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How to explain the Clozapine-induced sialorrhea?

Conference paper
Authors Jörgen Ekström
Tania Godoy
Riva A
Published in International Symposium on Morphological Sciences;Taotmina-Messina;18-22 september 2010
Pages 24
Publication year 2010
Published at Institute of Neuroscience and Physiology
Institute of Neuroscience and Physiology, Department of Pharmacology
Pages 24
Language en
Keywords amisulpride;clozapine;N-desmethylclozapine;sialorrhoea
Subject categories Physiology, Physiology

Abstract

About one-third of the schizophrenic patients receiving clozapine-therapy complain of hypersalivation, which is particularly troublesome during the night, and which may lead to discontinuation of the treatment. Objective measurements of the salivary flow are few, and data are, in fact inconsistent. The reported hypersalivation has, by some authors, even been attributed to a dysfunctional swallowing reflex. Animal experiments on the in vivo salivary effect of clozapine have been lacking until recently. We have established, using the anaesthetized rat as model, that clozapine, indeed, causes secretion from parotid and submandibular glands. The effect is small and "direct", indepentent of central nervous mechanisms, pre-synaptic intraglandular events and circulating catecholamines. It is exerted via muscarinic-M1-receptors, since it is abolished by pirenzepine. Clozapine exerts dual effects, since it inhibits secretion mediated via muscarinic-M3-receptors and α-adrenergic receptors and consequently, reduces both parasympathetic and sympathetic nerve evoked secretion. A main metabolite of clozapine is N-desmethylclozapine. Compared to its parent compound, we found this drug to exert stronger agonistic action via muscarinic M1-receptors and weaker antagonistic actions via M3-receptors and α-adrenergic receptors. Theoretically, N-desmethylclozapine adds its excitatory effect to that of clozapine. Moreover, the secretory response to the two drugs are gradually enhanced in surgically denervated glands. Thus theoretically, chronic blockade of M3- and α-receptors sensitizes the muscarinic-M1-receptors to clozapine and its metabolite as consequence of the prolonged pharmacological denervation. To conclude, during sleep the excitatory action of clozapine and N-desmethylclozapine will dominate, while during a meal, under reflex secretion, their inhibitory action is likely to dominate.

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