Bioactive 6-nitronorepinephrine identified in mammalian brain

Norepinephrine (NE) (von Euler, U. S. (1972) in Catecholamines (Blaschko, H., and Muscholl, E., eds.) pp. 186-230, Springer-Verlag, Berlin) and nitric oxide (NO.) function as neurotransmitters in the nervous system. We have shown that NE levels in the rat hypothalamic paraventricular nucleus (Shintani, F., Kato, R., Kinoshita, N., Kanba, S., Asai, M., and Nakaki, T.(1995) Proceedings of the Satellite Symposium, 4th IBRO World Congress on Neuroscience, Otsu, 1995) diminish in the presence of NO.. This observation prompted us to explore the possibility of an in vivo interaction between NE and NO. or NO.-related molecules. In fact, nitration of NE has been shown to occur in vitro (d'Ischia, M., and Costantini, C. (1995) Bioorg. Med. Chem. 3, 923-927). We now report the identification of 6-nitronorepinephrine in the mammalian brain. Amounts of 6-nitronorepinephrine in the rat brain were attenuated by intraperitoneal administration of an inhibitor of nitric oxide synthase, NG-nitro-L-arginine methyl ester (L-NAME). This was reversed by coadministration of L-arginine, suggesting that nitric oxide synthase participated in the formation of 6-nitronorepinephrine. Moreover, we found that 6-nitronorepinephrine inhibits the activity of catechol O-methyltransferase, as well as NE transport into rat synaptosomes. A rat brain microdialysis experiment showed that perfusion of 6-nitronorepinephrine into the rat paraventricular nucleus significantly elevated NE while decreasing 3-methoxy-4-hydroxyphenylglycol and that L-NAME administered intraperitoneally decreased NE and increased 3-methoxy-4-hydroxyphenylglycol. These observations suggest that 6-nitronorepinephrine generated in nuclei containing both adrenergic and nitrergic neurons inhibits NE inactivation. We propose that 6-nitronorepinephrine is a potential signal molecule linking the actions of NE and NO..

Tranilast inhibits the effects of platelet-derived growth factor on cell proliferation and induction of nitric oxide

The effects of tranilast on DNA synthesis and cell proliferation in cultured rat mesangial cells, treated with platelet-derived growth factor (PDGF), were investigated. Tranilast significantly inhibited PDGF-stimulated DNA synthesis and cell proliferation in a dose-dependent manner. In the absence of PDGF, it also enhanced cytokine-induced nitric oxide (NO) production, PDGF significantly inhibited cytokine-induced NO production, but tranilast completely abolished this inhibitory effect of PDGF. These results show that tranilast inhibits PDGF-induced proliferation of mesangial cells under both normal and inflammatory conditions.

Natriuretic peptide-augmented induction of nitric oxide synthase through cyclic guanosine 3',5'-monophosphate elevation in vascular smooth muscle cells

To elucidate the role of natriuretic peptides in vascular remodeling, the effects of atrial natriuretic peptide, brain natriuretic peptide, and C-type natriuretic peptide (CNP) on the induction of inducible nitric oxide (NO) synthase (iNOS) in rat aortic smooth muscle cells were examined. Although none of the peptides when applied alone induced the production of nitrite, a stable end product of NO, each peptide dramatically enhanced nitrite production induced by a cytokine combination of interleukin-1 alpha and tumor necrosis factor-alpha. Each natriuretic peptide stimulated intracellular cGMP accumulation in a dose-dependent manner. Time-dependent nitrite production by the cytokines was increased by CNP cotreatment and inhibited by NG-methyl-L-arginine, indicating involvement of the L-arginine-NO pathway. Northern blot analysis showed that the augmented nitrite production was accompanied by an increase in iNOS messenger RNA. A cGMP analog, 8-bromo-cGMP, completely mimicked all of the effects of CNP described above. A cGMP-dependent protein kinase inhibitor, KT5823, paradoxically increased nitrite production and iNOS messenger RNA levels induced by the combination of 8-bromo-cGMP and both cytokines or by the two cytokines only. These data demonstrate the stimulatory effect of cGMP on cytokine-induced iNOS and imply that natriuretic peptides may play a regulatory role in vascular remodeling via the production of large amounts of NO.

Cyclosporin A inhibits nitric oxide synthase induction in vascular smooth muscle cells

The effect of cyclosporin A on induction of nitric oxide synthase in rat aortic smooth muscle cells was examined. A combination of interleukin-1 alpha (100 U/mL) and tumor necrosis factor--alpha (5000 U/mL) induced accumulation of nitrite/nitrate, the stable end products of nitric oxide, in culture media within 48 hours. Cyclosporin A inhibited this nitrite/nitrate accumulation in a concentration-dependent manner with an IC50 of 4 x 10(-7) mol/L when applied simultaneously with the cytokines. The expression of inducible nitric oxide synthase messenger RNA (mRNA) induced by the combination of interleukin-1 alpha and tumor necrosis factor-alpha was inhibited by the cyclosporin A cotreatment. Cyclosporin A did not decrease inducible nitric oxide synthase mRNA stability in the presence of transcription inhibitor actinomycin D (5 micrograms/mL). Induction of nitrite/nitrate production by the combination of tumor necrosis factor-alpha and bacterial lipopolysaccharide or that of interleukin-1 alpha and interferon gamma (100 U/mL) was also inhibited by cyclosporin A cotreatment. Another inhibitor of calcineurin, FK506 (up to 10(-6) mol/L), had no effect on the induction of nitrite/nitrate production, suggesting the possibility that the inhibitory effect of cyclosporin A may be exerted by means of a novel pathway other than inhibition of calcineurin. These results indicate that cyclosporin A inhibits inducible nitric oxide synthase induction at the mRNA level and that inducible nitric oxide synthase in vascular smooth muscle cells can be a target for cyclosporin A, providing a possible mechanism for the interference of the drug with the balance of vasoactive substances.

Nitric oxide is important for mouse beta-cell line killing by peritoneal exudate cells obtained from cyclophosphamide treated non-obese diabetic mice

Macrophages from recent onset non-obese diabetic (NOD) mice showed cytotoxicity against the NOD mouse derived beta-cell line, MIN6N-9a. In this report, we examined whether nitric oxide is associated with beta-cell destruction. Peritoneal exudate cells (PEC), obtained from cyclophosphamide treated NOD mice showed higher cytotoxicity against MIN6N-9a compared to PECs from saline injected NOD mice (P < 0.01). This effect was suppressed in cells incubated with 0.5 mmol/l NG-methyl-L-arginine, a nitric oxide synthase inhibitor (P < 0.001). In addition, the nitrite concentration of the co-culture medium, as an index of nitric oxide production, increased in MIN6N-9a cells co-cultured with peritoneal exudate cells from cyclophosphamide injected NOD mice but not in co-culture with saline injected NOD mice (P < 0.05). Thus, nitric oxide plays an important role in beta-cell line destruction of macrophages obtained from NOD mice.

Up-regulation of nitric oxide synthase by estradiol in human aortic endothelial cells

We have examined the effects of sex hormones on calcium-dependent NO production and protein levels of NO synthase in cultured human aortic endothelial cells, which were treated with various doses of 17 beta-estradiol and testosterone for 8-48 h. Treatment with 17 beta-estradiol enhanced calcium-dependent NO production, but testosterone had exerted no effect. Western blot using monoclonal anti-human endothelial NO synthase antibody clarified that increased NO production by 17 beta-estradiol treatment was accompanied by increased NO synthase protein. Our results provide evidence that human endothelial NO synthase can be regulated by estrogens.

Pressure enhances endothelin-1 release from cultured human endothelial cells

The effect of pure pressure without shear stress or stretch on the release of endothelin-1 was investigated. Elevation of pressure significantly enhanced endothelin-1 release from cultured human umbilical vein endothelial cells. A calcium channel blocker, nifedipine, and a putative stretch-activated channel blocker, gadolinium, did not affect the pressure-induced endothelin-1 increase. On the other hand, a phospholipase C inhibitor, 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate, and protein kinase C inhibitors, 1-5-(isoquinolinylsulfonyl)-2-methylpiperazine and chelerythrine, significantly inhibited the pressure-induced endothelin-1 increase. Moreover, pure pressure reduced basal nitric oxide release, while pretreatment with a nitric oxide synthase inhibitor, NG-monomethyl-L-arginine, had no effect on the pressure-induced endothelin-1 increase. In conclusion, our results show for the first time that pressure enhances endothelin-1 release partially through activation of phospholipase C and protein kinase.

Involvement of interleukin-1 in immobilization stress-induced increase in plasma adrenocorticotropic hormone and in release of hypothalamic monoamines in the rat

We investigated whether interleukin-1 (IL-1) activity in the rat hypothalamus was increased by immobilization stress (IS), and whether pretreatment with an interleukin-1 receptor antagonist (IL-1Ra) is capable of inhibiting IS-induced elevations of hypothalamic norepinephrine (NE), dopamine (DA), and serotonin (5-HT) and the levels of their metabolites as well as of plasma adrenocorticotropic hormone (ACTH). IL-1 activity was estimated with a bioassay using mouse thymocyte proliferation in the presence of concanavalin A. IL-1Ra was administered directly into the anterior hypothalamus, and monoamines were determined using a microdialysis technique and an HPLC system. First, we found that levels of IL-1 activity in the rat hypothalamus reached a maximum at 60 min after starting IS. Second, IL-1Ra (2 micrograms) significantly inhibited IS-induced increases in hypothalamic NE, DA, and 5-HT levels as well as the levels of their metabolites. In addition, IL-1Ra (2 micrograms) also inhibited the IS-induced elevation of plasma ACTH levels. Third, timing effects of IL-1Ra administration on the IS-induced monoamines or ACTH responses were examined. IL-1Ra (2 micrograms) administered at 5 or 60 min before the start of IS, but not at 5 or 60 min after IS had been started, exerted inhibitory effects on these responses, indicating that the effects of IL-1 occurred within 5 min after the initiation of IS. In summary, these results suggest that IS enhances biologically active IL-1 in the hypothalamus, and that hypothalamic IL-1 plays a role in the regulation of IS-induced responses including elevated monoamine release in the hypothalamus and activation of the hypothalamo-pituitary-adrenal axis. Moreover, since 5 min is too short a time for IS to induce production of IL-1, IS may augment the effects of preexisting IL-1 in the hypothalamus.

Role of interleukin-1 in stress responses. A putative neurotransmitter

Recently, the central roles of interleukin-1 (IL-1) in physical stress responses have been attracting attention. Stress responses have been characterized as central neurohormonal changes, as well as behavioral and physiological changes. Administration of IL-1 has been shown to induce effects comparable to stress-induced changes. IL-1 acts on the brain, especially the hypothalamus, to enhance release of monoamines, such as norepinephrine, dopamine, and serotonin, as well as secretion of corticotropin-releasing hormone (CRH). IL-1-induced activation of the hypothalamo-pituitary-adrenal (HPA) axis in vivo depends on secretion of CRH, an intact pituitary, and the ventral noradrenergic bundle that innervates the CRH-containing neurons in the paraventricular nucleus of the hypothalamus. Recent studies have shown that IL-1 is present within neurons in the brain, suggesting that IL-1 functions in neuronal transmission. We showed that IL-1 in the brain is involved in the stress response, and that stress-induced activation of monoamine release and the HPA axis were inhibited by IL-1 receptor antagonist (IL-1Ra) administration directly into the rat hypothalamus. IL-1Ra has been known to exert a blocking effect on IL-1 by competitively inhibiting the binding of IL-1 to IL-1 receptors. In the latter part of this review, we will attempt to describe the relationship between central nervous system diseases, including psychological disorders, and the functions of IL-1 as a putative neurotransmitter.

[Two applications of in vivo brain microdialysis: administration of high-molecular-weight drugs through a microinjection tube and measurement of nitric oxide production]

A brain microdialysis technique has made it possible to determine neurotransmitter levels in the targeted region of the brain of a freely moving rat. In this article, two kinds of application of the brain microdialysis are demonstrated. First, to study central nervous effects of large molecular weight substances that cannot cross the blood-brain barrier, we used a microdialysis probe equipped with a microinjection tube for administering the substance in the same region into which the probe had been inserted. We proved that interleukin-1 beta (1 ng) injected directly into the anterior hypothalamus elicited releases of NE, DA and 5-HT, as well as increases in their metabolites. Second, using a new method combining a brain microdialysis technique with measurement of nitrite/nitrate by the Griess reaction, we demonstrated that activation of N-methyl-D-aspartate (NMDA) receptors in the cerebella of rats induces the release of nitric oxide (NO). Since L-NG-monomethyl-arginine (L-NMMA), which competitively blocks NO synthesis from L-arginine, significantly inhibited the release of nitrite/nitrate from the rat cerebellum, these results indicate that this new method is capable of measuring NO formation from L-arginine following the stimulation of NMDA receptors.

Inhibition by lithium of cyclic GMP formation without inhibition of nitric oxide generation in the mouse neuroblastoma cell (N1E-115)

We investigated the effects of lithium ion (Li+) on muscarinic receptor-mediated nitric oxide (NO) generation, and guanylate cyclase (GCase) activation using the mouse neuroblastoma clone, N1E-115. The levels of released NO were determined by measuring the levels of nitrite/nitrate in the incubation medium, and the activity of GCase was measured with an assay for cellular cyclic [3H] GMP levels. We determined that Li+ had no effects on muscarinic receptor-activated elevation of nitrite/nitrate levels, which were significantly inhibited by 100 microM L-NG-monomethylarginine, although it has been reported that Li+ inhibits muscarinic receptor-activated cyclic GMP formation in the cells. In addition, Li+ inhibited the cyclic GMP formation induced by an NO donor, sodium nitroprusside (SNP), in both intact cells and a crude cellular homogenate; thus, the inhibition by Li+ of muscarinic receptor-mediated cyclic GMP synthesis appeared to be at the level of GCase, but not NO synthase.

Beneficial circulatory effect of L-arginine

L-Arginine is an essential amino acid for infants and growing children. This amino acid is a substrate for at least five enzymes identified in mammals, including arginase, arginine-glycine transaminase, kyotorphine synthase, nitric oxide synthase (NOS) and arginine decarboxylase. L-Arginine exerts antihypertensive and antiproliferative effects on vascular smooth muscles. NOS and arginine decarboxylase appear to be important for the effect of L-arginine on the circulatory system, since each produces nitric oxide (NO), a potent vasodilator, and agmatine, an endogenous noncatecholamine ligand for central alpha-2 adrenoceptors, from L-arginine. Several issues must be clarified before the mechanisms by which L-arginine exerts its effects on the circulatory system can be fully understood.

Affinity of neuroleptics for D1 receptor of human brain striatum

We determined the inhibition-dissociation constant (Ki) of a number of neuroleptics for D1 receptors of normal human brain tissue using [3H]SCH23390 [R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3[benzazepine-7- ol]. SCH23390 had the highest affinity with a Ki of 0.76 nM. Among clinically used drugs, propericiazine showed the highest affinity with a Ki of 10 nM. When neuroleptics were classified according to chemical structures, the Ki values were as follows. Phenothiazines ranged from 10 nM to 250 nM. Butyrophenones ranged from 45 nM to 250 nM. Thioxanthenes ranged from 12 nM to 340 nM. Orthopramines were more than 10,000 nM. The Ki values for the binding site of this study were significantly correlated with those reported in studies using animal brain. The possible relationship between D1 receptors and negative symptoms is discussed.

Measurement by in vivo brain microdialysis of nitric oxide release in the rat cerebellum

Using a new method which combines a brain microdialysis technique and measurement of nitrite/nitrate levels by the Griess reaction, it has been proven that activation of N-methyl-D-aspartate (NMDA) receptors in the cerebelli of rats which had been under non-anesthetic and freely moving conditions induces the release of nitric oxide (NO). Since L-NG-monomethylarginine (L-NMMA), which competitively blocks NO synthesis from L-arginine, significantly inhibited the release of nitrite/nitrate from the rat cerebellum, these results indicate that the new method is capable of measuring NO formation from L-arginine following the stimulation of NMDA receptors. This method should prove useful for investigating the relation between brain functions such as behavior, learning and memory and NO in the central nervous system.

Pressure promotes DNA synthesis in rat cultured vascular smooth muscle cells

High blood pressure is one of the major risk factors for atherosclerosis. In this study, we examined the effects of pressure on cell proliferation and DNA synthesis in cultured rat vascular smooth muscle cells. Pressure without shear stress and stretch promotes cell proliferation and DNA synthesis in a pressure-dependent manner. Pressure-induced DNA synthesis was inhibited significantly by the phospholipase C (PLC) inhibitor 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate, the protein kinase C inhibitor H-7, 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine, staurosporine, and the tyrosine kinase inhibitor ([3,4,5-trihydroxyphenyl]methylene)propanedinitrile. To clarify whether activation of PLC and calcium mobilization are involved in pressure-induced DNA synthesis, production of 1,4,5-inositol trisphosphate (IP3) and intracellular Ca2+ was measured. Pure pressure increased IP3 and intracellular Ca2+ in a pressure-dependent manner. The increases in both IP3 and intracellular Ca2+ were inhibited significantly by 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate. This study demonstrates a novel cellular mechanism whereby pressure regulates DNA synthesis in vascular smooth muscle cells, possibly via activation of PLC and protein kinase C.

Physiological and clinical significance of nitric oxide

Nitric oxide, or NO., is a gas under atmospheric conditions. It is noxious because of its free-radical structure. It is biosynthesized from the amino acid L-arginine. The responsible enzymes are widely distributed in the human body. It has been shown that this simple molecule, NO., plays important roles in mammalian physiology. It is one of the factors regulating vascular tone and blood pressure, inhibition of platelet aggregation, neurotransmission in the peripheral and central nervous systems and macrophage function. Evidence for the pathophysiological significance of NO. is now accumulating.

Arachidonic acid blocks gap junctions between retinal horizontal cells

Horizontal cells in turtle retinae are electrically coupled via gap junctions, and the input resistances of the cells are too low to be measured. However, intracellular injection of arachidonic acid into horizontal cells caused great increases in the input resistances of the cells, and the cells could be easily polarized by intracellular current injection. The injection of arachidonic acid also caused decrease in light responses of horizontal cells to surround illumination, and blocked dye-couplings with Lucifer Yellow CH. On the other hand, injection of a lipoxygenase inhibitor or a guanylate cyclase inhibitor into horizontal cells suppressed the decoupling effect of arachidonic acid. These findings suggest that lipoxygenase metabolites of arachidonic acid block gap junctions by activating guanylate cyclase.

The role of cytotoxic macrophages in non-obese diabetic mice: cytotoxicity against murine mastocytoma and beta-cell lines

The cytotoxicity of macrophages from non-obese diabetic (NOD) mice against murine mastocytoma (P-815), and murine beta-cell lines having the NOD gene background (MIN6N-9a), were examined. Peritoneal exudate cells from 20-week-old mice showed higher cytotoxicity, measured as inhibition of thymidine uptake into P-815, than those from 12-week-old mice (p < 0.01). In cyclophosphamide-injected mice, cytotoxicity of peritoneal exudate cells had increased at 8 days post-injection, at which time the mice were not diabetic. To confirm macrophage cytotoxicity against pancreatic cells and examine its cytolytic mechanism, the cytotoxicity of peritoneal exudate cells from cyclophosphamide-injected NOD mice against MIN6N-9a cells was measured by the chromium release assay. These peritoneal exudate cells showed higher cytotoxicity as compared to those of saline-injected mice (p < 0.001). Macrophages were demonstrated to be the major component of peritoneal exudate cells (50%) by flowcytometric analyses. Cytotoxicity increased with macrophage enrichment by adhesion (p < 0.01). Furthermore, a macrophage toxin, silica, completely blocked the cytotoxicity (p < 0.001). Cytokines (interleukin 1 and tumour necrosis factor) and a nitric-oxide-producing vasodilator, sodium nitroprusside, were cytotoxic to MIN6N-9a cells but only sodium nitroprusside showed cytotoxicity when incubated for the same period as peritoneal exudate cells. Thus, macrophages play an important role in beta-cell destruction and soluble factors other than cytokines (e.g. nitric oxide) may be mediators of this early cytolytic process.

Dexamethasone inhibits nitric oxide synthase mRNA induction by interleukin-1 alpha and tumor necrosis factor-alpha in vascular smooth muscle cells

The effects of interleukin-1 alpha, tumor necrosis factor-alpha and dexamethasone on the induction of nitric oxide synthase mRNA in rat aortic smooth muscle cells were studied. Neither interleukin-1 alpha (up to 100 U/ml) nor tumor necrosis factor-alpha (up to 5000 U/ml) was capable of inducing nitrite/nitrate production and nitric oxide synthase mRNA in smooth muscle cells. In contrast, treatment for 12 hr or longer with a combination of the two synergistically induced nitrite/nitrate and cyclic GMP production in cell culture media and nitric oxide synthase mRNA, both of which were prevented by dexamethasone. Contamination with bacterial lipopolysaccharide, which may affect the induction of nitric oxide synthase, was below 30 pg/ml in all experiments. Our findings show that dexamethasone and these cytokines regulate the induction of nitric oxide synthase at the mRNA level in vascular smooth muscle cells.

Nitric oxide synthase mRNA in endothelial cells: synergistic induction by interferon-gamma, tumor necrosis factor-alpha and lipopolysaccharide and inhibition by dexamethasone

Regulation of nitric oxide synthase mRNA by interferon-gamma, tumor necrosis factor-alpha, bacterial lipopolysaccharide (LPS) and dexamethasone in rat aortic endothelial cells was examined. The combination of interferon-gamma (100 U/ml) and tumor necrosis factor-alpha (5000 U/ml) evoked a time-dependent increase in nitric oxide synthase mRNA and nitrite/nitrate production, both of which were inhibited by dexamethasone. Neither interferon-gamma (100 U/ml), tumor necrosis factor-alpha (5000 U/ml) nor LPS (100 ng/ml) alone was capable of increasing nitric oxide synthase mRNA and nitrite/nitrate production in these cells. However, combinations of two of the three agents synergistically increased both nitric oxide synthase mRNA and nitrite/nitrate production. When the three agents were applied simultaneously, nitric oxide synthase mRNA and nitrite/nitrate production were both markedly increased. LPS contamination, which may affect the induction of nitric oxide synthase, was below 20 pg/ml in all experiments unless LPS was added exogenously, namely, the effects observed were those of the cytokines themselves. Our results suggest that in endothelial cells, these cytokines regulate the production of nitric oxide at the level of nitric oxide synthase mRNA induction.

Increase in inositol tris-, pentakis- and hexakisphosphates by high K+ stimulation in cultured rat cerebellar granule cells

Effects of high K+ stimulation on inositol polyphosphate accumulations and intracellular free calcium concentration ([Ca2+]i) were investigated in cultured rat cerebellar granule cells. When the [3H]inositol-labelled cells were stimulated with KCl, concentration-dependent accumulations of [3H]Ins(1,4,5)P3, [3H]InsP5 and [3H]InsP6 were observed. Nifedipine (3 microM), a calcium channel antagonist, inhibited the high (KCl, 90 mM) K(+)-induced accumulations of these inositol polyphosphates. In Ca(2+)-depleted and EGTA-containing (0.1 mM) medium, the high K(+)-induced inositol polyphosphate accumulation were completely inhibited. Similar results were also observed in the case of [Ca2+]i. These results suggest that the rise in [Ca2+]i caused by activation of voltage-dependent calcium channels plays an important roles in the high K(+)-induced accumulation of [3H]Ins(1,4,5)P3, [3H]InsP5 and [3H]InsP6 in cultured rat cerebellar granule cells.

Characteristics of inositol polyphosphate metabolism in cultured adrenal chromaffin cells

1. Nicotine, high K+ and maitotoxin caused the inositol polyphosphate accumulation concomitant with 45Ca2+ uptake. 2. Angiotensin II (Ang II) and ATP induced the inositol polyphosphate accumulation without 45Ca2+ uptake. 3. Nifedipine-treatment and Ca(2+)-deprivation inhibited the high K(+)-induced inositol polyphosphate accumulation but failed to inhibit the Ang II-induced inositol polyphosphate accumulation. 4. 12-O-tetradecanoylphorbol-13-acetate inhibited the Ang II-induced inositol polyphosphate accumulation but failed to inhibit the high K(+)-induced one. 5. These results suggest that the formation of inositol polyphosphates may be regulated by two mechanisms, i.e. Ca2+ uptake-dependent mechanisms represented by high K+, and Ca2+ uptake-independent mechanisms represented by Ang II.

Interleukin-1 beta augments release of norepinephrine, dopamine, and serotonin in the rat anterior hypothalamus

We investigated the effects of interleukin-1 beta (IL-1 beta), administered directly into the rat anterior hypothalamus (AHY), on monoamine release in the same region by using a brain microdialysis technique and an HPLC-electrochemical detection system. First, to study the local effects of IL-1 beta, we used a microdialysis probe equipped with a microinjection tube for administering IL-1 beta in the same region into which the probe had been inserted. IL-1 beta (1 ng) injected directly into the AHY elicited release of norepinephrine (NE), dopamine (DA), and 5-HT, as well as increases in their metabolites, 4-hydroxy-3-methoxyphenylglycol, 3,4-dihydroxyphenylacetic acid, 4-hydroxy-3-methoxyphenylacetic acid, and 5-hydroxyindole-3-acetic acid, in the AHY. Vehicle alone exerted no effect on monoamine release. Although the elevated levels of NE and DA persisted for more than 6 hr after injection of IL-1 beta, the elevated levels of 5-HT were transient. Second, in order to investigate whether this effect of IL-1 beta is a direct action in the AHY, we performed in vitro experiments using hypothalamus slices. IL-1 beta (0.1 and 1 nM) increased the levels of each monoamine released from hypothalamic slices in a dose-dependent manner. These findings suggest that IL-1 beta acts directly on the hypothalamus to induce release of NE, DA, and 5-HT. Third, the roles of prostaglandins (PGs) in NE release in the AHY elicited by direct injection of IL-1 beta were examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of L-arginine-nitric oxide pathway in hypertension

OBJECTIVE

The present study was designed to investigate the effect of L-arginine administration on patients with essential and secondary hypertension by measuring haemodynamic parameters, neuroendocrine hormones and indicators of nitric oxide (NO) release.

DESIGN

Ten patients with essential hypertension and six with secondary hypertension (three with renovascular hypertension and three with primary aldosteronism) were enrolled in the study.

METHODS

L-Arginine was administered intravenously to the hypertensive patients. During L-arginine administration, blood pressure, heart rate, cardiac output and neuroendocrine hormones such as catecholamines, plasma renin activity and plasma aldosterone were measured. To examine whether L-arginine administration increases NO production, indicators of NO release in vivo such as plasma cyclic GMP, plasma citrulline and urinary excretion of nitrite and nitrate were measured simultaneously.

RESULTS

During administration, mean arterial pressure decreased, heart rate increased, cardiac output increased and total peripheral resistance decreased. The indicators of NO release increased simultaneously during administration. Catecholamine and plasma renin activity, rather than increasing in response to L-arginine-induced hypotension as expected, showed no significant changes except in patients with renovascular hypertension. In all patients plasma aldosterone levels decreased significantly in response to L-arginine administration, regardless of basal plasma renin activity and aldosterone levels.

CONCLUSIONS

These results suggest that exogenous L-arginine produces a vasodilatory effect by increasing NO production and that L-arginine, or released NO, modulates the release of neuroendocrine hormones in hypertensive subjects.