Lymphatic transport rate of noradrenaline during adrenergic thermogenesis

The lymphatic concentration of noradrenaline (NA) and lymph flow in the thoracic duct of cold-acclimated rats were measured under conditions of the quasi-stationary thermogenic response to i.v. infused NA. Both parameters increased linearly with increased rate of NA infusion. The lymphatic transport rate of NA is quadratically related to the infusion rate which indicates the same relation for the efflux of NA from blood into the extravascular space. This non-linear efflux of NA causes a non-linear thermogenic response to NA.     

Regional distribution of dopamine, 5-hydroxytryptamine,and noradrenaline in the rat vas deferens

The concentrations of dopamine (DA), 5-hydroxytryptamine (5-HT) and noradrenaline (NA) in the rat vas deferens divided in eight or four sections were determined by high performance liquid chromatography with electrochemical detection. Dopamine and NA had the same regional distribution; their concentrations were maximal near the prostatic end and decreased towards the epididymis. The concentration of 5-HT also decreased from the prostatic to the epididimal end, but 5-HT did not follow the same regional distribution as DA and NA. Reserpine (0.02 or 0.2 mg/kg, i.p., 24 hr) and 6-hydroxydopamine (2×80 mg/kg, i.v., 6 days) decreased the contents of DA and NA; the concentrations of both amines were modified to a similar extent. Reserpine also diminished the content of 5-HT. Pargyline (200 mg/kg, i.p., 2 hr) increased the concentration of 5-HT whilep-chlorophenylalanine (300 mg/kg, oral, 3 days) decreased the contents of the amine in some sections of the vas deferens. This study suggests that DA and NA co-exist in the same sympathetic neurons. Some of the 5-HT could be stored in mast cells as previously proposed, but the finding that tissue content of 5-HT changes after inhibiting the deamination or synthesis of the amine suggests that other source(s) of 5-HT distinct from mast cells exist in the rat vas deferens.     

Intracerebroventricular injections of noradrenaline affect brain energy metabolism of rainbow trout

To assess the role of noradrenaline (NA) as a possible regulator of brain energy metabolism in teleost fish, the impact of increased noradrenaline levels within the brain on several parameters of energy metabolism was assessed in rainbow trout brain. Accordingly, two different doses of noradrenaline, producing increases in brain NA levels comparable to those occurring in several physiological processes in nature, were selected. In a subsequent set of three different experiments, fish were intracerebroventricularly injected with 1 microL 100 g(-1) body weight of Cortland saline alone (control) or containing NA (5 nmol NA and 10 nmol NA); after 30 min, brain and plasma samples were taken to assess changes in parameters of energy metabolism due to NA treatment. The results obtained clearly show dose-dependent changes in NA-treated fish in several parameters, including decreased glycogen and ATP levels, increased lactate and pyruvate levels, decreased fructose 1,6-bisphosphatase activity, and increased pyruvate kinase and lactate dehydrogenase activities. Altogether, the present experiments show for the first time in a teleost fish evidence supporting that increased noradrenaline levels in the brain elicit metabolic changes in the brain (enhanced glycogenolysis and glycolysis), resulting in an increased energy demand. These metabolic changes may be related to those occurring under several physiological conditions in nature such as hypoxia, in which increased energy demand and increased noradrenaline levels occur in the brain simultaneously.     

Loss of noradrenaline transporter sites in frontal cortex of rats with acute (ischemic) liver failure

There is increasing evidence that central noradrenaline (NA) transport mechanisms are implicated in the central nervous system complications of acute liver failure. In order to assess this possibility, binding sites for the high affinity NA transporter ligand [3H]-nisoxetine were measured by quantitative receptor autoradiography in the brains of rats with acute liver failure resulting from hepatic devascularization and in appropriate controls. In vivo microdialysis was used to measure extracellular brain concentrations of NA. Severe encephalopathy resulted in a significant loss of [3H]-nisoxetine sites in frontal cortex and a concomitant increase in extracellular brain concentrations of NA in rats with acute liver failure. A loss of transporter sites was also observed in thalamus of rats with acute liver failure. This loss of NA transporter sites could result from depletion of central NA stores due to a reserpine-like effect of ammonia which is known to accumulate to millimolar concentrations in brain in ischemic liver failure. Impaired NA transport and the consequent increase in synaptic concentrations and increased stimulation of neuronal and astrocytic noradrenergic receptors could be implicated in the pathogenesis of the encephalopathy and brain edema characteristic of acute liver failure.     

Ascorbic acid suppresses the deconjugation of noradrenaline but not dopamine in plasma

The characteristics of hydrolysis of sulfoconjugated noradrenaline (NA) and dopamine (DA) in plasma using sulfatase were investigated. Ascorbic acid has been used as an antioxidant during the hydrolysis of conjugated NA or DA. Hydrolysis of NA sulfates was considerably inhibited by adding ascorbic acid (0.5-10 mM), and slightly inhibited by adding dithiothreitol (1-10 mM). In contrast, the hydrolysis of DA sulfates was not affected after either ascorbic acid or DTT treatment. On the basis of these findings, the levels of NA sulfates previously reported are found to be markedly lower than the actual levels of NA sulfates in human plasma.     

Genetic or pharmacological blockade of noradrenaline synthesis enhances the neurochemical, behavioral, and neurotoxic effects of methamphetamine

N -(2-chloroethyl)- N -ethyl-2-bromobenzylamine (DSP-4) lesions of the locus coeruleus, the major brain noradrenergic nucleus, exacerbate the damage to nigrostriatal dopamine (DA) terminals caused by the psychostimulant methamphetamine (METH). However, because noradrenergic terminals contain other neuromodulators and the noradrenaline (NA) transporter, which may act as a neuroprotective buffer, it was unclear whether this enhancement of METH neurotoxicity was caused by the loss of noradrenergic innervation or the loss of NA itself. We addressed the specific role of NA by comparing the effects of METH in mice with noradrenergic lesions (DSP-4) and those with intact noradrenergic terminals but specifically lacking NA (genetic or acute pharmacological blockade of the NA biosynthetic enzyme dopamine β-hydroxylase; DBH). We found that genetic deletion of DBH (DBH−/− mice) and acute treatment of wild-type mice with a DBH inhibitor (fusaric acid) recapitulated the effects of DSP-4 lesions on METH responses. All three methods of NA depletion enhanced striatal DA release, extracellular oxidative stress (as measured by in vivo microdialysis of DA and 2,3-dihydroxybenzoic acid), and behavioral stereotypies following repeated METH administration. These effects accompanied a worsening of the striatal DA neuron terminal damage and ultrastructural changes to medium spiny neurons. We conclude that NA itself is neuroprotective and plays a fundamental role in the sensitivity of striatal DA terminals to the neurochemical, behavioral, and neurotoxic effects of METH.     

Mecamylamine blockade of nicotine enhanced noradrenaline turnover in rat brain.

The administration of nicotine significantly enhanced the depletion in noradrenaline (NA) observed in the brains of male Sprague-Dawley rats following alpha methyl-para-tyrosine (αMPT) administration. These data indicate that nicotine enhances the turnover of NA in the rat brain. This effect of nicotine was completely blocked by mecamylamine administration while mecamylamine alone had no observed effect on NA content or turnover. These data are consistent with the action of mecamylamine as an effective antagonist of the action of nicotine in the rat brain.     

A modified screening method for rapid simultaneous determination of dopamine, noradrenaline and serotonin in the same brain region

A modification of previously published fluorimetric methods for brain noradrenaline (NA), dopamine (DA), and serotonin (5-HT) assay is presented in this paper. The modification improved the sensitivity to 5-HT and resulted in a less time-consuming and less expensive method for noradrenaline and dopamine determination. The assay can be used for simultaneous estimation of NA, DA and 5-HT as well as for turnover studies, utilizing catecholamine synthesis inhibition or monoaminoxidase inhibition.     

Effect of denervation and phentolamine on the thermogenic action of noradrenaline in rat skeletal muscle

Vascularly isolated skeletal muscle of the cold-acclimated (CA) rat was perfused with blood in situ or in vitro and the effect of denervation and an alpha-adrenolytic agent (phentolamine) on its oxygen consumption was studied in the resting state and after administering noradrenaline (NA). The resting metabolism of muscle in situ rose by 28% after denervation. The infusion of NA further raised the oxygen consumption of acutely denervated muscle perfused in situ of in vitro by 43%. The thermogenic effect of NA on muscle denervated two hours before the experiment was only transitory. Phentolamine raised the oxygen consumption of the innervated muscle in situ by 42%; the infusion of NA did not stimulate metabolism any further. Phentolamine reduced the vascular resistance of resting muscle, but did not inhibit the vasoconstriction during the infusion of NA. The results show that the thermogenic effect of infused NA in perfused muscle is inhibited not by acute denervation, but by a vasoconstriction, which cannot be prevented by the administration of an alpha-adrenolytic agent.     

Behavioural effects of 6-hydroxydopamine-induced depletion of spinal noradrenaline

Bilateral injection of 6-hydroxydopamine (4 micrograms/2 microL) into the caudal medulla of rats reduced spinal noradrenaline (NA) to 6% of control values. No significant NA depletion was observed in the hippocampus, cortex, or cerebellum, and a small loss of NA was found in the hypothalamus. These lesions were found to elevate significantly threshold shock levels necessary to elicit jump responses, and they also abolished the reflexive alternating motor movements produced by decapitation. These data support the hypothesis that spinal NA mechanisms modulate reflexive motor movements. However, no significant effect of these lesions was found on either spontaneous or amphetamine-induced locomotor activity, suggesting that spinal NA does not play a significant role in these behaviours.     

Pressor effects of systemic administration of methionine and leucine enkephalin in the conscious rat

Experiments were designed using conscious Sprague-Dawley rats to determine the blood pressure (BP) and heart rate (HR) responses to intravenous doses of (1) the adrenal catecholamines noradrenaline (NA) and adrenaline (A), (2) adrenal pentapeptides methionine enkephalin (ME) and leucine enkephalin (LE), (3) combination (i.v.) injections of both ME or LE with NA or A that modulate the hemodynamic responses when the adrenal catecholamines were given alone, and (4) the possible receptor mechanisms mediating the resultant BP and HR response to i.v. pentapeptide administration. NA (0.48 and 2.4 nmol) and A (0.3 and 1.5 nmol) given i.v. evoked potent, dose-related pressor responses associated with reflex bradycardia. ME and LE (1.6 - 48 nmol) elicited transient (10-20 s) increases in mean arterial pressure (MAP), which was associated either with no change in mean heart rate (MHR), such as ME, or with slight bradycardia (i.e., LE). Combining ME or LE (16 nmol) with NA (2.4 nmol) or A (0.3 or 1.5 nmol) did not change MAP and MHR from when these respective doses of NA or A were given alone. However, 16 nmol of ME or LE with a low dose of NA (0.48 nmol) increased the pressor response compared with NA (0.48 nmol) given alone. Other experiments whereby specific receptor blockers (naloxone, diprenorphine, atropine, propranolol, phentolamine or guanethidine) were given i.v. 5 min before subsequent i.v. administration of LE or ME (16 nmol) indicated that only phentolamine or guanethidine could completely suppress the pressor responses of LE and ME. Naloxone and diprenorphine pretreatment attenuated the pressor response of LE but did not affect the BP response to ME.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dopamine-beta-hydroxylase inhibition acutely stimulates rats hypothalamic noradrenaline and dopamine neuronal activity as assessed from metabolic ratios and circulating glucose and ACTH responses

Because central noradrenaline neuronal activity is tonically inhibited by noradrenaline (NA) itself via an action at prejunctional alpha 2-adrenoceptors, it was hypothesised that the blockade of central NA synthesis following acute dopamine-beta -hydroxylase (DBH) inhibition might primarily deplete prejunctional NA levels and result in an increase in central NA neuronal activity through reduced NA autoinhibition. This hypothesis was tested in the rat following the acute administration of the DBH inhibitors diethyldithiocarbamate (DDC) and cysteamine (CSH). Computerised gas chromatography/mass spectrometry was used to precisely measure the hypothalamic levels of NA and dopamine (DA) together with those of their primary neuronal metabolites dihydroxyphenylethyleneglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC), respectively. Both DDC (at 4 h) and CSH (at 30 min.) caused approximately a 50% reduction of hypothalamic NA concentrations. However this was associated with marked and highly significant increases in hypothalamic DHPG levels (by 50-100%) and in the hypothalamic ratio DHPG/NA. Also, when measured after CSH, the hypothalamic levels of the DHPG metabolite 3-methoxy-4-hydroxyphenylethyleneglycol were highly significantly increased. Consistent with increased DA neuronal activity, both DBH inhibitors raised DA and DOPAC levels and also the ratio DOPAC/DA in the hypothalami of treated rats and markedly suppressed serum prolactin levels (all p less than 0.01). The rise in hypothalamic concentrations of DHPG indicates that an increase in hypothalamic NA neuronal activity occurs following DBH inhibition. Significant elevations of blood glucose, corticosterone and ACTH were also observed after DBH inhibition. As we have previously demonstrated that increased central NA activity is associated with elevations of blood glucose, corticosterone and ACTH, these data provide further evidence for a functional increase in central NA activity caused by acute DBH inhibition. It is proposed that the increase in hypothalamic NA activity after DBH inhibition results from a primary depletion of the prejunctional alpha 2-active autoregulatory pool of NA.     

The influence of prolonged hyper- and hypothyroid states on the noradrenaline content of rat tissues and on the accumulation and efflux rates of tritiated noradrenaline.

The influence of chronic hyper- and hypothyroidism on the uptake and retention of tritiated noradrenaline ([3-H]NA) and on the endogenous noradrenaline (NA) content of various adrenergically innervated tissues was studied in thyroidectomized and sham-operated euthyroid rats. Half of the thyroidectomized rats were treated daily with thyroxine (25 mug/kg) for 3 or 12 weeks to simulate a condition of chronic hyperthyroidism, while the other half was left untreated to form a hypothyroid group. The body weight and the heart rate of each rat were measured at the end of each experiment, and in addition, at the end of the 3 week experiment, the oxygen consumption and the plasma thyroxine levels were measured to confirm the thyroid state of the animals. At the end of both experiments, each animal was given an intravenous injection of [3-H]NA and the [3-H]NA and the total endogenous NA content of the heart and various other adrenergically innervated tissues were measured on a timed schedule, to compare the initial accumulations and the rates of efflux of [3-H]NA under different thyroid states. Although the hyperthyroid rats had higher heart rates and heart weights, they were not significantly different from the euthyroid controls with respect to their body weights, tissue NA content, or accumulation and efflux rates of [3-H]NA. In contrast, the hypothyroid rats showed significantly lower heart and other tissue weights, but higher tissue concentrations of NA and rates of efflux of [3-H]NA than the euthyroid group. In the hypothyroid state, the NA turnover appeared to be increased as the [3-H]NA efflux rate was increased from the hearts and adrenal glands. There were no significant differences between the results of the 3 week and the 12 week experiments and no evidence that prolongation of the hyperthyroid state gave different results from those found by other workers who used much shorter treatment periods and larger doses of thyroxine to develop hyperthyroidism.     

Selective depletion of spinal noradrenaline abolishes post-decapitation convulsions

Previous data have suggested that spinal noradrenaline (NA) might be important in the normal expression of post-decapitation convulsions. This hypothesis was tested by selective depletion of spinal NA through stereotaxic infusions of 6-hydroxydopamine into the medulla in adult rats. This treatment was found to substantially reduce spinal NA and to abolish the post-decapitation convulsions. The results are discussed in terms of the mechanism underlying the involvement of NA in this reflex.     

Calorigenic response to noradrenaline following 6-hydroxydopamine treatment

Treatment of rats with 6-hydroxydopamine increased the calorigenic response to noradrenaline (NA). This was evident when NA was infused at rates which is untreated animals produced submaximal responses. The increased response was particularly evident in cold-acclimated rats and likely reflects a lack of uptake of the NA by adrenergic nerve terminals damaged by the drug.     

Effects of U-50,488H and U-50,488H withdrawal on catecholaminergic neurons of the rat hypothalamus

Previous report from our laboratory showed that morphine produces a stimulatory effect of hypothalamic noradrenaline (NA) turnover concurrently with enhanced pituitary-adrenal response after its acute injection and during withdrawal. In the present work we have studied the effects of acute and chronic administration of the kappa agonist U-50,488H as well as the influence of U-50,488H withdrawal on the activity of hypothalamic NA and dopamine (DA) neurons and on the activity of hypothalamic-pituitary-adrenal (HPA) axis. A single dose of U-50,488H (15 mg/kg i.p.) significantly increased hypothalamic NA and decreased DA turnover at the time of an enhanced corticosterone release. Rats rendered tolerant to the kappa agonist by administration of U-50,488H twice a day for 4 days showed no changes in corticosterone secretion. Additionally, a decrease in both hypothalamic MHPG (the cerebral NA metabolite) production and NA turnover was observed, whereas DOPAC concentration and DA turnover were enhanced, which indicate the development of tolerance towards the neuronal and endocrine actions of U-50,488H. After naloxone (3 mg/kg s.c.) administration to U-50,488H-tolerant rats, we found neither behavioural signs of physical dependence nor changes in hypothalamic catecholaminergic neurotransmission. In addition, corticosterone secretion was not altered in U-50,488H withdrawn rats. Present data clearly indicate that tolerance develops towards the NA turnover accelerating and DA turnover decreasing effect of U-50,488H. Importantly and by contrast to mu agonists, present results demonstrate that U-50,488H withdrawal produce no changes in hypothalamic catecholamines turnover or in corticosterone release (an index of the hypothalamus-pituitary-adrenal activity), which indicate the absence of neuroendocrine dependence on the kappa agonist. As has been proposed, this would suggest that the mu and the kappa receptor be regulated through different cellular mechanisms, as kappa agonists have a lower proclivity to induce dependence.     

Modifications of Ca2+ mobilization and noradrenaline release by S-nitroso-cysteine in PC12 cells

The effects of nitrogen monoxide (NO)-related compounds on cytosolic free Ca2+ concentrations ([Ca2+]i) and noradrenaline (NA) release in neurosecretory PC12 cells were investigated. The addition of S-nitroso-cysteine (SNC) stimulated [Ca2+]i increases from an intracellular Ca2+ pool continuously in a concentration-dependent manner. Other NO donors, which stimulate cyclic GMP accumulation, did not cause [Ca2+]i increases. After treatment with 0.2 mM SNC, transient increases in [Ca2+]i from the Ca2+ pool induced by caffeine were completely abolished. The addition of N-ethylmaleimide (NEM) caused sustained [Ca2+]i increases from the intracellular Ca2+ pool. Furthermore, caffeine did not stimulate further [Ca2+]i increases in PC12 cells pretreated with NEM. These findings suggest that SNC and NEM predominantly interact with a caffeine-sensitive Ca2+ pool. The addition of dithiothreitol (DTT) to 0.4 mM SNC-stimulated cells reduced [Ca2+]i to basal levels, and the addition of DTT to NEM-stimulated cells locked [Ca2+]i at high levels. The stimulatory effects of SNC but not NEM were not abolished by pretreatment with DTT. These findings suggest that modification of the oxidation status of the sulfhydryl groups on the caffeine-sensitive receptors by SNC or NEM regulates Ca2+ channel activity in a reversible manner. SNC did not stimulate NA release by itself but did inhibit ionomycin-stimulated NA release. In contrast, NEM stimulated NA release in the absence of extracellular CaCl2 and further enhanced ionomycin-stimulated NA release. Ca2+ mobilization by SNC from the caffeine-sensitive pool was not a sufficient factor, and other factors stimulating NA release may be negatively regulated by SNC.     

Changes in noradrenaline and histamine in monkey spinal cords traumatised by weight drop, compression and subsequent decompression

Levels of noradrenaline (NA) and histamine (H) in the spinal cord of monkeys at 8, 24 and 48 hr following 200 g/cm contusion injury, 50 g of compression injury at 8 hr and decompression for 16 and 40 hr following 8 hr of compression were studied in the traumatised and in an adjacent non-traumatised segment. The NA level doubled in the traumatised and non-traumatised segments at 8 hr contusion injury followed by a slow decline to control values at 24 and 48 hr of contusion injury. There was no change in NA content of the spinal cord segments at 8 hr of compression injury. Decompression for 16 hr following 8 hr of compression increased NA content of the traumatised segment. H levels decreased in the traumatised and non-traumatised segments at 24 and 48 hr of contusion injury. Compression for 8 hr elevated H in the traumatised and non-traumatised segments. On decompression H level was further increased in the traumatised segment.     

Presynaptic effects of neuropeptide Y on [3H]noradrenaline and [3H]acetylcholine release

The electrically evoked release of radioactivity from mouse vas deferens and rat hypothalamic slices preloaded with [3H]noradrenaline was measured. In addition the release of [3H]acetylcholine from longitudinal muscle strip of guinea-pig ileum was also measured. Neurochemical evidence has been obtained that neuropeptide Y (NPY), although it co-exists and is released with (-)-noradrenaline (NA), it behaves differently as far as its effect on presynaptic modulation of chemical neurotransmission is concerned. It exerts a frequency-dependent presynaptic inhibitory effect on noradrenaline release from mouse vas deferens but has no effect on the electrically evoked release of NA from rat hypothalamus. Unlike NA, NPY does not influence the release of [3H]acetylcholine from the longitudinal muscle strip of guinea-pig ileum and does not potentiate the presynaptic effect of NA. It seems very likely, that the inhibitory effect of NPY is mediated via receptors. Its action is concentration dependent. While exogenous noradrenaline inhibited the release of noradrenaline by 91%, the maximum inhibition reached with NPY was not higher than 60%, indicating that either the intrinsic activity of NPY is lower or much less axon terminals are equipped with NPY receptors. Peptide YY (PYY) also reduced the release of NA from mouse vas deferens.     

Diurnal variations in the catecholamine content in rat tissues. Effects of exogenous noradrenaline

Endogenous noradrenaline (NA) content of the interscapular brown adipose tissue (IBAT), and of the hypothalamus, as well as adrenaline (A) and NA content of the adrenals were measured in the morning and in the evening in rats treated with saline (controls) or with NA (1.6 mg kg-1 pp). NA content in IBAT and in hypothalamus of control animals varies diurnally. NA content in IBAT was significantly higher in the evening than in the morning. In the hypothalamus, these variations were different of those found in the IBAT. Exogenous NA applied both in the morning and in the evening increases significantly NA content in IBAT both in the morning and in the evening, but more in the evening. Unlike IBAT, NA content of the hypothalamus after NA administration does not change essentially. In the adrenal gland of control rats, A content only is changed during the day, being markedly lower in the evening. After NA injection both A and NA are not changed significantly.