Modification of certain pharmacological effects of ethanol by lipophilic alpha-1 adrenergic agonists.

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. In prazosin-pretreated mice, St 587 failed to reduce the hypnotic effect of ethanol, which provided strong evidence for the role of alpha-1 agonism for the hypnosis reducing effect of St 587. Hyperactivity induced in C57B1/6 mice by a subhypnotic dose of ethanol and St 587 was reported earlier. In the present study, St 587, cirazoline and (-)SKF 89748A produced similar response, but no correlation between this effect and ethanol hypnosis blockade could be established. Interestingly, this hyperactivity response was not exhibited by Swiss-Webster, BALB/c or DBA-2 mice--strains in which St 587 exerted little or no antagonism to ethanol-induced hypnosis. Of the alpha-1 agonists, only St 587 reduced the ethanol-induced hypothermia in C57B1/6 mice. St 587 also blocked this effect of ethanol in BALB/c mice in which this drug failed to reduce the ethanol-induced hypnosis. It was concluded that ethanol-induced hypothermia and hypnosis are not interrelated. None of the alpha-1 agonists modified the pentobarbitone-induced hypnosis or the rate of elimination of ethanol in C57B1/6 mice. In this strain, the reduction of the duration of ethanol-induced hypnosis by the alpha-1 agonists is a selective and centrally-mediated response.

Clorazepate use may prevent alcohol withdrawal convulsions.

Clorazepate dipotassium was administered orally for the five-day prophylactic treatment of potential, incipient and overt withdrawal signs and symptoms in 226 patients on admission to an inpatient alcohol treatment unit. Conservative estimates based on these patients' histories and on literature reports predicted that between 7 and 40 (3% to 18%) of these persons would be expected to have a withdrawal convulsion. No patients experienced convulsions. This complete absence of seizures suggests that clorazepate is effective in counteracting convulsive and other manifestations of the alcohol withdrawal syndrome.

Suitability of amfonelic acid-induced locomotor stimulation in mice as a model for the evaluation of classical and atypical antipsychotics.

The potential usefulness of amfonelic acid ( AFA ), a selective dopamine (DA)-releasing agent, in quantitatively assessing the antidopaminergic and antipsychotic potencies of drugs, was evaluated. The procedure consisted of determining the ED50S of a number of neuroleptics in inhibiting the locomotor-stimulant effect of amfonelic acid in mice. These results were compared with the published data on the relative potencies of the neuroleptics to induce catalepsy in rats, to block drug-induced stereotypy and to alleviate psychotic symptoms clinically. It was observed that the amfonelic acid model was as good as, but not superior to, the other three procedures in identifying the potencies of classical antipsychotics. This model, however, was able to predict the clinical effectiveness of two atypical antipsychotics, thioridazine and clozapine, much more accurately than could be achieved by the other methods. Certain other atypical antipsychotics such as, mezilamine , RMI 81, 582, sulpiride and sultopride also produced a dose-related blockade of the amfonelic acid induced locomotor stimulation in mice. The antagonism to amfonelic acid exhibited by mezilamine was weaker, and that of RMI 81,582 was stronger than that of chlorpromazine. Only large doses of the two benzamides were effective in blocking the effect of amfonelic acid, sultopride being about 3 times more effective than sulpiride in this regard. Another analogue of benzamide, YM-09151-2, known to have the profile of a classical antipsychotic, was more effective than haloperidol in blocking the stimulant effect of amfonelic acid. Trebenzomine , which is considered to have the properties of an atypical antipsychotic, although this was proved otherwise when tested clinically, actually potentiated the response of mice to amfonelic acid. Apomorphine antagonized the stimulant effect of amfonelic acid, which could be attributed to its agonist activity at presynaptic DA receptors. Apomorphine has been reported to have clinical antipsychotic effects. Certain non-antipsychotic drugs such as prazosin (but not phenoxybenzamine), promethazine, methysergide, diazepam, as well as the gamm -aminobutyric acid agonists, muscimol and THIP, also inhibited the amfonelic acid-induced locomotor stimulation. In spite of this drawback, the present procedure should prove to be a useful animal model for the evaluation of the antipsychotic potencies of drugs. Its ability to identify the potential usefulness of atypical antipsychotics is noteworthy.

Evidence for presynaptic antagonism by amantadine of indirectly acting central stimulants.

In mice, amantadine pretreatment (150 mg/kg, but not 10 mg/kg, 2 h prior to testing) markedly inhibited the locomotor stimulation produced by submaximal doses of d-amphetamine, amfonelic acid, methylphenidate, caffeine, memantin, phencyclidine, and cocaine. A 50-mg/kg dose was ineffective in blocking the effects of caffeine and memantin, but blocked the responses to the other five stimulants. Amantadine did not modify the locomotor stimulant effect of apomorphine in reserpinized mice. These results indicate that amantadine acts as a presynaptic antagonist to the above seven stimulants. Even the highest dose of amantadine did not modify the hyperactivity induced in mice by morphine and levorphanol. This result is consistent with evidence showing opiate actions at postsynaptic striatal neurons, sites where presumably amantadine is unable to exert an antagonist effect. Amantadine did not modify the central depressant effects of ethyl alcohol and pentobarbital. Amantadine could be of value as a pharmacological tool in understanding the mode of action of central stimulants, and in the management of stimulant abuse. The present data do not support the currently held view that the antiparkinsonism effect of amantadine results from its ability to potentiate the central effects of dopamine.

A new method for the evaluation of benzodiazepines based on their ability to block muscimol-induced myoclonic jerks in mice.

A number of clinically used benzodiazepines were tested for their effectiveness in blocking muscimol-induced myoclonic jerks in mice. Their ED50 values were determined from their dose-response curves. These data gave the following relative potencies with respect to diazepam: diazepam = 1, medazepam = 0.24, oxazepam = 1.27, flurazepam = 1.90, lorazepam = 3.01, nitrazepam = 3.93, clonazepam = 33.14, and flunitrazepam = 116.00. Because our earlier studies indicated that muscimol-induced myoclonic jerks probably originate from the spinal cord, the present method may prove to be suitable for quantitatively evaluating the effect of benzodiazepines on the spinal cord. The present results also indicate the possible value of flunitrazepam in the management of neurologic disorders in which preferential action on the spinal cord is desired.