Actions and interactions of norepinephrine and acetylcholine on sinus node potassium movements

The influence of norepinephrine and/or acetylcholine on K uptake of the guinea pig sinus node was investigated. Both "high" (10(-6) M) and "low" (10(-9) M) mediator concentrations were employed. The following results were obtained: 1) high concentration of norepinephrine increased K uptake; 2) high concentration of acetylcholine had a similar effect; 3) simultaneous exposure to both mediators did not lead to summation of the effects; 4) low concentration of norepinephrine depressed K uptake; 5) high concentration of acetylcholine overcame the inhibitory effect of the small concentration of norepinephrine; 6) 2-deoxy-D-glucose did not abolish the stimulating effect of acetylcholine on potassium uptake; and 7) strophanthidin abolished the stimulatory effect of norepinephrine, but not that of acetylcholine. The following conclusions are drawn: 1) both neuromediators in suitable concentrations increase K uptake in the sinus node; 2) the mechanism of such an increase is different, norepinephrine increasing the active and acetylcholine increasing the passive potassium transport; 3) a low concentration of norepinephrine depresses K uptake; and 4) when the two mediators are administered together, acetylcholine suppresses the action of norepinephrine on K transport.     

Effects of atrial natriuretic peptide and angiotensin III on the uptake and intracellular distribution of norepinephrine in medulla oblongata of the rat.

1. Ten micromoles angiotensin III decreased total 3H-norepinephrine uptake in medulla oblongata of the rat and 100 nM atrial natriuretic peptide increased it. These were the threshold concentrations for the peptides to modify the uptake of the amine. 2. A threshold concentrations (1 nM) of atrial natriuretic peptide reversed the effects produced by 10 microM angiotensin III on total 3H-norepinephrine uptake, but subthreshold angiotensin III concentrations failed to alter the effects produced by 100 nM atrial natriuretic peptide. 3. Angiotensin III, as well as atrial natriuretic peptide, modified only neuronal norepinephrine uptake and did not alter non-neuronal norepinephrine uptake. 4. Angiotensin III and atrial natriuretic peptide did not modify the intracellular distribution of norepinephrine in medulla oblongata.     

Regulation of Extracellular Dopamine by the Norepinephrine Transporter

Abstract: There is growing evidence of an interaction between dopamine and norepinephrine. To test the hypothesis that norepinephrine terminals are involved in the uptake and removal of dopamine from the extracellular space, the norepinephrine uptake blocker desmethylimipramine (DMI) was infused locally while the extracellular concentrations of dopamine were simultaneously monitored. DMI increased the extracellular concentrations of dopamine in the medial prefrontal cortex and nucleus accumbens shell but had no effect in the striatum. The combined systemic administration of haloperidol and the local infusion of DMI produced an augmented increase in extracellular dopamine in the cortex compared with the increase produced by either drug alone. This synergistic increase in dopamine overflow is likely due to the combination of impulse-mediated dopamine release produced by haloperidol and blockade of the norepinephrine transporter. No such synergistic effects were observed in the nucleus accumbens and striatum. Local perfusion of the α₂-antagonist idazoxan also increased the extracellular concentrations of dopamine in the cortex. Although the stimulation of extracellular dopamine by idazoxan and DMI could be due to the increased extracellular concentrations of norepinephrine produced by these drugs, an increase in dopamine also was observed in lesioned rats that were depleted of norepinephrine and challenged with haloperidol. This contrasted with the lack of an effect of haloperidol on cortical dopamine in unlesioned controls. These results suggest that norepinephrine terminals regulate extracellular dopamine concentrations in the medial prefrontal cortex and to a lesser extent in the nucleus accumbens shell through the uptake of dopamine by the norepinephrine transporter.     

Triiodothyronine binding and norepinephrine uptake in the heart and liver

Administration of norepinephrine to thyroidectomized rats activates sharply the [125I]triiodothyronine binding by heart mitochondria and liver nuclei. Epinephrine stimulates the binding by the heart mitochondria and decreases the intensity of this process in the liver and heart nuclei and liver mitochondria As compared to norepinephrine, adrenoxyl is weaker in activation of [125I] triiodothyronine binding by the heart mitochondria and stronger in intensification of binding by the liver nuclei. Physiological concentrations of thyroxine like adrenoxyl administered to intact animals 2h before investigations intensify the uptake of [3H] norepinephrine by sections of the auricles, myocardium and liver. Hyperthyroidization induces contrary changes inthe uptake of [3H] norepinephrine. Norepinephrine administration decreases sharply the uptake of [3H] norepinephrine by sections of the auricles and myocardium. The blocking of beta-adrenoreceptors weakens the uptake.     

Stimulatory Effect of Ascorbic Acid on Norepinephrine Biosynthesis in Digitonin-Permeabilized Adrenal Medullary Chromaffin Cells

The regulatory role of ascorbic acid in norepinephrine biosynthesis was studied using digitonin-permeabilized chromaffin cells. When permeabilized chromaffin cells were incubated with [3H]3,4-dihydroxyphenylethylamine ([3H]dopamine) in calcium-free medium, the amounts of radioactive dopamine and norepinephrine measured in the cell fraction were increased as a function of incubation time and dopamine concentration. Both the accumulation of dopamine and the formation of norepinephrine were shown to require the presence of Mg-ATP in the medium. These results indicate that the permeabilization of chromaffin cells by digitonin treatment does not disrupt the functions of chromaffin granules, including dopamine uptake, norepinephrine formation, and storage of these amines. Using this permeabilized cell system, the effect of ascorbic acid on the rates of dopamine uptake and hydroxylation was investigated. The formation of norepinephrine was stimulated by ascorbic acid at concentrations of 0.5-2 mM in the presence of Mg-ATP. By contrast, dopamine uptake was not affected by the presence or absence of ascorbic acid in the medium. These findings provide evidence that ascorbic acid may stimulate the conversion of dopamine to norepinephrine by increasing dopamine beta monooxygenase activity rather than by increasing the substrate supply of dopamine. These observations also suggest that the rate of norepinephrine biosynthesis in adrenal medullary cells may be regulated by the concentration of ascorbic acid within the cell cytoplasm.     

Ascorbic acid and Mg-ATP co-regulate dopamine beta-monooxygenase activity in intact chromaffin granules

Ascorbic acid and Mg-ATP were found to regulate norepinephrine biosynthesis in intact secretory vesicles synergistically and specifically, using the model system of isolated bovine chromaffin granules. Dopamine uptake into chromaffin granules was shown to be unrelated to the presence of Mg-ATP and ascorbic acid at external dopamine concentrations of 7.5 and 10 mM. Under these conditions of dopamine uptake, norepinephrine biosynthesis was enhanced 5-6-fold by Mg-ATP and ascorbic acid compared to control experiments with dopamine only. Furthermore, norepinephrine formation was enhanced approximately 3-fold by ascorbic acid and Mg-ATP together compared to norepinephrine formation in granules incubated with either substance alone. The action of Mg-ATP and ascorbic acid together was synergistic and independent of dopamine content of chromaffin granules as well as of dopamine uptake. The apparent Km of norepinephrine formation for external ascorbic acid was 376 microM and for external Mg-ATP was 132 microM, consistent with the larger amounts of cytosolic ascorbic acid and ATP that are available to chromaffin granules. Other physiologic reducing agents were not able to increase norepinephrine biosynthesis in the presence or absence of Mg-ATP. In addition, maximum enhancement of norepinephrine biosynthesis occurred only with the nucleotide ATP and the cation magnesium. The mechanism of the effect of ascorbic acid and Mg-ATP on norepinephrine biosynthesis was investigated and appeared to be independent of a positive membrane potential. The effect was also not mediated by direct action of ADP, ATP, or magnesium on the activity of soluble or particulate dopamine beta-monooxygenase. These data indicate that Mg-ATP and ascorbic acid specifically and synergistically co-regulate dopamine beta-monooxygenase activity in intact chromaffin granules, independent of substrate uptake. Although the mechanism is not known, the data are consistent with the possibility that the chromaffin granule ATPase mediates these effects.     

The uptake and subcellular distribution of aromatic amines in the brain of the rat

The hydroxylated phenylethylamines p-tyramine, m-tyramine, octopamine, metaraminol and norepinephrine were accumulated by homogenates of rat brain much more vigorously than β-phenethylamine or amphetamine. The affinity concentrations (K_m) for initial (5-min) uptake by homogenates of whole brain were 0.5, 3 and 6 μM for DL-norepine-phrine, p-tyramine and DL-octopamine, respectively. The uptake of these three hydroxylated compounds was much more vigorous in striatal tissue than in cortical tissue, and in both tissues the rate of uptake decreased in the sequence: norepinephrine > tyramine > octopamine. The uptake of these three substances was inhibited by reduced temperature, by lack of glucose, by CN- and DNP, and by desmethylimipramine, cocaine and ouabain. The uptake of norepinephrine and octopamine appeared to require Na⁺. Pretreatment of rats with reserpine or 6-hydroxydopamine decreased the ability of brain to take up norepinephrine or octopamine. Previously accumulated labelled phenylethylamines migrated in sucrose density gradients with a peak of radioactivity corresponding to an equilibrium position of catecholamine-containing nerve endings. The magnitude of the retention of [³H]amine in this synaptosornal peak decreased in the order: norepinephrine > octopamine > tyramine. The accumulated amines were released by sonic, osmotic and thermal stresses which disrupt neuronal membranes. The presence of a β-hydroxyl group appeared to protect amines from destruction by monoamine oxidase, presumably by virtue of uptake in presynaptic storage vesicles. During superfusion, tyramine and metaraminol appeared to displace [³H]norepinephrine from binding sites in brain slices.     

Reduced sympathetic neuronal uptake (uptake1) in a genetic model of desoxycorticosterone-NaCl hypertension

The effect of desoxycorticosterone (DOC)-NaCl treatment upon sympathetic neuronal uptake of norepinephrine (uptake1) was evaluated in strains of hypertension-resistant (SBN) and -prone (SBH) rats. Uninephrectomized animals were given either a placebo pellet sc and tapwater (untreated) or a 25-mg DOC pellet and 1% NaCl. Four weeks later, tail systolic pressure was significantly higher in DOC-NaCl SBH, 183 +/- 3 mm Hg, than SBN, 141 +/- 2 (P less than 0.01). [3H]Norepinephrine (NE) uptake was determined in heart slices of all four groups by incubation in Krebs buffer at 37 degrees C for 20 min at several concentrations. Preliminary studies confirmed that this is a measure of uptake1. Heart slices of DOC-NaCl-treated SBN and SBH rats had significantly reduced NE uptake at concentrations of 10-80 nM (P less than 0.01); there was no significant difference between SBN and SBH in this regard. Untreated SBH rats have been shown to have a defect in baroreflex regulation when normotensive. The results raise the possibility that the greater increase in arterial pressure caused by DOC-NaCl in SBH compared to SBN may be related to both the inborn difference in reflex function and an acquired reduction in inactivation of norepinephrine by sympathetic neuronal uptake.     

RAT BRAIN SYNAPTIC VESICLES: UPTAKE SPECIFICITIES OF [3H]NOREPINEPHRINE AND [3H]SEROTONIN IN PREPARATIONS FROM WHOLE BRAIN AND BRAIN REGIONS1

A fraction containing neurotransmitter storage vesicles was isolated from rat whole brain and brain regions, and the uptakes of [³H]norepinephrine and [³H]serotonin were determined in vitro. Norepinephrine uptake in vesicle preparations from corpus striatum was higher than in prep arations from cerebral cortex, and uptake in vesicles from the remainder (midbrain + brainstem + cerebellum) was intermediate. The K_m for norepinephrine uptake was the same in the three brain regions, but the regions differed in maximal uptake capacity by factors which paralleled total catecholamine concentration rather than content of norepinephrine alone. Intracisternal administration of 6-hydroxydopamine, but not of 5,6-dihydroxytryptamine, reduced vesicular norepinephrine uptake, and pretreat-ment with desmethylimipramine (which protects specifically norepinephrine neurons but not dopamine neurons from the 6-hydroxydopamine) only partially prevented the loss of vesicular norepinephrine uptake. These studies indicate that uptake of norepinephrine by rat brain vesicle preparations occurs in vesicles from norepinephrine and dopamine neurons, but probably not in vesicles from serotonin neurons. Uptake of serotonin by brain vesicle preparations exhibited time, temperature and ATP-Mg²⁺ requirements nearly identical to those of norepinephrine uptake. The affinity of serotonin uptake matched that of serotonin for inhibition of norepinephrine uptake, and the maximal capacity was the same for serotonin as for norepinephrine. Norepinephrine, dopamine and reserpine inhibited serotonin uptake in a purely competitive fashion, with K_is similar to those for inhibition of norepinephrine uptake. Whereas 5,6-dihydroxytryptamine treatment reduced synaptosomal serotonin uptake but not vesicular serotonin uptake, 6-hydroxydopamine reduced vesicular serotonin uptake in the absence of reductions in synaptosomal serotonin uptake. Thus, in this preparation, serotonin appears to be taken up in vitro into catecholamine vesicles, rather than into serotonin vesicles.     

SYNAPTIC VESICLES ISOLATED FROM RAT HEART: l-[3H]NOREPINEPHRINE UPTAKE PROPERTIES1

A fraction containing synaptic vesicles was isolated from rat heart by differential centrifugation, and the uptake of l-[³H]norepinephrine was studied in vitro., Uptake was highly dependent upon time and temperature, and was linear for 6 min at 30° or 4 min at 37°C. About 80% of the measured uptake required both ATP and Mg²⁺ and was inhibited by nanomolar concentrations of reserpine; no inhibition was obtained with cocaine. These properties are characteristic of storage vesicle uptake as opposed to synaptic membrane uptake. Uptake of norepinephrine was saturable and displayed a single K_m value of 2 μM. The uptake was completely stereospecific, as unlabeled dl-norepinephrine was less than half as effective as unlabeled l-norepinephrine in reducing uptake of l-[³H]norepinephrine. Norepinephrine uptake could be inhibited by various phenethylamines and indoleamines following the rank order: reserpine > harmaline > 5-hydroxytryptamine > dopamine > norepinephrine. The vesicle preparation also incorporated [³H]5-hydroxytryptamine and [³H]dopamine. 5-Hydroxytryptamine uptake displayed a K_m of 0.5 μM and a maximal uptake equivalent to that seen with norepineph-rine; dopamine uptake followed complex kinetics. Administration of reserpine in vivo or destruction of sympathetic neurons by long-term guanethidine treatment both eliminated the ability of the preparation to take up norepinephrine. Synaptic vesicles of cardiac sympathetic neurons thus resemble vesicles prepared from other central and peripheral catecholaminergic tissues; this method may be used readily to examine drug effects on rat heart synaptic vesicle function.     

Ascorbic acid regulation of norepinephrine biosynthesis in isolated chromaffin granules from bovine adrenal medulla

The effect of ascorbic acid on the conversion of dopamine to norepinephrine was investigated in isolated chromaffin granules from bovine adrenal medulla. Ascorbic acid was shown to double the rate of [3H]norepinephrine formation from [3H]dopamine, despite no demonstrable accumulation of ascorbic acid into chromaffin granules. The enhancement of norepinephrine biosynthesis by ascorbic acid was dependent on the external concentrations of dopamine and ascorbate. The apparent Km of the dopamine beta-hydroxylation system for external dopamine was approximately 20 microM in the presence or absence of ascorbic acid. However, the apparent maximum velocity of norepinephrine formation was nearly doubled in the presence of ascorbic acid. By contrast, the apparent Km and Vmax of dopamine uptake into chromaffin granules were not affected by ascorbic acid. Norepinephrine formation was increased by ascorbic acid when the concentration of ascorbate was 200 microM or higher; a concentration of 2 mM appeared to induce the maximal effect under the experimental conditions used here. The effect of ascorbic acid on conversion of dopamine to norepinephrine required Mg-ATP-dependent dopamine uptake into chromaffin granules. In contrast to ascorbic acid, other reducing agents such as NADH, glutathione, and homocysteine were unable to enhance norepinephrine biosynthesis. These data suggest that ascorbic acid provides reducing equivalents for hydroxylation of dopamine despite the lack of ascorbate accumulation into chromaffin granules. These findings imply the functional existence of an electron carrier system in the chromaffin granule which transfers electrons from external ascorbic acid for subsequent intragranular norepinephrine biosynthesis.     

Aerotolerant growth inAzospirillum brasilense induced by dihydroxyphenyl iron-binding compound

High concentrations of phosphate drastically inhibited the aerobic growth ofAzospirillum brasilense in liquid medium having a limiting concentration of combined nitrogen. No growth inhibition occurred if a high concentration of combined nitrogen was present. Aerobic growth occurred only in the presence of a very low amount of phosphate and this could be enhanced by adding norepinephrine. Addition of norepinephrine enhanced the O₂ uptake by cell suspensions by almost a factor of 3. All of the intermediates of the tricarboxylic acid metabolic cycle were actively oxidized in cell-free extracts and their rate of oxidation increased in the presence of norepinephrine.     

Dopamine and norepinephrine in the brains of hepatectomized rats

After complete hepatectomy in rats, there was a profound depletion of norepinephrine throughout the brain, whereas dopamine concentrations remained within the normal range. This suggests that in liver failure there is inhibition of norepinephrine synthesis at one of two processes subsequent to the formation of dopamine--that is, either the uptake of dopamine by vesicles or the hydroxylation of dopamine may be inhibited. However, other factors could contribute to the depletion of norepinephrine, including degeneration of its specific storage sites, displacement by false neurotransmitters, or an increased rate of catabolism. The present experiments do not allow a selection among these possibilities.     

High-Affinity Binding of [3H]Desipramine to Rat Brain: A Presynaptic Marker for Noradrenergic Uptake Sites

Abstract: High-affinity binding sites (apparent K _D= 1.5 nM) for [³H]desipramine have been demonstrated and characterized in membranes prepared from rat brain. The binding of [3H]desipramine was found to be saturable, reversible, heat-sensitive, sodium-dependent, and regionally distributed among various regions of the brain. High concentrations of [³H]desipramine binding sites were found in the septum, cerebral cortex, and hypothalamus, whereas lower concentrations were found in the medulla, cerebellum, and corpus striatum. A very good correlation ( r = 0.81, P < 0.001) was observed between the potencies of a series of drugs in inhibiting high-affinity [³H]desipramine binding and their capacity to block norepinephrine uptake into synaptosomes. In 6-hydroxydopamine-lesioned rats there was a marked decrease in [³H]norepinephrine uptake and [3H]desipramine binding with no significant alterations in either [³H]serotonin uptake or [³H]imipramine binding. These results suggest that the high-affinity binding of [³HJdesipramine to rat brain membranes is pharmacologically and biochemically distinct from the high-affinity binding of [3H]imipramine, and that there is a close relationship between the high-affinity binding site for [³H]desipramine and the uptake site for norepinephrine.     

Sympathetic Regulation of Glucose Uptake by the α1‐Adrenoceptor in Human Obesity

Objective: To investigate the involvement of α₁‐adrenoceptors in the sympathetic regulation of glucose uptake in human adipocytes. Research Methods and Procedures: Twenty‐four severely obese subjects participated in this study. The microdialysis technique was used to determine interstitial glucose concentration after stimulation of abdominal subcutaneous adipose tissue with the α₁‐agonist norfenefrine, the α_{1, 2}β‐agonist norepinephrine, and both agents in combination with the α₁‐antagonist urapidil. The effect of β‐adrenoceptor stimulation was assessed by orciprenaline. Changes in local blood flow were determined using the ethanol escape technique. Results: Both norfenefrine and norepinephrine induced a concentration‐dependent decrease of interstitial glucose concentration, with a greater decrease observed with norepinephrine. Preperfusion of adipose tissue with urapidil inhibited glucose decrease. The inhibition was overcome with high concentrations of norfenefrine and norepinephrine, respectively. Both adrenergic agents induced tachyphylaxia. Urapidil enhanced extracellular glucose level at high concentration. Blood flow decreased in the presence of norfenefrine and norepinephrine but increased in response to urapidil. The accelerated blood flow due to urapidil was counteracted by norepinephrine and norfenefrine. Orciprenaline decreased interstitial glucose concentration and increased nutritive blood flow. The observed changes in blood flow induced by adrenergic agents were not related to glucose uptake. Discussion: The stimulatory effect of the sympathetic nerves on glucose uptake in subcutaneous adipose tissue appears to be mediated by the α₁‐adrenoceptor. Norepinephrine enhances glucose entry into adipocytes independently of insulin action. In obese subjects with insulin resistance, the α₁‐adrenergic receptor may provide an important alternative pathway for glucose uptake.     

DEVELOPMENTAL CHARACTERISTICS OF PHENYLETHANOLAMINE AND OCTOPAMINE IN THE RAT BRAIN

Abstract— Phenylethanolamine and octopamine have been detected in the developing rat brain. Maximum concentration of these amines occurs early in development (16-17 days of gestation). At this developmental stage, the brain concentration of these amines is higher than that of norepinephrine. There is a sharp decline in the phenylethanolamine and octopamine concentrations on day 18 of gestation to approximately those of the adult. This decrease coincides with an increase in-monoamine oxidase activity of fetal brain, with an increase in the activities of tyrosine hydroxylase and dopamine-β-hydroxylase, and with the appearance of a saturable active uptake mechanism for norepinephrine. The administration of iproniazid, a monoamine oxidase inhibitor, to pregnant rats produced an increase in phenylethanolamine, octopamine and norepinephrine concentrations in the fetal rat brain at 16 days of gestation. p -Chlorophenylalanine, an inhibitor of phenylalanine hydroxylase, decreased fetal brain norepinephrine; this drug increased brain levels of phenylethanolamine and octopamine. The combined administration of iproniazid, p -chlorophenylalanine and phenylalanine to pregnant rats resulted in increased concentrations of octopamine and in a several-fold increase of phenylethanolamine levels; norepinephrine concentrations were sharply reduced. The possible significance of these findings in relation to pathological conditions such as phenylketonuria is discussed.     

Inhibition of potassium uptake by low concentrations of norepinephrine and dibutyryl cyclic AMP.

(1) The inhibition of potassium uptake by low concentration of norepinephrine (3 X 10-8 M) and of dibutyryl cyclic AMP (DBcAMP, 10 minus5 M) was studied in cardiac Purkyn? fibres. (2) The inhibitory action of DBcAMP on K uptake was abolished by the alpha blocker phentolamine. (3) Norepinephrine alone decreased K uptake and such inhibition was somewhat larger when DBcAMP was added. DBcAMP alone caused the usual decrease in K uptake but addition of norepinephrine abolished it. (4) The inhibition caused by norepinephrine reduced the increase in uptake caused by a high concentration (10 minus 3 M) of DBcAMP. (5) The inhibitory effect of norepinephrine was reversed in the presence of high concentration of magnesium (5.25 mM). (6) The inhibitory effect of norepinephrine was reversed by aminophylline and abolished by caffeine. (7) The inhibitory action of norepinephrine and BCcAMP was reversed or abolished, respectively, by imidazole. (8) It is concluded that the inhibition of potassium uptake by low concentration of DBcAMP is mediated by an alpha receptor mechanism and that possibly the "receptors" for this effect of norepinephrine and DBcAMP are located at different sites. Also it appears that DBcAMP may be acting at the membrane and that the action of methylxanthines and imidazole is not necessarily mediated only by a modification of phosphodiesterase activity.     

Synthesis of phosphatidylcholines in rat hepatocytes. Possible regulation by norepinephrine via an alpha-adrenergic mechanism

The effect of norepinephrine on phosphatidylcholine and phosphatidylethanolamine formation was investigated in short-term incubations with freshly isolated rat hepatocytes. In the presence of dl-propranolol, norepinephrine decreases the incorporation of [methyl-14C]choline into phosphatidylcholines in a dose-dependent manner. At a concentration of 50 microM, norepinephrine (plus 20 microM propranolol) inhibits the incorporation of [methyl-14C]choline over a wide range of choline concentrations (59% inhibition at 5 microM choline; 34% inhibition at 1 mM choline). Norepinephrine also decreases the incorporation rates of [1-14C]palmitic acid and [1-14C]oleic acid into phosphatidylcholines. The effect of norepinephrine is mediated through an alpha-adrenergic receptor. Norepinephrine (plus propranolol) does not decrease the uptake or phosphorylation rate of [methyl-14C]choline. Pulse-label and pulse-chase studies indicate that the conversion rate of phosphocholine to CDP-choline, catalyzed by CTP:phosphocholine cytidylyltransferase, is diminished by norepinephrine. In contrast with the inhibitory effect of norepinephrine on phosphatidylcholine synthesis, this hormone stimulates the formation of phosphatidylethanolamines from [1,2-14C]ethanolamine. This increased incorporation rate is apparent at ethanolamine concentrations above 25 microM. A combination of norepinephrine and propranolol decreases, however, the synthesis of phosphatidylcholines from [1,2-14C]ethanolamine. The results indicate that alpha-adrenergic regulation dissociates the synthesis of phosphatidylcholines from that of phosphatidylethanolamines.     

Electroconvulsive shock: sustained decrease in norepinephrine uptake affinity in a reserpine model of depression.

Electroconvulsive shock was given once daily for 9 consecutive days to chronically reserpinized mice. Shocked mice explored more actively than controls in an open field 18–20 hours after the last shock, suggesting a reversal of reserpine “depression”. The apparent K_m for the high-affinity active uptake of norepinephrine into crude synaptosome-rich homogenates of their cerebral cortices was higher. This suggested that repeated electroconvulsive shock lowered affinity for norepinephrine uptake. The V_max for norepinephrine uptake was also elevated, suggesting that the number of uptake sites had increased as well.     

Uptake and release of norepinephrine by rat brain tissue fractions prepared by ultrafiltration

Abstract— Isolated nerve endings were removed from crude homogenates of rat brain by Millipore filters of pore size 0-5-0-8 μm. Synaptosomes containing L-[³H]norepinephrine were incompletely removed from a non-ionic medium by 0-8 μm pore filters, but were nearly quantitatively removed from Krebs’medium, as demonstrated by density gradient subcellular distribution. In suspension, synaptosomes accumulated labelled norepinephrine. Catecholamine uptake was active; it was inhibited by ouabain, imipramine, cocaine, β-phenethylamine and amantadine. Bound norepinephrine was released by a high concentration of K⁺. Nerve endings trapped on ultrafilters behaved very similarly to synaptosomes suspended in Krebs’medium by actively accumulating norepinephrine and serotonin; they also possessed monoamine oxidase activity and norepinephrine was released from them by increased concentrations of K⁺. Ultrafiltration provides a simple, rapid method of preparing metabolically active synaptosomes.