Effect of ouabain and desipramine on the uptake and storage of norepinephrine and metaraminol

Receptors Involved in the Modulation of 5-Hydroxytryptamine Release in Bovine Cerebral Arteries

The uptake of [3H]5-hydroxytryptamine (5-HT) in bovine cerebral arteries was reduced by cocaine (1 μm), ouabain (100 μm), pretreatment with 6-hydroxydopamine (6-OHDA) (1·46 Mm, 10 min) and metitepine (1 μm). Electrically-stimulated tritium release was decreased by tetrodotoxin (0·8 μm), Ca-free medium, denervation with 6-OHDA (1·46 Mm, 10 min), 5-HT (10 μm), noradrenaline (1 μm) and the agonist of α2-adrenoceptors B-HT 920 (0·1 and 1 μm), enhanced by metitepine (1 μm, antagonists of presynaptic 5-HT1 receptors) and rauwolscine (1 μm, antagonist at α2-adrenoceptors, and also of 5-HT,1d receptors) and not affected by ketanserin (1 μm, antagonist of 5-HT2 receptors), methysergide (0·1 μm, antagonist of 5-HT1 and 5-HT2 receptors) and phentolamine (1 and 3 μm antagonist of α-adrenoceptors and less potent of 5-HT1 receptors). The inhibitory action of 10 μm 5-HT was partially reversed by phentolamine (3 μm) and cocaine (1 μm) and completely reversed by both metitepine (1 μm) and rauwolscine (1 μm). Ketanserin (1 μm), methysergide (0·1 μm) or phentolamine (1 μm) had no effect. Rauwolscine (1 μm) antagonized the inhibition induced by both noradrenaline (1 μm) and B-HT 920 (0·1 and 1 μm). 5-HT induced tritium release which was inhibited by cocaine (an antagonist of 5-HT3 receptors) and denervation with 6-OHDA. These results suggest that 5-HT is mainly accumulated in adrenergic nerve endings, that evoked [3H]5-HT release is modulated by 5-HT1-like receptors, but the participation of α2-adrenoceptors cannot be discounted, or more probably both types of receptors have features in common, and evoked [3H]5-HT release elicited by 5-HT may be partially mediated by activation of 5-HT3 receptors.

Regulation of GAP-43 expression by chronic desipramine treatment in rat cultured hippocampal cells

BACKGROUND

The importance of molecular and cellular changes in hippocampus in major depression and in the mechanism of action of antidepressants has become increasingly clear. Identification of novel targets for antidepressants in hippocampus is important to understanding their therapeutic effects.

METHODS

We used cDNA microarray to measure the expression patterns of multiple genes in primary cultured rat hippocampal cells. In situ hybridization and Northern and immunoblotting analysis were used to determine brain regional distribution and mRNA and protein levels of target genes.

RESULTS

After comparing hybridized signals between control and desipramine treated groups, we found that chronic treatment with desipramine increased the expression of six genes and decreased the expression of two genes. One of the upregulated genes is growth associated protein GAP-43. In situ hybridization revealed that desipramine increased GAP-43 gene expression in dentate gyrus but not other brain regions. Northern and immunoblotting analysis revealed that desipramine increased GAP-43 mRNA and protein levels. GAP-43 expression is also increased by another antidepressant, tranylcypromine, but not by lithium or haloperidol.

CONCLUSIONS

Because GAP-43 regulates growth of axons and modulates the formation of new connections, our findings suggest that desipramine may have an effect on neuronal plasticity in the central nervous system.

Effect of digitalis glycosides on norepinephrine release in the heart. Dual mechanism of action

The effect of ouabain on exocytotic and nonexocytotic norepinephrine release was investigated in perfused rat and guinea pig hearts. The overflow of endogenous norepinephrine and its neuronal metabolite 3,4-dihydroxyphenylethyleneglycol (DOPEG) was determined by high-pressure liquid chromatography. DOPEG served as the indicator of free axoplasmic norepinephrine concentrations. The overflow of the norepinephrine cotransmitter neuropeptide Y (NPY) was determined by radioimmunoassay and NPY was used as marker for exocytotic release. Electrical stimulation of the left stellate ganglion resulted in exocytotic norepinephrine release in rat and guinea pig hearts. Ouabain caused an increase in stimulation-induced norepinephrine overflow from rat and guinea pig hearts by 40%. However, overflow of NPY was decreased by 40%, indicating a reduced exocytosis rate. Ouabain increased both norepinephrine and NPY overflow, suggesting enhancement of exocytosis, when neuronal catecholamine uptake (uptake1) was blocked by desipramine or when presynaptic alpha 2-adrenoceptors were inhibited by yohimbine. The results demonstrate an interaction of ouabain with both calcium-dependent exocytosis and uptake1 of norepinephrine. Under calcium-free conditions, ouabain or potassium-free perfusate resulted in norepinephrine release from hearts when the axoplasmic norepinephrine concentration was elevated by the reserpinelike agent Ro 4-1284. This release was independent from neural activity, not accompanied by NPY overflow, and suppressed by the uptake1 blocker desipramine. These findings are in keeping with carrier-mediated nonexocytotic norepinephrine release that is caused by reversal of the transport direction of the uptake1 carrier. During myocardial ischemia nonexocytotic norepinephrine release was accelerated and enhanced by inhibition of Na+,K(+)-ATPase before ischemia. This study demonstrates the potential of digitalis glycosides to interact both with transmitter exocytosis and with the neuronal catecholamine transport system by Na+,K(+)-ATPase inhibition. Interaction with the catecholamine transport system involves both inhibition of norepinephrine inward transport and induction of norepinephrine outward transport, resulting in nonexocytotic norepinephrine release.

Octopamine uptake and metabolism in the insect nervous system

Several insect tissues were examined for their ability to take up octopamine in the presence and absence of sodium ions. The cockroach Malpighian tubules, ovary, and ventral nerve cord showed the highest level of sodium-dependent uptake. The adult firefly lantern exhibited substantial sodium-independent uptake. Some of these tissues were also examined for their ability to metabolize octopamine by N-acetylation. Measurable N-acetyltransferase activity was present in the cockroach ventral nerve cord, tobacco hornworm CNS, and firefly light organ. N-Acetylation is proposed to be the major metabolic pathway for octopamine in the cockroach (Periplaneta americana) nervous system. Several classes of compounds, including octopamine receptor agonists, tricyclic antidepressants, amphetamines, chloroethylbenzylamines, and some experimental insecticides, were tested for their ability to inhibit octopamine uptake and metabolism. The sodium-insensitive component of uptake was not inhibited by most compounds tested, but the sodium-sensitive component was strongly inhibited by xylamine, N-ethyl-N-chloroethyl-o-bromobenzylamine, and their aziridinium ions (60-100%). These compounds also effectively inhibited N-acetyl-transferase (IC50 values at or below 1 microM). Other good inhibitors of N-acetyltransferase included desipramine, synephrine, and an experimental insecticide, CGA 132427. Formamidine pesticides had limited effect on both processes, and neither action seems likely to be involved in their octopaminergic actions in vivo. Cocaine was unique in stimulating N-acetyltransferase activity. When inhibition of sodium-sensitive uptake is compared with inhibition of N-acetyltransferase in the cockroach ventral nerve cord, two groups of inhibitors are discernible. Type 1 compounds inhibit uptake without an effect on N-acetyltransferase, whereas type 2 compounds inhibit both processes. These results suggest a functional linkage between the uptake and acetylation of octopamine.

[3H]5-hydroxytryptamine uptake and release in cat cerebral arteries

1. Field electrical stimulation induced tritium release from cat cerebral arteries preincubated with [3H]serotonin (5-HT). 2. This release was markedly reduced by tetrodotoxin (0.8 microM), B-HT 920 (1 microM), denervation with 6-OH-dopamine (6-OHDA) and OCa2+, and increased by phentolamine (1 microM) and phorbol 12,13-dibutyrate (1 and 3 microM). 3. 5-HT (10 and 100 microM) and NA (0.1, 1 and 10 microM) caused concentration-dependent tritium release in control arteries, but not in those denervated with 6-OHDA. 4. [3H]5-HT uptake was greatly reduced by preincubation of arteries with cocaine (10 microM), ouabain (100 microM) or denervation with 6-OHDA. 5. 5-HT did not amplify contractions elicited by noradrenaline (NA) in middle cerebral arteries. 6. These data indicate: (1) 5-HT is mainly accumulated in adrenergic nerve endings; (2) 5-HT release is modulated by presynaptic alpha 2-adrenoceptors; (3) protein kinase C of perivascular adrenergic nerve endings participates in 5-HT release, and (4) 5-HT did not amplify NA responses.

Diuretic and natriuretic effect of a brain soluble fraction that inhibits neuronal Na+,K(+)-ATPase

The separation by Sephadex G-50 of two subfractions, peak I and II, from the brain soluble fraction has been previously described. These fractions were able to stimulate and inhibit synaptosomal membrane Na+,K(+)-ATPase, respectively (Rodríguez de Lores Arnaiz and Antonelli de Gómez de Lima, Neurochem. Res. 11, 933-948, 1986). Experimental evidence indicates that the alteration of Na+,K(+)-ATPase activity may result in changes of renal and cardiovascular parameters. In the present study, we have analyzed the effect of peak I and II fractions prepared from rat cerebral cortex on water and sodium excretion and on heart rate and arterial pressure in normotensive anesthetized rats. It was observed that water and sodium excretion were not modified by the administration of peak I fraction but that they were increased by peak II fraction. The cardiovascular parameters were not significantly modified by either of the fractions. The results indicate that brain soluble factor (s) which is (are) present in peak II fraction may modify some aspects of renal physiology after systemic administration.

Effects of ouabain on 86Rb-uptake, 3H-5-HT-uptake and aggregation by 5-HT and ADP in human platelets

In the search of sensitive models for actions of digitalis-like substances on intact cells or tissues, the effects of ouabain on human platelets were investigated. In a concentration-dependent manner ouabain 10(-8)-10(-4) M inhibited Na+-K+-ATPase activity measured as uptake of 86Rubidium (86Rb), with about 90% inhibition of the total uptake at ouabain greater than or equal to 10(-6) M. An almost identical concentration-effect curve was found for platelet uptake of 3H-serotonin (3H-5-HT). The platelet shape change reaction to exogenous 5-HT (1 X 10(-6) M) was suppressed by ouabain (10(-8)-10(-4) M) in a concentration-dependent manner, but with no clear maximum effect within the range tested. Aggregation induced by adenosine-di-phosphate (ADP 2 X 10(-6) M) was enhanced by ouabain 10(-8)-10(-6) M. At the highest concentration tested the rate of aggregation was increased by 31% and the change in light transmission by 54%. At low concentrations (less than 10(-9) M) of ouabain, there was a tendency towards increased aggregation as well as increased uptake of 86Rb, which may be a parallel to observations of positive inotropic effects of low concentration of glycosides, which do not inhibit Na+-K+-ATPase. The results show that human platelets can be used as a model tissue for studying effects of cardiac glycosides. This suggests that it may be useful for further investigations of the biological effects of agents with a similar effect profile, e.g. endogenous digitalis-like substances.

Acute effects of digoxin on total systemic vascular resistance in congestive heart failure due to dilated cardiomyopathy: a hemodynamic-hormonal study

The effects of the digitalis glycosides on systemic vascular resistance (SVR) in patients with congestive heart failure (CHF) are controversial. Most investigators report a reduction in total SVR, an action that has been attributed primarily to withdrawal of elevated sympathetic tone. Direct proof of this hypothesis is lacking, however, and the roles played by the renin-angiotensin-aldosterone and vasopressin systems have not been fully explored. Moreover, in several studies of patients with CHF, SVR did not decrease after the administration of digitalis. To clarify these issues, the hemodynamic and hormonal effects of digoxin were correlated in 11 normotensive men in sinus rhythm with CHF due to dilated cardiomyopathy. Patients were evaluated at rest and during submaximal exercise before and 6 hours after the intravenous infusion of 1.0 mg of digoxin (mean serum concentration 1.7 ng/ml). With digoxin therapy, heart rate, pulmonary wedge pressure and right atrial pressure declined and cardiac output increased. Although vasopressin was unchanged, both plasma norepinephrine concentrations and plasma renin activity decreased, the reduction in norepinephrine correlating with the increase in cardiac output. Despite these hemodynamic and hormonal effects, there was no change in total SVR at rest or during exercise. It is concluded that the improvement in cardiac function with digoxin in this patient group was a result of the inotropic properties of the drug, without an associated reduction in impedance. The failure of total SVR to decrease despite decreases in plasma norepinephrine levels and plasma renin activity might be explained by concomitant digitalis-induced vasoconstriction, impaired ability of arterioles to dilate in CHF, or offsetting alterations in other vasoactive hormone systems.

Contribution of the sympathetic nervous system to the hypertensive effect of a high sodium diet in stroke-prone spontaneously hypertensive rats

In stroke-prone spontaneously hypertensive rats (SHRSP) plasma norepinephrine levels and vascular reactivity to norepinephrine are increased and intravascular volume is reduced during the developmental phase of hypertension. Since the accelerated rise in blood pressure following sodium-loading in SHRSP cannot be attributed to the volume-retaining properties of sodium, the effects of an increased dietary intake of sodium on biochemical parameters of sympathetic vascular tone were investigated. The following results were obtained. First, the increased reactivity of vascular smooth muscle was further augmented in sodium-treated SHRSP; the degree of supersensitivity was positively correlated to the plasma sodium concentration. After blockade of the neuronal uptake by 30 microM cocaine, no difference in vascular reactivity to norepinephrine was detected between SHRSP on a normal and SHRSP on a high-sodium diet. Second, the inactivation of norepinephrine by the neuronal uptake was impaired in rats on a high-sodium diet, the impairment being more pronounced in SHRSP than in Wistar-Kyoto (WKY) rats. This decreased inactivation could be expected to cause higher concentrations of the neurotransmitter at the receptor site if the transmitter release from the nerve ending remains constant. Third, the release of norepinephrine and epinephrine into the plasma was increased in sodium-loaded SHRSP but not in sodium-loaded WKY. Cold exposure exaggerates these differences between normotensive and hypertensive rats. These findings suggest that a high-sodium intake modifies the transmission of sympathetic impulses at the level of the nerve terminal in both WKY and SHRSP. In the normotensive rats, moderate impairment of norepinephrine inactivation, however, was balanced by an appropriate reduction in central sympathetic discharge following sodium-loading. In the hypertensive rats, the peripheral disturbance in norepinephrine inactivation due to sodium-loading was obviously not balanced by an adequate withdrawal of central sympathetic discharge. The resultant hemodynamic change was a further increase in the sympathetically mediated vasoconstriction, which is regarded as at least one of the main mechanisms of the sodium-dependent acceleration of hypertension in SHRSP.

Effects of nifedipine on potassium-induced contraction and noradrenaline release in cerebral and extracranial arteries from rabbit

The present study was designed to evaluate the effects of the calcium antagonist nifedipine on potassium-evoked contractions and release of noradrenaline from sympathetic nerves in rabbit basilar and facial arteries. Contractions were measured isometrically in a small volume organ bath. While noradrenaline (NA) produced strong contractions in facial arteries, the majority of the basilar arteries responded only to the highest concentrations of NA employed (greater than 10 microM) with weak contraction. Prazosin (1 microM) and phentolamine (1-10 microM) effectively antagonized the responses to NA in both types of vessel. In contrast, contractions evoked by potassium (K+, 124 mM) were only slightly reduced by the alpha-adrenoceptor blocking agents, indicating that the participation of endogenous NA in maintaining the contractile response to K+ is either small or negligible in the vessel types studied. Nifedipine concentration-dependently inhibited K+-induced contractions in basilar and facial arteries, the former being significantly more affected as evidenced by the maximum inhibitions (approximately 80% compared to approximately 60%) and IC50 values (approximately 10 nM vs. approximately 30 nM). A combination of nifedipine (0.3 microM) and prazosin (1 microM) or phentolamine (1 microM) further suppressed the K+-evoked contractile response in facial arteries, but failed to do so in basilar arteries, when compared with the effect of nifedipine alone. The depressant effect of the alpha-adrenoceptor blockers was, however, still obtainable after reserpine treatment of the facial artery in vitro. Fluorescence histochemical demonstration of noradrenaline revealed a dense network of adrenergic nerve fibres in the walls of the basilar and facial artery. The vessels were also shown to accumulate 3H-NA and release it upon depolarization with K+. The uptake and subsequent release of 3H-NA were significantly reduced by desipramine (10 microM). Nifedipine (0.3-3.0 microM) failed to alter the K+-evoked 3H-NA efflux from sympathetic nerves in neither of the two vessel types. It may be concluded that nifedipine effectively inhibits K+-evoked contractions in isolated basilar and facial arteries from rabbit without interfering with nerve-mediated NA release. Possible explanations for this selective effect of nifedipine on muscle contraction are discussed.

Effects of sympathectomy on the in vitro alpha and beta-responses of the parotid gland

Amylase and K+ resease were measured in slices obtained from innervated and sympathetically denervated rat parotid glands. Amylase release induced by noradrenaline was found to be increased after chronic denervation. The postjunctional component of supersensitivity to noradrenaline was evidenced by an increase in the maximal response to this agonist. The maximal response of denervated glands was blocked by propranolol 10(-5) M. On the other hand, chronic denervation did not modify the alpha-adrenoceptor-mediated response, K+ release, either in the presence or in the absence of ouabain. It is concluded that, after sympathetic denervation, postjunctional supersensitivity develops for the beta-adrenoceptor-mediated but not for the alpha-adrenoceptors-mediated effects of noradrenaline.

Evidence for participation of catecholamines in cardiac action of ouabain: positive chronotropic effect

1 The shortening of cycle length (=positive chronotropic effect) by ouabain produced in isolated spontaneously beating atria of the guinea-pig was analyzed.2 The action of ouabain was dose-dependent; threshold response was seen at 1 x 10(-7) M, and maximal response occurred at 4 x 10(-7) M. The half-time of the ouabain effect was about 20 minutes.3 The positive chronotropic effect of ouabain was reduced to 40% by beta-adrenoceptor blockade (3.3 x 10(-9) M propranolol) or by reserpine-depletion of catecholamines. Incubation of reserpine-treated atria with noradrenaline partially restored the action of ouabain.4 The effect of ouabain was greatly dependent upon the calcium concentration. The optimal calcium level was 2.5 x 10(-3) M. Calcium and ouabain acted synergistically.5 Increasing calcium concentrations inhibited the positive chronotropic effect of noradrenaline in a manner similar to increasing ouabain concentrations.6 A hypothesis is proposed which explains the chronotropic effect of ouabain on the basis of two mechanisms: (1) increase of the catecholamine concentration affecting the pacemaker; (2) mobilization of calcium, i.e. increase of the biologically effective intracellular calcium level.

The effects of changes in ionic environment and modification of adrenergic function on the vascular responses to sympathomimetic amines

The responses to each of four sympathomimetic amines: noradrenaline 200 ng, octopamine 50 μg, metaraminol 20 μg and tyramine 100 μg were studied in the perfused rat mesentery preparation. Perfusion with Ca2+- and Mg2+-free solutions potentiated the responses to all four amines compared with control responses obtained during normal Krebs perfusion. Under perfusion conditions using either normal or Ca2+- and Mg2+-free Krebs solution, nialamide and reserpine retained their characteristic effects on the responses to each amine. Cocaine and desipramine abolished the responses to tyramine but potentiated those to noradrenaline and metaraminol under all perfusion conditions. The responses to each of the amines were only antagonized by ouabain when Ca2+ ions were present in the perfusion solution. It is concluded that perfusion with Ca2+- and Mg2+-free solution interferes with the normal uptake mechanisms occurring in the adrenergic neuron.