Evaluation of the passive permeability of antidepressants through pore-suspended lipid bilayer

HYPOTHESIS

The antidepressant drug imipramine, and its metabolite desipramine show different extents of interaction with, and passive permeation through, cellular membrane models, with the effects depending on the membrane composition. Through multimodal interrogation, we can observe that the drugs have a direct impact on the physicochemical properties of the membrane, that may play a role in their pharmacokinetics.

EXPERIMENTS

Microcavity pore-suspended lipid bilayers (MSLBs) of four different compositions, each with a different headgroup charge namely; zwitterionic dioleoylphosphatidylcholine (DOPC), mixed DOPC and negatively charged dioleoylphosphatidylglycerol (DOPG) (3:1), mixed DOPC and positively charged dioleoyltrimethylammoniumpropane (DOTAP) (3:1), and with increasing complex composition mimicking blood-brain-barrier (BBB) were prepared on gold and polydimethylsiloxane (PDMS) substrates using a Langmuir-Blodgett-vesicle fusion method. The molecular interaction and permeation of antidepressants, imipramine, and its metabolite desipramine with the lipid bilayers were evaluated using highly sensitive label-free electrochemical impedance spectroscopy (EIS) and surface-enhanced Raman spectroscopy (SERS). Drug-induced membrane packing/fluidity alterations were assessed using fluorescence lifetime imaging (FLIM) and fluorescence lifetime correlation spectroscopy (FLCS) of MSLB over microfluidic PDMS array.

FINDINGS

Using EIS to evaluate in real-time membrane admittance changes, we found that imipramine greatly increases the ion permeability of negatively charged DOPC:DOPG (3:1) membranes. The effect was observed also at neutral (DOPC) and to a lesser extent at positively charged DOPC:DOTAP(3:1) membranes. In contrast, desipramine had a much weaker impact on ion permeability across all bilayer compositions. Temporal capacitance data show that desipramine intercalates at negatively charged membrane thereby increasing the thickness of the membrane. The overall kinetics of the imipramine permeation is higher than that of desipramine. This was confirmed using SERS, which also provides an evaluation of drug passive permeation based on arrival time across the membrane. Using FLCS, we found that imipramine increases the lipid membrane fluidity, whereas desipramine lowers it, with the exception of the negatively charged membrane. A translocation rate pharmacokinetics model was established for the first time at the MSLB platform by real-time monitoring of the variation in membrane resistance of pristine DOPC and blood-brain-barrier (BBB) membrane.

Polycarbonate-coated magnetic nanoparticles for the extraction of imipramine and its primary metabolite from urine

This study introduces a reliable and inexpensive magnetic dispersive solid phase extraction to extract imipramine and its primary metabolite (desipramine) from urine samples. To accomplish this aim, Fe3 O4 magnetic nanoparticles were synthesized by sonication, subsequently, polycarbonate was precipitated gradually onto the surface of them to form the adsorbent. Extraction recoveries of 85% and 76%, enrichment factors of 57 and 51, limits of detection of 2.5 and 2.8 μg/L, and limits of quantification of 8.3 and 9.3 μg/L were obtained for imipramine and desipramine under the optimal conditions, respectively. In addition, relative standard deviations for intra- (n = 6) and inter-day (n = 5) precisions at two concentrations (50 and 100 μg/L of each analyte) were less than or equal to 4%. Short extraction time, good repeatability, high enrichment factors, and simplicity are the main advantages of the proposed method.

Characterization of D3 Autoreceptor Function in Whole Zebrafish Brain with Fast-Scan Cyclic Voltammetry

Zebrafish (Danio rerio) are ideal model organisms for investigating nervous system function, both in health and disease. Nevertheless, functional characteristics of dopamine (DA) release and uptake regulation are still not well-understood in zebrafish. In this study, we assessed D3 autoreceptor function in the telencephalon of whole zebrafish brains ex vivo by measuring the electrically stimulated DA release ([DA]max) and uptake at carbon fiber microelectrodes with fast-scan cyclic voltammetry. Treatment with pramipexole and 7-OH-DPAT, selective D3 autoreceptor agonists, sharply decreased [DA]max. Conversely, SB277011A, a selective D3 antagonist, nearly doubled [DA]max and decreased k, the first-order rate constant for the DA uptake, to about 20% of its original value. Treatment with desipramine, a selective norepinephrine transporter blocker, failed to increase current, suggesting that our electrochemical signal arises solely from the release of DA. Furthermore, blockage of DA uptake with nomifensine-reversed 7-OH-DPAT induced decreases in [DA]max. Collectively, our data show that, as in mammals, D3 autoreceptors regulate DA release, likely by inhibiting uptake. The results of this study are useful in the further development of zebrafish as a model organism for DA-related neurological disorders such as Parkinson's disease, schizophrenia, and drug addiction.

The evaluation of the changes in enzymatic antioxidant reserves and lipid peroxidation in chosen parts of the brain in an animal model of Parkinson disease

BACKGROUND

Parkinson's disease is a progressive neurodegenerative disorder, characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. The causes of Parkinson's disease are not fully understood; however, increasing evidence implicates oxidative stress.

OBJECTIVES

The study was aimed at assessing the nature of the changes in the oxidation-antioxidant balance in the cerebral cortex, striatum, hippocampus, thalamus, and cerebellum in a rat model of Parkinson's disease (PD).

MATERIAL AND METHODS

Sixteen male Wistar rats were divided into 2 groups: Icontrol, IIParkinson's disease. The 8-weeks-old animals were decapitated, their brains removed and the following structures dissected and then frozen for further biochemical assays: cerebral cortex, striatum, hippocampus, thalamus and cerebellum. The activities of: the catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), glutathione S-transferase (GST), superoxide dismutase (SOD) and the isoenzymes: Cu/ZnSOD and MnSOD; together with the malondialdehyde (MDA) and the total oxidative status (TOS) concentrations were measured in each structure.

RESULTS

A significantly increased activities of SOD, Cu/ZnSOD, GST and reduced GR activity and an increase of MDA concentration were observed in the striatum of PD rats, comparing to the control group, combined with a significantly reduced activities of GR,SOD, Cu/ZnSOD and an increased GPX activity and MDA concentration in the hippocampus, a significantly lower GR, SOD, MnSOD, Cu/ZnSOD, and GST activities in the cerebral cortex. A significantly lower GR activity, higher CAT activity and MDA concentration in the thalamus and a significantly increased GR activity in the cerebellum were observed in PD rats compared to the corresponding control group.

CONCLUSIONS

Oxidative stress in PD involves many brain structures and various antioxidant enzymes and oxidative status parameters become dysfunctional, depending on the area of the brain, which might reflect the complexity of the clinical symptoms of PD.

Nocturnal enuresis

INTRODUCTION

Nocturnal enuresis affects 15-20% of 5-year-old children, 5% of 10 year-old-children and 1-2% of people aged 15 years and over. Without treatment, 15% of affected children will become dry each year. Nocturnal enuresis is not diagnosed in children younger than 5 years, and treatment may be inappropriate for children younger than 7 years.

METHODS AND OUTCOMES

We conducted a systematic review and aimed to answer the following clinical question: What are the effects of interventions for relief of symptoms? We searched: Medline, Embase, The Cochrane Library and other important databases up to March 2007 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).

RESULTS

We found 14 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.

CONCLUSIONS

In this systematic review we present information relating to the effectiveness and safety of the following interventions: acupuncture, anticholinergics (oxybutynin, tolterodine, hyoscyamine), desmopression, dry bed training, enuresis alarm, hypnotherapy, standard home alarm clock, tricyclics (imipramine, desipramine).

Microheterogeneity of regional myocardial blood flows in low-perfused rat hearts evaluated by double-tracer digital radiography

Using (3)H- and (125)I-labeled desmethylimipramine (DMI) for regional flow tracers, we established a two-time measurement method for the spatial pattern of myocardial perfusion in cross-circulated rat hearts. Myocardial extractions and retentions of these tracers were confirmed to be satisfactory; however, the latter were less than 90% after 3 min at a perfusion rate of 2.9 ml/min/g, limiting the present application to a short-time perfusion measurement. Distributions of myocardial depositions were separated by subtraction digital radiography with 400-microm pixel resolution. Its feasibility was examined by regression analysis between local deposition densities of (3)H- and (125)I-DMI injected simultaneously. The slope, y-intercept, and correlation coefficient (r) of the regression line were 0.98+/-0.04, 0.02+/-0.04, and 0.95+/-0.03, respectively, indicating the validity of the present image subtraction technique. The spatial pattern of myocardial perfusion in response to flow reduction was evaluated by the injections of (3)H- and (125)I-DMI, respectively, before and after a nearly 70% flow reduction. A significant correlation between normalized density distributions of these tracers was found in both subepicardium (r=0.77+/-0.12) and subendocardium (r=0.73+/-0.20), indicating the stable pattern of myocardial perfusion. However, the coefficient of variation of tracer densities showed a decrease of subendocardial flow heterogeneity from 35+/-15% to 31+/-16%. Thus, flow differences between originally high- and low-flow regions in subendocardium were reduced on a relative basis during low perfusion.

Excess fatality from desipramine in children and adolescents

OBJECTIVE

To compare the case fatality rate (CFR) from desipramine ingestion in children and adolescents with that of other tricyclic antidepressants.

METHOD

All mentions of desipramine, amitriptyline, imipramine, nortriptyline, and doxepin in children and adolescents recorded in the American Association of Poison Control Centers Toxic Exposure Surveillance System from 1983 to 2002 were analyzed. The CFR for each drug was defined as the ratio of the number of deaths/number of mentioned exposures.

RESULTS

There were 24 fatalities in children younger than 6 years old (desipramine, n=10; amitriptyline, n=7; doxepin, n=3; imipramine, n=3; nortriptyline, n=1) and 144 fatalities in older children and adolescents (desipramine, n=56; amitriptyline, n=30; doxepin, n=16; imipramine, n=31; nortriptyline, n=11). The CFR from desipramine was significantly higher compared with the other tricyclic antidepressants in children younger than 6 years old (chi=36, p<.001) and in older children and adolescents (chi=155, p<.001). The CFR from desipramine exceeded that of amitriptyline, doxepin, imipramine, and nortriptyline by 7- to 8-, 4-, 6- to 12-, and 7- to 10-fold, respectively.

CONCLUSIONS

The excess CFR from desipramine in children and adolescents and the reports of sudden death in children treated with therapeutic doses call for caution in prescribing desipramine to children and adolescents.

Cardiac and extracardiac sympathetic denervation in Parkinson's disease with orthostatic hypotension and in pure autonomic failure

The uptake of 6-(18)F-fluorodopamine by cardiac noradrenergic nerves enables visualization of the sympathetic innervation of the left ventricular myocardium by PET. Patients with Parkinson's disease (PD) and orthostatic hypotension (OH) (PD+OH) or with pure autonomic failure (PAF) have markedly decreased myocardial 6-(18)F-fluorodopamine-derived radioactivity, consistent with cardiac sympathetic denervation, a phenomenon that neurochemical, neuropharmacologic, and, most recently, postmortem neuropathologic studies have confirmed. In this study, we examined whether 6-(18)F-fluorodopamine can visualize sympathetic innervation in extracardiac organs and, if so, whether patients with PD+OH or PAF have neuroimaging evidence of extracardiac noradrenergic denervation.

METHODS

To validate the method, healthy volunteers underwent 6-(18)F-fluorodopamine scanning of the head, thorax, and abdomen, with or without treatment with desipramine to block sympathoneural uptake of catecholamines. (13)N-Ammonia scanning was used to address possible group differences in 6-(18)F-fluorodopamine delivery by blood perfusion.

RESULTS

Desipramine treatment was associated with decreased 6-(18)F-fluorodopamine-derived radioactivity in the heart, renal cortex, and thyroid gland but not in the liver, spleen, renal pelvis, or salivary glands. Both the PD+OH group and the PAF group had decreased 6-(18)F-fluorodopamine-derived radioactivity in the heart (P < 0.0001) and renal cortex (P = 0.02 and P = 0.005, respectively). The PD+OH group also had decreased radioactivity in the thyroid gland (P = 0.01). Neither group had decreased radioactivity in the other organs, after correction for (13)N-ammonia-derived radioactivity.

CONCLUSION

6-(18)F-Fluorodopamine scanning visualizes sympathetic innervation in the heart, renal cortex, and thyroid gland. Both PD+OH and PAF involve decreased noradrenergic innervation that is most prominent in the heart but is also detectable in extracardiac organs.

Digital Radiographic Quantification of Myocardial Blood Flow Around a Transmyocardial Laser Channel in Rabbit Hearts

BACKGROUND

A mechanism underlying the benefits of transmyocardial laser revascularization (TMLR) has been presumed to be improvement in perfusion. We evaluated myocardial blood flow around a laser channel using digital radiography combined with a 3H-labeled desmethylimipramine ([3H]DMI) deposition.

METHODS AND RESULTS

A laser channel was created in the left ventricular wall using a YAG-laser in 6 non-ischemic rabbit hearts. After 8 weeks, [3H]DMI(1.11 MBq) was injected into the left atrium and the TMLR-treated myocardium was sectioned. Another 6 hearts were examined as controls. We measured [3H]DMI density in arbitrary units with digital radiography in the channel remnant, the surrounding area and a remote area. Flow distribution was quantified by the coefficient of variation of flows (CV). The surrounding area had the highest density (p < 0.001) and the lowest CV (p < 0.001), and had higher density (p < 0.001) and lower CV (p < 0.001) than the controls. There was no transmural difference in the density in all domains. The CV increased with depth in the remote area, as well as in controls (p < 0.001), but there was no transmural difference in the surrounding area.

CONCLUSIONS

The TMLR increases myocardial blood flow and decreases flow heterogeneity in the surrounding area. The disappearance of transmural difference in flow heterogeneity might indicate the remodeling of microcirculation to improve regional oxygen delivery.

Pattern differences between distributions of microregional myocardial flows in crystalloid- and blood-perfused rat hearts

Regional myocardial flow distributions in Langendorff rat hearts under Tyrode and blood perfusion were assessed by tracer digital radiography (100-μm resolution). Flow distributions during baseline and maximal hyperemia following a 60-s flow cessation were evaluated by the coefficient of variation of regional flows (CV; related to global flow heterogeneity) and the correlation between adjacent regional flows (CA; inversely related to local flow randomness). These values were obtained for the original images (642 pixels) and for coarse-grained images (322, 162, and 82 blocks of nearby pixels). At a given point in time during baseline, both CV and CA were higher in blood ( n = 7) than in Tyrode perfusion ( n = 7) over all pixel aggregates ( P < 0.05, two-way ANOVA). During the maximal hyperemia, CV and CA were still significantly higher in blood ( n = 7) than in Tyrode perfusion ( n = 7); however, these values decreased substantially in blood perfusion and the CV and CA differences became smaller than those at baseline accordingly. During basal blood perfusion, the 60-s average flow distribution ( n = 7) showed a smaller CV and CA than those at a given point in time ( P < 0.05, two-way ANOVA). Coronary flow reserve was significantly higher in blood than in Tyrode perfusion. In conclusion, the flow heterogeneity and the local flow similarity are both higher in blood than in Tyrode perfusion, probably due to the different degree of coronary tone preservation and the presence or absence of blood corpuscles. Under blood perfusion, temporal flow fluctuations over 60-s order are largely involved in shaping microregional flow distributions.

New reagents for detection of faecal occult blood

Imipramine hydrochloride (IPH) and desipramine hydrochloride (DPH), two widely used antidepressant drugs, are proposed as new reagents for detection of faecal occult blood. The usefulness of IPH and DPH in occult blood detection has been examined and compared with benzidine and stanoccult methods. The results show that the proposed reagents are selective and sensitive and gives reproducible results. The proposed methodology is much less subject to vegetable peroxidase, iron and vitamin C interference and can be performed on patients who are on a normal diet.

Noradrenergic lesions differentially alter the expression of two subtypes of low Km cAMP-sensitive phosphodiesterase type 4 (PDE4A and PDE4B) in rat brain

This study examined the effects of selective, central noradrenergic dennervation with 6-hydroxydopamine (6-OHDA) on the expression of type 4 phosphodiesterases (PDE4). Twenty-one days following i.c.v. injection of 6-OHDA (200 microg) hypothalamus, neostriatum, and cerebellum were dissected. Infusion of 6-OHDA reduced norepinephrine (NE) content in all the brain areas examined (to 17%, 76% and 16% of sham-operated controls in hypothalamus, striatum, and cerebellum, respectively). 6-OHDA injections also reduced dopamine levels in hypothalamus (53%) and neostriatum (68%). Administration of desipramine (20 mg/kg, i.p.) 30 min prior to 6-OHDA injection protected neostriatal and cerebellar noradrenergic neurons NE levels (110-122% of the control levels). Desipramine partially attenuated the 6-OHDA-mediated decrease in NE content of hypothalamus, but had little or no effect on either striatal or hypothalamic dopamine (DA) levels. Western blot analysis using a PDE4A-selective antibody revealed three major bands (109 kDa PDE4A5, 102 kDa PDE4AX and 76 kDa PDE4A1) in hypothalamus and striatum. Infusion of 6-OHDA decreased the expression of PDE4A5 and PDE4AX but not of PDE4A1 in hypothalamus, as determined by quantitative Western blotting. Pretreatment of rats with desipramine attenuated the 6-OHDA-induced down-regulation of PDE4A5 and PDE4AX bands in hypothalamus. The PDE4B selective antibody K118 labels 5 major bands in all the brain regions studied. One hundred kDa PDE4B3, 86 kDa PDE4B2 and a 78 kDa PDE4B band was identified using recombinant proteins. Treatment of rats with 6-OHDA resulted in a 52% decrease in the PDE4B3 and 58% decrease in 78 kDa PDE4B variant in hypothalamus; administration of desipramine attenuated the 6-OHDA-induced down-regulation of both PDE4B variants. Neither 6-OHDA nor desipramine altered striatal PDE4A or PDE4B isozymes. In contrast, cerebellar PDE4B3 variant is up-regulated by 6-OHDA treatment and were partially normalized to control values by desipramine pretreatment. These data demonstrate that PDE4 subtypes are differentially regulated by presynaptic noradrenergic activity and may play an important role in the maintaining homeostasis of noradrenergic signal transduction in rat brain.

Quantitation of presynaptic cardiac sympathetic function with carbon-11-meta-hydroxyephedrine

The purpose of this study was to validate an axially distributed blood-tissue exchange model for the quantitation of cardiac presynaptic sympathetic nervous system function that could be applied to PET images. The model accounts for heterogeneity in myocardial blood flow, differences in transport rates of 11C-meta-hydroxyephedrine (mHED) across the capillary endothelium and/or neuronal membranes, the virtual volumes of distribution in the interstitial space and neuron and retention of mHED in the neuronal vesicles.

METHODS

Multiple indicator outflow dilution and residue detection methods were used to measure the kinetics of radiolabeled intravascular space and interstitial space markers and 11C-mHED in isolated perfused rat heart at baseline and during norepinephrine neuronal transporter blockade with desipramine (DMI). The outflow dilution and residue detection data were modeled with a multiple pathway, four-region, axially distributed model of blood-tissue exchange describing flow in the capillary and exchange between regions using permeability-surface area products with units of clearance of milliliters per minute per gram. Meta-hydroxyephedrine may enter the nerve terminal via membrane transport, where it may be sequestered by first-order unidirectional uptake within vesicles. Release of mHED from the vesicles is modeled via exchange with the interstitial space.

RESULTS

After intracoronary injection, mHED transport across the capillary endothelium and in the interstitial space closely followed that of sucrose. Subsequently, mHED was retained in the heart, whereas sucrose washed out rapidly. With DMI the outflow dilution curves more closely resembled those of sucrose. Model parameters reflecting capillary-interstitial kinetics and volumes of distribution were unchanged by DMI, whereas parameters reflecting the neuronal transporter process and volumes of distribution in the nerve terminal and vesicular sequestration were markedly decreased by DMI. Application of the model to a pilot set of canine PET images of mHED suggests the feasibility of this approach.

CONCLUSION

Meta-hydroxyephedrine kinetics in the heart can be quantitated using an axially distributed, blood-tissue exchange model that accounts for heterogeneity of flow, reflects changes in neuronal function and is applicable to PET images.

Spatial fluctuation of regional myocardial blood flows

Digital radiography (100 pixels/mm2) combined with the technique of 3H-labeled desmethylimipramine deposition was employed to visualize regional blood flow distributions in rabbit left ventricular myocardium. A fluctuated pattern of myocardial flow and its dependence on arterial oxygen tension (PaO2) was evaluated with the coefficient of variation (CV) computed at each step of coarse-graining; flow images were revisualized by increasing pixel area (PA) step by step from 0.01 to 1 mm2. The CV values decreased with hypoxia at all resolution levels, suggesting that there is a vascular regulatory mechanism for making myocardial perfusion uniform in response to decreased PaO2. In both perfusion states, CV decreased with increasing PA. The relationship between CV and PA fitted the noninteger power law function, implying an apparent fractality of CV.

Diabetes impairs sciatic nerve hyperemia induced by surgical trauma: implications for diabetic neuropathy

The most widely used methods to assess nerve blood flow in diabetics rats are hydrogen clearance polarography and laser Doppler flowmetry, techniques requiring surgical exposure of the nerve. In these experiments, we examined the hypothesis that the trauma of surgical exposure introduces an important and hitherto largely unrecognized variable that could account for discordant reports on nerve blood flow changes induced by diabetes. We used the noninvasive (for sciatic nerve) reference sample microsphere method to quantify sciatic nerve blood flow in unexposed va. surgically exposed nerves in rats with streptozotocin-induced diabetes (at different temperatures and after curarization) and in unexposed vs. surgically exposed nerves in galactose-fed rats. Baseline resting blood flow in unexposed nerves in both animal models of diabetes was either normal or increased (but was decreased in diabetic rats given d-tubocurarine). Furthermore, the normal brisk hyperemic nerve blood flow response to the minimal trauma associated with surgical exposure of the nerve was markedly impaired in diabetic and in galactose-fed rats. Normalization of the blood flow response to trauma in galactose-fed rats by an aldose reductase inhibitor suggests that the impairment is linked to increased polyol pathway metabolism. These findings 1) confirm our previous findings that sciatic nerve blood flow in diabetic rats is increased or unchanged in unexposed nerves, while also confirming reports that in surgically exposed nerves blood flow is higher in control than in diabetic rats, and 2) indicate that blood flows in surgically exposed nerves are largely a measure of vascular responses to injury rather than (patho)physiological blood flow in undisturbed nerves.

Increased sciatic nerve blood flow in diabetic rats: assessment by "molecular" vs. particulate microspheres

Sciatic nerve blood flow in diabetic rats in typically increased or unchanged when assessed by the reference sample microsphere method in our laboratory. In contrast, blood flow is generally reported to be decreased approximately 50% when assessed with laser Doppler flowmetry or hydrogen clearance polarography. To address concerns that increased blood flow observed with microspheres might be anomalous because of their particulate nature and/or because insufficient numbers of microspheres are captured in the nerve, a plasma-soluble "molecular microsphere" ([3H]desmethylimipramine, mol wt = 266) and 11.3-micron 153Gd-labeled microspheres were injected sequentially to assess blood flow in rats with streptozotocin diabetes of 2-4 wk duration. Nerve blood flows in diabetic rats were increased 1.5- to 2-fold (vs. control rats) with both tracers; these increases were prevented by tolrestat, an inhibitor of aldose reductase. These observations indicate that blood flow in sciatic nerve (like that in retina and kidney) is increased early after the onset of diabetes and is 1) demonstrable with a plasma-soluble tracer as well as with particulate microspheres and 2) linked to increased metabolism of glucose via the sorbitol pathway.

Alterations of myocardial sympathetic innervation in response to hypoxia

The effects of altitude hypoxia on myocardial sympathetic nerve function were assessed in rats using metaiodobenzylguanidine (MIBG).

METHODS

To estimate the change in uptake-1 function induced by hypoxia, three sets of rats were submitted to 5-, 7- and 21-day hypoxia (hypobaric chamber at 410 Torr) and one set of control rats was injected with 25 muCi of 123I-MIBG. Four hours later, the rats were killed and 123I activity was counted in both ventricles. The proportion of MIBG fixed in the myocardium through the norepinephrine (NE) transporter (uptake-1) was evaluated indirectly in 5-day hypoxic and controls rats by the injection of desipramine before 123I-MIBG administration. Myocardial perfusion was evaluated in 5-day hypoxic rats and controls by 201Tl injection.

RESULTS

Myocardial 123I-MIBG activity was 0.253% +/- 0.036% kg dose/g-1 in controls and was decreased (0.188% +/- 0.029% kg dose/g-1, p = 0.001) in 5-day hypoxic rats. This decrease was not related to a change in cardiac perfusion. The decrease in MIBG uptake existed before the appearance of cardiac hypertrophy. Desipramine decreased MIBG uptake by 48% in controls and 17% in hypoxic rats, suggesting that the decrease predominantly affected MIBG uptake by the NE transporter.

CONCLUSION

Chronic hypoxia leads to a decrease in myocardial NE-uptake-1 function. This finding suggests that altered tissue oxygen supply could play a role in the decreased cardiac MIBG uptake reported in human cardiomyopathies.

EFFECT OF IMIPRAMINE AND SOME ANALOGUES ON THE UPTAKE OF 5-HYDROXYTRYPTAMINE BY HUMAN BLOOD PLATELETS IN VITRO

The inhibitory action of imipramine and some analogues on the uptake of 5-hydroxytryptamine by human blood platelets in vitro was investigated. In concentrations comparable with those reached in plasma during therapy, imipramine and the isosteric compound, amitriptyline, were more effective than their metabolites. Chlorpromazine was less effective than the latter and orphenadrine ineffective at the concentrations tested.

A COMPARISON OF IMIPRAMINE, CHLORPROMAZINE AND RELATED DRUGS IN VARIOUS TESTS INVOLVING AUTONOMIC FUNCTIONS AND ANTAGONISM OF RESERPINE

Seven structurally-related compounds consisting of three antidepressant drugs (imipramine, desmethylimipramine and amitriptyline), three tranquillizing agents (promazine, chlorpromazine and chlorprothixene) and a hybrid, desmethylpromazine, have been examined in a series of tests involving autonomic functions and antagonism of reserpine. Activities of the compounds in antagonizing reserpine-induced ptosis in rabbits and prolongation of alcohol hypnosis in mice give good correlation with their clinical actions, whilst their activities in augmenting excitation of rats by amphetamine and yohimbine toxicity in mice, and in reversing reserpine-induced bradycardia in rats offer further evidence for drug-induced sensitization to adrenergic or tryptaminic mechanisms, which is not however specific for antidepressant agents. No evidence has been obtained to indicate that a central parasympatholytic action is an important component of the antidepressant activity of imipramine and related drugs.

Assessment of noradrenergic functioning in patients with non-combat-related posttraumatic stress disorder: a study with desmethylimipramine and orthostatic challenges

The functioning of the noradrenergic system was assessed in 16 patients with non-combat-related posttraumatic stress disorder (PTSD) and the same number of age- and sex-matched healthy subjects by measuring (1) plasma norepinephrine (NE) levels in supine and upright postures, and (2) growth hormone (GH) responses to challenge with desmethylimipramine (DMI), a NE reuptake inhibitor. Subjects were cannulated at 08:30 h after an overnight fast. Blood samples were drawn for NE levels with subjects in a supine position and after 5 min of standing. After subjects were allowed to rest for 30 min in a supine position, a blood sample was drawn for basal GH (T-15) levels. The second baseline sample was drawn 15 min later (T0), at which time DMI (1 mg/kg) was given orally, and further blood samples were drawn at 90, 120, and 180 min. PTSD patients had significantly higher baseline NE levels and blunted NE responsivity to postural challenge compared with normal subjects. Basal and DMI-induced GH levels, on the other hand, did not differ in PTSD versus normal subjects. Overall, these findings suggest that non-combat-related PTSD patients have peripheral noradrenergic dysregulation, but central postsynaptic alpha 2-adrenergic receptor sensitivity is not altered in this patient population.

Biological and clinical validation of atypical depression

Depressed patients with (a) mood reactivity alone (MR group), (b) mood reactivity plus one or more associated features (atypical depression, AD group), and (c) patients with neither mood reactivity nor atypical depression (non-MR/AD group) were compared on their cortisol response to 75 mg of desipramine (DMI), a relatively selective norepinephrine reuptake inhibitor. AD patients exhibited a significantly higher cortisol response to DMI compared with MR and non-MR/AD patients, suggesting that atypical depression may be associated with a less impaired norepinephrine system. MR and non-MR/AD patients did not differ, suggesting that mood reactivity alone is not associated with the biological profile observed in atypical depression. Results indicate that while mood reactivity may be necessary for the diagnosis of atypical depression, the additional presence of at least one associated symptom is required for a distinct biological profile. Our findings provide further biological validation of the concept of atypical depression.

Cardiac sympathetic nervous activity in congestive heart failure. Evidence for increased neuronal norepinephrine release and preserved neuronal uptake

BACKGROUND

Increased concentrations of norepinephrine in coronary sinus plasma reported in congestive heart failure (CHF) could result from increased cardiac sympathetic nerve firing and norepinephrine release or from failure of neuronal uptake mechanisms to recapture released norepinephrine. We have applied neurochemical indexes of cardiac sympathetic nerve function in heart failure patients to delineate the underlying neural pathophysiology.

METHODS AND RESULTS

Cardiac norepinephrine synthesis, assessed from the cardiac overflow of the norepinephrine precursor dihydroxyphenylalanine (DOPA), intraneuronal metabolism estimated from the overflow of the intraneuronal metabolite dihydroxyphenylglycol (DHPG), neuronal norepinephrine reuptake assessed from the fractional extraction of plasma-tritiated norepinephrine and production of tritiated DHPG across the heart, and norepinephrine spillover to plasma were examined in eight patients with CHF caused by coronary artery disease (left ventricular ejection fraction of 26 +/- 5%, mean +/- SEM) and 14 age-matched healthy subjects. Cardiac norepinephrine spillover was increased eightfold in CHF subjects (127 ng/min versus 14 ng/min in healthy subjects; standard error of the difference [SED], 8 ng/min; P < .002), and cardiac DOPA was increased twofold (P < .02). The fractional extraction of tritiated norepinephrine across the heart was marginally less in CHF subjects (0.63 versus 0.73 in normal subjects; SED, 0.02), but the extent to which pharmacological neuronal uptake blockade with desipramine reduced the cardiac extraction of tritiated norepinephrine (by 71% versus 73% in normal subjects) and reduced the production of tritiated DHPG derived from uptake and intraneuronal metabolism of tritiated norepinephrine was similar in CHF patients and healthy subjects.

CONCLUSIONS

The marked increase in norepinephrine spillover from the heart in CHF attributable to coronary artery disease results primarily from an increase in sympathetic nerve firing and neuronal release of norepinephrine, not from faulty neuronal reuptake of norepinephrine.

Regulation of tissue noradrenaline in the rat myocardial infarction model of chronic heart failure

OBJECTIVE

The aim was to evaluate mechanisms regulating tissue noradrenaline in congestive heart failure.

METHODS

Tissue noradrenaline was measured in the conscious post myocardial infarction rat model of congestive heart failure and in sham operated rats (1) under control conditions, (2) 6 h after inhibition of tyrosine hydroxylase by the intraperitoneal administration of alpha-methyl-para-tyrosine (AMPT) (100 mg.kg-1 every 2 h), (3) 6 h after AMPT with desipramine pretreatment (0.3 mg.kg-1), and (4) following exhaustive exercise after AMPT. Tissue noradrenaline was extracted with perchloric acid and measured by high performance liquid chromatography with electrochemical detection.

RESULTS

In control animals without drug, tissue noradrenaline concentration was lower in the following tissues in the rats with myocardial infarction compared with the sham operated group: left and right ventricles, spleen, soleus and white gastrocnemius muscles, kidney cortex, and tail artery. After AMPT, tissue noradrenaline concentration in the sham operated group was significantly lower than control; in the myocardial infarction group the fall in noradrenaline was only significant in the kidney, and group differences were no longer present. In the sham operated animals, coadministration of desipramine with AMPT attenuated the fall in tissue noradrenaline caused by AMPT in the heart and spleen. With exercise to exhaustion, cardiac noradrenaline was lower in rats with myocardial infarction than in sham operated rats, but higher in the soleus muscle.

CONCLUSIONS

These data suggest that tissue noradrenaline depletion in congestive heart failure is not isolated to the heart, and it occurs despite activation of mechanisms that might be operating to conserve neuronal noradrenaline. One mechanism may be reduced organ blood flow to retard diffusion of noradrenaline into the circulation. If this increases interstitial noradrenaline concentration, it would facilitate prejunctional alpha 2 receptor restraint on noradrenaline release. Metabolic coronary vasodilatation during exercise reverses this process, and makes the heart most susceptible to noradrenaline depletion in congestive heart failure.

Isolated presynaptic inotropic beta-adrenergic supersensitivity of the transplanted denervated human heart in vivo

BACKGROUND

The regulation of contractility of the transplanted heart depends on circulating catecholamines resulting from cardiac denervation. Supersensitivity to circulating catecholamines may result from loss of presynaptic neuronal uptake or upregulation of postsynaptic beta-adrenergic receptors.

METHODS AND RESULTS

Dose-response curves using the beta-adrenergic receptor agonists isoprenaline (no neuronal uptake) and epinephrine (neuronal uptake) were performed in vivo. The inotropic response was measured echocardiographically as the increase of fractional shortening (delta FS) and the increase of the systolic pressure/dimension ratio (delta P/D). The inotropic response to increasing doses of isoprenaline (5-20 ng/kg.min) was identical in 36 heart transplant recipients compared with 13 control subjects: delta FS during 20 ng/kg.min isoprenaline amounted to 18.2 +/- 6.2% versus 17.4 +/- 4.0% (NS) and delta P/D to 2.3 +/- 1.2 mm Hg/mm versus 2.2 +/- 0.5 mm Hg/mm (NS), respectively. A vagally mediated indirect negative inotropic effect in the innervated hearts was excluded by identical inotropic responses to isoprenaline in control subjects without and after atropine pretreatment. The inotropic response to increasing doses of epinephrine (10-40 ng/kg.min) was significantly augmented in 13 heart transplant recipients compared with 11 control subjects: delta FS during 40 ng/kg.min epinephrine amounted to 19.9 +/- 2.6% versus 8.6 +/- 2.0% (p less than 0.001) and delta P/D to 2.3 +/- 0.9 mm Hg/mm versus 0.6 +/- 0.3 mm Hg/mm (p less than 0.001), respectively. Pretreatment with desipramine (blockade of neuronal uptake) in control subjects resulted in a significantly increased inotropic response: delta FS during 40 ng/kg.min epinephrine amounted to 17.6 +/- 3.6% (p less than 0.001 versus untreated controls, NS versus heart transplant recipients) and delta P/D to 1.7 +/- 0.8 mm Hg/mm (p less than 0.001 versus untreated controls, NS versus heart transplant recipients).

CONCLUSIONS

These findings provide evidence against a postsynaptic inotropic supersensitivity or subsensitivity of the beta-adrenergic receptor-effector system of the transplanted denervated human heart in vivo. However, a marked presynaptic inotropic supersensitivity is present because of denervation-associated loss of neuronal catecholamine uptake.

Neurotensin-induced miosis: the role of dopaminergic pathways

In this study we investigated the role that dopaminergic pathways play in the miotic effect exerted by neurotensin after intracameral administration. Neurotensin was injected into the anterior chamber (AC) at a dose of 30 micrograms to 4 groups of albino rabbits which had previously undergone the following treatment: a) desmethylimipramine IM and, after 30 min, 6-hydroxydopamine IV 7 days prior to the neurotensin administration; b) haloperidol IM for 15 days; c) haloperidol AC 10 minutes before the neurotensin administration. Our data confirm previous observations regarding the miotic activity of neurotensin and suggest that the dopaminergic system plays an important role in the miotic effect of neurotensin.

A pilot study of a neuroendocrine test battery in posttraumatic stress disorder

Eight female patients who fulfilled DSM-III criteria for posttraumatic stress disorder (PTSD) took part in this study. They were each assessed using the dexamethasone suppression test, the desipramine/growth hormone stimulation test, which examines alpha-2-adrenoceptor functioning, and the buspirone/prolactin test, which is thought to examine 5-HT receptor functioning. A control group consisting of age- and sex-matched healthy subjects was also tested. For each subject the three tests were conducted over 5 days. Hormone assays were carried out blind to diagnosis. Overall no differences on any of the three tests were detected between the patients and controls. The results do not support a link between PTSD and major depression.

Responses of growth hormone to desipramine in endogenous and non-endogenous depression

Desipramine, a monoamine reuptake inhibitor, was used to stimulate release of growth hormone (GH) in 29 DSM-III major depressives and in 10 healthy controls. Eighteen of the depressives showed a blunted response. The GH-stimulation test was unable to distinguish endogenous from non-endogenous patients. The 13 dexamethasone non-suppressors were more likely to have a blunted GH response than the 14 suppressors. The results indicate that at least a subset of non-endogenous depressives have significant neuroendocrine abnormality.

Alpha-2 adrenergic receptor function in post-stroke depression

The growth hormone (GH) response to desipramine was measured in ten patients meeting criteria for post-stroke depression (PSD), eight age-matched post-stroke (PS) non-depressed patients and eight healthy controls. Responses were significantly blunted in patients with PSD. These findings suggest diminished alpha-2 adrenoceptor function may be an important marker for PSD.

Neuroendocrine challenge tests in depression: a study of growth hormone, TRH and cortisol release

Thirty drug-free patients fulfilling the DSM-III criteria for major depression serially underwent the dexamethasone suppression test (DST), thyroid stimulating hormone (TSH) test and a growth hormone (GH) challenge test with oral desipramine. Fifty-three per cent of the sample showed a blunted GH response, 47% were DST non-suppressors while 26% had a blunted TSH response. Eighty per cent of patients showed some biological abnormality. There was no clear association between any of these abnormalities. Neither was there any association between the neuroendocrine parameters studied and the severity of depression or patient gender. There was a trend for increasing GH blunting and DST non-suppression with increasing age.

Assessment of central noradrenergic functioning in irritable bowel syndrome using a neuroendocrine challenge test

Desipramine, the monoamine reuptake inhibitor, acts predominantly on noradrenergic neurones, and via alpha-2 receptors brings about the release of growth hormone in normal healthy subjects. Thirteen patients with a diagnosis of irritable bowel syndrome, 10 normal controls and eight patients with peptic ulcer disease were each given a challenge test of desipramine 1 mg/kg body weight. Growth hormone release over a 3 h period was monitored. A blunted response was defined as a failure of growth hormone levels to rise at least 5 mU/l above baseline. Of the 13 patients with irritable bowel syndrome 11 showed such a blunting. The results suggest abnormal central alpha-2 receptor functioning in irritable bowel syndrome.

Biochemical characterization and purification of the neuronal sodium-dependent noradrenaline transporter

The protein properties of the neuronal sodium-dependent noradrenaline (NA) transporter of PC12 (rat pheochromocytoma) cells and of bovine adreno-medullary cells were studied by means of binding of 3H-desipramine (3H-DMI). 3H-DMI binding was decreased by proteases, phospholipase A2, by disulfide reducing agents and by the sulfhydryl-group alkylating agent N-ethylmaleimide. The NA transporter was partially purified by anion exchange and affinity chromatography. Tritiated desmethylxylamine (3H-DMX) bound irreversibly and in a DMI-sensitive manner to two PC12 membrane proteins (32kd and 53kd) which may represent components of the NA transporter.