Acute effects of antipsychotic drugs on cardiovascular responses to stress

Effects of antipsychotics on intravenous sedation with midazolam and propofol during dental treatment for patients with intellectual disabilities

BACKGROUND

Some patients with intellectual disabilities (ID) are prescribed antipsychotic drugs for symptomatic treatment of behavioural disorders. Nevertheless, it can still prove difficult to perform dental treatments safely for some patients with ID. In such cases, treatment under intravenous sedation (IVS) is one option. Sedative, hypnotic and α-blocking effects of antipsychotic drugs may cause adverse events, such as severe hypotension, among patients who take antipsychotic drugs regularly. This study aimed to investigate the effects of oral antipsychotic medication on cardiovascular function during IVS. Accordingly, we compared mean blood pressure (MBP) and heart rate (HR) between patients who regularly take antipsychotic drugs and patients who do not.

METHODS

Thirty-seven patients with ID were enrolled in this study. All participants were outpatients of Special Care Dentistry of general hospital and received dental treatment under IVS performed with a combination of midazolam and propofol. Eighteen patients regularly took antipsychotics (medication group), and 19 patients were not currently taking antipsychotics (non-medication group). MBP, HR, dose, and effect-site concentration of intravenous sedative medications were measured at three points: 'before IVS', 'at optimal sedation', and 'during dental treatment'.

RESULTS

The magnitude of reduction of MBP was significantly smaller in the medication group than in the non-medication group (P < 0.023). However, there were no differences in MBP, HR, dose, and effect-site concentration of midazolam and propofol between groups at any point.

CONCLUSION

These results suggest that antipsychotic medication may not have clinically significant adverse effects on cardiovascular fluctuations during dental treatment under IVS for persons with ID.

Sigma-1 receptor ligands improves ventricular repolarization-related ion remodeling in rats with major depression disorder

RATIONALE

It has been reported that patients with major depressive disorder (MDD) are prone to developing ventricular arrhythmias. Moreover, the Sigma-1 receptor not only plays a crucial role in MDD but has also been shown to have antiarrhythmic properties. The Sigma-1 receptor is a common receptor related to depression and ventricular arrhythmias.

OBJECTIVE

We analyzed the effects of the Sigma-1 receptor on depression and ventricular repolarization-related ion remodeling in MDD rats.

METHODS

MDD was induced in rats by chronic unpredictable mild stress (CUMS), and 28 days later, the rats were subjected to behavior tests. Protein expression was measured by western blotting, and cardiac morphological changes were observed by Masson staining. Electrophysiological measurement of the myocardium was performed with the whole-cell patch-clamp technique.

RESULTS

Compared with the control rats, the MDD rats exhibited lower transient outward potassium current (Ito) and L-type calcium current (ICa-L) amplitudes. On the other hand, a trend of depolarization of Ito and hyperpolarization of ICa-L was observed in the MDD rats. Thus, we investigated the effect of fluvoxamine, a Sigma-1 receptor agonist, on Ito and ICa-L. Fluvoxamine enhanced Ito and altered its current kinetics, as shown by acceleration of activation and recovery from inactivation. In contrast, fluvoxamine inhibited the Ca2+ by hyperpolarizing the steady-state activation of ICa-L. All these effects were blocked by BD1047.

CONCLUSION

Taken together, our results indicate that Sigma-1 receptor modulates the functions of Ito and ICa-L to possibly exert antiarrhythmic effects.

Adipose tissue as a target for second-generation (atypical) antipsychotics: A molecular view

Schizophrenia is a neuropsychiatric disorder that chronically affects 21 million people worldwide. Second-generation antipsychotics (SGAs) are the cornerstone in the management of schizophrenia. However, despite their efficacy in counteracting both positive and negative symptomatology of schizophrenia, recent clinical observations have described an increase in the prevalence of metabolic disturbances in patients treated with SGAs, including abnormal weight gain, hyperglycemia and dyslipidemia. While the molecular mechanisms responsible for these side-effects remain poorly understood, increasing evidence points to a link between SGAs and adipose tissue depots of white, brown and beige adipocytes. In this review, we survey the present knowledge in this area, with a particular focus on the molecular aspects of adipocyte biology including differentiation, lipid metabolism, thermogenic function and the browning/beiging process.

The Associations between Central Nervous System Diseases and Haemostatic Disorders

The aim of this review was to examine the relationship between the occurrence of central nervous system (CNS) diseases, the medicines used in their treatment and the blood coagulation process. The paper mainly focuses on the effects of antidepressant and antipsychotic drugs. Special attention has been paid to the influence of drugs on platelets, the vascular endothelium, plasma coagulation and fibrinolysis, regarding coagulation.

Clozapine, chlorpromazine and risperidone dose-dependently reduce emotional hyperthermia, a biological marker of salience

RATIONALE

We recently introduced a new rat model of emotional hyperthermia in which a salient stimulus activates brown adipose tissue (BAT) thermogenesis and tail artery constriction. Antipsychotic drugs, both classical and second generation, act to reduce excessive assignment of salience to objects and events in the external environment. The close association between salient occurrences and increases in body temperature suggests that antipsychotic drugs may also reduce emotional hyperthermia.

OBJECTIVES

We determined whether chlorpromazine, clozapine, and risperidone dose dependently reduce emotionally elicited increases in BAT thermogenesis, cutaneous vasoconstriction, and body temperature in rats.

METHODS

Rats, chronically instrumented for measurement of BAT and body temperature and tail artery blood flow, singly housed, were confronted with an intruder rat (confined within a small wire-mesh cage) after systemic pre-treatment of the resident rat with vehicle or antipsychotic agent. BAT and body temperatures, tail blood flow, and behavioral activity were continuously measured.

RESULTS

Clozapine (30 μg-2 mg/kg), chlorpromazine (0.1-5 mg/kg), and risperidone (6.25 μg-1 mg/kg) robustly and dose-relatedly reduced intruder-elicited BAT thermogenesis and tail artery vasoconstriction, with consequent dose-related reduction in emotional hyperthermia.

CONCLUSIONS

Chlorpromazine, a first-generation antipsychotic, as well as clozapine and risperidone, second-generation agents, dose-dependently reduce emotional hyperthermia. Dopamine D₂ receptor antagonist properties of chlorpromazine do not contribute to thermoregulatory effects. Interactions with monoamine receptors are important, and these monoamine receptor interactions may also contribute to the therapeutic effects of all three antipsychotics. Thermoregulatory actions of putative antipsychotic agents may constitute a biological marker of their therapeutic properties.

Effect of risperidone on plasma d-serine concentration in rats post-administered with d-serine

AIMS

Risperidone (Ris) is a second-generation antipsychotic (SGA) used to treat patients with schizophrenia. Additional interventions that increase plasma d-serine (d-Ser) levels could provide improved amelioration of the negative symptoms of schizophrenia. In the present study, we studied whether Ris pretreatment altered the concentration of plasma d-Ser administered intraperitoneally. In addition, the effects of Ris and its main metabolite, 9-hydroxyrisperidone (9-OHRis), on rat d-amino acid oxidase (DAO) activity were examined in vitro.

MATERIALS AND METHODS

Ris (0, 0.5, 1.0, or 3.0mg/kg), followed by d-Ser (20mg/kg), were administered intraperitoneally (i.p.) to male Sprague-Dawley rats, and the time-courses of plasma d-Ser, Ris, and 9-OHRis concentrations were examined. Inhibition of DAO activity in rat cerebellar and kidney preparations by Ris and 9-OHRis were measured spectrophotometrically.

KEY FINDINGS

Significant increases in plasma d-Ser levels were observed in rats treated with both Ris and d-Ser. This effect occurred in a Ris dose-dependent manner, and the areas under the plasma d-Ser concentration-time curves were similar in rats treated with Ris (1.0mg/kg) and with a commercial DAO inhibitor, 3-methylpyrazole-5-carboxylic acid (1.0mg/kg). Rat plasma analyses showed that 9-OHRis was rapidly produced from Ris; however, high concentrations of Ris and 9-OHRis produced weak DAO inhibition in vitro, suggesting that some other pharmacological effect of Ris and/or 9-OHRis might contribute to its effects on plasma d-Ser levels.

SIGNIFICANCE

The combined administration of Ris and d-Ser may increase plasma d-Ser levels, suggesting that this approach could reduce the dose of d-Ser required for these patients.

Inhibitory effects of sigma-1 ligands on handling-induced tachycardia in conscious tethered rats

We used conscious tethered Sprague-Dawley rats to evaluate the cardiovascular effects of four sigma-1 (σ1 ) agonists and five antagonists, given alone or in combination. All drugs were administered as a single intraperitoneal dose. The agonists were given at doses reported as efficacious in rodent cognition models, while the antagonists were administered at doses neutralizing agonist effects in vivo. Systolic blood pressure (SBP) and heart rate (HR) were continuously recorded for 20 min before and 60 min postadministration. Immediately after injection, a sudden, transitory increase in HR and SBP was noted in all animals, because of the stress induced by handling. For both parameters, a peak value (ΔHRmax and ΔSBPmax ) and an area under the curve of changes from baseline over the period 5-20 min postinjection (ΔHR_AUC5-20 min and ΔSBP_AUC5-20 min ) were calculated. Three of the four σ1 agonists (SKF-10,047, dehydroepiandrosterone (DHEAS), Compound 14) significantly reduced ΔHR_AUC5-20 min value without changing ΔHRmax , while the fourth one, SA-4503, had no significant effect. None of the antagonists (haloperidol, rimcazole, NE-100, and BD1047) reduced, and even one (progesterone) enhanced the stress-induced effects on HR. No changes in SBP were noted with any compound. When the antagonist NE-100 was administered just before SKF-10,047, it completely reversed the inhibitory effects of the σ1 agonist on HR increase. In conclusion, we demonstrated for the first time the involvement of σ1 receptors in the regulation of handling-induced tachycardia in the conscious rat. Although additional investigations are needed to fully understand this role, it might offer new therapeutic perspectives to σ1 ligands in the cardiovascular sphere.

Cardiovascular autonomic modulation by nitric oxide synthases accounts for the augmented enalapril-evoked hypotension in ethanol-fed female rats

In this study, we investigated the role of nitric oxide synthase (NOS) isoforms in the enhanced enalapril-evoked hypotension in ethanol-fed female rats by examining the effect of the selective inhibitors of eNOS [N(5)-(1-iminoethyl)-l-ornithine; l-NIO], nNOS (N(ω)-propyl-l-arginine; NPLA), or iNOS (1400W) inhibition on the cardiovascular effects of enalapril in ethanol- (5% w/v) fed rats and in their pair-fed controls. In liquid diet-fed control rats, enalapril- (10 mg/kg) evoked hypotension was abolished by l-NIO (20 mg/kg), but not by NPLA (1 mg/kg) or 1400W (5 mg/kg), suggesting a preferential role for eNOS in this response. Enalapril had no effect on spectral indices of hemodynamic variability or +dP/dtmax (myocardial contractility). However, in ethanol-fed rats, the greater enalapril-evoked hypotension was associated with reductions in (i) +dP/dtmax, (ii) low-frequency/high-frequency ratio of interbeat intervals (IBILF/HF), suggesting cardiac parasympathetic dominance, and (iii) low-frequency spectral band of systolic blood pressure (BP), a marker of vasomotor sympathetic tone. While NPLA or 1400W attenuated the enalapril-evoked hemodynamic and autonomic responses in ethanol-fed rats, l-NIO virtually abolished the hypotensive response and was more efficacious in rectifying autonomic responses to enalapril. Together, these findings implicate NOS isoforms, particularly eNOS, in the altered cardiovascular autonomic control that leads to the augmented enalapril-evoked hypotension in ethanol-fed female rats.

Reduced cardiac contractile force due to sympathovagal dysfunction mediates the additive hypotensive effects of limited-access regimens of ethanol and clonidine in spontaneously hypertensive rats

Our previous attempts to investigate the long-term hemodynamic interaction between ethanol and clonidine in telemetered spontaneously hypertensive rats (SHRs) were hampered by the lack of a sustained hypotensive response to continuous clonidine exposure. This limitation was circumvented when we adopted a limited-access clonidine (8:30 AM-4:30 PM) paradigm in a recent study. The latter paradigm was employed here to evaluate the ethanol-clonidine interaction and possible roles of myocardial function and autonomic control in this interaction. Changes in blood pressure (BP), heart rate, maximum rate of rise in BP wave (+dP/dt(max)), and spectral cardiovascular autonomic profiles were measured by radiotelemetry in pair-fed SHRs receiving clonidine (150 μg/kg/day), ethanol [2.5% (w/v)], or their combination during the day for 12 weeks. Ethanol or clonidine elicited long-term decreases in BP, and their combination caused additive hypotensive response. Significant reductions in +dP/dt(max) were observed upon concurrent treatment with ethanol and clonidine, in contrast to no effect for individual treatment. In addition, the combined treatment increased the high-frequency (HF) spectral band of interbeat interval (IBI-HF(nu), 0.75-3 Hz) and decreased low-frequency (IBI-LF(nu), 0.2-0.75 Hz) bands and IBI(LF/HF) ratios. Clonidine-evoked reductions in plasma and urine norepinephrine and BP-LF spectral power (measure of vasomotor sympathetic tone) were not affected by ethanol. In conclusion, concurrent treatment with ethanol and clonidine shifts the sympathovagal balance toward parasympathetic dominance and elicits exaggerated hypotension as a result of a reduction in cardiac contractile force.

Role of Myocardial Contractility and Autonomic Control in the Hypotensive Response to a Limited Access Ethanol Paradigm in SHRs

BACKGROUND

Previous experimental studies that evaluated the chronic hemodynamic effect of ethanol employed the continuous exposure protocol of ethanol, which does not mimic the pattern of alcohol consumption in humans. This study dealt with the long-term hemodynamic and cardiovascular autonomic effects of ethanol, in a limited-access regimen in telemetered spontaneously hypertensive rats (SHRs).

METHODS

Changes in blood pressure (BP), heart rate (HR), myocardial contractility (dP/dt(max)), and spectral cardiovascular autonomic profiles during the ethanol exposure period (2.5 or 5% w/v, 8 h/d, 8:30 am till 4:30 pm) were followed for 12 weeks.

RESULTS

Compared with control pair-fed SHRs, body weight and urine output, osmolality, and potassium levels were decreased in SHRs receiving 5% but not 2.5% ethanol. Blood pressure showed progressive falls during ethanol-feeding periods with a maximum effect observed at week 5. The peak hypotensive effect was maintained thereafter in SHRs receiving 5% ethanol in contrast to steady rises in BP in the 2.5% ethanol group to near-control levels by the conclusion of the study. Heart rate was slightly but significantly increased by ethanol 5% whereas dP/dt(max) showed persistent reductions. Power spectral analysis showed that ethanol attenuated the baroreflex gain of HR as suggested by the reductions in index alpha, the spectral index of spontaneous baroreflex sensitivity (BRS).

CONCLUSIONS

It is concluded that limited access ethanol drinking in SHRs elicited hypotension that was concentration dependent and mediated, at least partly, through reductions in myocardial contractility. Baroreflex sensitivity attenuation by ethanol appeared to have limited the tachycardic response to ethanol and perhaps its capacity to offset the evoked hypotension.

Intermittent Clonidine Regimen Abolishes Tolerance to Its Antihypertensive Effect: A Spectral Study

The development of tolerance to the antihypertensive effect of clonidine and related imidazolines is clinically recognized. Here, we employed a restricted daytime (8:30 AM until 4:30 PM) clonidine regimen to establish a model of sustained hypotension in spontaneously hypertensive rats (SHRs). Blood pressure (BP), heart rate (HR), and myocardial contractility (dP/dt(max)) were measured by radiotelemetry in pair-fed SHRs receiving liquid diets with or without clonidine (150 microg/kg per day) for 12 weeks. The cardiovascular autonomic control was assessed by power spectral analysis [fast Fourier transformations (FFT)] of hemodynamic variability. Clonidine had no effect on dP/dt(max) and significantly decreased BP and HR during the 8 hour exposure periods throughout the study duration. BP returned to control levels during overnight periods, with no signs of rebound hypertension. FFT analysis of interbeat intervals (IBI) showed pronounced decreases and increases of spectral powers in low-frequency (IBI-LF, 0.20-0.75 Hz) and high-frequency (IBI-HF, 0.75-3 Hz) bands, respectively, in clonidine-treated rats. The IBI(LF/HF) ratio was significantly reduced by clonidine, suggesting cardiac parasympathetic dominance. Clonidine also decreased the vasomotor sympathetic tone, as reflected by the reduced BP-LF spectral density. The sympathoinhibitory effect of clonidine is further confirmed by the significant reductions in urinary norepinephrine levels. Clonidine increased urine output during the 8 hour treatment period but not during the 24 hour period. Plasma and urine osmolality and electrolytes were not altered by clonidine. It is concluded that by adopting the limited-access paradigm, tolerance to the hypotensive and sympathoinhibitory actions of clonidine and, possibly, its side effects, could be minimized.

Clozapine increases cutaneous blood flow and reduces sympathetic cutaneous vasomotor alerting responses (SCVARs) in rats: comparison with effects of haloperidol

RATIONALE

Clozapine inhibits sympathetic outflow to the cutaneous vascular bed. Clozapine reverses hyperthermia and cutaneous vasoconstriction induced by 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) or by lipopolysaccharide (LPS). Clozapine also reverses cutaneous vasoconstriction elicited by exposure to cold. These actions distinguish clozapine from haloperidol. Clozapine could also inhibit sympathetic cutaneous vasomotor alerting responses (SCVARs), vasoconstrictor episodes that reflect emotional/psychological function, and this property might also distinguish clozapine from haloperidol.

OBJECTIVES

Experiments in rats determined whether clozapine and haloperidol inhibit SCVARs, and whether SR46349B (a 5HT2A receptor antagonist), 8-OH-DPAT (a 5-HT1A agonist), L741,626 (a dopamine D2 antagonist) or SCH23390 (a dopamine D1 antagonist) have clozapine-like effects on SCVARs.

METHODS

Mean level and pulse amplitude of the tail artery Doppler flow signal were recorded in conscious freely moving rats before and after alerting stimuli (e.g. tapping the cage), and expressed as a SCVAR index (fall to zero flow implies SCVAR index of 100%, no fall implies 0%).

RESULTS

Clozapine (0.0625-1.0 mg/kg, s.c.) dose-dependently increased resting tail blood flow. After 1 mg/kg, the SCVAR index was 18+/-1%, compared with 83+/-2% after vehicle. SR46349B (0.01-1.0 mg/kg) and 8-OH-DPAT (0.25 mg/kg) had similar but less potent effects on cutaneous blood flow and on SCVARs. Haloperidol (0.005-0.5 mg/kg) and L741,626 (1 mg/kg) had no or little effect on these variables. SCH23390 mildly inhibited SCVARs.

CONCLUSIONS

Clozapine, but not haloperidol, increases resting cutaneous blood flow and decreases SCVARs. Antagonism at 5-HT2A receptors and agonism at 5-HT1A receptors could contribute to these actions.

Thermoregulatory, motor, behavioural, and nociceptive responses of rats to 3 long-acting neuroleptics

We investigated physiological effects of intramuscular injections of the following 3 long-acting neuroleptics commonly used in wildlife management: haloperidol (0.05, 0.1, and 0.5 mg/kg body mass), zuclopenthixol acetate (0.5, 1, and 5 mg/kg), and perphenazine enanthate (1, 3, and 10 mg/kg), in a rat model. Body temperature and cage activity were measured by intra-abdominal telemeters. Nociceptive responses were assessed by challenges to noxious heat and pressure. Haloperidol (0.5 mg/kg) produced a significant nocturnal hypothermia (p < 0.05) and decreased nighttime cage activity and food intake. Zuclopenthixol (5 mg/kg) significantly decreased nighttime body temperature and cage activity and, at 1 mg/kg and 5 mg/kg, significantly decreased food intake 5–17 h after injection (p < 0.05). Perphenazine (10 mg/kg) significantly decreased nighttime body temperature and cage activity and, at all doses, significantly decreased food intake 5–17 h after injection (p < 0.05). Significant analgesic activity was evident in rats given 5 mg/kg zuclopenthixol up to 40 h after injection, and 10 mg/kg perphenazine from 48 to 96 h after injection (p < 0.0001). Zuclopenthixol (5 mg/kg) and perphenazine (10 mg/kg) had significant antihyperalgesic activities at 16 h postinjection and 24–48 h postinjection, respectively (p < 0.0001). Haloperidol had no significant antinociceptive activity at doses tested. Motor function was impaired in rats given 0.5 mg/kg haloperidol, 5 mg/kg zuclopenthixol and 10 mg/kg perphenazine. Effects of long-acting neuroleptics on body temperature, feeding, and activity were short-lasted and should not preclude their use in wildlife. Antinociceptive actions were longer-lasting, but were nonspecific, and we recommend additional analgesics for painful procedures during wildlife management. Key words: body temperature, spontaneous activity, food intake, antinociception, motor function, long-acting neuroleptic.

Alterations in behavioral responses to a cholinergic agonist in post-pubertal rats with neonatal ventral hippocampal lesions: relationship to changes in muscarinic receptor levels

Excitotoxic neonatal ventral hippocampal (NVH) lesion in rats is considered as a putative animal model of schizophrenia as lesioned animals show characteristic post-pubertal emergence of neurochemical and behavioral abnormalities analogous to some of those seen in this disease. Converging evidence points to the involvement of central cholinergic system in this neuropsychiatric disorder, and our previous studies have suggested that cholinergic neurotransmission may be altered in post-pubertal NVH lesioned rats. We investigated here muscarinic receptor reactivity in NVH lesioned animals by measuring the effects of the muscarinic receptor agonist oxotremorine on physiological responses known to be modulated by these receptors such as body temperature, salivation, tremor, pain, and prepulse inhibition of the acoustic startle (PPI). Quantitative receptor autoradiography revealed that post-pubertal NVH lesioned animals display increased levels of [3H]pirenzepine/M1-like and [3H]AFDX-384/M2-like receptor binding sites in the striatum, nucleus accumbens, and in subareas of the dorsal hippocampus. Moreover, in response to the systemic administration of oxotremorine (0.25 mg/kg), post-pubertal NVH lesioned rats exhibited increases in salivation and tremor, and a greater reduction in body temperature compared to sham control animals. Increases in the hot-plate latency were also observed suggesting enhanced antinociceptive effects of oxotremorine in post-pubertal NVH lesioned animals. Finally, oxotremorine (0.1 and 0.25 mg/kg) disrupted PPI in post-pubertal sham control rats while the muscarinic receptor antagonist biperiden (0.5 and 1.0 mg/kg) normalized this behavior in NVH lesioned rats. Taken together, these findings reveal that post-pubertal NVH lesioned rats display enhanced muscarinic receptor responsiveness, which may relate to some behavioral abnormalities reported in this animal model.

Involvement of serotonin1A receptors in cardiovascular responses to stress: a radio-telemetry study in four rat strains

We studied the effect of treatment with the serotonin-1A (5-HT1A) receptor ligands buspirone, 8-hydroxy-di-propyl-aminotetralin (8-OH-DPAT), and (8-[2-(2,3-dihydro-1,4-benzodioxin-2-yl-methylamino)ethyl]-8-azaspiro[4,5]decane-7,9-dione methyl sulphonate (MDL73,005EF) on blood pressure and heart rate increases to open field stress. We compared Spontaneously Hypertensive Rats (SHR), Fawn-Hooded (FH) rats, Wistar-Kyoto (WKY) rats, and Sprague-Dawley (SD) rats instrumented with radio-telemetry probes. Buspirone treatment reduced the blood pressure increase in SHR, FH rats, and WKY rats and heart rate increase in FH rats and WKY rats. 8-OH-DPAT treatment reduced the blood pressure increase in FH rats and WKY rats, but had no effect in SHR and enhanced the pressor response in SD rats. This treatment reduced the heart rate increase in FH rats and WKY rats only. Similarly, MDL73,005EF treatment reduced the blood pressure increase in FH rats and WKY rats, but had no effect in SHR and enhanced this response in SD rats. Little effect of this treatment was seen on heart rate changes. For comparison, diazepam treatment abolished the pressor response in SD rats and reduced it in FH rats and WKY rats, but not SHR. Differential effects of the treatments were also seen between strains for locomotor activity in the open field, although behavioural changes could not explain the effects of the drugs on cardiovascular responses. These data suggest that 5-HT1A receptors are involved in cardiovascular stress responses; however, the extent of this involvement differs between rat strains and the drugs used. These results could be important for our understanding of possible anxiolytic properties of antipsychotic drugs with affinity for the 5-HT1A receptor.

Clozapine and olanzapine, but not haloperidol, reverse cold-induced and lipopolysaccharide-induced cutaneous vasoconstriction

RATIONALE

Reduction of body temperature is used as predictor of psychotropic drug action. The cutaneous circulation functions as a heat-loss component of temperature regulation. Clozapine and olanzapine reverse hyperthermia and sympathetically-mediated cutaneous vasoconstriction induced by MDMA (3,4-methylenedioxymethamphetamine, ecstasy), suggesting that these drugs might reverse other forms of sympathetically mediated cutaneous vasoconstriction.

OBJECTIVES

Clozapine and olanzapine were compared with haloperidol with respect to their ability to reverse cold-induced and LPS (lipopolysaccharide)-induced cutaneous vasoconstriction in rabbits.

METHODS

Cutaneous blood flow was measured in conscious rabbits by Doppler ultrasonic flow probe implanted around the central ear artery, and body temperature was measured telemetrically. After control observations, animals were transferred from 26 to 10 degrees C, or LPS (0.5 microLg/kg IV) was administered. After 30 min, clozapine, olanzapine or haloperidol was administered and ear pinna blood flow and body temperature were measured for another 30 min.

RESULTS

Clozapine, in a dose responsive manner (1, 2.5 and 5 mg/kg IV), substantially reversed cold-induced ear pinna vasoconstriction and reduced body temperature. Clozapine (1 mg/kg IV) reversed LPS-induced cutaneous vasoconstriction and reduced the LPS-induced rise in body temperature. Olanzapine had generally similar effects. Haloperidol (1 mg/kg IV in cold experiments and 0.2 mg/kg IV in LPS experiments) did not reverse ear pinna vasoconstriction, or affect body temperature.

CONCLUSIONS

Both clozapine and olanzapine, but not haloperidol, reverse physiologically induced cutaneous sympathetic vasomotor discharge. Because of the close link between psychological function and sympathetic regulation of cutaneous blood flow, similar neuropharmacological mechanisms might underly the cutaneous vasodilating action and the psychotropic actions of atypical antipsychotic drugs.