CHOLINE AND ACETYLCHOLINE IN RATS: EFFECT OF DIETARY CHOLINE

Abstract– The concentration of free choline in peripheral tissues (duodenum, heart, kidney, liver, stomach and plasma) of rats was found to be related to the amount of free choline in the diet. Under steady-state conditions, the concentration of free choline in plasma varied from a minimum of approx 6 nmol/ml (in rats fed a choline-deficient diet) to a maximum value not exceeding 21 nmol/ml. The concentration of plasma choline was elevated above 21 nmol/ml for a short time after parenteral administration of choline chloride or one of its precursors (CDP choline or phosphorylcholine), but was not affected by stress, endocrine manipulations, drug treatments or the time of day when rats were killed. The metabolism of intravenously administered [methyl-³H] choline was accelerated in peripheral tissues (except plasma) of choline-deficient rats, indicating that free choline is not preserved during choline deficiency by a reduction in its rate of turnover. Furthermore, the decrease in concentration of plasma choline that occurred in rats fed a choline-deficient diet was prevented by addition of deanol (dimethylaminoethanol) to the diet. These results indicate that free choline in peripheral tissues of rats is derived from both free choline in the diet, and from precursors of choline present within the diet. In contrast to the effects in peripheral tissues, the concentration of free choline in brain was not reduced by dietary deprivation of free choline; however, the increase in free choline that occurred when rats were decapitated was reduced in brains by deficiency of choline, suggesting a decrease in the concentration of esterified forms of cerebral choline. The concentration of acetylcholine was not reduced in the brain, duodenum, heart, kidney or stomach of 21-week old rats raised from birth on a choline-deficient diet, in the duodenum of rats given a choline-deficient diet for 1, 5 or 11 days, or in brains of rats deprived of free choline for 1 or 11 days. However, the rate of in vivo synthesis of ACh from [methyl-³H]choline was accelerated in cholinergic tissues that were depleted of free choline (i.e. duodenum, heart and stomach).     

Influence of choline and ethanolamine administration on choline and ethanolamine phosphorylating activities of mouse liver and kidney.

The administration of ethanolamine to adult male mice resulted in a significant increase in ethanolamine kinase activity in liver and kidney. Similarly, choline administration resulted in a significant increase in choline kinase activity in liver and kidney. The administration of ethanolamine resulted in enhancement of choline kinase activity concomitantly with ethanolamine kinase activity in liver and kidney. The administration of choline, however, did not result in any significant increase in ethanolamine kinase activity in liver or kidney. Cycloheximide administration along with choline-ethanolamine prevented the increase in kinase activity in liver and kidney. The results obtained have been discussed in relation to the regulatory role of choline kinase and ethanolamine kinase by de novo synthesis in response to enhanced substrate concentration, the secondary nature of choline kinase induction on ethanolamine administration, and possible distinction between choline kinase and ethanolamine kinase.     

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)     

Staphylococcal enterotoxin B toxicity in BALB/c mice: Effect on T-cells, plasma cytokine levels and biochemical markers

Abstract Groups of BALB/c mice were treated with a sub-lethal dose (60 μg) of staphylococcal enterotoxin B (SEB) intraperitoneally and were sacrificed at 2, 5, 8, or 10 h post-injection. Organ, blood plasma and lymph node samples from these mice were analyzed. Plasma levels of urea, creatinine and alanine aminotransferase were significantly raised above normal by 5 h post-injection. However, alkaline phosphatase levels showed an erratic increase after toxin administration and, after administration of 10–40 μg SEB per mouse, were consistently at least 30% below normal levels at 24 h post-injection. Weight change was also monitored but found to be inconsistent. Lung, spleen and kidney samples appeared normal on histopathological examination, but liver samples showed minor polymorph infiltration and congestion. TNF-α, and IL-1 α levels in the plasma were raised by 8 h to picogram levels per ml of plasma, whereas IFN-γ and IL-2 were raised by 2 h to nanogram levels per ml of plasma. Lymph node cells taken from mice treated with toxin were given a secondary stimulation with toxin in vitro. Although the response of the cells was lower than normal on assay at four days, a time response curve showed a peak in cell responsiveness to secondary stimulation with toxin at three days. These data indicate that biochemical markers and cytokine levels are affected by the administration of SEB to mice and may be used as indicators of toxicity.     

Inhibition of cancer growth by resveratrol is related to its low bioavailability

The relationship between resveratrol (RES) bioavalability and its effect on tumor growth was investigated. Tissue levels of RES were studied after i.v. and oral administration of trans-resveratrol (t-RES) to rabbits, rats, and mice. Half-life of RES in plasma, after i.v. administration of 20 mg t-RES/kg b.wt., was very short (e.g., 14.4 min in rabbits). The highest concentration of RES in plasma, either after i.v. or oral administration (e.g., 2.6 +/- 1.0 microM in mice 2.5 min after receiving 20 mg t-RES/kg orally), was reached within the first 5 min in all animals studied. Extravascular levels (brain, lung, liver, and kidney) of RES, which paralleled those in plasma, were always < 1 nmol/g fresh tissue. RES measured in plasma or tissues was in the trans form (at least 99%). Hepatocytes metabolized t-RES in a dose-dependent fashion (e.g., 43 nmol of t-RES/g x min in the presence of 20 microM tRES), which means that the liver can remove circulating RES very rapidly. In vitro B16 melanoma (B16M) cell proliferation and generation of reactive oxygen species (ROS) was inhibited by t-RES in a concentration-dependent fashion (100% inhibition of tumor growth was found in the presence of 5 microM t-RES). Addition of 10 microM H(2)O(2) to B16M cells, cultured in the presence of 5 microM t-RES, reactivated cell growth. Oral administration of t-RES (20 mg/kg twice per day; or included in the drinking water at 23 mg/l) did not inhibit growth of B16M inoculated into the footpad of mice (solid growth). However, oral administration of t-RES (as above) decreased hepatic metastatic invasion of B16M cells inoculated intrasplenically. The antimetastatic mechanism involves a t-RES (1 microM)-induced inhibition of vascular adhesion molecule 1 (VCAM-1) expression in the hepatic sinusoidal endothelium (HSE), which consequently decreased in vitro B16M cell adhesion to the endothelium via very late activation antigen 4 (VLA-4).     

Uptake and Storage of Choline by Rat Brain: Influence of Dietary Choline Supplementation

In order to elucidate the regulation of the levels of free choline in the brain, we investigated the influence of chronic and acute choline administration on choline levels in blood, CSF, and brain of the rat and on net movements of choline into and out of the brain as calculated from the arteriovenous differences of choline across the brain. Dietary choline supplementation led to an increase in plasma choline levels of 50% and to an increase in the net release of choline from the brain as compared to a matched group of animals which were kept on a standard diet and exhibited identical arterial plasma levels. Moreover, the choline concentration in the CSF and brain tissue was doubled. In the same rats, the injection of 60 mg/kg choline chloride did not lead to an additional increase of the brain choline levels, whereas in control animals choline injection caused a significant increase; however, this increase in no case surpassed the levels caused by chronic choline supplementation. The net uptake of choline after acute choline administration was strongly reduced in the high-choline group (from 418 to 158 nmol/g). Both diet groups metabolized the bulk (greater than 96%) of newly taken up choline rapidly. The results indicate that choline supplementation markedly attenuates the rise of free choline in the brain that is observed after acute choline administration. The rapid metabolic choline clearance was not reduced by dietary choline load. We conclude that the brain is protected from excess choline by rapid metabolism, as well as by adaptive, diet-induced changes of the net uptake and release of choline.     

Oxindole, a Sedative Tryptophan Metabolite, Accumulates in Blood and Brain of Rats with Acute Hepatic Failure

Abstract: Rats treated with oxindole (10–100 mg/kg i.p.), a putative tryptophan metabolite, showed decreased spontaneous locomotor activity, loss of the righting reflex, hypotension, and reversible coma. Brain oxindole levels were 0.05 ± 0.01 nmol/g in controls and increased to 8.1 ± 1.7 or 103 ± 15 nmol/g after its administration at doses of 10 or 100 mg/kg i.p., respectively. To study the role that oxindole plays in the neurological symptoms associated with acute liver failure, we measured the changes of its concentration in the brain after massive liver damage, and we investigated the possible metabolic pathways leading to its synthesis. Rats treated with either thioacetamide (0.2 and 0.4 g/kg i.p., twice) or galactosamine (1 and 2 g/kg i.p.) showed acute liver failure and a large increase in blood or brain oxindole concentrations (from 0.05 ± 0.01 nmol/g in brains of controls to 1.8 ± 0.3 nmol/g in brains of thioacetamide-treated animals). Administration of tryptophan (300–1,000 mg/kg p.o.) caused a twofold increase, whereas administration of indole (10–100 mg/kg p.o.) caused a 200-fold increase, of oxindole content in liver, blood, and brain, thus suggesting that indole formation from tryptophan is a limiting step in oxindole synthesis. Oral administration of neomycin, a broad-spectrum, locally acting antibiotic agent able to reduce intestinal flora, significantly decreased brain oxindole content. Taken together, our data show that oxindole is a neurodepressant tryptophan metabolite and suggest that it may play a significant role in the neurological symptoms associated with acute liver impairment.     

Disposition and hepatoprotection by phosphatidyl choline liposomes in mouse liver

Small unilamellar liposomes with an average diameter of 80 nm were prepared from phosphatidyl choline of various sources using the dialysis method with cholate as a detergent. When 14C-labeled soybean liposomes were intravenously injected into male NMRI mice, up to 10% of the total label was found in the liver lipid. The uptake was dose-dependent and reached an apparent saturation 4 h after injection. The liver maintained a constant radioactivity corresponding to 1.9 +/- 0.13 mg phospholipid/g liver until ten hours after injection of 850 mg labeled phosphatidyl choline/kg body wt. Little radioactivity was taken up by the spleen. Analogous doses of liposomes prepared from egg yolk phosphatidyl choline led to a radioactivity corresponding to 1.3 +/- 0.4 mg lipid/g liver 4 h after injection. Liposomes with a similar size were prepared from hydrated, i.e., saturated phosphatidyl choline. After intravenous administration of these liposomes, an amount of 5.3 +/- 0.5 mg labeled lipid was found per g liver after 4 h. In contrast to unsaturated liposomes, 5.8 +/- 0.8 mg lipid per gram spleen was trapped by the spleen. The pharmacodynamic effect of these different liposomes was studied in benzo[a]pyrene-pretreated mice intoxicated with 400 mg/kg paracetamol. Animals which received paracetamol exhibited serum alanine aminotransferase activities of 4220 +/- 1140 units/l after 4 h and exhaled 120 +/- 19 nmol ethane kg-1 h-1. When pretreated with 850 mg soybean phosphatidyl choline/kg body wt. (i.v.) 2 h prior to paracetamol, the increase in serum transaminase activity was reduced to 117 +/- 104 units/l and ethane exhalation amounted to 18 +/- 8 nmol kg-1 h-1. In contrast, similar pretreatment with egg yolk phosphatidyl choline or hydrated phosphatidyl choline failed to protect against paracetamol-induced hepatotoxicity. The different pharmacodynamic effects of the two phosphatidyl cholines of plant or animal origin cannot be explained on the basis of their different pharmacokinetics. In the case of soybean phosphatidyl choline liposomes, the amount of radioactive lipid found in the liver correlated with the hepatoprotective potency.     

Inhibition of arginine synthesis by urea: A mechanism for arginine deficiency in renal failure which leads to increased hydroxyl radical generation

We have reported that (1) the synthesis of GSA, a uremic toxin, increases depending on the urea concentration and (2) GSA is formed from argininosuccinic acid (ASA) and the hydroxyl radical or SIN-1 which generates superoxide and NO simultaneously. However, an excess of NO, which also serves as a scavenger of the hydroxyl radical, inhibited GSA synthesis. We also reported that arginine, citrulline or ammonia plus ornithine, all of which increase arginine, inhibit GSA synthesis even in the presence of urea. To elucidate the mechanism for increased GSA synthesis by urea, we investigated the effect of urea on ASA and arginine, the immediate precursor of NO.Isolated rat hepatocytes were incubated in 6 ml of Krebs-Henseleit bicarbonate buffer containing 3% bovine serum albumin, 10 mM sodium lactate, 10 mM ammonium chloride and with or without 36 mM of urea and 0.5 or 5 mM ornithine at 37°C for 20 min. In vivo experiments, 4 ml/100 g body weight of 1.7 M urea or 1.7 M NaCl were injected intra-peritoneally into 5 male Wistar rats. Two hours after the intra-peritoneal injection of urea or 1.7 M NaCl, blood, liver and kidney were obtained by the freeze cramp method and amino acids were determined by an amino acid analyzer (JEOL:JCL-300).ASA in isolated hepatocytes was not detected with or without 36 mM (200 mgN/dl) urea, but the arginine level decreased from 36 to 33 nmol/g wet cells with urea. Ornithine which inhibits GSA synthesis, increased ASA markedly in a dose dependent manner and increased arginine. At 2 h after the urea injection the rat serum arginine level decreased by 42% (n = 5), and ornithine and citrulline levels increased significantly. Urea injection increased the ASA level in liver from 36–51 nmol/g liver but this was not statistically significant.We propose that urea inhibits arginine synthesis in hepatocytes, where the arginine level is extremely low to begin with, which decreases NO production which, in turn, increases hydroxyl radical generation from superoxide and NO. This may, also, be an explanation for the reported increase in oxygen stress in renal failure.     

Tumour-localizing properties of porphyrins. In vivo studies using free and liposome encapsulated aminolevulinic acid.

1. Using different doses of free and liposome encapsulated aminolevulinic acid (ALA) (between 2 and 8 mg/animal), given i.p., s.c. and intra-tumoural (i.t.), in vivo porphyrin synthesis by tumour, red blood cells (RBC) and different organs from tumour-bearing mice (TBM) and normal mice (NM) at different times, up to 24 hr after ALA administration, was examined. 2. It was found that by giving entrapped ALA, at a dose of 6 mg/animal (or 200 mg/kg wt), after 10 hr, a high level of porphyrin accumulation in the tumour was produced (7 micrograms/g tissue). Low synthesis occurred in muscle, lung, brain, RBC and skin; in spleen, kidney and liver synthesis is significant after 10 hr, but after 24 hr returned to normal values in the spleen and to about 2-3 micrograms/g tissue in the kidney and liver. 3. The tumour/skin porphyrin concentration ratio after 10 hr was nearly 30, the highest so far reported. 4. These results support our previous in vitro findings, indicating that free or encapsulated ALA might be used for early diagnosis of cancer and in photodynamic therapy.     

The effect of volatile antioxidants of plant origin on leukemogenesis in mice

The effect of savory essential oil added with drinking water (150 ng/ml) or with feed (2.5 μg/g) on the lifetime of AKR mice and the parameters of oxidative stress in animal blood were investigated. It was found for the first time that long-term administration of an essential oil in low doses increased the average lifetime of mice by 20–35% and was accompanied by a decrease in the hemolysis level and the content of lipid peroxidation products in erythrocytes of mice, as well as alteration in the structural state of their membranes and stabilization of polyunsaturated fatty acids level in mice liver cells.     

Central injections of noradrenaline and adrenaline differentially affect plasma free fatty acid and glucose in conscious pigeons (Columba livia)

The possible involvement of central noradrenergic and/or adrenergic circuits in central mechanisms controlling free fatty acids and glucose levels was investigated in conscious pigeons. The effects of intracerebroventricular injections of noradrenaline (80 nmol) or adrenaline (80 nmol) on plasma free fatty acids and glucose concentrations were examined. The possible role of the autonomic nervous system, of sympathetic terminals and of pituitary hormone release in the metabolic responses induced by intracerebroventricular injections of adrenaline and noradrenaline was investigated by systemic pretreatment with a ganglionic blocker (hexamethonium, 1 mg/100 g), guanethidine (5 mg/100 g), and somatostatin (15 μg/100 g), respectively, 15 min before intracerebroventricular administration of adrenaline, noradrenaline or vehicle. Intracerebroventricular noradrenaline injections strongly increased plasma free fatty acid concentration but evoked no change in blood glucose levels, while adrenaline treatment increased glycemia without affecting free fatty acid levels. Hexamethonium did not block the increase in plasma free fatty acids induced by noradrenaline, while somatostatin pretreatment abolished noradrenaline-induced lipolysis during the experimental period. Adrenaline-induced hyperglycemia was blocked by systemic injections of somatostatin, hexamethonium and guanethidine. The present results suggest that: (1) adrenergic and noradrenergic mechanisms may participate in central control of blood glucose and free fatty acids, respectively, as observed in mammals, (2) noradrenaline-induced lipolysis may be mediated by pituitary mechanisms, and (3) postganglionic sympathetic fibers, possibly innervating the endocrine pancreas, may be involved in adrenaline-induced hyperglycemia. Accepted: 14 April 2000     

THE UPTAKE OF [3H]CHOLINE BY SNAIL (HELIX POMATIA) NERVOUS TISSUE IN VITRO

Abstract— When suboesophageal ganglia of the snail Helix comalia were incubated at 25°C in a medium containing [³H]choline, tissue: medium ratios of about 14:1 were obtained after 20 min incubation, and only 15°, of the accumulated choline was metabolized to form [³H]acetylcholine. The uptake of [³H]choline showed saturation kinetics and was dependent upon temperature and sodium ions. Kinetic analysis suggested the existence of a high affinity uptake process (K_m= 1.7 μM, V_max= 0.21 nmol/g/min) and a low affinity process (K_m= 100 μM, V_max= 1.2 nmol/g/min). The high affinity uptake differed from the low affinity system in that it was sensitive to various metabolic inhibitors and was competitively inhibited by low concentrations of hemicholinium- and acetylcholine. Neither uptake system was greatly influenced by the absence of calcium, potassium or magnesium ions or by the presence of low concentrations of 5-HT, dopamine. tetrabenazine, chlorpromazine, decamethonium, nalaxone or imipramine. The high affinity uptake process may be important in supplying choline for the biosynthesis of acetylcholine in cholinergic neurons.     

Porphyromonas gingivalis surface components induce interleukin-1 release and tyrosine phosphorylation in macrophages

Abstract (1 → 3)-β- d -Glucans have a variety of biological and immunopharmacological properties, and they are used clinically as biological response modifiers (BRMs). Clinically, these glucans have often been used for long periods by multiple dosing. During studies on the clearance and metabolism of the glucans in mice, we have found that, in the case of a single dose, the glucan was cleared from blood eventually, and remained constant in the organs for at least one month. Here, we investigated the clearance of glucans from the blood following multiple dosing using MRL lpr/lpr mice with an autoimmune disease. Two kinds of glucans, GRN from Grifola frondosa and SSG from Sclerotinia sclerotiorum , were administered to the mice once a week for more than 35 weeks (250 μg/week/mouse by the intraperitoneal route). Examination of the blood clearance of the glucans in these mice revealed that the glucan concentrations were always high (about 20 μg/ml for GRN and 200 μg/ml for SSG). It is also shown that the glucans were significantly deposited in the liver and spleen of these mice. These findings suggest that administration of a large quantity of the glucan saturated the reticuloendothelial system, resulting in circulation of the glucan in the blood.     

Butyrobetaine is equal to L-carnitine in elevating L-carnitine levels in rats

This work shows that butyrobetaine administered to rats in a single dose can be highly effective in elevating L-carnitine levels in all tissues. This ability of butyrobetaine was compared to that of L-carnitine. In an experiment with tracer dose of the compounds, 12 h following administration of [3H]butyrobetaine plasma and tissues contained radioactivity exclusively in L-carnitine and in similar amounts as in the other group of animals receiving L-[3H]carnitine. This was observed both after intraperitoneal and oral administration of the compounds. In the loading experiments 100 mumol [3H]butyrobetaine was administered orally to one group and 100 mumol L-[3H]carnitine to the other group of animals and 12 h later it was found that butyrobetaine caused the same increments in L-carnitine as L-carnitine administration. The increments in the organs of the butyrobetaine-treated group (in decreasing order) were as follows: kidney, 1227 nmol/g vs. 652 nmol/g; liver, 469 nmol/g vs. 258 nmol/g; muscle, 1043 nmol/g vs. 881 nmol/g; plasma, 79.4 nmol/ml vs. 39.3 nmol/ml. Butyrobetaine (100 mumol) caused similar increments when it was administered intraperitoneally. Based on these results butyrobetaine can be considered as a potential agent for L-carnitine supplementation therapy.     

Suppressed expression of calcium-binding protein regucalcin mRNA in the renal cortex of rats with chemically induced kidney damage

The alteration of Ca²⁺-binding protein regucalcin mRNA expression in the kidney cortex of rats administered cisplatin and cephaloridine, which can induce kidney damage, was investigated. Cisplatin (0.25, 0.5 and 1.0 mg/100 g body weight) or cephaloridine (25, 50 and 100 mg/100 g) was intraperitoneally administered in rats, and 1, 2 and 3 days later they were sacrificed. The alteration in serum findings after the administration of cisplatin (1.0 mg/100 g) or cephaloridine (50 and 100 mg/100 g) demonstrated chemically induced kidney damage; blood urea nitrogen (BUN) concentration increased markedly and serum inorganic phosphorus or calcium concentration decreased significantly. Moreover, the administration of cisplatin (1.0 mg/100 g) or cephaloridine (100 mg/100 g) caused a remarkable increase of calcium content in the kidney cortex of rats, indicating kidney damage. The expression of regucalcin mRNA in the kidney cortex was markedly reduced by the administration of cisplatin or cephaloridine in rats, when the mRNA levels were analyzed by Northern blotting using rat liver regucalcin cDNA (0.9 kb). The mRNA decreases were seen with the used lowest dose of cisplatin or cephaloridine. The present study clearly demonstrates that the mRNA expression of Ca²⁺-binding protein regucalcin in the kidney cortex of rats is decreased by chemically induced kidney damage.     

ACETYLCHOLINE METABOLISM AND CHOLINE UPTAKE IN CORTICAL SLICES

Abstract— The uptake of [¹⁴C]choline was studied in cortical slices from rat brain after their incubation in a Krebs-Henseleit medium containing either 4.7 m m -KCl (low K), 25 m m -KCl (high K) or 25 m m -KCl without calcium (Ca free, high K). With 0.84 μ m -[¹⁴C]choline in the medium the uptake per gram of tissue was 0.62 nmol after incubation in low K medium, 1.13 nmol after incubation in high K medium and 0.78 nmol after incubation in a Ca free, high K medium. The differences caused by potassium were greater in fraction P₂ than in fractions P₁ and S₂. With 17 and 50 μ m -[¹⁴C]choline in the medium greater amounts of [¹⁴C]choline were taken up, but the effect of potassium on the uptake almost disappeared. The amount of radioactive material in fraction P₂ followed Michaelis-Menten kinetics with K _m values of 2.1 and 2.3 μ m after incubation in low and high K medium, respectively. Hemicholinium-3 only slightly inhibited choline uptake from a medium with 0.84 μ m -[¹⁴C]choline, but it abolished the extra-uptake induced by high K medium. The radioactivity in the slices consisted mainly of unchanged choline and little ACh was formed after incubation in low K medium, but after incubation in high K medium 50% of the choline taken up was converted into ACh. The hemicholinium-3 sensitive uptake of choline, the conversion of choline into ACh and the synthesis of total ACh, were stimulated about 7–8-fold by potassium. It is concluded that in cortical slices from rat brain all choline used for the synthesis of ACh is supplied by the high-affinity uptake system, of which the activity is geared to the rate of ACh synthesis.     

Comparative tissue ascorbic acid studies in fishes

Comparative tissue ascorbic acid levels in four species of major carp viz., Labeo rohila, L. calbasu, Cirrhina tnrigala and Catla catla , were investigated. The ascorbic acid level was found to be the highest in the spleen in the four species studied (range 430–380 μg/g) followed by the anterior (adrenal) kidney, gonads, liver, renal kidney, brain and/or eye. Heart and blood had the lowest levels (range 26–18 μg/ml) amongst the tissues studied. Overall tissue ascorbic acid levels were the highest in L. rohita and the lowest in C. mrigala . Investigation on seasonal variations in blood and kidney ascorbic acid levels of Notopterus notopterus revealed peak levels in spring (February-April) and the lowest levels in the postspawning period (August-September).     

Induction of metallothionein in rat tissues following subchronic exposure to mercury shown by radioimmunoassay

Although the analysis of metallothionein (MT) by radioimmunoassay (RIA) is not a common technique, its use is preferred over other methods since it offers the advantages of sensitivity and specificity. In this paper we present data on the basal levels of MT in rat tissues and physiological fluids of female Sprague-Dawley rats. The mean basal MT concentrations of the following organs and fluids were determined by RIA to be: liver (9.8 μg/g), kidney (68 μ/g), brain (0.8 μg/g), spleen (1.0 μg/g), heart (5.4 μg/g), plasma (11 ng/ml), and urine (200–300 μg/g creatinine). Following subcutaneous exposure to inorganic mercury (0.2 μmol/kg/d, 5 d a week for up to 4 wk), the metal accumulated primarily in the kidney. There was also a simultaneous accumulation of zinc in the liver and of zinc and copper in the kidney. Induction of MT did take place in liver, kidney, brain, and spleen. No increases in the MT contents of blood and urine were noted. The excess zinc and copper in the kidney of exposed animals were found to be associated predominantly with MT. No overt signs of mercury toxicity were noted in these animals and the incidence of proteinurea was nil. The data are discussed with reference to methods of MT determination in animal tissues and in relation to mercury metabolism and toxicity.