Endogenous Norepinephrine Levels Research Articles

BRL 8242 (2-[2-benzimidazolyl]-amino-2-imidazoline dihydrochloride), a new inhibitor of dopamine-β-hydroxylase with antihypertensive activity

BRL 8242 (2-[2-benzimidazolyl]-amino-2-imidazoline dihydrochloride) was found to inhibit dopamine-β-hydroxylase in vitro and in vivo and to have antihypertensive activity. The effect on dopamine-β-hydroxylase in vitro was shown by inhibition of the conversion of phenylethylamine to phenylethanolemine, using enzyme extracted from rat adrenals. In vivo, BRL 8242 inhibited 3H-noradrenaline but not 3H-dopamine biosynthesis from 3H-L-dopa in rat brain. Furthermore, the compound lowered endogenous noradrenaline levels in both rat brain and heart whilst increasing the concentration of brain dopamine. In both metacorticoid hypertensive and normotensive rats, BRL 8242 lowered blood pressure. This response was dose related and correlated well with the reduction of endogenous noradrenaline in the tissues examined. It is therefore suggested that the inhibition of dopamine-β-hydroxylase by BRL 8242 may account for its blood pressure lowering activity.

Effects of a single administration of clozapine on mouse brain catecholamines.

Abstract The effects of clozapine on the accumulation and disappearance of 14C‐labelled catecholamines formed from 14C‐tyrosine, and on the endogenous levels of catecholamines have been studied in mouse brain. Rather low doses of clozapine increased noradrenaline accumulation and disappearance (from 2.5 and 0.16 mg/kg, respectively), whereas dopamine accumulation was only increased from 10 mg/kg and disappearance after 80 mg/kg. However, in the dosage interval of 1.25 to 5 mg/kg dopamine disappearance was decreased. Endogenous noradrenaline levels were decreased from 10 mg/kg in contrast to the dopamine levels which remained unchanged, except in the dosage interval 2.5 to 10 mg/kg, where they were elevated, at the same time at which dopamine disappearance was decreased. It is concluded that clozapine differs biochemically from the typical neuroleptics by changing the metabolism of noradrenaline in doses much lower than those influencing dopamine metabolism. It is suggested that this property together with the ability of clozapine to decrease dopamine disappearance in a certain dose range, could contribute to the unique psychopharmacological action of clozapine.

Endogenous levels of catecholamines in the rat myocardium following exposure to stress

Following exposure of male rats to irregular signalled footshock from which they could escape, the endogenous level of norepinephrine in the myocardium was significantly reduced. In atria the depletion of endogenous norepinephrine was significant following 1 day of stress. This significant depletion was maintained following 4 days of stress but began to return towards control levels by Day 10. A similar, but less pronounced pattern was seen with the ventricles. Little if any epinephrine was detected in both control and stress atria and ventricles. From the results presented it is postulated that irregular signalled footshock results in an inhibition of neuronal uptake.

α-MSH and MIF-I effects on catecholamine levels and synthesis in various rat brain areas

Attempts were made to find a biochemical correlate with previously observed behavioral alterations after administration of α-melanocyte-stimulating hormone (MSH) and MSH release-inhibiting factor (MIF-I). Brains of intact and hypophysectomized (hypox) rats were analyzed for endogenous catecholamine levels and the disappearance rate of endogenous norepinephrine (NE) after treatment with the tyrosine hydroxylase inhibitor α-methyl-para-tyrosine (AMPT). The studies undertaken show the following: (1) After the injection of MSH (100 μg/kg IP daily × 3) and AMPT, samples in different groups of intact and hypox rats were taken at 0, 1, 2, 4 and 6 hrs in 7 different brain areas. In the mid-brain area for the intact group of rats, the rate of disappearance of NE was faster and for the hypox rats it was slower than the rate for control rats not treated with the peptides. NE levels in the same area at time 0 were 11 percent lower than controls in hypox rats and unchanged in unoperated animals. (2) After the injection of MIF-I (20 mg/kg IP daily ×3) in similar experiments as with MSH, a reduced rate ( p<0.05) of NE disappearance for the first 4 hr and an increased rate ( p<0.05) of NE disappearance for the last 2 hr of the experiments occurred for both the intact and hypox rats in the mid-brain area where endogenous NE levels were lowered by 11 and 12 percent at 0 min. In no other brain areas were alterations in NE breakdown found in both the intact and hypox rat groups. Behavioral changes have been found previosly under similar experimental conditions in both intact and hypox rats. (3) Rates of dopamine disappearance in experiments similar to those described for NE disappearance indicated that in the striatal brain area no change was found in the intact rats after either MSH or MIF-I, whereas a decrease in DA disappearance was found for hypox rats during the six hour experimental period only after MSH. The results indicate that a correlation between behavioral changes, rates of disappearance and endogenous levels of NE in the mid-brain area may occur after MIF-I at the times examined but that a similar correlation for MSH did not appear likely.

Endogenous brain norepinephrine levels following bilateral olfactory bulb ablation

Changes in endogenous norepinephrine (NE) levels after bilateral olfactory bulb section have been found to occur in the rat brain. Since olfactory tract projections are confined to the ventral adrenergic pathway, and this pathway projects to the pyriform cortex, it was decided to examine the distribution of endogenous NE between the pyriform cortex and the remaining neocortex. It was demonstrated that significant reductions in NE content occurred in both brain regions, although the greater reduction occurred in the pyriform cortex. There were no significant changes in hypothalamic NE. It is concluded that sensory deprivation plus olfactory system damage induce specific changes in central function, which relate to noradrenergic pathways.

Neonatal 6-hydroxydopamine treatment: Noradrenaline levels and in vitro 3H-catecholamine synthesis in discrete brain regions of adult rats

Endogenous noradrenaline levels are elevated in medulla oblongata, mesencephalon, pons and thalamus of adult rats which had been treated with 6-hydroxydopamine on days 1, 2, 8 and 15 after birth. Levels in spinal cord, cerebellum, hippocampus/amygdala and cortex are depressed, whereas no significant changes are observed in striatum, hypothalamus and medulla spinalis. The rate at which medulla oblongata synthesizes tritiated noradrenaline and dopamine from tritiated tyrosine in vitro is markedly enhanced. No effect was apparent on catecholamine synthesis in hypothalamus. Tritiated noradrenaline synthesis, but not tritiated dopamine synthesis, in the cortex is depressed. These results support the view that neonatal 6-hydroxydopamine treatment causes a degeneration of noradrenaline nerve terminals in the cortex and induces an increase in noradrenaline terminals in the medulla oblongata.

EVIDENCE FOR EXTRANORADRENERGIC DOPAMINE‐β‐HYDROXYLASE ACTIVITY IN RAT SALIVARY GLAND

Abstract—Three days after superior cervical ganglionectomy of adult Sprague‐Dawley rats, the levels of endogenous norepinephrine, the uptake process for [3H]norepinephrine and the activity of tyrosine hydroxylase decreased 99 per cent in the ipsilateral salivary gland. In contrast, the activity of dopamine‐β‐hydroxylase and DOPA decarboxylase fell to 30 per cent of the activity of the contralateral innervated gland. Examination of the cofactor requirements, the characteristics of activation by cupric ion and the immunologic identity of this residual hydroxylase activity indicated that it was authentic dopamine‐β‐hydroxylase. The residual dopamine‐β‐hydroxylase in the denervated gland had the same subcellular distribution as the enzyme in the innervated salivary gland. Procedures that caused atrophy or hypertrophy of the acinar cells did not affect the total content of dopamine‐β‐hydroxylase in the denervated salivary gland. Chemical sympathectomy with 6‐hydroxy‐dopamine caused a 40 per cent decrement in the serum levels of dopamine‐β‐hydroxylase but a 30 per cent increase in its activity in the denervated salivary gland. Although denervation caused a complete loss of endogenous norepinephrine in the salivary gland, it resulted in only a 15 per cent decrement in the levels of endogenous octopamine and β‐phenylethanolamine, two other products of dopamine‐β‐hydroxylase.

Norepinephrine metabolism in the rat brain following acute and chronic administration of thyrotropin releasing hormone.

Synthetic thyrotropin releasing hormone (TBH) was administered to albino rats in order to determine the effects of this drug on norepinephrine-H3 metabolism in the brain. With the possible exception of a slight enhancement of release, acute or chronic administration of TRH had little effect on the disposition and metabolism of norepinephrine-H3 in rat brain. In addition, no significant changes were found in brain levels of endogenous norepinephrine, serotonin or dopamine following the injection of TRH. Thus, little evidence was found to support a possible relationship between the reported clinical antidepressant activity of TRH and its effects on norepinephrine metabolism in brain.

Alterations in turnover and endogenous levels of norepinephrine in cerebral cortex following electrical stimulation and acute axotomy of cerebral noradrenergic pathways

The turnover and endogenous levels of norepinephrine (NE) in the cerebral cortex (including the hippocampus) were measured after acute axotomy and electrical stimulation of the ascending NE pathways originating from the locus coeruleus. Acute unilateral axotomy of the dorsal NE pathway induces a small increase of NE in the cerebral cortex (ipsilateral vs. contralateral) and a decreased metabolism of NE (as estimated after synthesis inhibition by α-methyl-p-tyrosine). Electrical stimulation (20 Hz) of the locus coeruleus leads to a rapid decrease of NE levels to about 60% of the controls and new steady state levels of NE were reached in 7.5 min. After terminating the stimulation, the levels of NE in the cerebral cortex returned to normal within about 30 min. Electrical stimulation (20 Hz) of the locus coeruleus, after inhibition of NE synthesis, results in a biphasic decline of NE. The first phase is ended in about 2 min (30% decrease) after stimulation, the second phase persists for at least 30 min. The rate of decline of levels of NE in the cerebral cortex in the first phase is about 10 times higher than the rate of decline of the second phase. These results indicate that the level of NE in the cerebral cortex is in part dependent on the nerve impulse flow through the adrenergic fibres and are in favor of the concept of a multiple storage form for NE in the central nerve terminals.

Comparative Studies of Neurotransmitter Substances in the Maturing and Aging Central Nervous System of the Chicken

Publisher Summary This chapter focuses on some aspects of cholinergic and monoaminergic neurotransmission and the changes occurring during aging. Because the changes occurring during aging are frequently better explained if these changes are compared with early developmental changes, the entire life span was examined. One of the frequent functional characteristics of aging is the slowing of reflex activity, the appearance of tremor-like movements and the loss of short memory. All these phenomena may be attributed to the decline in central nervous system (CNS) neuronal integrative mechanisms with aging. The activities of acetylcholinesterase and choline acetyltransferase, the hydrolyzing and synthesizing enzymes of acetylcholine, were the indices used for cholinergic neurotransmission and endogenous levels of norepinephrine and 5-hydroxytryptamine were indices of monoaminergic neurotransmission. The changes in neurotransmission in the cerebral hemispheres with aging are of importance in view of the role of the cerebral cortex in memory phenomena.

Further evidence for the heterogeneous storage of noradrenaline in central noradrenergic terminals

The time course of noradrenaline disappearance has been estimated in the rat cerebral cortex after the injection of FLA 63, an inhibitor of the last step of noradrenaline synthesis. This drug (40 mg/kg) was shown to block 3H-noradrenaline formation from 3H-dopamine within 5 min after its administration. Endogenous levels of noradrenaline decreased in two distinct phases which may correspond to the amine utilization in two compartments, A and B. The compartment A (functional compartment) contained about 20% of the total noradrenaline stores. The turnover rate of noradrenaline in this compartment was estimated to be about 7 times that of noradrenaline in compartment B (main storage compartment). The total turnover rate of noradrenaline calculated from the biphasic decline of noradrenaline seen after FLA 63 was approximately 600 ng/g/h. The synthesis rate of noradrenaline was estimated on the basis of the initial accumulation (10 min) of this amine after monoamine oxidase inhibition by either pargyline (75 mg/kg) or pheniprazine (5 mg/kg) and was found to be 420 and 560 ng/g/h, respectively. The complementarity of the results concerning the rate of noradrenaline synthesis obtained by two different experimental approaches provides further support for the two compartment model of the noradrenaline stores in central noradrenergic terminals. Moreover the results reveal a very high turnover rate of noradrenaline in the “functional” compartment.

Evidence of adrenergic-cholinergic interaction in the central nervous system II. Dopamine and its analogues

The effects of dopamine (DA), 5-hydroxydopamine (5-OH-DA), and 6-hydroxydopamine (6-OH-DA) administered into the cerebro spinal fluid on choline acetylase (ChAc) activity, endogenous levels of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in the rat brain were studied. In vitro tests, showed that dopamine and 6-OH-DA at concentrations of 10 −2 to 10 −4 M significantly decreased ChAc activity. Chronic studies showed that both DA and 5-OH-DA activated ChAc whereas 6-OH-DA caused an initial decrease in the enzyme activity followed rapid recovery after 4 days. DA treatment increased the levels of NE and DA in the brain whereas 5-HT level was not significantly changed. 5-OH-DA treatment markedly reduced the levels of NE, increased the levels of 5-HT but did not significantly affect the DA level. 6-OH-DA treatment caused a significant reduction in NE, a small decrease in DA level, and no significant change in the level of 5-HT. The data showed interaction between the various monoamines and their effects on ChAc activity. These findings support the concept suggested in previous studies on the control of eating behaviour, of an adrenergic-cholinergic interaction in the central nervous system.

Effect of cyclic AMP on morphine analgesia tolerance and physical dependence.

ADENOSINE-3′,5′-MONOPHOSPHATE (cAMP) has often been suggested as a second messenger which mediates the action of a variety of hormones1. The presynaptic location of the cAMP system, and the demonstration of a cAMP dependent protein kinase in mammalian brain tissue, suggest a possible role for cAMP in the central nervous system2. It has been suggested, for example, that cAMP may participate in the secretion of acetylcholine3 and the hypophyseal releasing factors in the hypothalamus3. In vitro4 and in vivo5 studies indicate that some putative neurohormones increase cAMP synthesis by activating adenyl cyclase. The effect of cAMP on brain biogenic amines has also been studied. Shein et al.6 showed an increase in serotonin (5-HT) synthesis from tryptophan by cAMP in pineal culture. Tagliamonte et al.7 reported that injection of cAMP into the lateral ventricle of rats increases the 5-HT turnover in brain. Results obtained in our laboratory in mice (I. K. H., H. H. L. and E. L. W., unpublished results) indicate that cAMP decreases the endogenous level of cerebral norepinephrine (NE) and dopamine (DA) as well as the conversion of 14C-tyrosine into 14C-CA (catecholamines).

Neonatal sympathectomy by 6-hydroxydopamine in the rat: No effects on behavior but changes in endogenous brain norepinephrine

NEONATAL sympathectomy produced in young rats by repeated systemic injections of 6-hydroxydopamine (6-OHDA) had no effect upon several behavioral measures including open field activity, the learning and retention of an avoidance task or the emergence with maturation of sex linked activity differences in the open field. In comparison with control rats, at either 43 or 104 days of age, 6-OHDA treated animals showed increased levels of endogenous norepinephrine in the lower brainstem but decreased norepinephrine in the cerebral cortex. Hypothalamic norepinephrine contents were the same.

Biochemical basis of heart function. VI. Influence of cations on norepinephrine transport, storage, and synthesis in the isolated perfused rat heart.

The effects of Ca2+ (0–5 mM), Mg2+ (0–16 mM), K+ (0–20 mM), and Na+ (0–145 mM) on the uptake, subcellular distribution, and release of exogenously given 3H-norepinephrine were investigated in the isolated perfused rat heart. The uptake of 14C-tyrosine, the synthesis of 14C-catecholamines, and the endogenous levels of norepinephrine were also determined under these experimental conditions. The uptake of 3H-norepinephrine was markedly decreased on perfusing the hearts with media containing low concentrations of Na+. Addition of Ca2+ to the perfusion medium containing Na+ increased the uptake of 3H-norepinephrine while Mg2+ or K+ had no effect. Increasing the concentration of Na+ from 0 to 145 mM in the perfusion medium increased the 3H-label in the granular fraction and decreased it in the soluble fraction whereas Ca2+, Mg2+, or K+ did not show any action. The spontaneous release of 3H-label was not influenced by the presence or absence of Ca2+, Mg2+, or K+ in the medium. On the other hand, the absence of Na+ was found to accelerate the spontaneous release of 3H-label and this effect was further enhanced when Ca2+ was also omitted from the perfusion medium. Increasing the concentrations of Ca2+ or Na+ in the perfusion medium decreased the rate of synthesis of 14C-catecholamincs from 14C-tyrosine whereas Mg2+ and K+ showed no effect. Absence of Na+, but not of K+, Ca2+, or Mg2+, resulted in a decrease in the endogenous level of norepinephrine. The amount of newly synthesized 14C-catecholamines in the perfusate was more on perfusing the hearts with Ca2+-free or Na+-free medium. These results are consistent with the view that Na+ is required for storage as well as uptake of norepinephrine in the adrenergic nerve terminals in the heart. Ca2+ appears necessary for the optimal uptake of norepinephrine due to Na+ and has been shown to inhibit the spontaneous release of norepinephrine due to Na+ lack. In addition, Na+ and Ca2+ reduce the rate of synthesis of catecholamines in the adrenergic nerve endings in the heart.

Dopamine- -hydroxylase in the rat brain: developmental characteristics.

Abstract— A sensitive and specific assay for dopamine‐8‐hydroxylase (DBH) in the rat brain has been developed. The enzyme in the brain has requirements for cofactors and affinity for substrate similar to DBH in the adrenal medulla. DBH activity was demonstrable in the brain of the fetal rat at 15 days of gestation; there was an increase in DBH activity with maturation that preceded and paralleled the rise in levels of endogenous norepinephrine until 3 weeks after birth. There was a shift in the distribution of total DBH activity from the caudal to the rostral regions of the brain during development. In the adult brain, DBH was highly localized in the nerve terminals. Between 17 days of gestation and adult‐hood, there was 2300‐fold increase in the DBH activity that sedimented with sheared‐off nerve terminals.

Effects of amantadine hydrochloride on catecholamine metabolism in the brain of the rat

We have examined the effects of the cyclic amine, amantadine, on the metabolism of catecholamines in the rat. Large doses of the drug had minimal effects on cardiac norepinephrine stores, but produced small decreases in concentrations of norepinephrine in the brain, while having less effect on dopamine and no effect on serotonin. The drug altered the metabolism of previously intrathecally administered [ 3H]norepinephrine: there were small decreases of [ 3H]norepinephrine, but clear decreases of [ 3H]deaminated catechol metabolites and marked increases of [ 3H]normetanephrine for 1–6 hr, at times paralleling decreases in endogenous norepinephrine levels. Later, smaller increases of [ 3 H] deaminated-O- methylated products appeared. These metabolic changes were not due to inhibition of monoamine oxidase by this drug, as amantadine had no effect on the deamination of [ 14C]serotonin or [ 3H]norepinephrine even at high concentrations in vitro or doses in vivo. Amantadine decreased the retention by isolated nerve endings in vitro of previously intrathecally injected [ 3H]norepinephrine by a very small amount and competitively inhibited the initial uptake of [ 3 H]d,l- norepinephrine by nerve endings of whole brain, with a K i of approximately 1.5 × 10 −5 M. This inhibition of uptake was somewhat greater in the cerebral cortex than in the corpus striatum. There was much less inhibition of the uptake of [ 3H]dopamine in both regions. Thus, part of the action of this drug in Parkinson's disease may be due to inhibition of uptake and retention of catecholamines at central nerve terminals. However, since the doses required to produce changes in vivo were much higher than those used clinically, these findings may reflect non-specific or toxic effects of the drug.

Effect of angiotensin on noradrenaline-3H accumulation and synthesis in vivo.

The effect of slow intravenous infusion of angiotensin (0.017, 0.17, and 1.7 μg/min/100 g) on the endogenous noradrenaline (NA) level and on the accumulation and synthesis of NA-3H was studied in rat heart, spleen, and aorta. No significant changes in endogenous NA level were observed in rat aorta and heart after infusion of angiotensin for 1 h. In the spleen, only, a statistically significant lowering of NA was observed with 0.17 and 1.7 μg/min/100 g of angiotensin. The entry of NA-3H into nerve terminals was not affected by angiotensin, but the retention of the amine in a nonmetabolized state was significantly reduced. The angiotensin action varied from one organ to another, reflecting the differences in their capacity to accumulate and metabolize NA. Angiotensin potentiated the inhibitory effect of desmethylimipramine and ouabain on NA accumulation. The incorporation of tyrosine-3H into adrenergic nerves was not blocked by angiotensin infusion, while the amount of newly sythesized catecholamines-3H was significantly reduced. It is suggested that angiotensin modulates the exchange and retention of NA by adrenergic nerves, possibly through an ionic membrane mechanism.

Differential effects of D- and L-amphetamine on behavior and on catecholamine disposition in dopamine and norepinephrine containing neurons of rat brain

Summary We have compared the effects of D - and L -amphetamine on the disposition of intraventricularly administered [3H]norepinephrine and [3H]dopamine and on endogenous catecholamine in various regions of the rat brain. In behavioral experiments the effects of D - and L -amphetamine on locomotor activity and on compulsive gnawing behavior were also compared. In brain areas where norepinephrine is the predominant catecholamine, D -amphetamine but not its L -isomer inhibited [3H]catecholamine accumulation and lowered endogenous norepinephrine levels. In the corpus striatum, a dopaminergic brain region, both D - and L -amphetamine markedly reduced accumulation of [3H]catecholamines. D -Amphetamine was 10 times as potent as L -amphetamine in enhancing locomotor activity, but was only twice as active in evoking compulsive gnawing behavior. Our results suggest that brain norepinephrine is selectively involved in mediating amphetamine-induced locomotor stimulation while a dopaminergic component may participate in eliciting the compulsive gnawing syndrome.

Degeneration and regrowth of adrenergic nerve fibers in the rat peripheral tissues after 6-hydroxydopamine.

Histofluorescent and biochemical changes in the adrenergic nervous system were followed up in rat tissues after one single intravenous injection of a high dose of 100 mg/kg of 6-hydroxydopamine (6-OH-DA). This treatment results in the rapid disappearance of terminal and preterminal fibers in the iris, atria, and small arteries of rats, whereas endogenous noradrenaline pools of the heart are 95% depleted. The capacity of the adrenergic nerve to take up and accumulate tritiated noradrenaline is reduced proportionally to the reduction in endogenous noradrenaline levels. These changes are compatible with the concept of a complete sympathectomy induced by the specific toxic action of 6-OH-DA on the adrenergic fibers. This sympathectomy is not permanent, however, and numerous bundles of preterminal fibers start to grow in the iris and atria within 4 to 5 days following injection. Progressively, in the following weeks, these fibers distribute over the whole organ and give birth to terminal fibers which form a new adrenergic plexus in these tissues. A completely normal innervation is restored 2 to 3 months after administration of 6-OH-DA. The endogenous noradrenaline levels rise progressively in parallel to the development of the new plexus of fibers. Since a complete regeneration of the adrenergic innervation can be demonstrated in the weeks following injection of 6-OH-DA, it appears that this compound can selectively destroy the adrenergic terminal and preterminal fibers without causing a degeneration of the adrenergic ganglion cells.