Hydroxytryptophol and 5-hydroxyindoleacetic acid concentrations were significantly correlated in healthy, psychotic, and depressed subjects, but not in alcoholics. 5-Hydroxytryptophol concentrations in CSF of psychotic and depressed subjects were not different from those of healthy controls (4.22 pmol/ml +/- 0.15, SEM). In healthy subjects, hereditary factors seemed to have little influence on the CSF level of 5-hydroxytryptophol.     

Inhibitors of Histamine Methylation in Brain Promote Formation of Imidazoleacetic Acid, Which Interacts with GABA Receptors

Abstract: In brain, the precursor of imidazoleacetic acid (IAA), a GABA_A agonist but a GABA_C antagonist, is not known. In the periphery, IAA derives from oxidation of histamine. But in brain, histamine is thought to be metabolized solely by histamine methyltransferase (HMT), forming tele -methylhistamine (t-MH) and tele -methylimidazoleacetic acid (t-MIAA). We showed that [³H]histamine (intracerebroventricularly) could be converted to IAA in brains of rats, a process increased by inhibition of HMT. This demonstrated that brain can oxidize histamine and suggested that endogenous histamine might also be oxidized if HMT activity were reduced. We examined, in rat cerebral cortex, effects of the following HMT inhibitors (mg/kg i.p.): metoprine (10), tacrine (10), velnacrine (10, 30), and physostigmine (1, 2). Tacrine was a potent inhibitor ( K _i∼ 22 n M ). To measure histamine in tissue that contained HMT inhibitors, we developed a gas chromatography-mass spectrometry method. After 2 h, all drugs reduced endogenous levels of t-MH and t-MIAA and increased levels of histamine and IAA. Our results show that inhibition of HMT promotes oxidation of histamine in brain, probably by shunting histamine to an alternative metabolic pathway. Formation of IAA provides a novel interaction between histaminergic and GABAergic systems in brain. Accumulation of IAA should be considered when inhibitors of HMT are used to probe brain histamine function.     

Histamine Metabolites in Cerebrospinal Fluid of the Rhesus Monkey (Macaca mulatto): Cisternal-Lumbar Concentration Gradients

Similar to metabolites of other aminergic transmitters, histamine metabolites of brain, tele-methylhistamine (t-MH) and tele-methylimidazoleacetic acid (t-MIAA), could have a concentration gradient between rostral and caudal sites of CSF. To test this hypothesis, cisternal and lumbar CSF samples were collected in pairs from eight monkeys (Macaca mulatta), and levels of t-MH and t-MIAA were measured by gas chromatography-mass spectrometry. pros-Methylimidazoleacetic acid (p-MIAA), an endogenous isomer of t-MIAA that is not a histamine metabolite, was also measured. Cisternal levels (in picomoles per milliliter, mean +/- SEM) of t-MH (9.9 +/- 1.4) and t-MIAA (40.8 +/- 7.6), but not of p-MIAA (9.7 +/- 1.2), exceeded those in lumbar CSF (t-MH, 1.8 +/- 0.3; t-MIAA, 6.8 +/- 0.9; p-MIAA, 8.6 +/- 0.6) in every monkey. The magnitudes of the mean cisternal-lumbar concentration gradients for t-MH (6.6 +/- 1.1) and t-MIAA (6.5 +/- 1.3) were indistinguishable. These gradients exceed those of metabolites of most other transmitters. There was no gradient for the levels of p-MIAA. The cisternal, but not lumbar, levels of t-MH and t-MIAA were correlated. There was no significant difference between the means of the metabolite concentration ratios (t-MIAA/t-MH) in cisternal (4.0 +/- 0.4) and lumbar (4.4 +/- 0.9) CSF. The steepness of these gradients suggests that levels of t-MH and t-MIAA in lumbar CSF might be useful probes of histaminergic metabolism in brain.     

Effects of Rat Ovariectomy on CSF Monoamine Metabolite Levels and Elimination

Cerebrospinal fluid (CSF) was removed from the third ventricle of anesthetized male, female, and ovariectomized rats. CSF 3,4-dihydroxyphenylethylamine and serotonin metabolite levels [dihydroxyphenylacetic acid, homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA)] were determined on 15-min samples by liquid chromatography coupled with electrochemical detection. Monoamine oxidase inhibition was used for studying metabolite turnover in the CSF. No difference was observed between male, ovariectomized, and sham-operated female rats. However, ventricular CSF HVA and 5-HIAA levels were significantly higher in the ovariectomized than in the sham-operated rats. These differences do not reflect effects of ovariectomy on brain metabolite production but indicate slower metabolite elimination from the CSF.     

Motor Activity Increases Tryptophan, 5-Hydroxyindoleacetic Acid, and Homovanillic Acid in Ventricular Cerebrospinal Fluid of the Conscious Rat

An investigation was made into the effects of running (1 h at 20 m/min) on central serotonergic and dopaminergic metabolism in trained rats. Methodology involved continuous withdrawal of cerebrospinal fluid (CSF) from the third ventricle of conscious rats and measurements of tryptophan (TRP), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA) levels during a 2 h post-exercise period. All three compounds were increased during the hour following exercise and returned to their basal values within an hour later. CSF flow rate was stable when metabolite levels were elevated. Brain determinations indicated that CSF metabolite variations only qualitatively paralleled brain changes. Indeed, post-exercise TRP, 5-HIAA, and HVA levels were increased to a greater extent in brain when compared to CSF. It is suggested that increased serotonergic and dopaminergic metabolism, caused by motor activity, may be involved in the behavioral effects of exercise.     

Concentration Gradients of Free and Total γ-Aminobutyric Acid and Homocarnosine in Human CSF: Comparison of Suboccipital and Lumbar Sampling

Abstract: Concentrations of free and total γ-aminobutyric acid (GABA) and homocarnosine were determined in sequential aliquots of the first 30 ml of CSF obtained by lumbar puncture in five patients. Rostrocaudal gradients were calculated and compared to gradients estimated by determining concentrations of these substances in CSF obtained by simultaneous suboccipital and lumbar punctures in four more patients. In the lumbar fractions study, rostrocaudal mean gradients of 0.36, 36, and 21 pmol/ml for free GABA, total GABA, and homocarnosine, respectively, were calculated. In the suboccipital/lumbar study, gradients of 0.33, 30, and 24 pmol/ml for free GABA, total GABA, and homocarnosine, respectively, were estimated. These results indicate that valid comparison of CSF concentrations of these substances is restricted to similar fractions and suggest that in CSF the substances originate largely from brain rather than from peripheral sources.     

In Vivo Studies Identify 5a-Pregnan-3a-o1-20-one as an Active Anesthetic Agent

Mice were anesthetized with 5 alpha-[3H]pregnan-3 alpha-ol-20-one. Brain levels for 5 alpha-pregnan-3 alpha-ol-20-one and its five major metabolites (5 alpha-pregnanedione, k0, k1, k2, k3) were compared at behavioral endpoints that are characteristic of the anesthetized state. The results support the hypothesis that 5 alpha-pregnan-3 alpha-ol-20-one mediates the anesthetic response, and they weigh against the hypothesis that any of its metabolites is solely responsible for the onset or the maintenance of the anesthetized state. For an administered dose of 3 mg/kg, brain levels (means +/- SEM) for 5 alpha-pregnan-3 alpha-ol-20-one at the time of the loss of the righting response (n = 10) and at the time of the return of the righting response (n = 6) were 7.24 +/- 0.61 pmol/mg of brain tissue and 3.63 +/- 0.26 pmol/mg of brain tissue, respectively. No metabolite level was lower at the return of the righting response than at the loss of the righting response. 5 alpha-Pregnan-3 alpha-ol-20-one brain levels increased consistently with the percentage of anesthetized mice. This was not the case for any of the metabolites. Fifty percent of the mice were anesthetized when the 5 alpha-pregnan-3 alpha-ol-20-one level was 4.5 pmol/mg of brain tissue.     

Analysis of monohydroxyeicosatetraenoic acids and F2-isoprostanes as markers of lipid peroxidation in rat brain mitochondria

We have introduced two specific techniques for the quantitative measurement of monohydroxyeicosatetraenoic acids (HETEs) and F2-isoprostanes by gas chromatography-mass spectrometry/negative ion chemical ionization (GC-MS/NICI) to study lipid peroxidation in isolated rat brain mitochondria by iron/ascorbate. The analysis of HETEs involved hydrogenation, solid phase extraction on a C18-cartridge, formation of pentafluorobenzyl bromide and trimethylsilyl ether derivatives. In the case of F2-isoprostanes, the analytical procedure was similar to that of HETEs except that the hydrogenation step was omitted. We found that HETE content (sum of 5-, 8-12-, and 15-isomers) in freshly prepared rat brain mitochondria was 220 +/- 40pmol/mg protein. The corresponding content for the F2-isoprostane, 8-iso-PGF2alpha, was 0.21 +/-+/- 0.10 pmol/mg protein. HETEs and 8-iso-PGF2alpha were predominantly present in the esterified form. The content of both HETEs and 8-iso-PGF2alpha were increased in presence of iron/ascorbate as oxidation system. After 30 min incubation with Fe2+ ascorbate, the content of HETE isomers was increased about 6-fold compared with baseline levels whereas that for 8-iso-PGF2alpha was elevated 100-fold. Formation of HETEs and F2-isoprostanes corresponded to the consumption of arachidonic acid (AA) and alpha-tocopherol, respectively. There were almost no changes in the content of free (non-esterified) HETEs and 8-iso-PGF2alpha during the course of iron/ascorbate induced oxidation of the brain mitochondria. Our data provide the first direct evidence for the presence of HETEs and F2-isoprostanes in freshly isolated rat brain mitochondria and that esterified HETEs and 8-iso-PGF2alpha are predominantly generated during iron/ascorbate induced lipid peroxidation. Sensitive quantification of these products of non-enzymatic lipid peroxidation as indicators of oxidant injury opens new areas of investigation regarding the role of free radicals in the pathogenesis of human diseases. In addition, HETEs and F2-isoprostanes may be important mediators for mitochondrial functions.     

Expression of adrenomedullin2/intermedin in human brain, heart, and kidney

Adrenomedullin2/intermedin (AM2/IMD) is a novel member of the calcitonin/calcitonin gene-related peptide (CGRP) family. In the present study, we developed a specific radioimmunoassay of human AM2/IMD. Expression of AM2/IMD was studied in the human brain, pituitary, heart and kidney obtained at autopsy by radioimmunoassay and immunocytochemistry. Immunoreactive-AM2/IMD was detected by radioimmunoassay in human brains (range; 0.163-1.495 pmol/g wet weight), pituitaries (4.46+/-0.689 pmol/g wet weight, mean+/-S.E.M, n=3), left ventricles of hearts (0.251+/-0.0321 pmol/g wet weight, n=4), kidneys (3.49+/-1.18 pmol/g wet weight, n=5), and plasma obtained at healthy subjects (24.7+/-1.78 pmol/l, n=3). Reverse-phase high performance liquid chromatography showed that immunoreactive-AM2/IMD in human brain, kidney and plasma extracts were eluted in the position of authentic AM2/IMD. Additional peaks eluted earlier were found in the brain tissue and plasma. Immunocytochemistry showed that immunoreactive-AM2/IMD was localized in paraventricular and supraoptic nuclei of hypothalamus, anterior and posterior lobes of pituitary, cardiomyocytes, pericardial adipocytes, vascular endothelial cells of pericardial veins, and vascular smooth muscle cells of coronary arteries and renal arterioles as well as in renal tubular cells. The present study has shown expression of AM2/IMD in various types of cells in the central nervous system and the cardiovascular system, and suggested possible (patho)physiological roles of AM2/IMD in these systems.     

Small Rises in Plasma Choline Reverse the Negative Arteriovenous Difference of Brain Choline

The concentrations of free choline in blood plasma from a peripheral artery and from the transverse sinus, in the CSF, and in total brain homogenate, have been measured in untreated rats and in rats after acute intraperitoneal administration of choline chloride. In untreated rats, the arteriovenous difference of brain choline was related to the arterial choline level. At low arterial blood levels (less than 10 microM) as observed under fasting conditions, the arteriovenous difference was negative (about -2 microM), indicating a net release of choline from the brain of about 1.6 nmol/g/min. In rats with spontaneously high arterial blood levels (greater than 15 microM), the arteriovenous difference was positive, implying a marked net uptake of choline by the brain (3.1 nmol/g/min). The CSF choline concentration, which reflects changes in the extracellular choline concentration, also increased with increasing plasma levels and closely paralleled the gradually rising net uptake. Acute administration of 6, 20, or 60 mg of choline chloride/kg caused, in a dose-dependent manner, a sharp rise of the arterial blood levels and the CSF choline, and reversed the arteriovenous difference of choline to markedly positive values. The total free choline in the brain rose only initially and to a quantitatively negligible extent. Thus, the amount of choline taken up by the brain within 30 min was stored almost completely in a metabolized form and was sufficient to sustain the release of choline from the brain as long as the plasma level remained low. We conclude that the extracellular choline concentration of the brain closely parallels fluctuations in the plasma level of choline.(ABSTRACT TRUNCATED AT 250 WORDS)