Mivazerol, a novel compound with high specificity for alpha 2 adrenergic receptors: binding studies on different human and rat membrane preparations

Novel applications of sleep pharmacology as delirium therapeutics

Sleep-wake and circadian disruption (SCD) is a core feature of delirium. It has been hypothesized that SCD contributes to delirium pathogenesis; therefore, interventions that prevent or reverse SCD represent an array of promising opportunities in relation to delirium. This review explores the relationship between sleep-wake/circadian physiology and delirium pathophysiology with a focus on neurotransmitter systems. Across potential targets aimed at preventing or treating delirium, three broad approaches are considered: 1. Pharmacological mechanisms that contribute to physiological sleep may preserve or restore next-day cognition in patients with or at risk for delirium (e.g., alpha 2 agonists, dopamine 2 antagonists, serotonin 2 A antagonists, dual orexin receptor antagonists, or GHB agonists); 2. Pharmacological mechanisms that promote wakefulness during the day may combat hypoactive delirium (e.g., adenosine 2 A antagonists, dopamine transporter antagonists, orexin agonists, histamine 3 antagonists); and 3. Melatonergic and other circadian interventions could strengthen the phase or amplitude of circadian rhythms and ensure appropriately entrained timing in patients with or at risk for delirium (e.g., as informed by a person's preexisting circadian phase).

Suppression of P2X3 receptor-mediated currents by the activation of α2A -adrenergic receptors in rat dorsal root ganglion neurons

Aims

The α₂‐adrenergic receptor (α₂‐AR) agonists have been shown to be effective in the treatment of various pain. For example, dexmedetomidine (DEX), a selective α_2A‐AR agonist, can be used for peripheral analgesia. However, it is not yet fully elucidated for the precise molecular mechanisms. P2X3 receptor is a major receptor processing nociceptive information in primary sensory neurons. Herein, we show that a functional interaction of α_2A‐ARs and P2X3 receptors in dorsal root ganglia (DRG) neurons could contribute to peripheral analgesia of DEX.

Methods

Electrophysiological recordings were carried out on rat DRG neurons, and nociceptive behavior was quantified in rats.

Results

The activation of α_2A‐ARs by DEX suppressed P2X3 receptor‐mediated and α,β‐methylene‐ATP (α,β‐meATP)‐evoked inward currents in a concentration‐dependent and voltage‐independent manner. Pre‐application of DEX shifted the α,β‐meATP concentration‐response curve downwards, with a decrease of 50.43 ± 4.75% in the maximal current response of P2X3 receptors to α,β‐meATP in the presence of DEX. Suppression of α,β‐meATP‐evoked currents by DEX was blocked by the α_2A‐AR antagonist BRL44408 and prevented by intracellular application of the G_i/o protein inhibitor pertussis toxin, the adenylate cyclase activator forskolin, and the cAMP analog 8‐Br‐cAMP. DEX also suppressed α,β‐meATP‐evoked action potentials through α_2A‐ARs in rat DRG neurons. Finally, the activation of peripheral α_2A‐ARs by DEX had an analgesic effect on the α,β‐meATP‐induced nociception.

Conclusions

These results suggested that activation of α_2A‐ARs by DEX suppressed P2X3 receptor‐mediated electrophysiological and behavioral activity via a G_i/o proteins and cAMP signaling pathway, which was a novel potential mechanism underlying analgesia of peripheral α_2A‐AR agonists.

The Role of the α2-Adrenoceptor Agonist Dexmedetomidine in Postsurgical Sedation in the Intensive Care Unit

Dexmedetomidine was evaluated for sedation of 401 postsurgical patients in this double-blind, randomized, placebocontrolled, multicenter trial. Dexmedetomidine or saline was started on arrival in the intensive care unit (ICU) (1.0 mcg/kg for 10 minutes), then titrated at 0.2 to 0.7 mcg/kg/h to effect. Patients could be given propofol if necessary. Morphine was administered for pain. Sixty percent of the dexmedetomidine patients required no other sedative to maintain an RSS ≥ 3; 21% required < 50 mg propofol. In contrast, 76% of the control group received propofol; 59% required ≥ 50 mg. Dexmedetomidine patients required significantly less morphine for pain relief (P < .001). Continuously given throughout the ICU stay, dexmedetomidine had no effect on respiratory rate, oxygen saturation, duration of weaning, or times to extubation. Nurses judged the dexmedetomidine patients were easier to manage. Later, fewer dexmedetomidine patients remembered pain or discomfort. The majority of dexmedetomidine patients maintained blood pressures within normal range, without rebound. Hypertension, atelectasis, and rigors occurred more frequently in the control group, while hypotension and bradycardia occurred more frequently in the dexmedetomidine group. Preoperative cardiovascular conditions were not risk factors for dexmedetomidine patients.

New therapeutic uses for an alpha2 adrenergic receptor agonist--dexmedetomidine in pain management

Dexmedetomidine was initially approved for clinical use as a sedative. Its development in pain management has been limited. Dexmedetomidine has analgesic effects and analgesic-sparing properties, especially for patients with obstructed airways. Mixing dexmedetomidine with local anesthetics is a promising new avenue to enhance local anesthetics' effectiveness. Peripheral, spinal and supraspinal α(2A)-ARs are responsible for the analgesic function of dexmedetomidine. Animal studies have shown that antinociceptive synergism results from co-application of dexmedetomidine and opioids or local anesthetics. Dexmedetomidine has potential adverse effects such as hypotension and bradycardia. Therefore, dexmedetomidine is contraindicated for patients suffering from bradycardia or using β-adrenergic antagonists. Clinical trials of dexmedetomidine in chronic pain or hyperalgesia are lack.

Hypothermic responses to infection are inhibited by alpha2-adrenoceptor agonists with possible clinical implications

BACKGROUND

alpha(2)-Adrenoceptor agonists are currently used as primary sedative agents in high dependency patients who are at high risk of sepsis. Clinical surveillance of such patients relies in part on their ability to mount appropriate responses to infection, in particular thermal responses. Thermoregulatory responses to infection are well studied in the rat and in this species, and humans, infection can induce febrile, hypothermic, or mixed hypothermic and febrile responses. The involvement of noradrenergic systems in thermal responses to infection prompted the hypothesis that ligands that act on adrenoceptors may interfere with the normal thermal responses to infection.

METHODS

In this study on rats, the effect of infusion of the selective alpha(2)-agonist, mivazerol, on hypothermic and plasma corticosterone responses induced by bacterial lipopolysaccharide (LPS) was investigated.

RESULTS

Clinically effective doses of mivazerol (4.8 and 10 microg kg(-1) h(-1)) had no effect on body temperature alone. However, mivazerol significantly inhibited the typical thermoregulatory response to bacterial LPS in a dose-dependent manner. This effect was mimicked by the selective alpha(2)-agonist, UK14304-18 (6 microg kg(-1) h(-1)), and antagonized by the alpha(2)-antagonist, RX811059A (7 microg kg(-1) h(-1)). The alpha(2)-ligands had no effect on basal or LPS-induced corticosterone levels.

CONCLUSIONS

These data suggest that early thermoregulatory responses to infection can be selectively antagonized by ligands that activate alpha(2)-adrenoreceptors. High dependency patients receiving alpha(2)-adrenoceptor agonists may not be capable of mounting a normal thermal response to infecting organisms and clinical monitoring using core temperature to detect infection may therefore be unreliable in these vulnerable patients.

Neuroprotective effect of mivazerol, an alpha 2-agonist, after transient forebrain ischemia in rats

BACKGROUND

We examined whether mivazerol, an alpha2-agonist, had neuroprotective effects after transient forebrain ischemia in rats.

METHODS

Male Sprague-Dawley rats, anesthetized with halothane, were assigned to one of four groups (n=10 each): control (C, normal saline) and mivazerol 10 microg/kg (M10), 20 microg/kg (M20) and 40 microg/kg (M40) groups. Thirty minutes after drug administration, forebrain ischemia was induced with hemorrhagic hypotension and bilateral carotid artery occlusion for 10 min, and then the brain was reperfused. The neurologic outcome was evaluated 24 h, 48 h and 7 days after ischemia, followed by histologic evaluation.

RESULTS

The survival rate during 7 days was significantly lower in group M40 than in groups M10 and M20 (P<0.05). The neurologic outcome was significantly better in groups M10 and M20 than in group M40 7 days after ischemia (P<0.05). The number of intact neurons in hippocampal CA1 was significantly greater in group M20 than in the other groups (P<0.05). Neuronal injury in the neocortex was significantly less in group M20 than in groups C and M40 (P<0.05).

CONCLUSIONS

Our results suggest that mivazerol, up to 20 microg/kg, provides neuroprotective effects, whereas 40 microg/kg may exaggerate neuronal injury after transient forebrain ischemia in rats.

The pharmacological basis of contemporary pain management

Pain management has become an increasingly well researched area in medicine over recent years, and there have been advances in a number of areas. While opioids remain an integral part of pain-management strategies, there is now an emphasis on the use of adjuvant drugs, such as paracetamol and anti-inflammatory agents, which through physiological or pharmacological synergism, both enhance pain control and reduce opioid use. The management of neuropathic pain continues to be a challenge. Anti-epileptics and antidepressants, together with clonidine and ketamine, provide the foundations for treatment. Another area of interest has been the widespread use of patient-controlled analgesia and the administration of some drugs, especially opioids, by means other than traditional oral and parenteral routes. The number of new drugs that have reached the stage of clinical trials has been small, yet they offer exciting possibilities. The epibatidine analogue ABT-594 and zinconitide both offer novel approaches to the management of neuropathic pain states, while selective cyclo-oxygenase-2 inhibitors and nitroaspirins may see advances in the management of nociceptive pain states.

alpha-2 and imidazoline receptor agonists. Their pharmacology and therapeutic role

Clonidine has proved to be a clinically useful adjunct in clinical anaesthetic practice as well as in chronic pain therapy because it has both anaesthetic and analgesic-sparing activity. The more selective alpha-2 adrenoceptor agonists, dexmedetomidine and mivazerol, may also have a role in providing haemodynamic stability in patients who are at risk of peri-operative ischaemia. The side-effects of hypotension and bradycardia have limited the routine use of alpha-2 adrenoceptor agonists. Investigations into the molecular pharmacology of alpha-2 adrenoceptors have elucidated their role in the control of wakefulness, blood pressure and antinociception. We discuss the pharmacology of alpha-2 adrenoceptors and their therapeutic role in this review. The alpha-2 adrenoceptor agonists are agonists at imidazoline receptors which are involved in central blood pressure control. Selective imidazoline agonists are now available for clinical use as antihypertensive agents and their pharmacology is discussed.

Potentiation of barbiturate-induced alterations in presynaptic noradrenergic function in rat frontal cortex by imidazol(in)e alpha2-adrenoceptor agonists

1. In order to resolve the extent to which presynaptic noradrenergic mechanisms contribute to the anaesthetic-sparing effects of alpha2-adrenoceptor agonists in vivo microdialysis was used to investigate the combined effects of sodium pentobarbitone and imidazol(in)e alpha2-adrenoceptor agonists on extracellular levels of noradrenaline (NA) in the rat frontal cortex. 2. Dialysate levels of NA were markedly reduced by the addition of TTX (2 microM) or by the removal of calcium in the perfusate. These data imply that dialysate NA levels are ultimately dependent on exocytotic release mechanisms from afferent coeruleo-cortical neurones. 3. Systemic administration of sodium pentobarbitone (85 mg kg(-1), i.p.) induced general anaesthesia and reduced NA levels by 92% after 30 min. The restoration of basal levels 90 min later was closely associated with a return of the corneal blink reflex. 4. Basal NA levels in conscious animals were not affected by an intravenous infusion of equally radioactive solutions of either imidazoline (clonidine) or imidazole (mivazerol) alpha2-adrenoceptor agonists. The dose rate employed for each compound was 2 microg kg(-1) h(-1) over 2 h. 5. The co-administration of intravenous clonidine or mivazerol, each at 2 microg kg(-1) h(-1) for 2 h, with sodium pentobarbitone (85 mg kg(-1), i.p.), produced a marked and prolonged reduction in NA efflux. After 2 h, NA levels remained suppressed by 95% (clonidine) and 80% (mivazerol) and animals remained deeply anaesthetized. 6. The accumulation of tritium in brain tissue was 42-73% lower across all brain regions examined after [3H]-mivazerol administration than after [3H]-clonidine administration. Sodium pentobarbitone did not alter the accumulation of tritium in brain tissue after the administration of either alpha2-adrenoceptor agonist. 7. These data demonstrate that alpha2-adrenoceptor agonists potentiate the inhibitory effects of sodium pentobarbitone on extracellular levels of NA in the frontal cortex. Further studies will be necessary to establish a causal role of noradrenergic mechanisms in the potentiation of anaesthesia by selective alpha2-adrenoceptor agonists.

Catecholamine activation in the vasomotor center on emergence from anesthesia: the effects of alpha2 agonists

The rostral ventrolateral medulla (RVLM) controls the vascular system and may contribute to postoperative hypertension. It comprises adrenergic cardiovascular neurons, a site for action of alpha2-adrenergic agonists. Because alpha2 agonists minimize perioperative circulatory activation, we asked the following question: do alpha2 agonists, such as clonidine and mivazerol, blunt the catecholamine activation observed in the RVLM on emergence from anesthesia? Halothane-anesthetized, paralyzed rats had their ventilatory, circulatory, and acid-base stability controlled. All pressure points and incisions were infiltrated with local anesthetics. With in vivo electrochemistry, a catechol signal was recorded in the RVLM during 150 min of stable halothane anesthesia (saline-halothane group); for 120 min after halothane discontinuation (saline-emergence group); after emergence and administration of the reference alpha2 agonist, clonidine 7 microg/kg or 21 microg/kg I.V. (50% or 90% effective dose [ED50 or ED90], respectively); and after emergence and administration of a new alpha2 agonist, mivazerol 20 microg/kg or 150 microg/kg I.V. (ED50 or ED90). Under halothane, dose-response curves for the RVLM catecholamine signal were constructed for mivazerol and an alpha2 antagonist, idazoxan (ED50 2.3 mg/kg I.V.). Stable halothane anesthesia (n = 5) led to no change in mean arterial pressure (MAP), heart rate (HR), or catechol signal (CAOC). During emergence from anesthesia, the MAP, HR, and CAOC increased (n = 5). Clonidine led to a near total suppression of the RVLM catecholamine activation noticed on emergence from anesthesia (n = 5). Hypertension was partially blunted with clonidine 7 microg/kg (n = 5). Tachycardia was partially blunted with mivazerol 20 microg/kg (n = 5). Pretreatment with idazoxan suppressed all the effects of mivazerol (n = 5).

IMPLICATIONS

On emergence from anesthesia, alpha2 agonists modify the activity of adrenergic cardiovascular neurons located within the vasomotor center, as assessed by in vivo electrochemistry. We provide a rationale for the use of alpha2 agonists on emergence from anesthesia in coronary/hypertensive patients.

Mivazerol prevents the tachycardia caused by emergence from halothane anesthesia partly through activation of spinal alpha 2-adrenoceptors

BACKGROUND

Mivazerol (MIV) is an alpha 2-adrenoceptor agonist designed to prevent adverse cardiac outcome in perioperative patients. The present study was undertaken to determine whether the hyperdynamic state observed at emergence from halothane (HAL) anesthesia in rats could be modulated by MIV and to explore the mode of action of MIV under such conditions.

METHODS

Male Sprague Dawley rats were anesthetized with 1% HAL and assisted for respiration (N2O-O2: 70-30%). MIV 2.2-15.3 micrograms.kg-1.h-1 i.v. was infused 30 min before withdrawal of anesthesia and compared for heart rate (HR) and systolic arterial blood pressure (SAP) to control animals treated with saline. In some experiments, animals were pretreated with intrathecal pertussis toxin (T2 level, 0.5 microgram, 7 d), or i.v. rauwolscine (0.34 mg/kg, 5 min) or were bilaterally stellectomized (30 min) prior to withdrawal of HAL.

RESULTS

Increases in HR (65 bpm, +20%) and in SAP (25 mmHg, +26%) were observed immediately upon discontinuation of HAL and remained constant for at least 30 min. The increase in HR was abolished by removal of the stellate ganglia. MIV dose-dependently inhibited the increase in HR from 4.8 micrograms.kg-1.h-1 (68% reduction, P < 0.05) without affecting HR or SAP during anesthesia. Inhibition of HR increase was of 98% at 15.3 micrograms.kg-1.h-1. This effect was abolished by rauwolscine, and partially (50%) inhibited by pertussis toxin pre-treatment.

CONCLUSION

These results demonstrate that withdrawal of HAL anesthesia in the rat produces a sustained increase in HR due to activation of the sympathetic system and that MIV inhibits this tachycardia via activation of alpha 2-adrenoceptors located at least in part in the spinal cord.

Basal forebrain cholinergic immunolesion by 192IgG-saporin: evidence for a presynaptic location of subpopulations of alpha 2- and beta-adrenergic as well as 5-HT2A receptors on cortical cholinergic terminals

To study whether the changes in cortical noradrenergic and serotonergic mechanisms observed in patients with Alzheimer's disease are the consequence of reduced cortical cholinergic activity, a novel colinergic immunotoxin (conjugate of the monoclonal antibody 192IgG against the lower affinity nerve growth factor receptor with the cytotoxic protein saporin, 192IgG-saporin) was used to produce a specific and selective loss of cholinergic cells in rat basal forebrain nuclei. To correlate the responses to cholinergic immunolesion in cholinoceptive cortical target regions with cholinergic hypoactivity, quantitative receptor autoradiography to measure adrenoceptors and 5-hydroxytryptamine (5-HT) receptor subtypes, and histochemistry to estimate acetylcholinesterase activity, were performed in adjacent brain sections. alpha 1-adrenoceptor and 5-HT1A receptor binding were not affected by cholinergic immunolesion in any of the cortical and hippocampal regions studied. However, cholinergic immunolesion resulted in significantly reduced alpha 2- and beta-adrenoceptor as well as 5-HT2A receptor binding in a number of cortical and hippocampal regions displaying a reduced activity of acetylcholinesterase, already detectable seven days after a single injection of 192IgG-saporin and persisting up to three months post lesion without any significant recovery. The data suggest that at least a subpopulation of alpha 2- and beta-adrenoceptor as well 5-HT2A receptor subtype is present on cortical and hippocampal cholinergic terminals originating in the basal forebrain. The lesion-induced receptor changes suggest that the alterations in cortical 5-HT2 receptor binding observed in patients with Alzheimer's disease might be secondary to cholinergic deficits.

The novel alpha 2-adrenoceptor agonist [3H]mivazerol binds to non-adrenergic binding sites in human striatum membranes that are distinct from imidazoline receptors

The alpha 2 adrenergic agonist [3H]mivazerol labelled two populations of binding sites in membranes from the human striatum. Forty per cent of the sites labelled by 3 nM [3H]mivazerol corresponded to alpha 2 adrenergic receptors as they displayed a high affinity for (-)-adrenaline and for rauwolscine. The remaining binding was displaced by mivazerol with a pIC50 of 6.5 +/- 0.1. These sites displayed higher affinity for dexmedetomidine (pIC50 = 7.1 +/- 0.1), but much lower affinity for clonidine (pIC50 < 5.0) and for idazoxan (pIC50 = 5.1 +/- 0.1). Mivazerol also showed low affinity for the [3H]clonidine-labelled I1 imidazoline receptors and for the [3H]idazoxan-labelled I2 receptors (pIC50 = 5.1 and 3.9, respectively). These results suggest that the non-adrenergic [3H]mivazerol binding sites are distinct from the imidazoline receptors in the human striatum.

Mivazerol, a new alpha 2-adrenergic agonist, blunts cardiovascular effects following surgical stress in pentobarbital-anesthetized rats

BACKGROUND

Mivazerol is a new and selective alpha 2-adrenoceptor agonist, devoid of hypotensive effects, which has been designed to prevent adverse cardiac outcome in perioperative patients with, or at risk coronary artery disease.

METHODS

In the present study, the effects of mivazerol on hemodynamic changes induced by trachea-exposure surgery stress were investigated in pentobarbital-anesthetized rats, and compared to those of dexmedetomidine.

RESULTS

Intravenous infusion of 3 different doses of mivazerol (3.75, 7.5 and 15 micrograms.kg-1.h-1) did not significantly alter BP but caused a dose-related decrease in HR. The maximal decrease in HR was approximately 87 beats/min. Contrary to mivazerol, dexmedetomidine (7.5 micrograms.kg-1.h-1, i.v.) decreased both BP (11 +/- 3.2 mmHg) and HR. The maximum decrease in HR was approximately 104 beats/min. Surgical stress produced a rapid increase in BP (maximal increase of 50 mmHg) and HR (maximal increase of 100 beats/min), which lasted for at least 15 min. Constant infusion of mivazerol, at dose of 15 micrograms.kg-1.h-1, beginning 20 min prior to surgery and lasting for 35 min, significantly inhibited surgical stress-induced increases in BP (P < 0.05) and HR (P < 0.001). Dexmedetomidine, at a dose which produced hypotension and profound bradycardia prior to surgery, did not have any effect on the surgical stress-induced elevation in BP (P > 0.05), but prevented the increase in HR (P < 0.05). Pretreatment with the alpha 2-adrenoceptor antagonist rauwolscine (0.5 mg/kg, i.v.) blocked the bradycardia induced by mivazerol as well as the inhibitory effect of mivazerol on surgical stress-induced elevations in HR and BP.

CONCLUSION

Mivazerol attenuates surgical stress-induced elevations in BP and HR during pentobarbital anesthesia in rats, and these effects are mediated by stimulation of alpha 2-adrenoceptors. Unlike dexmedetomidine, mivazerol does not reduce BP, and is also more potent than dexmedetomidine in blunting surgical stress-induced increases in BP in pentobarbital-anesthetized rats.

Mivazerol, a selective alpha 2-adrenoceptor agonist, attenuates tachycardia by intrathecal injection of N-methyl-D-aspartate in the rat

The intravenous (i.v.) infusion of mivazerol, a new selective alpha 2-adrenoceptor agonist, produced a significant decrease in heart rate but not in blood pressure in pentobarbital-anesthetized Sprague-Dawley rats. The tachycardic response to intrathecal (i.t.) injection of N-methyl-D-aspartic acid (NMDA) was significantly attenuated by the i.v. infusion of mivazerol. The i.t. pretreatment with yohimbine significantly attenuated the bradycardic response to i.v. mivazerol and blocked the effect of mivazerol on the tachycardic response to i.t. NMDA. These results suggest that (1) the bradycardic effect of mivazerol is mediated, at least partly, by spinal alpha 2-adrenoceptors; and (2) there is a possibility of functional antagonism between spinal alpha 2-adrenoceptors and NMDA receptors in the regulation of heart rate.

Peripheral alpha 2-adrenoceptor-mediated sympathoinhibitory effects of mivazerol

Mivazerol is a new compound that could potentially reduce perioperative cardiovascular morbidity and mortality in patients with or at risk of coronary disease and submitted to surgery. This action of mivazerol depends on a well documented centrally mediated reduction in sympathetic nerve activity, but a direct peripheral decrease in sympathetic neurotransmitter release induced by activation of prejunctional alpha 2-adrenoceptors located on sympathetic nerve endings could also contribute. To investigate this issue, the effects of mivazerol on the pressor, systemic and regional hemodynamic (pulsed Doppler technique) as well as on the cardiac responses to electrical stimulation of the spinal cord (SCS) were measured in pithed rats in the absence and in the presence of mivazerol. Mivazerol exerted strong sympathoinhibitory effects: SCS-induced increases in blood pressure, total peripheral resistance and heart rate were dose-dependently reduced by mivazerol, but among the regional vascular beds investigated, only the hindlimb vasoconstrictor responses were significantly drug-affected. All these sympathoinhibitory effects of mivazerol were abolished by prior yohimbine administration. Simultaneously, mivazerol did not induce any postjunctional adrenoceptor blockade as it did not affect noradrenaline cardiac and hemodynamic effects. On the contrary, through postjunctional alpha 2-adrenoceptor stimulation, mivazerol, in this pithed preparation, dose-dependently increased blood pressure, total peripheral and hindlimb vascular resistances, but heart rate was not affected. We conclude that, in the pithed rat, mivazerol exerts strong peripheral sympathoinhibitory effects. The mechanism involved is prejunctional alpha 2-adrenoceptor activation as i) mivazerol does not display any postsynaptic alpha-adrenoceptor blocking effect--it even behaves as as postsynaptic alpha 2-adrenoceptor agonist--and ii) yohimbine abolishes mivazerol's sympathoinhibitory effects. Thus, direct peripheral together with central mechanisms contribute to mivazerol's sympathoinhibitory effects and ultimately to its cardioprotective action.

The effects of alpha 2-adrenergic stimulation with mivazerol on myocardial blood flow and function during coronary artery stenosis in anesthetized dogs

The central sympatholytic effect of alpha 2 agonists may be beneficial during myocardial ischemia, but could be opposed by their peripheral vasoconstrictive effect. We studied the effects of mivazerol during periods of moderate coronary artery stenosis in anesthetized dogs. Mivazerol decreased heart rate (from 125 +/- 6 to 106 +/- 6 bpm) and cardiac output (from 4.4 +/- 0.6 to 1.8 +/- 0.2L/min) under normal conditions, while mean arterial pressure did not change. Mivazerol reduced blood flow in nonischemic myocardium and in the ischemic epicardial layer, but blood flow was preserved in the ischemic midmyocardial and subendocardial layer. Mivazerol had no effect on myocardial oxygen extraction during the stenoses, and regional myocardial oxygen consumption was unchanged. However, mivazerol decreased myocardial oxygen demand from 4.51 +/- 0.51 to 3.17 +/- 0.24 mumol.min-1.g-1, thereby reducing oxygen deficiency of ischemic myocardium to values significantly lower than in the placebo group (from 1.07 +/- 0.32 to 0.47 +/- 0.41 mumol.min-1.g-1). Mivazerol had no effect on myocardial lactate production during the stenoses. We conclude that mivazerol reduced myocardial oxygen demand while blood flow was preserved in the inner layers of ischemic myocardium.

Effects of immobilization stress on hippocampal monoamine release: modification by mivazerol, a new alpha 2-adrenoceptor agonist

Mivazerol is a new and selective alpha 2-adrenoceptor agonist which has demonstrated anti-ischemic effects, both in animals and in patients with myocardial ischemia. In the present study, mivazerol was evaluated for its ability to inhibit the release of catecholamines and serotonin (5-HT) in the hippocampus of freely moving rats, and also was compared to clonidine. In vivo microdialysis in combination with high-performance liquid chromatography (HPLC) was employed. Intravenous administration of mivazerol (8.0 micrograms/kg) had no effect on basal outflow of norepinephrine (NE), dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC). In contrast, clonidine (8.5 micrograms/kg, i.v.) attenuated the basal release of DOPAC, which has been proposed to reflect NE biosynthesis, suggesting that clonidine has an inhibitory effect on NE synthesis. In addition, both mivazerol and clonidine decreased the spontaneous release of 5-HT, which provided further evidence that alpha 2-adrenoceptors in the hippocampus modulate 5-HT. Sixty-min immobilization stress significantly increased the release of NE (177 +/- 28%), DA (209 +/- 46%) and DOPAC (337 +/- 72%). Mivazerol (2.5, 8.0 and 25 micrograms/kg, i.v.) completely prevented the immobilization stress-induced enhancement of NE, DA and DOPAC, which was equi-effective to clonidine at a dose of 8.5 micrograms/kg, i.v. These findings demonstrate that mivazerol has a profound modulatory effect on stress-induced neurotransmitter release in the hippocampus, at dose levels reported to protect against myocardial ischemia.