The influence of four centrally-acting alpha-1 adrenoceptor agonists, namely, 2(2-chloro-5-trifluoromethylphenylimino) imidazolidine (St 587), cirazoline, (-) 1,2,3,4-tetrahydro-8-methoxy-5-methylthio-2-naphthalenamine ((-)SKF 89748A) and 2-(2-methylindazol-4-imino)imidazolidine (Sgd 101/75) on the pharmacological effects of ethanol was investigated. All four drugs reduced the duration of ethanol-induced hypnosis in C57B1/6 mice, this effect being proportional to their relative potencies to exert central alpha-1 agonism.
The anesthetic-reducing property of medetomidine far exceeds that seen with other alpha 2-adrenergic agonists (e.g., clonidine). This study examined whether medetomidine possesses hypnotic-anesthetic actions. Dexmedetomidine (the d-enantiomer of medetomidine) induced loss of righting reflex in rats (i.e., hypnosis) at doses greater than 100 micrograms/kg i.p.; sleep-time was dose-dependent up to 1000 micrograms/kg i.p. The l-enantiomer of medetomidine (MPV-1441) did not induce hypnosis even when administered up to 30,000 micrograms/kg i.p.
Dexmedetomidine, a highly selective and potent alpha-2 adrenoceptor agonist, reduces halothane anesthetic requirements by over 90% in rats. The present study examined whether dexmedetomidine produces a hypnotic-anesthetic action in rats. Dexmedetomidine induced a hypnotic-anesthetic state in rats characterized by loss of righting reflex at doses greater than or equal to 0.1 mg/kg. This response was dose-dependent between 0.1 and 3 mg/kg.
Dexmedetomidine, a highly selective and potent agonist at alpha-2 adrenoceptors, produces a hypnotic-anesthetic action in rats. The mechanism for this response may involve an inhibitory G-protein and increased conductance through a potassium channel. To investigate this, the effects of pertussis toxin, a specific inactivator of inhibitory G-proteins, and 4-aminopyridine, a blocker of potassium channels, on the hypnotic-anesthetic response to dexmedetomidine were studied in rats.
The effects of chronic administration of the calcium channel antagonist verapamil on the anesthetic effects of a novel specific alpha 2-receptor agonist (dexmedetomidine) were studied in rats. It is presumed that this agonist acts on both pre- and postsynaptic alpha 2-adrenoceptors. To determine whether the central postsynaptic receptors are involved in the anesthetic interactions between these drugs, rats were treated with DSP-4 to deplete endogenous norepinephrine. Loss of the righting reflex was used to determine the presence of anesthesia and the duration of hypnosis.
Previously, we demonstrated that dexmedetomidine, an alpha 2 agonist, produces a hypnotic-anesthetic response in rats via activation of central alpha 2 adrenoceptors and that this response could be enhanced by the alpha 1 antagonist prazosin. In the current experiment we investigated whether central alpha 1 adrenoceptor stimulation antagonizes the alpha 2 adrenoceptor-mediated hypnotic response.
The role of serotonergic pathways in the hypnotic response to dexmedetomidine was examined in neurochemical and behavioral studies. Following acute administration of dexmedetomidine, loss of righting reflex and changes in serotonin (5-hydroxytryptamine, 5-HT) and norepinephrine turnover in different brain regions (locus coeruleus and hippocampus) were assessed. In separate experiments, the effect of dexmedetomidine on 5-HT turnover was measured in rats rendered tolerant to the hypnotic effects of dexmedetomidine.
The effect of tizanidine given as a premedication on perioperative hemodynamics (mean blood pressure, heart rate), sedation, hypnosis and midazolam requirements for induction were assessed in 68 patients scheduled for elective surgery under general anesthesia. Patients were assigned to three groups. Group 1 was premedicated 90 min prior to induction with tizanidine 4 mg po (n = 28); group 2 was premedicated with tizanidine 2 mg po (n = 12); group 3 received no premedication (n = 28).
The Journal of Pharmacology and Experimental Therapeutics
This study characterizes the pharmacokinetic-pharmacodynamic (PK-PD) relationships of the cardiovascular, EEG, hypnotic and ventilatory effects of the alpha-2 adrenergic agonist dexmedetomidine in rats. Dexmedetomidine was administered by a single rapid infusion (n = 6) and by an infusion regimen of gradually increasing rate (n = 8). HR, mean arterial pressure (MAP) and EEG signals were recorded continuously, as was the time at which the rats woke up spontaneously from drug-induced sleep, a measure of hypnosis.
Tourette's disorder is a neuropsychiatric disorder characterised clinically by motor and vocal tics, which may be associated to conductual disorders such as obsessive-compulsive disorder (OCD) and attention-deficit hyperactivity disorder (ADHD). Although the neurochemistry of Tourette's disorder is not well known, there are some effective therapies for tics, OCD and ADHD. However, these are not devoid of adverse effects. Tics only require treatment when they interfere with the functioning of the patient.
