Albert A. Manian

A comparative study of certain pharmacologic responses following acute and chronic administrations of chlordiazepoxide

Abstract Certain pharmacological responses in mice and rats were contrasted following acute and chronic administrations of chlordiazepoxide. In both species, studies were conducted after oral or intraperitoneal administration of drug. The tests used were (a) hexobarbital sleeping time, (b) hotplate analgesia, (c) maximal electroshock seizure, (d) spontaneous motor activity, (e) forced locomotor activity (rotarod) and (f) pit avoidance learning. Differences in drug response between acute and chronic treatment groups were compared using several dosage regimens. Differences attributable to handling were minimized by using identical dosage schedules and by treating those animals which received drug acutely with solvent given repeatedly during the experimental period. Several instances of tolerance to the depressant actions of chlordiazepoxide were observed after fourteen days of treatment in this study. Such reduced effectiveness was evident in all the tests used. Evidence was obtained in animals tested for anticonvulsant properties at one and at 20 hours following drug administration which suggested that an increase in the rate of metabolism participated in the mechanisms of such tolerance.

Actions of phenothiazine analogues on dopamine-sensitive adenylate cyclase in neuronal and glial-enriched fractions from rat brain.

Abstract Dopamine (DA) at 10 −4 M readily activated adenylate cyclase in homogenates of neuronal and glial-enriched fractions prepared from rat cerebral cortex, thalamus, striatum and the total homogenate from the striatum. Several derivatives of phenothiazines were tested for their ability to modify either the control component or the DA-sensitive receptor moiety of the enzyme. Dihydroxy analogues of chlorpromazine (CPZ), prochlorperazine, perphenazine. promazine and 7.8-dioxo-CPZ exhibited the most potent antagonism of either basal or DA-induced activation of the enzyme. In some cases at lowest concentrations the basal activity of adenylate cyclase was enhanced by these dihydroxy compounds. Parent compounds and corresponding monohydroxy metabolites of CPZ, prochlorperazine, perphenazine and fluphenazine were less potent toward antagonism of control enzyme preparations, but nevertheless exerted rather powerful antagonism at the DA-sensitive receptor site of adenylate cyclase. In this regard, 8-hydroxy derivatives were somewhat more potent than respective 7-hydroxy derivatives. Likewise, prochlorperazine and corresponding analogues were overall the most potent compounds. The 7-methoxy derivative of CPZ, along with thiothixene. thioridazine and haloperidol, was observed to exert a weaker antagonism of the DA-sensitive enzyme. Weakest inhibitory actions on either control or DA-sensitive sites of adenylate cyclase were seen with promazine, 2-OH- and 3-OH-promazine, clozapine, promethazine. CPZ-SO and 7,8-diMeO-CPZ. Phenothiazine, 3-OH-phenothiazine and 2-Cl-7,8-dioxo-phenothiazine were without effect. These findings suggest that molecular actions of pharmacologically active phenothiazines within the central nervous system are not totally reflected by the parent compounds, but may instead be additionally manifested by one or more metabolites.

Radioassay of chlorpromazine and its metabolites in plasma

Conditions have been established for the quantitative formation of radiolabeled derivatives of chlorpromazine, chlorpromazine sulfoxide and their demethylated analogs in plasma extracts.Tritiated N-acetyl derivatives are formed from the demethylated compounds and C14-quaternary amines from the tertiary amines by acetylation and methylation, respectively. These reactions are quantitative over a wide range of concentrations.The reactions may be performed sequentially when chloropromazine and its Nor derivatives (or chlorpromazine sulfoxide and its Nor derivatives) exist in a single extract. Herein, the mixture is first acetylated and subsequently methylated. The labeled derivatives are quantitatively separated and recovered by selective solvent partition.An extraction procedure has been suggested by which chlorpromazine and its Nors may be separated from chlorpromazine sulfoxide and its Nor derivatives so that each fraction may be subjected to the sequential acetylation and methylation reactions. Recoveries of μg quantities of standards from plasma are less than quantitative, probably because of losses due to glass adsorption and protein binding, but may be corrected with appropriate internal standards. As low as 15–20 ng/ml of each compound are measurable in a 3 ml plasma aliquot.The method has been applied to a limited number in vivo experiments in dogs and in humans.

The metabolism of hydroxychlorpromazines by rat liver microsomes

Abstract The metabolism of a series of chlorpromazine derivatives was studied with a fortified preparation of rabbit liver microsomes. All of the monohydroxylated derivatives underwent mono- N -demethylation as the principal metabolic pathway. In addition, these hyaroxychlorpromazines were shown to undergo further hydroxylation to form ortho-dihydroxychlorpromazines, which were then mono- O -methylated. Thus, 7-hydroxychlorpromazine, a major metabolite of chlorpromazine, was apparently converted with this system to a mono- O -methylated 7,8-dihydroxychlorpromazine, which represents a new metabolic pathway.

Muscarinic cholinergic receptor binding: Influence of pimozide and chlorpromazine metabolites

Abstract The relative muscarinic anticholinergic actions of phenothiazines and related drugs are thought to regulate the propensity of these agents to elicit extrapyramidal side effects, especially those resembling the symptoms of Parkinsons disease. Pimozide, which closely resembles the butyrophenones in its chemical structure and its potent and selective dopamine receptor blockade, differs from the butyrophenones in its relatively low incidence of extrapyramidal side effects. In assays of the binding of 3H-quinuclidinyl benzilate (QNB) to muscarinic sites, pimozide displays a high affinity for these cholinergic receptors, similar to drugs, such as thioridizine and clozapine, which also have a low incidence of extrapyramidal side effects. This observation supports the notion that muscarinic anticholinergic actions can ameliorate the propensity of a drug to elicit extrapyramidal effects. The structure-activity relationships of chlorpromazine metabolites in binding to muscarinic sites in the brain parallels some of their structure-activity relationships as neuroleptic agents. 7-Hydroxychlorpromazine, which has been proposed as an antischizophrenic drug, binds to the muscarinic receptor with a potency similar to that of chlorpromazine itself, suggesting that the incidence of extrapyramidal side effects of 7-hydroxychlorpromazine might be similar to those of chlorpromazine.

Reactivity of various phenothiazine derivatives with oxygen and oxygen radicals

Abstract 7,8-Dihydroxychlorpromazine, 7,8-dihydroxyprochlorperazine and 7,8-dihydroxyperphenazine all reacted with O 2 to make hydrogen peroxide (H 2 O 2 ). The rate of reaction between the ortho -dihydroxyphenothiazines and O 2 was increased by superoxide dismutase, an enzyme which catalyzes the dismutation of the superoxide radical (O 2 − ) to H 2 O 2 and O 2 . This indicated the formation of O 2 − during the autoxidation of the ortho -dihydroxyphenothiazines. Several phenothiazines lacking the ortho -dihydroxy groups did not consume O 2 at a detectable rate (did not generate H 2 O 2 ). All ortho -dihydroxyphenothiazines tested also reacted with O 2 in the presence of methional to form ethylene. Ethylene formation was inhibited by catalase and hydroxyl radical (·OH) trapping agents, such as sodium benzoate; this indicated ·OH formation from the ortho -dihydroxyphenothiazines. In addition, several nonhydroxylated phenothiazines and monohydroxylated phenothiazines inhibited ethylene generation from 6-aminodopamine, which also generates ·OH. This inhibition was probably mediated by a reaction between the phenothiazine and ·OH. All of the above reactions (generation of H 2 O 2 , O 2 − or ·OH or reaction with ·OH) may be responsible for some of the beneficial and/or adverse effects of administered phenothiazines.