The pharmacological properties of a phenothiazine derivative thioproperazine have been compared with those of chlorpromazine, and the modifications by some anti-Parkinsonian drugs of its actions on the central nervous system have been studied. Thioproperazine was less potent than chlorpromazine in lowering blood pressure and antagonizing adrenaline in the cat, in depressing respiratory rate in the rabbit, in producing hypothermia and analgesia and in reducing the minimum anaesthetic dose of hexobarbitone in mice, and in protecting rats from convulsions induced by tryptamine. It was roughly equipotent to chlorpromazine in reducing locomotor activity of mice. Thioproperazine was more potent than chlorpromazine in protecting grouped mice from the acute toxicity of dexamphetamine, in preventing the acute behavioural disturbances produced by dexamphetamine in the rat, in producing a state of experimental catatonia in the rat and in preventing the emetic action of apomorphine in the dog. Hyoscine, benztropine or promethazine greatly reduced the ability of thioproperazine to prevent behavioural changes due to dexamphetamine in the rat and also abolished symptoms of experimental catatonia produced by thioproperazine. In contrast, the antiapomorphine activity of thioproperazine in the dog was not reduced to any extent by hyoscine or benztropine.
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