Up-regulation of cell surface insulin receptor by protein kinase C-alpha in adrenal chromaffin cells: involvement of transcriptional and translational events

Our previous study showed that treatment of cultured bovine adrenal chromaffin cells with phorbol 12, 13-dibutyrate (PDBu) or 12-O-tetradecanoylphorbol 13-acetate (TPA) caused a rapid (<15 min) and persistent (>15 h) translocation of both conventional (c) protein kinase C-alpha (PKC-alpha) and novel PKC-epsilon (but not atypical PKC-zeta) from cytosol to membranes, whereas thymeleatoxin (TMX) increased the similar but selective membrane association of only cPKC-alpha. In the present study, chronic (>/=12 h) treatment of chromaffin cells with PDBu raised cell surface (125)I-insulin binding without altering the K(D) value; it developed in a concentration (EC(50) = 1.9 nM)-and time (t(1/2) = 14.6 h)-dependent manner, reaching its maximum 115% increase at 48 h. Either TPA (30 nM) or TMX (EC(50) = 6.4 nM) also increased (125)I-insulin binding by 97 or 88%, whereas the biologically inactive 4alpha-TPA had no effect. The increasing effect of PDBu (30 nM for 24 h) on (125)I-insulin binding was significantly blocked, even when H7, an inhibitor of PKC, was added at 8 h after the initiation of PDBu treatment. Concurrent treatment with brefeldin A, an inhibitor of vesicular transport from the trans-Golgi network, cycloheximide, an inhibitor of protein synthesis, or 5,6-dichlorobenzimidazole riboside, an inhibitor of RNA synthesis, abolished the PDBu-induced increment of (125)I-insulin binding. Western blot analysis, using antibody against the beta-subunit of the insulin receptor, showed that treatment with PDBu (30 nM) or TMX (EC(50) = 2.3 nM) increased levels of insulin receptor precursor (approximately 190 kDa; t(1/2) = 7.1 h) and insulin receptor beta-subunit (t(1/2) = 15.4 h), causing their almost maximum 52 and 59% rises, respectively, at 24 h. Northern blot analysis revealed that PDBu or TMX increased levels of insulin receptor mRNAs by approximately 35% as soon as 3 h, producing its monophasic peak approximately 76% increases at 24 h. All of these increasing effects of PDBu and TMX on (125)I-insulin binding and insulin receptor beta-subunit and insulin receptor mRNA levels were entirely prevented by simultaneous treatment with Gö6976, a selective inhibitor of cPKC. These results suggest that long-term activation of cPKC-alpha up-regulates the density of the cell surface insulin receptor via transcriptional/translational events.

Analysis of neutrophil proteins of patients with Behçet's disease by two-dimensional gel electrophoresis

Protein changes in the neutrophils of patients with Behçet's disease were analyzed by high resolution two-dimensional gel electrophoresis to investigate the pathological features of Behçet's disease. Two clear protein spots were found to be differently expressed between healthy volunteers and patients with Behçet's disease. One was a 53 kDa protein with pI 5.2 that was detected in healthy volunteers but was nearly absent in the patients. The other was a 40 kDa protein with pI 5.2 that was detected in the patients but nearly absent in the healthy volunteers. Analysis of the N-terminal amino acid sequence of the 40 kDa protein revealed that it was a truncated actin with an N-terminus of Met-44. The presence of the truncated actin in the neutrophils of patients was confirmed by Western blot analysis using an antibody to the C-terminus of actin. The 53 kDa protein could not be identified because its N-terminus was blocked. The presence of the truncated actin in the neutrophils of the patients may be important in understanding the pathology of Behçet's disease.

Protein kinase C-alpha and -epsilon down-regulate cell surface sodium channels via differential mechanisms in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, our [3H]saxitoxin ([3H]STX) binding, immunoblot, and northern blot analyses specified protein kinase C (PKC) isoform-specific posttranscriptional and posttranslational mechanisms that direct down-regulation of cell surface Na channels. Immunoblot analysis showed that among 11 PKC isoforms, adrenal chromaffin cells contained only conventional (c)PKC-alpha, novel (n)PKC-epsilon, and atypical (a)PKC-zeta. Treatment of adrenal chromaffin cells with 100 nM 12-O-tetradecanoylphorbol 13-acetate (TPA) or 100 nM phorbol 12,13-dibutyrate (PDBu) caused a rapid (<15 min) and sustained (>15 h) translocation of PKC-alpha and -epsilon (but not -zeta) from cytosol to membranes, whereas a biologically inactive 4alpha-TPA had no effect. Thymeleatoxin (TMX), an activator of cPKC, produced similar membrane association of only PKC-alpha at 100 nM, with the potency of TMX being comparable with those of TPA and PDBu. Treatment with either 100 nM TPA or 100 nM TMX reduced cell surface [3H]STX binding to a comparable extent at 3, 6, and 12 h, whereas TPA lowered the binding to a greater extent than TMX at 15, 18, and 24 h; at 15 h, Gö6976, a specific inhibitor of cPKC, completely blocked TMX-induced decrease of [3H]STX binding while preventing by merely 57% TPA-induced decrease of [3H]STX binding. Treatment with 100 nM TPA lowered the Na channel alpha-subunit mRNA level between 3 and 12 h, with its maximum 52% fall at 6 h, and it was accompanied by a subsequent 61 % rise of the beta1-subunit mRNA level at 24 h. Gö6976 failed to prevent TPA-induced reduction of the alpha-subunit mRNA level; TMX did not change the alpha- and beta1-subunit mRNA levels throughout the 24-h treatment. Brefeldin A, an inhibitor of vesicular exit from the trans-Golgi network, augmented TPA- and TMX-induced decrease of [3H]STX binding at 1 and 3 h. Our previous and present studies suggest that PKC down-regulates cell surface Na channels without altering the allosteric gating of Na channels via PKC isoform-specific mechanisms; cPKC-alpha promotes Na channel internalization, whereas nPKC-epsilon decreases the alpha-subunit mRNA level by shortening the half-life of alpha-subunit mRNA without changing its gene transcription.

Lipid composition in long-day and short-day forms of the black bean aphid, Aphis fabae

Long-day reared winged (alate) virginoparae from laboratory stock cultures which had been reared throughout larval development on bean stipules were significantly smaller (0.46+/-0.02 mg; mean+/-SEM) than short-day-reared gynoparae (0.69+/-0.04 mg; the winged autumn migrant) which completed development on intact beans. When winged virginoparae were raised from the third stadium on bean seedlings they grew larger (0.86+/-0.02 mg) but the gynoparae contained proportionally more total lipid (12.1+/-0.4%, gynoparae; 7.4+/-0.6%, stipule-reared virginoparae; 9.2+/-0.8%, seedling-reared virginoparae). Wingless aphids (apterae) were heavier, whether reared in short (0.99+/-0.03 mg) or long days (0.95+/-0.04 mg) but the lipid content was low (4.5+/-0.7% and 4.9+/-0.6%, respectively). The triacyl-, diacylglycerol and the phospholipid contents followed this trend but analysis of the fatty acid moieties of the triacylglycerides showed phenotypic differences. The ratios of myristic acid:palmitic acid were significantly higher in the winged forms than the wingless forms and were much higher in the gynoparae than the winged virginoparae. Short-day-reared wingless females also had a higher myristic acid:palmitic acid ratio than long-day-reared apterae, possibly reflecting the embryonic gynoparae maturing in their ovaries.

Protein kinase C and the opposite regulation of sodium channel alpha- and beta1-subunit mRNA levels in adrenal chromaffin cells

Our previous [3H]saxitoxin binding and 22Na influx assays showed that treatment of cultured bovine adrenal chromaffin cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) or phorbol 12,13-dibutyrate (PDBu), an activator of protein kinase C (PKC), decreased the number of cell surface Na channels (IC50 = 19 nM) but did not alter their pharmacological properties; Na channel down-regulation developed within 3 h, reached the peak decrease of 53% at 15 h, and was mediated by transcriptional/translational events. In the present study, treatment with 100 nM TPA lowered the Na channel alpha-subunit mRNA level by 34 and 52% at 3 and 6 h, followed by restoration to the pretreatment level at 24 h, whereas 100 nM TPA elevated the Na channel beta1-subunit mRNA level by 13-61% between 12 and 48 h. Reduction of alpha-subunit mRNA level by TPA was concentration-dependent (IC50 = 18 nM) and was mimicked by PDBu but not by the biologically inactive 4alpha-TPA; it was prevented by H-7, an inhibitor of PKC, but not by HA-1004, a less active analogue of H7, or by H-89, an inhibitor of cyclic AMP-dependent protein kinase. Treatment with cycloheximide, an inhibitor of protein synthesis, per se sustainingly increased the alpha-subunit mRNA level and decreased the beta1-subunit mRNA level for 24 h; also, the TPA-induced decrease of alpha-subunit mRNA and increase of beta1-subunit mRNA were both totally prevented for 24 h by concurrent treatment with cycloheximide. Nuclear run-on assay showed that TPA treatment did not alter the transcriptional rate of the alpha-subunit gene. A stability study using actinomycin D, an inhibitor of RNA synthesis, revealed that TPA treatment shortened the t(1/2) of alpha-subunit mRNA from 18.8 to 3.7 h. These results suggest that Na channel alpha- and beta-subunit mRNA levels are differentially down- and up-regulated via PKC; the process may be mediated via an induction of as yet unidentified short-lived protein(s), which may culminate in the destabilization of alpha-subunit mRNA without altering alpha-subunit gene transcription.

Hypertriglyceridemia in rats induced by consumption of a food-derived carcinogen, 2-amino-1-methyl-phenylimidazo[4,5b]pyridine (PhIP)

2-Amino-1-methyl-phenylimidazo[4,5b]pyridine (PhIP), the most abundant mutagenic heterocyclic amine produced in cooked meat and fish, is known to be a carcinogen for rats and mice. This study provides the first evidence for hypertriglyceridemia in rats exposed to PhIP, suggesting its potential risk to induce not only carcinogenesis, but also atherosclerosis, and highlighting the potential importance of PhIP for humans.

Cyclic AMP-dependent synthesis and release of adrenomedullin and proadrenomedullin N-terminal 20 peptide in cultured bovine adrenal chromaffin cells

Adrenomedullin and proadrenomedullin N-terminal 20 peptide are peptides with multiple physiological functions and are most abundant in adrenal medulla. We studied whether the cAMP-dependent pathway is involved in the regulation of synthesis and release of adrenomedullin and proadrenomedullin N-terminal 20 peptide in cultured bovine adrenal chromaffin cells. Exposure of the cells to dibutyryl cAMP (dbcAMP) increased a progressive accumulation of immunoreactive-adrenomedullin and immunoreactive-proadrenomedullin N-terminal 20 peptide in the extracellular medium, while reciprocally decreasing their cellular content in a time-dependent manner. The decrease of levels of both peptides in the cells was much greater in extent than the increase of the peptides in the medium. H89, an inhibitor of cAMP-dependent protein kinase attenuated these changes, induced by dbcAMP. The resulting changes by dbcAMP and H89 were similar to those of chromogranin B, a marker peptide of chromaffin granule. Northern blot analysis showed that the mRNA encoding these peptides, detected as a band of 1.6 kb, was decreased by the treatment with dbcAMP. The effect of dbcAMP on mRNA was attenuated by H89, and was reversible as the decreased mRNA level caused by dbcAMP could be returned to control levels by culturing cells after removal of dbcAMP. These results suggest that the cAMP-dependent protein kinase pathway stimulates the release of adrenomedullin and proadrenomedullin N-terminal 20 peptide, whereas it lowers synthesis of these peptides via the reduction of their transcript level.

Medial prefrontal cortex is involved in the discriminative stimulus effects of nicotine in rats

RATIONALE

Central nicotinic receptors have been reported to be involved in the discriminative stimulus (DS) effects of nicotine.

OBJECTIVES

The purpose of the present study was to investigate the role of the medial prefrontal cortex (mPFC) and the medial habenular nucleus (mHb) in the DS effects of nicotine.

METHODS

Substitution tests with nicotine administered into mPFC and mHb were conducted in rats trained to discriminate nicotine (0.5 mg/kg, SC) from saline in a two-lever, food reinforced, operant task.

RESULTS

Nicotine (40 microg) administered into mPFC substituted for nicotine (0.5 mg/kg, SC), whereas nicotine administered into mHb did not.

CONCLUSIONS

Together with our previous study indicating that the nucleus accumbens and the ventral tegmental area are partially involved in the DS effects of nicotine, the present study suggests that mPFC is primarily involved in the DS effects of nicotine.

Effect of oxygen deficiency on response of CR-39 on board scientific balloons

We should be careful about the effect of oxygen deficiency on polymeric track detectors even at balloon altitude. Results of balloon experiments and calibration experiments in a vacuum chamber at different pressures show that the effect of oxygen deficiency becomes serious at a pressure below 10 hPa.

[Comparative studies on antiparkinsonian agents, talipexole and bromocriptine, evaluated by contralateral rotational behavior in unilaterally nigral-lesioned rats]

The stimulating effect of antiparkinsonian drugs, talipexole and bromocriptine, on the striatal postsynaptic dopamine receptors were studied by measuring contralateral rotational behavior in rats. The nigro-striatal dopamine system of rats was degenerated by unilateral injection of 6-hydroxydopamine (6-OHDA, 8 micrograms/rat) into substantia nigra. By subcutaneous administration, talipexole at 0.16 mg/kg and bromocriptine at 10.24 mg/kg induced significantly increased rotational behavior to the contralateral direction to the lesioned side. The onset of the effect was 30 min for talipexole and 90 min for bromocriptine. By intragastric administration, talipexole at 0.4 mg/kg and bromocriptine at 20.48 mg/kg significantly increased the rotational behavior, and the onset of the effect was 60 min for talipexole and 180 min for bromocriptine. Rotational behavior induced by talipexole was suppressed by a D2 antagonist, sulpiride (40 mg/kg, s.c.), but not by a D1 antagonist, SCH23390 (1 mg/kg, s.c.). In contrast, rotational behavior induced by bromocriptine was suppressed by both sulpiride and SCH23390. These results indicated that when the nigrostriatal dopaminergic functions are disrupted, talipexole stimulates the striatal postsynaptic dopamine receptors at much lower doses than bromocriptine. Also it was indicated that the stimulating effect of talipexole is solely mediated by dopamine D2 receptors, whereas the effect of bromocriptine is mediated by both D1 and D2 receptors.

[Mechanism of nicotine dependence]

This article reviews the current studies on the mechanism of nicotine dependence. In the process of nicotine dependence, there are four major determinants: reinforcing effects, tolerance, craving and withdrawal. 1) The positive reinforcing effects of nicotine are important especially for the initiation of nicotine self-administration. These effects are considered to be induced by the ability of nicotine to promote the release of catecholamines, acetylcholine, beta-endorphine, glucocorticoid, and other kinds of hormones. 2) However, tolerance gradually develops to the positive reinforcing effects of nicotine, as nicotine is repeatedly self-administered. 3) Craving is defined as the uncontrollability of the urge to take drugs, which is a core aspect of recent ICD-10 or DSM-IV descriptions. Craving for nicotine is caused and enhanced by the following three factors; psychic withdrawal symptoms such as anxiety, depression and dysphoria, conditioning processes leading to the association of nicotine effects with environmental stimuli, and memory of the reinforcing effects of nicotine. 4) Neither somatic withdrawal symptoms nor mental disorders related to nicotine dependence is significant. 5) As for the neurobiology of nicotine dependence, the reward system is focused as a putative responsible region involved not only in the reinforcing effects of nicotine but also in the psychic withdrawal symptoms. The amygdala-nucleus accumbens connection may be intimately involved in the association between nicotine effects and environmental stimuli. And neuronal circuits involved in memory function may be implicated in the manifestation of craving and relapse, but the details remain to be solved.

Selective inhibition by riluzole of voltage-dependent sodium channels and catecholamine secretion in adrenal chromaffin cells

We examined the effects of riluzole, a neuroprotective drug, on voltage-dependent Na channels, nicotinic receptors, and voltage-dependent Ca channels, as well as catecholamine secretion, in comparison with those of verapamil and nicardipine, in primary cultures of bovine adrenal chromaffin cells. Riluzole inhibited veratridine-induced 22Na influx via voltage-dependent Na channels even in the presence of ouabain, an inhibitor of Na,K-ATPase. Blockade of Na channels by riluzole was concentration-dependent with an IC50 of 5.3 microM. It was associated with a similar concentration-related reduction of veratridine-induced 45Ca influx via voltage-dependent Ca channels, and of catecholamine secretion. Riluzole had no effect on 45Ca influx caused by high K, which directly activates voltage-dependent Ca channels, and on nicotine-induced 22Na influx, which passes through the nicotinic receptors. Verapamil and nicardipine attenuated 22Na influx caused by veratridine or nicotine at the same concentrations as they suppressed high K-induced 45Ca influx. The inhibitory effect of riluzole on veratridine-induced 22Na influx disappeared at high concentrations of veratridine. A potentiation of veratridine (site 2 toxin)-induced 22Na influx caused by alpha-scorpion venom (site 3 toxin), beta-scorpion venom (site 4 toxin), or brevetoxin PbTx-3 (site 5 toxin), occurred in the presence of riluzole in the same manner as in control cells. These results suggest that riluzole binds to the veratridine site in voltage-dependent Na channels. It does not impair the cooperative interaction between the functional peptide segments of Na channels, but selectively inhibits gating of Na channels, thereby reducing Ca influx via Ca channels and catecholamine secretion. In contrast, verapamil and nicardipine suppress Na influx both Na channels and nicotinic receptors.

Effects of dietary alpha-linolenic, eicosapentaenoic and docosahexaenoic acids on hepatic lipogenesis and beta-oxidation in rats

The effects of dietary alpha-linolenic, eicosapentaenoic and docosahexaenoic acids on the enzyme activities related to hepatic lipogenesis and beta-oxidation were compared under constant polyunsaturated/monounsaturated/saturated fatty acids and n-6/n-3 ratios of dietary fats in rats. Dietary fat containing linoleic acid as the sole polyunsaturated fatty acid (PUFA) was also given as a control. The concentration of serum triglyceride and phospholipid in the three n-3 PUFA groups was lower than in the linoleic acid group. The hepatic triglyceride concentration was lower and the phospholipid concentration was higher in the three n-3 PUFA groups than in the linoleic acid group. Cytosolic fatty acid synthase (FAS) activity was lower in the n-3 PUFA groups than in the linoleic acid group, the reduction being more predominant in the eicosapentaenoic acid and docosahexaenoic acid groups than in the alpha-linolenic acid group. The cytosolic activities of the NADPH-generating enzymes, glucose-6-phosphate dehydrogenase (G6PDH) and the malic enzyme, were lower in the three n-3 PUFA groups. The activity of carnitine palmitoyltransferase (CPT) in mitochondria was higher only in the eicosapentaenoic acid group than in the other groups. The activity of Mg(2+)-dependent phosphatidate phosphohydrolase (PAP) in microsomes and cytosol was lower in the eicosapentaenoic and docosahexaenoic acid groups than in the linoleic acid group, while there was no effect of dietary fats on the activities of diacylglycerol acyltransferase (DGAT) and glycerol-3-phosphate acyltransferase (G3PAT) in microsomes. The CTP: phosphocholine cytidylyltransferase (CT) activity in the homogenate was lower in the n-3 PUFA groups, the reduction being more prominent in the eicosapentaenoic and docosahexaenoic acid groups than in the alpha-linolenic acid group. The choline kinase (CK) activity in cytosol was lower in the eicosapentaenoic acid group than in the linoleic acid group. These results showed that dietary alpha-linolenic, eicosapentaenoic and docosahexaenoic acids differently influenced hepatic lipogenesis and the partition of fatty acid into oxidation or glycerolipid synthesis.

Association between hepatic triacylglycerol accumulation induced by administering orotic acid and enhanced phosphatidate phosphohydrolase activity in rats

Orotic acid is known to cause fatty liver, but it is unclear whether this is caused partly by stimulation of the enzymes for triacylglycerol (TG) synthesis. To understand the change of hepatic TG metabolism in fatty liver induced by orotic acid, we determined the liver tissue TG level and phosphatidate phosphohydrolase (PAP) activity over time in rats fed on a diet containing orotic acid (OA). A dietary lipid content of 10% was achieved by using n-6 fatty acid-rich corn oil in experiment 1, and n-6 fatty acid-rich safflower oil (SO) and n-3 fatty acid-rich fish oil (FO) with the same polyunsaturated fatty acid/monounsaturated fatty acid/saturated fatty acid (P/M/S) ratio in experiment 2. In experiment 1, an increase in the hepatic TG level due to OA intake was observed from day 5 onwards, the level rising approximately 6-fold by day 10. The activity of hepatic microsomal PAP, the rate-limiting enzyme in TG synthesis, increased markedly from day 5 onwards, concurrent with the liver diacylglycerol concentration. A strong correlation (r = 0.974) was observed between the hepatic TG level and microsome-bound PAP activity. In experiment 2, we investigated the effects of dietary fatty acid on OA-induced fatty liver. Compared with the n-6 fatty acid-rich vegetable oil diet, the relative increase in hepatic TG was smaller with the n-3 fatty acid-rich FO diet, and hepatic PAP activity fell markedly to the level for an OA-free diet. In addition, the hepatic TG accumulation and serum TG concentration were lower in the FO group than in the SO group. Nevertheless, because the hepatic TG level was low, it seems that the inhibition of liver PAP activity by FO possibly had a strong influence on the accumulation of TG in the liver. In conclusion, enhanced TG synthesis mediated by changes in liver PAP activity was involved in the hepatic TG accumulation induced by OA administration, this change being markedly suppressed by dietary n-3 fatty acids.

Drug dependence study on vigabatrin in rhesus monkeys and rats

The dependence potential of vigabatrin (gamma-vinyl GABA; R(-)/S(+)-4-amino-5-hexenoic acid, CAS 60643-86-9, MDL 71,754) was assessed in rhesus monkeys and rats. In the test of cross physical dependence potential, morphine- and barbital-dependent monkeys were both withdrawn from the respective drugs and the ability of vigabatrin to suppress the withdrawal signs was assessed. In morphine-dependent monkeys, subcutaneous doses of vigabatrin at 256 and 1000 mg/kg did not suppress withdrawal signs while subcutaneous doses of codeine phosphate at 4 and 8 mg/kg clearly suppressed the withdrawal signs. In barbital-dependent monkeys, subcutaneous and intravenous dose of vigabatrin, both at 1000 mg/kg, did not suppress the withdrawal signs, while intragastric doses of diazepam at 8 and 16 mg/kg clearly suppressed them. Thus, while the cross-physical dependence potential of codeine/morphine and of diazepam/barbital was clearly observable, vigabatrin appeared to have no such potential. In the test of physical dependence-producing potential with the drug-admixed food method in rats, vigabatrin and diazepam were given to rats mixed with food for 28 days in an increasing dosage schedule, followed by feeding a drug-free diet to observe withdrawal signs for 7 days. Upon withdrawal, no decrease in food intake or body weight was observed in the vigabatrin-treated groups, and the gross condition of the animals did not differ from that in the control group. In contrast, food intake and body weight decreased markedly in the diazepam group, and most rats showed hyperreactivity to external stimuli. Thus, while the physical dependence-producing potential of diazepam was clearly demonstrated, such potential was not shown with vigabatrin. In the test of reinforcing effect, 4 monkeys were allowed to self-administer pentobarbital at 1 mg/kg/infusion, or vigabatrin at 16, 32, and 64 mg/kg/infusion, intravenously through an indwelling catheter. Each drug was preceded and followed by saline self-administration for at least 7 days. Active self-administration of pentobarbital was observed in all monkeys tested, while the self-administration rate of vigabatrin did not differ from saline. Thus, while the reinforcing effect of pentobarbital was clearly observed, such effect was not observable with vigabatrin. Based on these results, it was considered that vigabatrin was devoid of dependence potential.

[Effects of the age on the apoptotic and proliferative reactions in the constant light-exposed rat retina]

The effects of age (5-3 weeks old) on apoptotic changes in the rat photoreceptor cells induced by 3 days of constant light exposure were examined using TUNEL (TdT-mediated dUTP nick end labeling). The effects on the expression of the Ki67-antigen, which is a proliferative marker, in these photoreceptor cells were also examined by immunohistochemistry. The results suggested that the number of positive cells in the outer nuclear layer of the superior hemisphere is higher than in the inferior nuclear layer in both the TUNEL reaction and the distribution of the Ki67 antigen, and that the number of positive cells increases with age in general. The cells of monocytes/macrophages may locally proliferate in the retina to phagocytose the apoptotic bodies owing to the degeneration of photoreceptor cells. The present findings revealed that the rates of these reactions may generally increase with age.

[Lectin-histochemical study of early postnatal eyelid epithelium of the rat]

The glycoconjugates in neonate rat eyelids at postnatal day 0 or 1 were examined by lectin histochemistry. Maackia amurensis lectin II, which recognizes sialic acid alpha 2, 3 galactose beta 1, 3 N-acetylgalactosamine (Gal beta 1, 3 GalNAc) or sialic acid alpha 2, 3 galactose beta 1, 4 N-acetylglucosamine, bound to the cell membranes of the epithelial basal cells, suggesting that the glycoconjugates containing these sugar chains are present on their cell membranes. With respect to the binding of the Gal beta 1, 3 GalNAc-specific lectin, jacalin, whose binding is not inhibited by the terminal sialic acid, bound to the cell membranes of the epithelial basal cells, whereas peanut agglutinin, whose binding is inhibited by the terminal sialyl residue, did not bind to their cell membranes. These findings suggest that all the residues of Gal beta 1, 3 GalNAc in the glycoconjugates of their cell membranes are sialylated as the mature form.

[Glycohistochemical analysis of rat eyelid epithelium]

The glycoconjugates in eyelids of adult rats were examined by lectin histochemistry and in situ hybridization histochemistry. Since Maackia amurensis lectin II and jacalin bound to the cell membranes of basal and apical epithelial cells, sialic acid alpha 2,3 galactose (Gal) beta 1,3 N-acetylgalactosamine (GalNAc) sequence is present in the glycoconjugates of their cell membranes. Peanut agglutinin bound to the cell membranes of spinous cells in the middle of the epithelium, suggesting that Gal beta 1, 3 GalNAc sequence is present in their glycoconjugates. The mRNA of Gal beta 1,3 GalNAc alpha 2,3-sialyltransferase was detected in the cytoplasm of the epithelial cells other than the basal cells. This observation suggests that sialoglycoconjugates may be newly synthesized in the spinous and apical cells, while the glycoconjugates in the cell membranes of basal cells may be produced at an early stage of development and are stable without turnover.

Inhibitory effects of oren-gedoku-to and its components on cholesteryl ester synthesis in cultured human hepatocyte HepG2 cells: evidence from the cultured HepG2 cells and in vitro assay of ACAT

The pharmacological effects of Oren-gedoku-to (OGT), a Japanese-Chinese traditional herbal medicinal mixture on lipid biosynthesis were investigated in cultured human hepatocyte HepG2 cells. The addition of OGT (0.5 and 4.2 mg/ml), which had no effect on cell proliferation and cellular protein content, caused a marked decrease in the cellular cholesterol content, particularly cholesteryl ester content following 24 h incubation. The incorporation of 14C-oleate into cellular cholesteryl ester fraction was also reduced remarkably during incubation for 6 and 24 h. The effects of OGT, its components and its main active chemicals on acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity were studied in vitro to explore the mechanism by which OGT inhibits cholesteryl ester formation. The data confirmed that OGT, in a dose-dependent manner, and its components (Scutellaria baicalensis, Coptis japonica, Gardenia jasminoides and Phellodendron amurense) remarkably inhibit ACAT activity. Among the main active chemicals of OGT, baicalein, a kind of flavonoid, decreased ACAT activity in a dose-dependent fashion from the level of 10(-6)M. These results strongly suggest that OGT reduces the cholesteryl ester formation in human hepatocytes by inhibiting ACAT, and that baicalein may, in part, be responsible for ACAT inhibition.

Up-regulation of sodium channel subunit mRNAs and their cell surface expression by antiepileptic valproic acid: activation of calcium channel and catecholamine secretion in adrenal chromaffin cells

Treatment of cultured bovine adrenal chromaffin cells with a therapeutic concentration (0.6 mM) of valproic acid (VPA) for > 24 h caused a time-dependent (t1/2 = 74 h) increase in [3H]saxitoxin binding up to 1.4-fold without altering the KD value; it was prevented by the simultaneous treatment with cycloheximide (an inhibitor of protein synthesis). VPA also raised Na+ channel alpha- and beta 1-subunit mRNA levels 1.4- and 1.7-fold at 24 h, and 1.6- and 1.8-fold at 72 h, respectively. Chronic (but not acute) exposure to VPA enhanced 22Na+ influx caused by various concentrations of veratridine 1.4-2.1-fold, even when assayed in the presence of Na+,K(+)-ATPase inhibitor, but did not change the EC50 value of veratridine. Ptychodiscus brevis toxin-3 allosterically potentiated veratridine-induced 22Na+ influx by approximately 2-fold in VPA-treated cells as in nontreated cells. Long-term treatment with VPA augmented veratridine-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion, but had no effect on 45Ca2+ influx and catecholamine secretion caused by high K+ (a direct activation of voltage-dependent Ca2+ channels). Chronic treatment with VPA also enhanced nicotine-induced 22Na+ influx via the nicotinic receptor-ion channel complex 1.2-1.4-fold with little change in the EC50 value of nicotine, thereby increasing the nicotine-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion. These results suggest that chronic treatment with VPA up-regulates cell surface expression of Na+ channels via the transcription/translation-dependent mechanisms, and probably of nicotinic receptors, thereby resulting in the enhancement of Ca2+ channel gating and catecholamine secretion.

Nitric oxide-dependent and -independent norepinephrine release in rat mesenteric arteries

The role of nitric oxide (NO) in endogenous norepinephrine (NE) release in the perfused isolated rat mesenteric vasculature was examined. NE overflow elicited by electrical field stimulation (EFS) at various frequencies was significantly smaller at 24 than at 37 degrees C. The pressor response upon EFS at 8 and 10 Hz, however, was higher at 24 than at 37 degrees C. When production of NO was blocked by N omega-nitro-L-arginine (L-NNA), NE overflow upon EFS at each frequency of stimulation was diminished by 50% at 37 degrees C but remained unchanged at 24 degrees C, whereas the pressor response elicited by EFS became greater at 37 than at 24 degrees C. These effects of L-NNA were reversed by L-arginine, but not by its D-enantiomer. Sodium nitroprusside, an NO donor, increased EFS-elicited NE overflow at 24 degrees C but had no effect at 37 degrees C. These results demonstrate that NE release is NO dependent and NO independent. The NO-dependent mechanism is more sensitive to cooling than the NO-independent mechanism. The increase in EFS-elicited perfusion pressure at 24 degrees C may be due to reduction in synthesis of NO (a potent vasodilator), thus unmasking the effect of NE and other noncatecholamine vasoconstrictors.

Neurochemical analysis of the psychotoxicity of methamphetamine and cocaine by microdialysis in the rat brain

To examine the neurochemical mechanism underlying the development of psychotoxicity by methamphetamine and cocaine, the levels of dopamine, serotonin and their metabolites were determined by in vivo microdialysis in the brains of freely moving rats. Methamphetamine (0.5 mg/kg, s.c.) or cocaine (10 mg/kg, i.p.) was repeatedly administered for 8 to 21 experiment days, and after confirming the development of sensitization to the stimulating effect of the drugs on spontaneous motor activity, a microdialysis probe was implanted into the nucleus accumbens (N.Acc.) or striatum of the brain of the treated rats. Then, each test drug was readministered to the rats and dopamine and DOPAC or serotonin and 5-HIAA concentrations were determined. In the N.Acc. of untreated control rats, methamphetamine increased dopamine to about 4 times the preadministration value along with a decrease of DOPAC. Methamphetamine also increased serotonin to about twice the preadministration value along with no change in 5-HIAA. Cocaine increased dopamine to about 4 times along with a slight decrease in DOPAC. In the treated rats as compared with the untreated rats, the increasing effect of methamphetamine on dopamine in the N.Acc. was enhanced but that of cocaine was not. Also, the serotonin levels were lower than in the untreated rats and 5-HIAA was unchanged. In the striatum of untreated rats, methamphetamine increased dopamine to about 3 times the preadministration value along with a slight decrease in DOPAC. In the treated rats, the increasing effect of methamphetamine on dopamine in the striatum was enhanced, and the DOPAC level was higher than in the treated rats. The present study suggests that the dopamine level at the N.Acc. does not necessarily reflect the sensitization to spontaneous motor activity, and that enhancement of the motor activity does not seem to be the best model for psychotoxic manifestation.

Up-regulation of functional voltage-dependent sodium channels by insulin in cultured bovine adrenal chromaffin cells

Treatment of cultured bovine adrenal chromaffin cells with 100 nM insulin raised [3H]saxitoxin ([3H]-STX) binding in a time-dependent manner (t1/2 = 26 h). Insulin (100 nM for 4 days) increased the Bmax of [3H]STX binding by 49% without changing the KD value and also augmented the maximal influx of 22Na+ due to 560 microM veratridine by 39% without altering the EC50 value of veratridine. The stimulatory effect of insulin on 22Na+ influx was concentration-dependent with an EC50 of 3 nM, whereas insulin-like growth factor (IGF)-I had little effect at 1 nM. Ptychodiscus brevis toxin-3 allosterically potentiated veratridine (100 microM)-induced 22Na+ influx by approximately twofold in both insulin-treated cells and untreated cells. Veratridine-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion were also enhanced by insulin treatment, whereas insulin did not alter nicotine-induced 22Na+ influx via the nicotinic receptor-ion channel complex and high-K+ (direct activation of voltage-dependent Ca2+ channels)-induced 45Ca2+ influx. Stimulatory effects of insulin on [3H]-STX binding and veratridine-induced 22Na+ influx were nullified by simultaneous treatment with either 5,6-dichlorobenzimidazole riboside, an inhibitor of RNA synthesis, or cycloheximide, an inhibitor of protein synthesis, whereas insulin treatment did not appreciably increase the level of mRNA encoding the Na+ channel alpha-subunit. These results suggest that the binding of insulin to insulin (but not IGF-I) receptors mediates the up-regulation of functional Na+ channel expression at plasma membranes; this up-regulation may be due, at least in part, to the de novo synthesis of an as yet unidentified protein(s).

[Comparison of the effects of nicotine and methamphetamine on extracellular dopamine in the nucleus accumbens of behaviorally sensitized rats]

Repeated administration of nicotine (NCT) and methamphetamine (MAP) produced a progressive enhancement (sensitization) in the increasing effects on spontaneous motor activity in rats. The purpose of this study was to compare the effects of NCT and MAP on the extracellular levels of dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens of behaviorally sensitized rats by in vivo microdialysis. NCT 0.5 mg/kg, sc did not change the DA and DOPAC levels in drug-naive rats, but it showed an increase in the DA levels in rats sensitized to NCT. MAP 0.5 mg/kg, sc increased DA levels and decreased DOPAC levels in drug-naive rats, but it showed a smaller increase in DA levels in rats sensitized to MAP than in drug-naive rats. On the other hand, the basal levels of DA were increased in sensitized rats produced by MAP, but not in those produced by NCT. The present results suggest that NCT and MAP produce behavioral sensitization through the action on the mesolimbic dopaminergic system, but the manner of action of these drugs is different.

Receptors for atrial natriuretic peptide in adrenal chromaffin cells

Receptors for atrial natriuretic peptide (ANP) in isolated bovine adrenal chromaffin cells were characterized. 125 I-ANP specifically bound to the cells with a Kd of 103 pM and a Bmax of 5.6 fmol/10(6) cells (16.5 fmol/mg of cell protein). C-ANF, a highly selective ligand for ANP-C receptors of natriuretic peptides, did not compete for 125 I-ANP binding at concentrations up to 10nM. Chemical cross-linking of 125I-ANP to the cells showed a single molecular size of the 120 kDa binding site on SDS gel electrophoresis under reducing conditions. CNP, a specific peptide for the ANP-B receptor, was much less potent than ANP in inhibiting 125 I-ANP binding and in displacing 125 I-ANP from the 120 kDa band. These results suggest that ANP specifically binds to the ANP-A receptor of 120 kDa and that there is no ANP-C receptor in bovine adrenal chromaffin cells.

Protein kinase C-mediated down-regulation of voltage-dependent sodium channels in adrenal chromaffin cells

Treatment of cultured bovine adrenal chromaffin cells with 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C (PKC), decreased [3H]saxitoxin ([3H]STX) binding in a concentration (IC50 = 19 nM)- and time (t1/2 = 4.5 h)-dependent manner. TPA (100 nM for 15 h) lowered the Bmax of [3H]STX binding by 53% without altering the KD value. Phorbol 12,13-dibutyrate (PDBu) also reduced [3H]STX binding, whereas 4 alpha-TPA, an inactive analogue, had no effect. The inhibitory effect of TPA was abolished when H-7 (an inhibitor of PKC), but not H-89 (an inhibitor of cyclic AMP-dependent protein kinase), was included in the culture medium for 1 h before and during TPA treatment. Simultaneous treatment with TPA in combination with either actinomycin D or cycloheximide, an inhibitor of protein synthesis, nullified the effect of TPA. TPA treatment also attenuated veratridine-induced 22Na+ influx but did not alter the affinity of veratridine for Na channels as well as an allosteric potentiation of veratridine-induced 22Na+ influx by brevetoxin. These results suggest that an activation of PKC down-regulates the density of Na channels without altering their pharmacological features; this down-regulation is mediated via the de novo synthesis of an as yet unidentified protein(s), rather than an immediate effect of Na channel phosphorylation.

Up-regulation of functional voltage-dependent sodium channels by cyclic AMP-dependent protein kinase in adrenal medulla

Treatment of cultured bovine adrenal chromaffin cells with dbcAMP increased [3H]STX binding with an EC50 of 126 microM and a half-effective time of 12 h; dbcAMP (1 mM x 18 h) raised the Bmax approximately 1.5-fold without altering the Kd value. Forskolin (0.1 mM) or IBMX (0.3 mM) also increased [3H]STX binding, while dbcGMP had no effect. Effects of dbcAMP and forskolin were abolished by H-89, an inhibitor of cAMP-dependent protein kinase. Cycloheximide (10 microgram/ml) and actinomycin D (10 microgram/ml), inhibitors of protein synthesis, nullified the stimulatory effect of dbcAMP, whereas tunicamycin, an inhibitor of protein glycosylation, had no effect. Treatment with dbcAMP augmented veratridine-induced 22Na influx, 45Ca influx via voltage-dependent Ca channels and catecholamine secretion, while the same treatment did not alter 45Ca influx and catecholamine secretion caused by high K (a direct activation of voltage-dependent Ca channels) [25]. Na influx via single Na channel calculated from 22Na influx and [3H]STX binding was quantitatively similar between non-treated and dbcAMP-treated cells. Brevetoxin allosterically enhanced veratridine-induced 22Na influx approximately 3-fold in dbcAMP-treated cells as in non-treated cells. These results suggest that cAMP-dependent protein kinase is involved in the modulation of Na channel expression in adrenal medulla.

Large- and small-conductance Ca(2+)-activated K+ channels: their role in the nicotinic receptor-mediated catecholamine secretion in bovine adrenal medulla

In cultured bovine adrenal chromaffin cells, charybdotoxin and iberiotoxin (inhibitors of the large-conductance Ca(2+)-activated K+ channel) as well as apamin (an inhibitor of the small-conductance Ca(2+)-activated K+ channel), at 1-100 nM, suppressed carbachol-induced 86RB+ efflux, augmented carbachol-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion and had no effect on carbachol-induced 22Na+ influx via nicotinic receptors, a prerequisite for Ca2+ channel activation by carbachol. 45Ca2+ influx caused by high K+ (a direct activation of voltage-dependent Ca2+ channels) was also enhanced by these K+ channel inhibitors, with the concentration-response curves being similar to those for carbachol-induced 45Ca2+ influx. Dendrotoxin and mast cell degranulating peptide (inhibitors of voltage-dependent K+ channels), on the other hand, did not alter carbachol-induced 86Rb+ efflux or 45Ca2+ influx. These results suggest that the stimulation of nicotinic receptors eventually opens large- and small-conductance Ca(2+)-activated K+ channels, and that the blockade of these Ca(2+)-activated K+ channels results in gating of voltage-dependent Ca2+ channels and thereby augments catecholamine secretion from bovine adrenal chromaffin cells.

Mutations in the Norrie disease gene: a new mutation in a Japanese family

Images

Combined effects of pravastatin and probucol on high-density lipoprotein apolipoprotein A-I kinetics in cholesterol-fed rabbits

The combined effects of pravastatin and probucol on high- density lipoprotein (HDL) apolipoprotein (apo) A-I kinetics in cholesterol (Ch)-fed rabbits were investigated. Japanese White rabbits were treated with 0.15% pravastatin and 0.5% Ch (group 1) or 0.15% pravastatin plus 1% probucol and 0.5% Ch (group 2) for 2 months. After treatment, the serum total cholesterol levels in groups 1 and 2 had significantly (p < 0.01) increased (37.4 +/- 6.7 mg/dl vs 117.1 +/- 46.4 mg/dl, and 31.4 +/- 4.9 mg/dl vs 143.0 +/- 84.5 mg /dl, respectively). The serum HDL-cholesterol levels in both groups decreased (18.2 +/- 2.8 mg/dl, vs 16.2 +/- 3.7 mg/dl p < 0.01 for group 1; 18.2 +/- 1.9 mg/dl vs 15.5 +/- 4.5 mg/dl, ns for group 2). Apo A-I kinetics were assessed by injecting (125)I-labeled HDL intravenously into both groups of rabbits, and taking blood samples periodically for 6 days. Kinetic parameters calculated from apo A-I specific radioactivity decay curves showed that the apo A-I fractional catabolic rates in rabbits fed pravastatin and Ch (group 1) were significantly less than those in rabbits fed pravastatin plus probucol and Ch (group 2) (0.546 +/- 0.017 /day vs 0.730 +/- 0.126 /day, p < 0.05), while the synthetic rate of apo A-I was lower in group 2 than in group 1 (14.76 +/- 1.71 mg/kg per day vs 11.21 +/- 2.38 mg/kg per day, respectively, p < 0.01). These data indicate that pravastatin and probucol have different effects on HDL-apo A-I kinetics in a diet which includes cholesterol.

[Distribution of alpha 2,3-sialyltransferase mRNA in rat iris and ciliary body]

The distribution of alpha 2,3-sialyltransferase (alpha 2,3-ST) mRNA in the rat iris and ciliary body was investigated with in situ hybridization histochemistry. Strong expression of alpha 2,3-ST mRNA was detected in the inner epithelial layer of the ciliary body and weak expression in the iris epithelium. Since the synthesis of sialoglycoconjugates is completed by terminal sialylation by the action of sialyltransferase (ST), the ST-expressed portions are considered to produce sialoglycoconjugates. Hence, the source of the sialoglycoconjugates found in the inner epithelial layer of the ciliary body in previous histochemical studies is the same epithelial cell.

Pharmacological effects of dai-saiko-to on lipid biosynthesis in cultured human hepatocyte HepG2 cells

The pharmacological effects of Dai-saiko-to, a Japanese and Chinese traditional medicinal mixture (Kampohozai), on lipid biosynthesis were investigated in cultured human hepatocyte HepG2 cells. The addition of Dai-saiko-to (0.5 mg/ml), which had no significant effect on cell proliferation, caused a marked decrease in the intracellular triglyceride content with no significant changes in the other lipid fraction. At the same time, the incorporation of 14C-acetate or 3H-glycerol into the triglyceride or diglyceride fractions also decreased significantly. These results suggest that Dai-saiko-to decreases hepatic triglyceride biosynthesis, which might contribute to a reduction in plasma VLDL levels.

[Binding of amaranthin in human retina]

The binding of amaranthin, specific for Gal beta 1,3 GalNAc and sialic acid Gal beta 1,3 GalNAc sequences, to the human retina was investigated with avidin biotinylated peroxidase. Amaranthin bound to the cone and rod photoreceptors, inner plexiform layer, ganglion cells, and nerve fibers. Since peanut agglutinin, specific for Gal beta 1,3 GalNAc, selectively binds to cones, we conclude that O-glycoside-linked glycoconjugates are present on the surfaces of both cones and rods: Gal beta 1,3 GalNAc and sialic acid Gal beta 1,3 GalNAc are terminal sugars of the glycoconjugates around cones and rods, respectively.

Reinforcing effect as a function of infusion speed in intravenous self-administration of nicotine in rhesus monkeys

The influence of infusion speed on the reinforcing effect of nicotine (NIC) 30 micrograms/kg/infusion was studied in rhesus monkeys using intravenous self-administration at infusion speeds of 5.2, 1.3, and 0.3 micrograms/s under a fixed-ratio 5 schedule with a 15-min time-out after each intake. The 24-h self-administration rate was observed in 3 periods of 8 days each for each speed, separated by saline self-administration periods of 2 weeks each. As a result, when a fixed infusion speed of 5.2 micrograms/s was used throughout the 3 periods, the average rates of NIC were not significantly different each other, but when the infusion speed was changed from 5.2 to 1.3, and then to 0.3 micrograms/s, the average rates significantly decreased. The plasma level following a single-dose infusion of NIC 30 micrograms/kg positively correlated with the infusion speeds. These results indicate that the reinforcing effect of NIC is a function of the infusion speed, most likely through elevation of the peak level of NIC in the plasma.

Serum lipoprotein(a) levels before and after subtotal thyroidectomy in subjects with hyperthyroidism

Lipoprotein(a) [Lp(a)], a lipoprotein that structurally resembles low-density lipoprotein (LDL), contains apolipoprotein(a) [apo(a)] and apolipoprotein B-100 (apo B). There exists a close inverse correlation between serum concentrations of LDL or apo B and concentrations of thyroid hormone in patients with thyroid disease, probably due to a change in LDL receptor activity. To clarify the relations between thyroid hormone and Lp(a), we measured serum Lp(a) levels in 13 hyperthyroid subjects before treatment (stage H), during the euthyroid stage induced immediately before performing a subtotal thyroidectomy (stage E), and during the hypothyroid stage observed transiently after the operation (stage L). The mean serum concentration of Lp(a) increased significantly (P = .01) from 9.4 mg/dL in stage H to 26.8 in stage L through the level of 15.5 mg/dL in stage E. There was no significant difference between the mean serum concentration of Lp(a) in these patients in stage E and healthy controls (14.2 mg/dL). There was a low but statistically significant negative correlation between the Lp(a) level and the serum free thyroxine (fT4) concentration (r = .31, P < .05). The results suggest that thyroid hormone is a potent modulator of Lp(a) metabolism.

Novel mutation at the initiation codon in the Norrie disease gene in two Japanese families

We have identified a new mutation of Norrie disease (ND) gene in two Japanese males from unrelated families; they showed typical ocular features of ND but no mental retardation or hearing impairment. A mutation was found in both patients at the initiation codon of exon 2 of the ND gene (ATG to GTG), with otherwise normal nucleotide sequences. Their mothers had the normal and mutant types of the gene, which was expected for heterozygotes of the disease. The mutation of the initiation codon would cause the failure of ND gene expression or a defect in translation thereby truncating the amino terminus of ND protein. In view of the rarity and marked heterogeneity of mutations in the ND gene, the present apparently unrelated Japanese families who have lived in the same area for over two centuries presumably share the origin of the mutation.

Characterization of [3H]brevetoxin binding to voltage-dependent sodium channels in adrenal medullary cells

We have previously reported that in bovine adrenal chromaffin cells Ptychodiscus brevis toxin-3 (PbTx-3) does not alter the veratridine-induced 22Na influx when given alone, but increases the influx of 22Na when co-applied with either alpha- or beta-scorpion venom (Wada et al. 1992). In the present study, we characterized [3H]PbTx-3 binding in bovine adrenal chromaffin cells. [3H]PbTx-3 binding was saturable, reversible and of high-affinity with an equilibrium dissociation constant (Kd) of 32.0 +/- 4.9 nmol/l and a maximum binding capacity (Bmax) of 6.2 +/- 1.2 pmol/4 x 10(6) cells (4.5 +/- 0.9 pmol/mg cell protein). A Hill plot revealed the lack of cooperative interaction among the binding sites. Unlabelled PbTx-3 inhibited [3H]PbTx-3 binding with an IC50 of 31 nmol/l. However, tetrodotoxin, veratridine, alpha- and beta-scorpion venom, or veratridine in combination with either alpha- or beta-scorpion venom did not alter [3H]PbTx-3 binding. All these results suggest that PbTx-3 binds to a site (site 5) distinct from the previously known four toxin binding sites, which does not gate voltage-dependent Na channels by itself, but is specifically involved in the allosteric modulation of Na channels in adrenal medullary cells.

Dietary modifications of the biliary bile acid glycine:taurine ratio and activity of hepatic bile acid-CoA:amino acid N-acyltransferase (EC 2.3.1) in the rat

Effects of dietary manipulations on the biliary bile acid glycine:taurine (G:T) ratio and the activity of hepatic bile acid-CoA:amino acid N-acyltransferase (EC 2.3.1) in the post-mitochondrial fraction of liver homogenates were examined in the rat. The G:T ratio in rats fed on the diet containing 100 g pectin/kg (2.18) was markedly higher than that in the animals fed on the diet containing 100 g cellulose/kg (0.09). The diets containing either 10 g cholesterol/kg or 5 g sodium cholate/kg, especially the latter, also increased the G:T ratio (0.77 and 2.33 respectively) compared with a control diet free of these steroids (0.34). When the saturating concentrations of taurine (20 mM) and glycine (100 mM) were the substrates, dietary pectin relative to cellulose significantly increased the activity of both taurine- and glycine-dependent bile acid-CoA:amino acid N-acyltransferase, but neither dietary bile acid nor cholesterol influenced it. In spite of the marked difference in the G:T ratio among the rats given various types of experimental diet, the bile acid-CoA:amino acid N-acyltransferase reaction produced taurine-but little glycone-conjugated bile acid when both taurine and glycine coexisted at physiological concentration ranges in the assay media. Dietary manipulations modified the hepatic taurine concentrations and the changes were inversely correlated with those in the G:T ratio. However, hepatic concentration of taurine (1.67-4.82 mumol/g) in rats given various types of experimental diet was comparable with or even higher than the reported Michaelis constant (Km) value of N-acyltransferase for this compound (0.8-2.5 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Functional relation between nitric oxide and noradrenaline for the modulation of vascular tone in rat mesenteric vasculature

As previously reported, N omega-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide (NO) synthesis, decreased transmural field stimulation (TFS)-induced noradrenaline overflow from the isolated perfused rat mesenteric vasculature attached to the intestine. The decrease was attenuated by L-arginine. This suggests that NO may increase noradrenaline release (Yamamoto et al. 1993). The present experiments with this preparation were done in order to monitor changes in vascular perfusion pressure caused by TFS or by noradrenaline infusion in parallel with those in the noradrenaline outflow caused by TFS in the presence of atropine (0.1 mumol/l) (to block acetylcholine-induced release of endothelial NO) and of indomethacin (3 mumol/l) (to inhibit L-NNA-induced production of vasoconstrictor prostanoids). (1) TFS (2-10 Hz) caused a frequency-dependent increase in noradrenaline overflow and perfusion pressure. (2) L-NNA (10 and 30 mumol/l) caused a concentration-dependent inhibition of TFS-induced noradrenaline overflow, whereas the TFS-induced pressure increase was augmented by L-NNA in a concentration-dependent manner. At any given concentration of L-NNA, the potentiation of vasoconstriction by L-NNA became greater in magnitude as the frequency of the TFS was raised. (3) Infusion of noradrenaline (0.38-6 nmol) caused a dose-dependent increase in perfusion pressure up to a value comparable with that caused by TFS. The pressure increase in response to noradrenaline infusion was also enhanced by L-NNA, relatively, to a greater extent than the enhancement, by L-NNA, of the pressure response to TFS.(ABSTRACT TRUNCATED AT 250 WORDS)

[Rotational behavior induced by methamphetamine and cocaine in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopamine system]

The purpose of this study was to compare the ability of intravenously administered methamphetamine and cocaine to facilitate dopaminergic transmission, based on the ability of these drugs to induce rotational behavior in rats with unilateral 6-hydroxydopamine lesions of the substantia nigra. The doses of methamphetamine and cocaine ranged from 0.25 mg/kg to 4 mg/kg which was equivalent to 50% of the minimum dose which caused convulsion. Methamphetamine induced more marked ipsilateral rotational behavior than did cocaine. The present results suggest that methamphetamine produces longer duration of the facilitation of dopaminergic transmission both in the nucleus accumbens and in the striatum than does cocaine.

Effects of simvastatin, a cholesterol synthesis inhibitor, on phosphatidylcholine synthesis in HepG2 cells

The effects of the addition of a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, simvastatin, to the medium on sterol synthesis and phosphatidylcholine (PC) synthesis were studied in HepG2 cells. The cells were cultured with simvastatin at concentrations of 10(-7) and 10(-6) mol/L for 6 hours, and radioactive lipid precursors were added 1 hour before harvesting. Simvastatin inhibited cholesterol synthesis from [14C]acetate in a dose-dependent manner. It also decreased the incorporation of [14C]choline into PC by 30%; this decrease was accompanied by a decrease in phosphocholine cytidylyltransferase activity in cell homogenates. Simvastatin had no significant effects on the incorporation of [3H]glycerol into phospholipids. These data indicate that simvastatin has two different functions: inhibition of HMG-CoA reductase and depression of de novo synthesis of PC via the cytidine diphosphate-choline pathway, which, in turn, may result in a decrease in plasma lipid levels.

[Withdrawal characteristics following frequent intravenous administration of several opioids in rats]

Characteristics of withdrawal signs of several opioids were compared in rats after short-term frequent intravenous infusions. Male Sprague-Dawley rats with catheters implanted in the jugular veins were infused with a fixed dose of a drug hourly for 72 hrs. Thirty min after the final infusion, naloxone 4 mg/kg, s.c. was administered and withdrawal signs were observed for 1 hr and the severity of the withdrawal signs was scored, classified into a behavioral sign score, autonomic sign score, and body weight loss score. As a result, total withdrawal scores of morphine, methadone, d-propoxyphene, loperamide, tramadol, and pentazocine were significantly higher than that of saline, with the highest score being observed for 4 mg/kg or more of morphine. The total score of ethylketocyclazocine was slightly but significantly higher than that of saline. Buprenorphine and thebaine produced no observable withdrawal signs. The behavioral sign score tended to be higher than the other 2 scores in the drugs showing relatively low but significant total scores such as tramadol, pentazocine, and ethylketocyclazocine, while the score of autonomic signs or the body weight loss tended to be higher in drugs showing high total scores. Thus, in the case of opioids, it is considered that the severity of withdrawal signs was mainly derived from the autonomic signs including diarrhea which may result in body weight loss.

Effects of methamphetamine, dopamine and noradrenaline administered into the nucleus accumbens of rats discriminating subcutaneous methamphetamine

Since the nucleus accumbens has been hypothesized to centrally mediate the discriminative effects of psychomotor stimulants, the discriminative effects of methamphetamine (MA) as well as dopamine (DA) and noradrenaline (NA) were observed by intracerebral administration of these drugs into the nucleus accumbens in rats discriminating subcutaneous MA from saline. These rats were trained and maintained to discriminate between MA at 0.5 mg/kg, s.c. and saline under a fixed ratio 10 schedule for food reinforcement in a 2-lever operant chamber situation. Guide cannulae were implanted bilaterally into the nucleus accumbens. In the substitution tests, the drug was administered into the nucleus accumbens. MA at 10 micrograms per rat substituted for subcutaneous MA in 4 out of 5 rats but neither DA at 10-40 micrograms per rat (n = 7) nor NA at 10-40 micrograms per rat (n = 4) substituted for subcutaneous MA. On the other hand, the same drugs administered into the nucleus accumbens induced increased spontaneous motor activity as also observed in six other untrained rats. MA, DA or NA alone each at 10 micrograms per rat increased spontaneous motor activity. The discriminative effects of MA are considered to be mediated in the nucleus accumbens of rats. Although DA or NA alone administered into the nucleus accumbens showed similar increasing motor activity effects as those of MA, the discriminative effects of exogenous DA or NA alone administered into the same brain area were different from those of MA in the present experimental condition.