Inhibitory Effect Of Desipramine Research Articles

GluN2B-containing NMDA receptors as possible targets for the neuroprotective and antidepressant effects of fluoxetine

Accumulating evidence has indicated the involvement of glutamatergic neurotransmission in the pathophysiology of excitotoxicity and in the mechanism of action of antidepressants. We have previously shown that tricyclic desipramine and the selective serotonin reuptake inhibitor fluoxetine inhibit NMDA receptors (NMDARs) in the clinically relevant, low micromolar concentration range. As the different subtypes of NMDARs are markedly different in their physiological and pathological functions, our aim was to investigate whether the effect of antidepressants is subtype-specific.Using whole-cell patch-clamp recordings in rat cortical cell cultures, we studied the age-dependence of inhibition of NMDA-induced currents after treatment with desipramine and fluoxetine, as the expression profile of the NMDAR subtypes changes as a function of days in vitro. We also investigated the inhibitory effect of these antidepressants on NMDA-induced currents in HEK 293 cell lines that stably expressed rat recombinant NMDARs with GluN1a/GluN2A or GluN1a/GluN2B subunit compositions.The inhibitory effect of desipramine was not age-dependent, whereas fluoxetine displayed a continuously decreasing inhibitory profile, which was similar to the GluN1/GluN2B subtype-selective antagonist ifenprodil. In HEK 293 cells, desipramine equally inhibited NMDA currents in both cell lines, whereas fluoxetine showed an inhibitory effect only in cells that expressed the GluN1/GluN2B subtype.Our data show that fluoxetine is a selective inhibitor of GluN2B-containing NMDARs, whereas desipramine inhibits both GluN1/GluN2A and GluN1/GluN2B subtypes. As the clinical efficacy of these drugs is very similar, the putative NMDAR-associated therapeutic effect of antidepressants may be mediated only via inhibition of the GluN2B-containing subtype. The manifestation of the GluN1/GluN2B-selectivity of fluoxetine suggests the neuroprotective potential for this drug in both acute and chronic neurodegenerative disorders.

The effects of desmethylimipramine on cyclic AMP-stimulated gene transcription in a model cell system

The present study utilised an in vitro cell model of the cAMP signalling pathway to investigate the actions of desipramine (DMI) and other psychoactive agents on cAMP-driven gene transcription. The model comprised CHOβ 2 SPAP cells; Chinese hamster ovary cells expressing human β 2 adrenoceptors and a secreted placental alkaline phosphatase (SPAP) reporter gene with multiple cAMP response elements (CREs) in its promoter region. SPAP assays showed DMI to inhibit isoprenaline or forskolin-enhanced gene transcription in a time and concentration-dependent manner (IC 50 = 16.6 ± 2.0 μM after 18 h). This effect of DMI was not dependent upon activity at the levels of the β 2 receptor, cAMP accumulation or phosphorylation of the transcription factor, cAMP response element binding protein (CREB). The inhibitory effects were maintained in the presence of DMI for at least 3 weeks and were mimicked by exposure to norfluoxetine (the major metabolite of fluoxetine; IC 50 = 7.2 ± 1.8 μM) and the neuroleptics, chlorpromazine and clozapine, all at a concentration of 10 μM. Amphetamine (10 μM, 18 h) enhanced SPAP gene transcription. Ca 2+ imaging experiments ruled out an inhibitory effect of DMI on Ca 2+ influx as concluded by previous studies. The results suggest a molecular target for DMI that lies downstream of CREB phosphorylation. Whether the inhibitory action of DMI is common to naturally expressed CRE-driven genes involved in adaptive responses to antidepressants in vivo remains to be determined.

Different Effects of Desipramine on Bufuralol 1"-Hydroxylation by Rat and Human CYP2D Enzymes

Inhibitory effects of desipramine (DMI) on rat and human CYP2D enzymes were studied using bufuralol (BF) 1''-hydroxylation as an index. Inhibition was examined under the following two conditions: 1) DMI was co-incubated with BF and NADPH in the reaction mixture containing rat or human liver microsomes or yeast cell microsomes expressing rat CYP2D1, CYP2D2 or human CYP2D6 (co-incubation); 2) DMI was preincubated with NADPH and the same enzyme sources prior to adding the substrate (preincubation). When either rat liver microsomes or recombinant CYP2D2 was employed, the preincubation with DMI (0.3 microM) caused a greater inhibition of BF 1''-hydroxylation than the co-incubation did, whereas BF 1''-hydroxylation by rat CYP2D1 was not markedly affected under the same conditions. The inhibitory effect of DMI on BF 1''-hydroxylation by human liver microsomal fractions or recombinant CYP2D6 was much lower than that on the hydroxylation by rat liver microsomes or CYP2D2. Kinetic studies demonstrated that the inhibition-type changed from competitive for the co-incubation to noncompetitive for the preincubation in the case of CYP2D2, whereas the inhibition-type was competitive for both the co-incubation and the preincubation in the case of CYP2D6. Furthermore, the loss of activity of rat CYP2D2 under the preincubation conditions followed pseudo-first-order kinetics. Binding experiments employing the recombinant enzymes and [(3)H]-DMI revealed that CYP2D2 and CYP2D6 were the only prominent proteins to which considerable radioactive DMI metabolite(s) bound. These results indicate that rat CYP2D2 biotransforms DMI into reactive metabolite(s), which covalently bind to CYP2D2, resulting in inactivation of the enzyme. In contrast, human CYP2D6 may also biotransform DMI into some metabolite(s) that covalently bind to CYP2D6, but that do not inactivate the enzyme.

Effect of desipramine on Ca 2+ levels and growth in renal tubular cells

The in vitro effect of desipramine on renal tubular cell is unknown. In Madin–Darby canine kidney (MDCK) cells, the effect of desipramine on intracellular Ca 2+ concentration ([Ca 2+] i) was measured by using fura-2. Desipramine (>25 μM) caused a rapid and sustained rise of [Ca 2+] i in a concentration-dependent manner (EC 50=50 μM). Desipramine-induced [Ca 2+] i rise was prevented by 40% by removal of extracellular Ca 2+ but was not altered by L-type Ca 2+ channel blockers. In Ca 2+-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca 2+-ATPase, caused a monophasic [Ca 2+] i rise, after which desipramine failed to release more Ca 2+; in addition, pretreatment with desipramine partly decreased thapsigargin-induced [Ca 2+] i increase. U73122, an inhibitor of phospholipase C, did not change desipramine-induced [Ca 2+] i rise. Incubation with 10–100 μM desipramine enhances or inhibits cell proliferation in a concentration- and time-dependent manner. The inhibitory effect of desipramine on proliferation was not extracellular Ca 2+-dependent. Apoptosis appears to contribute to desipramine-induced cell death. Together, these findings suggest that desipramine increases baseline [Ca 2+] i in renal tubular cells by evoking both extracellular Ca 2+ influx and intracellular Ca 2+ release, and can cause apoptosis.

Inhibition of G protein-activated inwardly rectifying K+ channels by various antidepressant drugs.

G protein-activated inwardly rectifying K+ channels (GIRK, also known as Kir3) are activated by various G protein-coupled receptors. GIRK channels play an important role in the inhibitory regulation of neuronal excitability in most brain regions and the heart rate. Modulation of GIRK channel activity may affect many brain functions. Here, we report the inhibitory effects of various antidepressants: imipramine, desipramine, amitriptyline, nortriptyline, clomipramine, maprotiline, and citalopram, on GIRK channels. In Xenopus oocytes injected with mRNAs for GIRK1/GIRK2, GIRK2 or GIRK1/GIRK4 subunits, the various antidepressants tested, except fluvoxamine, zimelidine, and bupropion, reversibly reduced inward currents through the basal GIRK activity at micromolar concentrations. The inhibitions were concentration-dependent with various degrees of potency and effectiveness, but voltage- and time-independent. In contrast, Kir1.1 and Kir2.1 channels in other Kir channel subfamilies were insensitive to all of the drugs. Furthermore, GIRK current responses activated by the cloned A1 adenosine receptor were similarly inhibited by the tricyclic antidepressant desipramine. The inhibitory effects of desipramine were not observed when desipramine was applied intracellularly, and were not affected by extracellular pH, which changed the proportion of the uncharged to protonated desipramine, suggesting its action from the extracellular side. The GIRK currents induced by ethanol were also attenuated in the presence of desipramine. Our results suggest that inhibition of GIRK channels by the tricyclic antidepressants and maprotiline may contribute to some of the therapeutic effects and adverse side effects, especially seizures and atrial arrhythmias in overdose, observed in clinical practice.

Pharmacological characterization of N,N-dimethyl-2-(2-amino-4-methylphenyl thio)benzylamine as a ligand of the serotonin transporter with high affinity and selectivity.

Serotonin transporter has a key-role in regulation of serotoninergic function, and is involved in numerous neurodegenerative and psychiatric disorders. To obtain an efficient radioactive ligand allowing the study of this transporter in vitro and in vivo, we synthesized a new diphenyl sulfide derivative, N,N-dimethyl-2-(2-amino-4-methylphenylthio)benzylamine or MADAM. We present here extensive pharmacological characterization of this compound. [3H]MADAM bound to serotonin transporters with a very high affinity in vitro on rat cortical membranes, at least 2 times better than the most commonly used radioactive probes (Kd, 60 pM; Bmax, 543 fmol/mg of protein). Competition studies showed few inhibitory effect of nisoxetine (Ki = 270 nM), no inhibitory effect of desipramine or 1-[2-(diphenylmethoxy) ethyl]-4-(3-phenylpropyl)piperazine (GBR 12935) (Ki >1000 nM), and strong effect of paroxetine (Ki = 0.32 nM) and citalopram (Ki = 1.57 nM). Therefore, MADAM has around 1000-fold better selectivity for the serotonin transporter than for other transporters. Autoradiographic studies both on rat and postmortem human brain slices demonstrated that the distribution of [3H]MADAM parallels the localization of serotonin transporters and is prevented by known inhibitors of them. The high affinity and selectivity of [3H]MADAM for the serotonin transporter show that it is very valuable for studies using in vitro approaches. The high selectivity and low nonspecific binding of [3H]MADAM on the postmortem human brain, together with preliminary in vivo results with [11C]MADAM, is a new argument for future use of this ligand in in vivo studies of the distribution, pharmacology, and pathophysiology of the serotonin transporter in the human brain with positron emission tomography.

Activation of a renin–angiotensin system in ischemic cardiac sympathetic nerve endings and its association with norepinephrine release

We had reported that in the ischemic heart, locally formed bradykinin (BK) and angiotensin II (Ang II) activate B 2- and AT 1-receptors on sympathetic nerve terminals (SNE), promoting reversal of the norepinephrine (NE) transporter in an outward direction (i.e., carrier-mediated NE release). Although both BK and Ang II contribute to ischemic NE release, Ang II is likely to play a more important role. Since BK is formed by ischemic SNE, we questioned whether cardiac SNE also contribute to local Ang II formation, in addition to being a target of Ang II. SNE were isolated from surgical specimens of human right atrium and incubated in ischemic conditions. These SNE released large amounts of endogenous NE via a carrier-mediated mechanism, as evidenced by the inhibitory effect of desipramine on this process. Moreover, two renin inhibitors, pepstatin-A and BILA 2157 BS, the ACE inhibitor enalaprilat and the AT 1-receptor antagonist EXP3174 prevented ischemic NE release. Western blot analysis revealed the presence of renin in cardiac SNE. Renin abundance increased more than three-fold during ischemia. Thus, renin is present in cardiac SNE and is activated during ischemia, eventually culminating in Ang II formation, stimulation of AT 1-receptors and carrier-mediated NE release. Our findings uncover a novel autocrine mechanism, by which Ang II, formed at SNE in myocardial ischemia, elicits carrier-mediated NE release by activating prejuntional AT 1-receptors.

Ischemia promotes renin activation and angiotensin formation in sympathetic nerve terminals isolated from the human heart: contribution to carrier-mediated norepinephrine release.

We recently reported that in the ischemic human heart, locally formed angiotensin II activates angiotensin II type 1 (AT(1)) receptors on sympathetic nerve terminals, promoting reversal of the norepinephrine transporter in an outward direction (i.e., carrier-mediated norepinephrine release). The purpose of this study was to assess whether cardiac sympathetic nerve endings contribute to local angiotensin II formation, in addition to being a target of angiotensin II. To this end, we isolated sympathetic nerve endings (cardiac synaptosomes) from surgical specimens of human right atrium and incubated them in ischemic conditions (95% N(2,) sodium dithionite, and no glucose for 70 min). These synaptosomes released large amounts of endogenous norepinephrine via a carrier-mediated mechanism, as evidenced by the inhibitory effect of desipramine on this process. Norepinephrine release was further enhanced by preincubation of synaptosomes with angiotensinogen and was prevented by two renin inhibitors, pepstatin-A and BILA 2157BS, as well as by the angiotensin-converting enzyme inhibitor enalaprilat and the AT(1) receptor antagonist EXP 3174 [2-N-butyl-4-chloro-1-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl] methyl]imidazole-5-carboxylic acid]. Western blot analysis revealed the presence of renin in cardiac sympathetic nerve terminals; renin abundance increased ~3-fold during ischemia. Thus, renin is rapidly activated during ischemia in cardiac sympathetic nerve terminals, and this process eventually culminates in angiotensin II formation, stimulation of AT(1) receptors, and carrier-mediated norepinephrine release. Our findings uncover a novel autocrine/paracrine mechanism whereby angiotensin II, formed at adrenergic nerve endings in myocardial ischemia, elicits carrier-mediated norepinephrine release by activating adjacent AT(1) receptors.

Lesion of the bulbospinal noradrenergic pathways blocks desipramine-induced inhibition of the C-fiber evoked nociceptive reflex in rats

Desipramine-induced inhibition of spinal cord nociceptive transmission was studied in rats with or without lesion of the bulbospinal noradrenergic system by recording the C-fiber evoked nociceptive reflex from a hind limb. Bulbospinal noradrenergic projections were lesioned by injecting intrathecally 20 μg of 6-hydroxydopamine 2 weeks before the electrophysiological experiments. Results show that desipramine (5, 10 and 20 mg/kg intraperitoneally) produced dose-dependent inhibition of the C reflex response duration in rats having intact noradrenergic bulbospinal systems. The inhibitory effect of desipramine was reduced or even abolished in rats pre-treated with 6-hydroxydopamine. In addition, [ 3H]-noradrenaline uptake was significantly lower in spinal cord slices arising from 6-hydroxydopamine lesioned animals, as compared to that from intact rats. These observations support the notion that the antinociceptive activity of antidepressants with noradrenergic selectivity depends on a normal rate of endogenous noradrenaline released by bulbospinal neurons.

Effect of the tricyclic antidepressant desipramine on protein kinase C in rat brain and rabbit platelets in vitro.

Protein kinase C (PKC), which participates in cellular responses to various stimuli such as hormones, neurotransmitters and growth factors, is essential for cell proliferation and differentiation. Desipramine, which is a tricyclic antidepressant, inhibited PKC activity in concentrations starting from 0.1 mmol/L in rat brain and its inhibitory effect on PKC activity did not involve competitive inhibition with calcium. However, rabbit platelets incubated with desipramine showed a biphasic dose-response change in PKC activity in vitro. The stimulatory effect of desipramine on PKC activity in rabbit platelets was observed over a concentration range of 0.5-2.0 mmol/L, and an inhibitory effect on PKC activity in platelets began to be seen at a concentration of 3.0 mmol/L desipramine. The stimulatory effects of desipramine and calcium on PKC activity in platelets appear to be occurring by the same mechanism. Several lines of evidence indicate that neurotransmitter uptake is linked to PKC activation. The present study supposes that the inhibitory effect of desipramine on neurotransmitter uptake may, at least in part, be associated with its inhibitory or stimulatory effect on PKC.

Cardiac sympathetic nerve function assessed by [ 131I]metaiodobenzylguanidine after ischemia and reperfusion in anesthetized dogs

Background. Accumulation of 131I-labeled metaiodobenzylguanidine ([ 131I]MIBG), a radiolabeled norepinephrine analog, is reduced in infarcted myocardium, suggesting loss of cardiac sympathetic nerve viability. Histopathologic studies, however, indicate that the nerve endings are morphologically intact. Experiments were therefore designed to determine the mechanism of reduced MIBG accumulation. Methods and Results. Desipramine, a specific blocker of neuronal norepinephrine reuptake, was used to separate the portions of total myocardial [ 131I]MIBG accumulation attributable to neuronal and nonneuronal uptake mechanisms. Sixteen dogs underwent circumflex coronary artery occlusion for 60 minutes followed by a 5-hour reperfusion. [ 131I]MIBG was injected intravenously 1 hour after reperfusion. The left ventricle was removed and incubated in triphenyltetrazolium chloride to identify infarcted and viable myocardium within the zone at risk. Preliminary studies in sham-operated dogs showed that pretreatment with desipramine (5 mg/kg) reduced [ 131I]MIBG accumulation 4 hours after injection to 38.9% of untreated controls. Chemical sympathectomy by topical phenol resulted in a similar decrease in [ 131I]MIBG accumulation (to 45.7% of normal), and desipramine did not produce further inhibition of [ 131I]MIBG accumulation over that produced by phenol alone, indicating that the inhibitory effect of desipramine on neuronal accumulation of [ 131I]MIBG was essentially complete. In dogs undergoing ischemia-reperfusion, myocardial samples from infarcted and viable postischemic areas showed 64.5% ± 11.8% and 84.7% ± 9.1% of normal [ 131I]MIBG activity, respectively (both, p < 0.01 vs normal area, n = 9). With desipramine pretreatment ( n = 7), accumulation of [ 131I]MIBG decreased in all areas. Neuronal accumulation was reduced uniformly in infarcted, viable postischemic, and normal areas by 30% to 35% compared with sham-operated controls. In contrast, nonneuronal accumulation was only 39.3% in infarcted areas and 84.6% in viable postischemic areas compared with normal areas, and these decreases accounted entirely for the reduced total [ 131I]MIBG accumulation. Conclusions. Reduced [ 131I]MIBG accumulation in infarcted myocardium after 60 minutes of ischemia and 5 hours of reperfusion is attributable to a deficit in nonneuronal accumulation and not to decreased accumulation by sympathetic nerves.

The effect of desipramine on basal and naloxone-stimulated cortisol secretion in humans: interaction of two drugs acting on noradrenergic control of adrenocorticotropin secretion.

Desipramine (DMI), a tricyclic antidepressant and norepinephrine (NE) reuptake blocker, is reported to induce ACTH and cortisol release acutely in humans, probably by facilitating central NE neurotransmission. Tricyclic antidepressant therapy, including DMI, normalizes the ACTH and cortisol hypersecretion that often accompanies depression. The mechanism of hypothalamic-pituitary-adrenal (HPA) axis inhibition by DMI in humans is unknown. In rats, DMI reduces the activity of the locus ceruleus, a major source of NE innervation of the hypothalamic paraventricular nucleus, the site of CRH neurons. Naloxone induces ACTH and cortisol release in humans through a noradrenergic-mediated mechanism and a probable consequent stimulation of hypothalamic CRH release. To study the interaction of these drugs on NE neurotransmission and, hence, HPA axis activity in humans, we administered DMI alone and with naloxone in a randomized, double blind, placebo-controlled protocol in eight healthy male volunteers. DMI (75 mg, orally) was given 180 min before naloxone (125 micrograms/kg BW, i.v.). Plasma ACTH and cortisol were measured at frequent intervals from 60 min before to 120 min after naloxone treatment. Plasma cortisol levels were 77% higher 180 min after DMI compared to those after placebo treatment (287 +/- 17 vs. 162 +/- 14 nmol/L; P = 0.000005). DMI reduced the naloxone-induced rise in cortisol (P = 0.02), but there was no change in the integrated cortisol response. The increase in basal plasma ACTH levels after DMI treatment did not reach statistical significance. DMI significantly increased systolic blood pressure and heart rate consistent with an effect on the noradrenergic control of the cardiovascular system. In summary, DMI increased basal cortisol levels consistent with facilitation of NE neurotransmission and, hence, hypothalamic CRH release. However, DMI had no enhancing effect on naloxone-induced cortisol release. This contrasts with the synergy observed when non-antidepressant agents that increase NE neurotransmission are given with naloxone to humans. DMI increases glucocorticoid feedback sensitivity in the rat HPA axis after several weeks through up-regulation of central corticosteroid receptors. However, this slowly developing effect is unlikely to occur during these acute studies. The effect of DMI on naloxone-induced cortisol release is consistent with an inhibitory effect on central noradrenergic control of ACTH release, perhaps at the locus ceruleus. This is the first human study to suggest an inhibitory effect of DMI on central noradrenergic control of ACTH release.

Effects of single and repeated treatment with antidepressants on apomorphine-induced yawning in the rat: the implication of α-1 adrenergic mechanisms in thed-2 receptor function

Acute (10 or 20 mg/kg IP) and subchronic (2 x 5 or 10 mg/kg IP daily for 7 days) effects of desipramine, imipramine, maprotiline, (+)- and (-)-oxaprotiline enantiomers as well as selective 5-HT-uptake inhibitors citalopram and ifoxetine on yawning, induced by low doses of apomorphine, were investigated in the rat. In addition, the effects of alpha-1 receptor agonist adrafinil and antagonist prazosin were also tested. After acute treatment, desipramine, the stereoselective NA-uptake inhibiting (+)-enantiomer of oxaprotiline, and the alpha-1 agonist adrafinil, markedly and significantly suppressed yawning. Prazosin, in contrast, clearly potentiated it. This potentiating effect was abolished by the pretreatment with (+)-oxaprotiline and adrafinil. Other drugs were inactive. After subchronic administration, yawning was antagonized by NA-uptake-inhibiting antidepressants, including imipramine and maprotiline. By comparison to the acute treatment, the inhibitory effects of desipramine and (+)-oxaprotiline were considerably enhanced. Neither selective 5-HT-uptake inhibitors nor (-)-oxaprotiline (levoprotiline) were active. Antidepressants therefore modulate the functional activity of D-2 receptors, activated by low doses of apomorphine, predominantly by the virtue of their noradrenergic enhancing properties. This modulatory effect appears to be mediated by alpha-1 adrenergic receptors.

Characterization of the release of neuropeptide Y (NPY) induced by tyramine from synaptosomal preparations of rabbit jejunum

The effect of tyramine on the secretion of neuropeptide Y-like immunoreactivity (NPY-LI) was investigated in a synaptosomal fraction prepared from rabbit jejunum. In addition to evoking the release of norepinephrine (NE), tyramine induced a dose-dependent increase of NPY-LI secretion which was insensitive to tetrodotoxin and was not affected by the removal of calcium ions from the bathing medium. Desipramine reduced the effectiveness of tyramine but did not influence the basal output of NPY-LI. There was a positive correlation between the inhibitory effect of desipramine on the NPY release and on the uptake of [ 14C]tyramine into synaptosomes. Guanethidine, however, at a concentration insufficient to block the uptake of tyramine reduced the release of both NE and NPY. These data suggest that tyramine enters into nerve terminals through a desipramine-sensitive mechanism, resulting in the co-release of NE and NPY which can be reduced by guanethidine.

Effect of steroids on the inhibition of platelet 5HT uptake by desipramine and other antidepressants

The inhibitory effect of desipramine on platelet 5HT uptake was tested ex vivo and in vitro in control, adrenalectomised and triamcinolone-treated rats. In both situations, the inhitory effect of desipramine was augmented in adrenolactomised rats and decreased in triamcinolone-treated rats. These changes in desipramine sensitivity were accompanied by changes in the uptake kinetic components, Km and Vmax. In in vitro studies, the IC50 of clomipramine, fluvoxamine, zimelidine, imipramine and nomifensine was decreased in adrenalectomised rat platelets and increased in corticosterone-, dexamethasone- or triamcinolone-treated rat platelets. Deoxycorticosterone had no effect. Testosterone only affected the IC50 of desipramine and nomifensine.

Effects of desipramine, trifluoperazine and other inhibitors of calmodulin on the secretion of catecholamines from the adrenal medulla and postganglionic sympathetic nerves of the salivary gland.

The effects of various drugs, known to be inhibitors of calmodulin, were tested on the secretion of catecholamines (CA) from the adrenal medulla and sympathetic nerves of the salivary gland of the rat. Secretion of CA from the perfused adrenal gland was evoked by injection of acetylcholine (ACh, 50 micrograms), excess K (700 micrograms), or transmural stimulation of splanchnic nerves (300 pulses at 10 Hz). Release of 3H-noradrenaline in the perfused salivary gland was evoked by transmural stimulation at 3 Hz for 30 s. CA secretion was reduced in a dose-dependent manner by 0.3 microM to 10 microM desipramine or imipramine. The effect of low doses (0.3 microM) was more pronounced on the secretion evoked by ACh and splanchnic nerve stimulation than that by excess K. The inhibition was independent of the frequency of nerve stimulation. Trifluoperazine (10-100 microM) and chlorpromazine (10-100 microM) reduced CA secretion evoked by all of the three procedures. The inhibitory effects of desipramine, trifluoperazine and chlorpromazine were completely reversed within 1 h after their washout. Secretion of CA obtained after reintroduction of Ca to the adrenal gland previously perfused with Ca-free medium was not blocked by desipramine or trifluoperazine. In fact, these agents markedly enhanced the secretory response. None of the drugs enhanced spontaneous secretion of CA from the adrenal gland during the nonstimulation period. Adrenal medullary cells accumulated significant amounts of Ca45 (0.88 pg/mg) after stimulation with ACh.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrogen induced inhibition of 3H-noradrenaline release in the uterus and portal vein of the rat.

The influence of estrogen treatment on 3H-noradrenaline release, induced by potassium or calcium, was studied in isolated preparations of the uterus and the portal vein of the rat. Uterine strips of oophorectomized rats responded with contraction followed by transient relaxation when immersed in a medium containing 127 mM potassium. The transient relaxation was accompanied by an increased rate of 3H-noradrenaline efflux. When the uterine strips were bathed in calcium-free potassium solution, addition of calcium (3 mM) evoked an increased outflow of 3H-noradrenaline coinciding with a relaxation phase of the contractile response to calcium. After estrogen treatment of the rats the pattern of response was altered. The uterus then responded to potassium and calcium with sustained contractures and with a relatively small (potassium) or with no (calcium) increase of 3H-noradrenaline efflux. Normetanephrine (5 X 10(-5) M) did not influence the uptake or release of 3H-noradrenaline in either non-estrogenized or estrogen treated rats uterus. Calculations, based on the amounts of 3H-noradrenaline released by potassium and on the inhibitory effects of desipramine (10(-5) M) on neuronal uptake of noradrenaline, suggested that similar amounts of tracer were accumulated in the adrenergic nerves of both non-estrogenized treated preparations. Tyramine (10(-4) M) had a weaker stimulatory effect on 3H-noradrenaline release than potassium, and the tyramine induced release was not inhibited by estrogen treatment. Strips of the rat portal vein responded to potassium with an increased rate of 3H-noradrenaline efflux. As in the uterus, estrogen treatment reduced the release of 3H-noradrenaline in response to potassium. The adrenolytic effect of estrogen is possibly due to reduced entry of calcium ions into the nerve terminal.

ROLE OF ENDOGENOUS CATECHOLAMINES IN THE ANTI‐INFLAMMATORY ACTIVITY OF α‐ADRENOCEPTOR BLOCKING AGENTS

1 Drugs which release or modify the response to catecholamines were examined for their effect on the permeability of the mouse peritoneal vascular bed to circulating plasma albumin, labelled with Evans blue.2 Phenoxybenzamine, phentolamine, piperoxane, yohimbine or cocaine reduced the extravasation of Evans blue into the peritoneum, an effect which was antagonized by beta-adrenoceptor blocking drugs. The inhibitory effect of desipramine on the extravasation of Evans blue was less completely antagonized by beta-adrenoceptor blockade.3 Inhibition of catecholamine biosynthesis, ganglion blockade or adrenergic neurone blockade antagonized the reduction in dye extravasation by alpha-adrenoceptor blocking agents and cocaine, but had no significant effect on the response to desipramine. The inhibitory effects of alpha-adrenoceptor blocking agents on dye extravasation were not prevented by bilateral adrenalectomy.4 Mice subjected to the procedure for estimation of vascular permeability excreted increased amounts of adrenaline and noradrenaline. Pretreatment with phenoxybenzamine, piperoxane or cocaine further increased catecholamine excretion, but desipramine caused only a small increase in catecholamine excretion which did not correlate with its effect on dye extravasation.5 It is suggested that phenoxybenzamine, phentolamine, piperoxane and cocaine reduce vascular permeability in the mouse peritoneum by releasing and/or potentiating the effects of endogenous catecholamines on beta-adrenoceptors. Endogenous catecholamines do not appear to be involved in the anti-inflammatory activity of desipramine.

Inhibition of the uptake of tritiated catecholamines by antidepressant and related agents

The inhibitory effects of desipramine and some related agents on the uptake of tritiated noradrenaline in slices of cerebral cortex of the mouse and the uptake of tritiated dopamine in slices of the corpus striatum of the rabbit were investigated. The effect of the drugs, administered in vivo, on the uptake of noradrenaline was compared with their antagonizing effect on the decrease of motor activity (sedation), ptosis and hypothermia produced by reserpine and tetrabenazine. In vitro, all the agents with the exception of UCB 6249 inhibited the uptake of the catecholamines. Lu 3-010, desipramine and imipramine were considerably more powerful in inhibiting the uptake of noradrenaline than of dopamine. In vivo, only these compounds and (±)-amphetamine inhibited the uptake of noradrenaline and antagonized the ptosis and hypothermia produced by reserpine, and the ptosis induced by tetrabenazine. UCB 6249 antagonized sedation and ptosis produced by tetrabenazine but not by reserpine.