Quantitative assessment of the central versus peripheral effect of intravenous clonidine using baroreflex equilibrium diagrams.

Clonidine is a first-generation central antihypertensive that reduces sympathetic nerve activity (SNA). Although clonidine also exerts peripheral vasoconstriction, the extent to which this vasoconstriction offsets the centrally mediated arterial pressure (AP)-lowering effect remains unknown. In anesthetized rats (n = 8), we examined SNA and AP responses to stepwise changes in carotid sinus pressure under control conditions and after intravenous low-dose (2 µg/kg) and high-dose clonidine (5 µg/kg). In the baroreflex equilibrium diagram analysis, the operating-point AP under the control condition was 115.2 (108.5-127.7) mmHg [median (25th-75th percentile range)]. While the operating-point AP after low-dose clonidine was not significantly different with or without the peripheral effect, the operating-point AP after high-dose clonidine was higher with the peripheral effect than without [81.3 (76.2-98.2) mmHg vs. 70.7 (57.7-96.9), P < 0.05]. The vasoconstrictive effect of clonidine partly offset the centrally mediated AP-lowering effect after high-dose administration.

The preclinical discovery of lofexidine for the treatment of opiate addiction.

INTRODUCTION: Lofexidine is one therapeutic option used for treating the onslaught of sympathetic outflow that typically commences upon induction of opiate withdrawal. It was approved for opiate detoxification in the UK, most of EU, and a select few countries worldwide during the 1980s and the 90s. Within the US and Canada, however, it remains an experimental drug. AREAS COVERED: The following article highlights lacunae in extant knowledge about the molecular pharmacology of lofexidine. Furthermore, the article provides a brief discussion on the nature and shortcomings of clinical trials for this drug that have been conducted over the past 30 years across the world. It also provides a discussion of the market factors and regulatory considerations responsible for the rather limited use of lofexidine thus far. EXPERT OPINION: Many lessons can be learned from the 40-year-long development of lofexidine. Indeed, unless there is an urgent need to address an unmet and/or immediate health threat, preclinical development is dictated by pharmacoeconomic considerations. Lofexidine would likely have been excluded for further development in this day and age given the existence and value of clonidine as well as the lack of insurance coverage for opiate addiction. It should be noted, however, that although there have been many oversights in the past, current experimentation and clinical trials are beginning to address the mistakes made through the exploration of single enantiomers and controlled-release preparations.

Neuroendocrine assessment of serotonergic, dopaminergic, and noradrenergic functions in alcohol-dependent individuals.

BACKGROUND: Alcohol dependence has been associated with reduced function of serotonin, dopamine as well as noradrenaline activities in several neuroendocrine studies. To our knowledge, there is, however, no study investigating all these 3 systems with the use of neuroendocrine methods in one and the same alcohol-dependent individual. METHODS: Alcohol-dependent individuals (n = 42) and controls (n = 28) participated in the neuroendocrine test series. Central serotonergic neurotransmission was assessed by the prolactin (PRL) response to citalopram (CIT). The postsynaptic DRD2 function was measured by the growth hormone (GH) response to apomorphine (APO) and the postsynaptic α2-adrenoceptor function by GH response to clonidine (CLON). RESULTS: In the alcohol-dependent individuals, the PRL concentrations were significantly lower at the time points 240 minutes and 300 minutes after CIT administration and mean delta PRL value was significantly reduced by 45% in comparison with controls. There were no significant differences in APO-GH and CLON-GH concentrations at any time points or in mean delta GH values between the groups. An impaired monoaminergic profile, including all 3 systems, was significantly more frequent in alcohol-dependent individuals than controls (43% vs. 6% respectively). CONCLUSIONS: The monoaminergic dysfunction was restricted to an impairment of the serotonergic system, suggesting that this system is especially vulnerable to long-term and excessive alcohol consumption. Moreover, impaired monoaminergic profiles, including low responses in 2 or 3 systems, were more frequently observed in alcohol-dependent individuals than in controls. Such impaired profiles may be of clinical importance, but further studies are needed.

Assessment of clonidine effect as premedicative drug on kidney function.

OBJECTIVE: To assess the effect of oral clonidine as a premedicative drug on 24-hour urine output, urine specific gravity, plasma renin activity as well as serum and urine electrolytes levels. METHODS: This prospective study was carried out on 60 women aged 20-40 years old undergoing repair of cystocoele-rectocoele perineorraphy under general anaesthesia in Asali Hospital in 2004 in Khorramabad, Iran. Subjects were randomly divided into two equal groups of 30 each. Group I and group II received clonidine tablet at the dose of 5 microg/kg and placebo tablet, respectively, 90 minutes before induction of general anesthesia. In this study, blood and urine samples were taken for laboratory measurements prior as well as 6 hours after taking the tablets. Differences between the two groups were compared through Mann-Whitney u-test, chi2 test and t-student test. P-value < 0.05 was considered statistically significant. RESULTS: There were no significant changes before and after receiving tablets in urine and blood Na and K as well as urine specific gravity in group II (P > 0.05). Group I had higher urine Na and K level (P = 0.001), however, no differences had been shown in blood Na and K level (P > 0.05). Urine specific gravity was lower in group I after receiving tablet (P < 0.009). A significant increase in 24-hour urine output (P = 0.001) and a marked decrease in plasma renin activity was seen in group I (P = 0.001). CONCLUSION: This study suggests that clonidine is a safe premedicative drug in anaesthesia and does not change the serum electrolytes levels.

Repeated assessment of cardiovascular and respiratory functions using combined telemetry and whole-body plethysmography in the rat.

INTRODUCTION: As the currently recommended laboratory techniques for assessing cardiovascular and respiratory functions are telemetry and plethysmography, we therefore combined both in a single rodent model. The purpose of the present work was to assess the potential influence of body growth on the recorded parameters, to verify the sensitivity of the system to detect well known pharmacological effects of reference drugs, and to determine their reproducibility over time. METHODS: Telemetry instrumented rats were enrolled in successive experiments over a total of 5 months. In each run, they were placed in individual plethysmography chambers for 6h, and received a single intraperitoneal injection of vehicle or test compound. Heart rate, blood pressure, body temperature and respiratory parameters were measured in real time. Six of these 16 rats were submitted 5 times at one month intervals to a vehicle injection, and six rats received theophylline (30 mg/kg) twice at 4 months interval. Nine other reference compounds were also tested at a single dose. RESULTS: Analysis of baseline data mainly showed correlations between body weight or age and heart rate, as well as tidal volume. In the five successive runs, handling-induced perturbations were noted in all the parameters during 60 to 90 min. The effects of the different reference drugs were consistent with data published in animals and man. The response to theophylline was qualitatively similar at 4 months interval. DISCUSSION: We established a combined model of telemetry and plethysmography in the conscious rat, allowing the reuse of the animals over several successive pharmacodynamic studies. Although a shift of some parameters, particularly heart rate and tidal volume, was noted with age and body weight, this can easily be managed by appropriate design measures. We showed that the combined system can detect negative or positive effects on both cardiovascular and respiratory functions with enough sensitivity.

Attenuation of hemodynamic responses following laryngoscopy and tracheal intubation -- comparative assessment of clonidine and gabapentin premedication.

OBJECTIVE: The present study was conducted to compare the effect of clonidine and gabapentin premedication in modifying the hyperdynamic response following laryngoscopy and tracheal intubation. METHODS AND MATERIALS: Seventy-five ASA I-II patients of both sexes (37 males (49.3%), 38 females (50.7%)) 18 to 45 years (mean 32.8 +/- 8.65 yr.) were randomly allocated into three equal groups (25 each). Group-1 received 0.2 mg clonidine, Group-2 received placebo and Group-3 received 900 mg gabapentin, 120 minute before operation. Heart rate, systolic, diastolic and mean arterial blood pressure were measured before induction of anesthesia, before laryngoscopy, and 1, 3, 5, 10 min after intubation. RESULTS: Analysis revealed that the heart rate, systolic, diastolic and mean arterial blood pressure significantly differed between groups (p<0.001, p = 0.003, p<0.001, p<0.001, respectively). The highest rates of heart rate, systolic, diastolic and mean arterial blood pressure were in the placebo group and in one minute after laryngoscopy, and the lowest rate were in the gabapentin group at the time of 1, 3, 5 and 10 after laryngoscopy, except that the lowest rate of heart rate in 10 min after laryngoscopy was in clonidine group. CONCLUSION: The data propose that both clonidine and gabapentin have effective role in blunting hyperdynamic responses after laryngoscopy, more so with gabapentin.

Transient allodynia pain models in mice for early assessment of analgesic activity.

BACKGROUND AND PURPOSE: The most common preclinical models of neuropathic pain involve surgical ligation of sensory nerves, which is especially difficult in mice. Transient models of chemically sensitized allodynia are potentially useful for rapidly characterizing the analgesic profile of compounds and conducting mechanistic studies. EXPERIMENTAL APPROACH: Increasing doses of NMDA, sulprostone (an EP1/EP3 prostaglandin receptor agonist) or phenylephrine (an alpha (1) adrenoceptor agonist) were injected intrathecally (i.t.) or i.p., and animals were subsequently assessed for allodynia. The effects of receptor antagonists and analgesic compounds on allodynia were also assessed. KEY RESULTS: A comparison of total body doses that cause allodynia following spinal or systemic administration indicated that NMDA induces allodynia in the spinal cord while sulprostone and phenylephrine act through a peripheral mechanism. Inhibition of the allodynia with receptor antagonists indicated that each agent induces allodynia by a distinct mechanism. The three models were benchmarked using compounds known to be active in neuropathic pain patients and nerve injury animal models, including gabapentin, amitriptyline and clonidine. CONCLUSIONS AND IMPLICATIONS: These transient allodynia models are a useful addition to the toolbox of preclinical pain models. They are simple, rapid and reproducible, and will be especially useful for characterizing the pain phenotype of knockout mice.

An optimised methodology for the neurobehavioural assessment in rodents.

INTRODUCTION: The most widely used test to identify undesired effects of drugs on the central and the peripheral nervous system is the neurobehavioural observation battery adapted from that first described by Irwin in mice. As a neurobehavioural assessment is based on observations; thus, all factors involved need to be controlled and standardised to make the data collected objective, reproducible, reliable and predictive of safety liabilities. METHODS: An observation battery comprising 58 signs with assigned full details of numerical scores was defined, and a standard design with associated recording, presenting and analysing data system was established. Validation studies were conducted with chlorpromazine, amphetamine, diazepam or clonidine given orally to rats or mice, in order to assess if this methodology could clearly differentiate the profile of effects produced by these compounds. The analysis of data from 80 control rats allowed for the assessment of the normal behaviour in order to characterise the inter-individual, daytime-related variability and the habituation of animals to the procedure. RESULTS: The reference compounds induced their typical and expected transient effects on neurobehaviour, observed both in the home cage and open-arena, and on body temperature. In particular, amphetamine induced a stimulation of the nervous system activities and marked hyperthermia. Chlorpromazine, diazepam and clonidine induced depressive, anxiolytic or sedative effects associated with hypothermia. The analysis of data collected in control animals allowed for the identification of 6 signs which scored differently from the assigned normality at the first handling occasion due to the characteristic fear reactions to the unknown, and 9 signs at 8 h post-dose due to the animal's habituation to experimental conditions and handling. DISCUSSION: The neurobehavioural changes expected by reference compounds administration were detected. These results confirm that by using this methodology the normal behaviour of the rat and the mouse, the daytime-related variability and the habituation of animals can be characterised, allowing a refined, reliable and reproducible neurobehavioural assessment of test substances in rodents.

Transdermal clonidine: therapeutic considerations.

Transdermal clonidine was approved by the US Food and Drug Administration in 1984 for the treatment of mild-to-moderate hypertension alone or in combination with a diuretic. Clonidine is released from the patch at a constant rate and thus displays a pharmacokinetic pattern not dissimilar to that of infusion therapy. Transdermal clonidine, like oral clonidine, is effective first- or second-line therapy for most forms of hypertension. More recently, transdermal clonidine has found alternative uses in the areas of smoking cessation, posttraumatic stress disorder, menopausal hot flashes, and alcohol and opiate withdrawal syndromes. The not infrequent development of a dermatitis, together with a substantially greater cost than oral clonidine, have been the major undoings for transdermal clonidine.

Noninvasive assessment of gastric emptying by near-infrared fluorescence reflectance imaging in mice: pharmacological validation with tegaserod, cisapride, and clonidine.

Noninvasive near-infrared fluorescence reflectance imaging (FRI) is an in vivo technique to assess physiological and molecular processes in the intact organism. Here we describe a method to assess gastric emptying in mice. TentaGel beads with covalently bound cyanine dye (Cy5.5) conjugates as fluorescent probe were administered by oral gavage. The amount of intragastric beads/label was derived from the fluorescence signal intensity measured in a region of interest corresponding to the mouse stomach. The FRI signal intensity decreased as a function of time reflecting gastric emptying. In control mice, the gastric half-emptying time was in agreement with literature data. Pharmacological modulation of gastric motility allowed the evaluation of the sensitivity of the FRI-based method. Gastric emptying was either stimulated or inhibited by treatment with the 5-HT(4) receptor agonists tegaserod (Zelnorm) and cisapride or the alpha(2)-receptor agonist clonidine, respectively. Tegaserod and cisapride dose-dependently accelerated gastric emptying. In contrast, clonidine dose-dependently delayed gastric emptying. In conclusion, FRI using fluorescently labeled beads allows the reliable determination of gastric emptying as well as the assessment of pharmacological interventions. The technique thus offers the potential to characterize molecular targets and pathways involved in physiological regulation and pharmacological modulation of gastric emptying.

Prospective assessment of tizanidine for spasticity due to acquired brain injury.

OBJECTIVE: To determine if orally delivered tizanidine will control spastic hypertonia due to acquired brain injury. DESIGN: Randomized, double-blind, placebo-controlled, crossover design, with 2 8-week treatment arms separated by a 1-week washout period at baseline. Patients were randomly assigned to receive tizanidine or a matching placebo. SETTING: Tertiary care outpatient and inpatient rehabilitation center attached to a university hospital. PARTICIPANTS: Seventeen persons recruited in a consecutive manner, 9 of whom had suffered a stroke and 8 a traumatic brain injury, and had more than 6 months of intractable spastic hypertonia. INTERVENTION: Over a 6-week period, subjects were slowly titrated up to their maximum tolerated dose (up to 36 mg/d). Following a 1-week drug taper and 1-week period in which no study drug was administered, patients were then crossed over to the other study medication following an identical titration regime. MAIN OUTCOME MEASURES: Subjects were evaluated for dose and effect throughout the trial as well as for side effects. Data for Ashworth rigidity scores, spasm scores, deep tendon reflex scores, and motor strength were collected on the affected upper extremity (UE) and lower extremity (LE). Differences over time were assessed via descriptive statistics, Friedman's analysis, and Wilcoxon's signed-rank. Data are reported as the mean +/- 1 standard deviation. RESULTS: Following 4 weeks of treatment when subjects reached their maximal tolerated dosage, the average LE Ashworth score on the affected side decreased from 2.3 +/- 1.4 to 1.7 +/- 1.1 (p <.0001). The spasm score decreased from 1.0 +/- 0.9 to 0.5 +/- 0.8 (p =.0464), while the reflex score was not statistically significant decreasing from 2.2 +/- 1.0 to 2.0 +/- 1.1 (p =.0883). The average UE Ashworth score on the affected side decreased from 1.9 +/- 1.1 to 1.5 +/- 0.9 (p <.0001). There was no significant change in the UE spasm and reflex scores. While there were positive placebo effects on motor tone, the active drug was still significantly better than placebo for decreasing LE tone (p =.0006) and UE tone (p =.0007). With a reduction in motor tone, there was an increase in motor strength (p =.0089). The average dosage at 4 weeks was 25.2mg/d. CONCLUSION: Tizanidine is effective in decreasing the spastic hypertonia associated with acquired brain injury, which is dose-dependent. There are limitations on its use due to side effects related to drowsiness.

Clinical assessment of clonidine in the treatment of new-onset rapid atrial fibrillation: a prospective, randomized clinical trial.

PURPOSE: The role of digoxin and verapamil in the control of ventricular response in rapid atrial fibrillation is well established. This study investigates how clonidine compares with these standard therapies in rate control for new-onset rapid atrial fibrillation. We set out to test the hypothesis that clonidine effectively reduces heart rate in patients with new-onset rapid atrial fibrillation. SUBJECTS AND METHODS: Forty patients were seen in the emergency department with new-onset (< or =24 hours' duration), stable, rapid atrial fibrillation. Eligible patients were randomized to receive either clonidine, digoxin, or verapamil. Changes in heart rate and blood pressure over 6 hours, as well as frequency of conversion to sinus rhythm were recorded and analyzed. RESULTS: The mean reduction in heart rate over 6 hours was 44.4 beats/min (95% confidence interval [CI] 28.4-60.4 beats/min) in the clonidine group, 52.1 beats/min (95% CI 40.8-63.4 beats/min) in the digoxin group, and 41.8 beats/min (95% CI 22.5-61.0 beats/min) in the verapamil group. Analysis of variance of the heart rate changes in the 3 groups after 6 hours was not significant (P =.55). At 6 hours, 7 of 12 clonidine patients, 8 of 15 digoxin patients, and 7 of 13 verapamil patients remained in atrial fibrillation (P =.962 on chi(2)). CONCLUSION: Clonidine controls ventricular rate in new-onset atrial fibrillation with an efficacy comparable to that of standard agents.

Physiological, pharmacological and neurohormonal assessment of autonomic function in progressive supranuclear palsy.

The clinical features of progressive supranuclear palsy (PSP) overlap with other parkinsonian syndromes, including multiple system atrophy (MSA). Autonomic dysfunction is a characteristic of MSA, but has also been described in PSP. We therefore report results from a series of physiological studies of cardiovascular autonomic function in 35 PSP and 20 MSA subjects, and 26 age-matched healthy control subjects. The response to growth hormone-clonidine testing, a neuropharmacological assessment of central adrenoceptor function, was also assessed in 14 PSP and 10 MSA subjects, and compared with 10 controls. None was on medication which may have affected the results. Orthostatic hypotension did not occur in PSP subjects or controls, unlike MSA subjects. Overall there was no evidence of sympathetic vasoconstrictor failure in PSP subjects, unlike MSA subjects, although the pressor response to mental arithmetic was reduced. Cardiac parasympathetic function was affected in only a minority (three of 35) of PSP subjects and was abnormal in MSA subjects. After clonidine administration, growth hormone rose in PSP subjects (median increase 4.3; interquartile range 1.8-7.8 mU/l) and controls, unlike MSA subjects (0.9; 0.3-2.4 mU/l; P < 0.005, Mann-Whitney U-test). In conclusion, in PSP subjects, responses to both physiological and pharmacological tests provided evidence against widespread autonomic dysfunction; this differed markedly from MSA subjects. Thus, cardiovascular autonomic dysfunction should be an exclusionary feature in the diagnosis of PSP.

Functional assessment of recombinant human alpha(2)-adrenoceptor subtypes with cytosensor microphysiometry.

We applied the Cytosensor Microphysiometry system to study the three human alpha(2)-adrenoceptor subtypes, alpha(2A), alpha(2B) and alpha(2C), expressed in Chinese hamster ovary (CHO) cells, and assessed its potential in the quantitative monitoring of agonist activity. The natural full agonist, (-)-noradrenaline, was used to define agonist efficacy. The imidazole derivative dexmedetomidine was a potent full agonist of all three receptor subtypes. The imidazolines clonidine and UK 14,304 (5-bromo-N-(4, 5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine) appeared to be partial agonists at alpha(2B)-adrenoceptors (E(max) approximately 60% of (-)-noradrenaline) but full agonists at alpha(2A)- and alpha(2C)-adrenoceptors. The responses mediated by all three alpha(2)-adrenoceptor subtypes were partly inhibited by the sodium-hydrogen (Na(+)/H(+)) exchange inhibitor, MIA (5-(N-methyl-N-isobutyl)-amiloride). The agonist responses were totally abolished by pretreatment with pertussis toxin in cells with alpha(2A)- and alpha(2C)-adrenoceptors, and partly abolished in cells with alpha(2B)-adrenoceptors. The residual signal in alpha(2B)-cells was sensitive to the intracellular Ca(2+)chelator, BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid acetoxymethyl ester). Cholera toxin (which acts on G(s)-proteins) had no effect on the agonist responses. The results suggest that the extracellular acidification responses mediated by all three human alpha(2)-adrenoceptor subtypes are dependent on Na(+)/H(+)exchange and G(i/o) pathways, and that alpha(2B)-adrenoceptors are capable of coupling to another, G(i/o)-independent and Ca(2+)-dependent signaling pathway.

An assessment of the peripheral antinociceptive potential of remoxipride, clonidine and fentanyl in sheep using the forelimb tourniquet.

A modification of the intravenous regional anaesthesia technique was used to assess the peripheral antinociceptive effect of remoxipride, clonidine and fentanyl. Drugs administered intravenously via peripheral catheters were restricted to the distal limb and nociceptive threshold test site by prior inflation of a tourniquet proximal to both the catheter and a threshold-testing device. Lignocaine (1 mg/kg) induced peripheral antinociception during tourniquet inflation. Clonidine (6 micrograms/kg) only induced significant elevations in thresholds after tourniquet deflation. A low dose of remoxipride (2 mg/kg), which had no systemic antinociceptive effect, produced antinociception after its restriction to the periphery. Peripheral administration of saline and tourniquet-induced restriction of blood flow to the distal limb did not alter threshold values. Peripheral administration of fentanyl was used to test a further modification of the injection protocol designed to reduce the incidence of leakage into the systemic circulation. Fentanyl administration (11.2 micrograms/kg) failed to elicit an increase in thresholds when it was restricted to the distal limb test site. The contribution of a peripheral mechanism to the antinociception induced by systemic administration of a higher remoxipride dose (7.5 mg/kg) was investigated using an inflated tourniquet to exclude remoxipride from the periphery. Exclusion of remoxipride from the periphery reduced its antinociceptive effect, i.e. threshold values were lower than if remoxipride was allowed free access to the limb prior to tourniquet inflation. The technique described here was effective in demonstrating that the increase in noninflammatory nociceptive thresholds seen with clonidine and fentanyl is not peripherally mediated whilst that seen with remoxipride has a peripheral component.

Oral clonidine premedication decreases energy expenditure in human volunteers.

PURPOSE: Clonidine not only stops postoperative shivering and decreases oxygen consumption, but also decreases energy expenditure with or without a reduction in shivering during recovery from anaesthesia. It is important to see if clonidine decreases energy expenditure at rest since this may contribute to a postoperative decrease in energy expenditure. The authors tested the hypothesis that oral clonidine decreases energy expenditure at rest. METHODS: Twenty healthy male volunteers were randomly assigned to one of two groups. Ten volunteers received oral clonidine approximately 5 micrograms.kg-1 (clonidine group), while the remaining 10 volunteers received placebo (control group). Blood pressure, heart rate, body temperature at the tympanic membrane, sedation score graded from 1 (alert) to 5 (sleeping and difficult to be aroused by tactile stimulation) were measured before and at 30-min intervals for three hours after administration of clonidine or placebo. Measurements of energy expenditure and respiratory quotient were made with a head canopy system at one-minute intervals and averaged over 15 min before, and at 30, 60, 90, 120, and 180 min after administration of clonidine or placebo. RESULTS: Sedation score increased from 1 to 3 (median) after clonidine administration. Energy expenditure decreased from 1452 +/- 225 kcal.24hr-1 (mean +/- SD) at baseline to 1258 +/- 175 kcal.24hr-1 at 180 min after clonidine administration (P < 0.05). CONCLUSION: This study suggests that oral clonidine at a dose of 5 micrograms.kg-1 decreases energy expenditure at rest.

A hidden Markov model approach to neuron firing patterns.

Analysis and characterization of neuronal discharge patterns are of interest to neurophysiologists and neuropharmacologists. In this paper we present a hidden Markov model approach to modeling single neuron electrical activity. Basically the model assumes that each interspike interval corresponds to one of several possible states of the neuron. Fitting the model to experimental series of interspike intervals by maximum likelihood allows estimation of the number of possible underlying neuron states, the probability density functions of interspike intervals corresponding to each state, and the transition probabilities between states. We present an application to the analysis of recordings of a locus coeruleus neuron under three pharmacological conditions. The model distinguishes two states during halothane anesthesia and during recovery from halothane anesthesia, and four states after administration of clonidine. The transition probabilities yield additional insights into the mechanisms of neuron firing.