Involvement of the opioid system in the central antisecretory action of alpha-2 adrenoceptor agonists in rat |
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Authors: | Katalin Müllner Klra Gyires Susanna Furst |
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Institution: | Department of Pharmacology and Pharmacotherapy, Semmelweis University, Faculty of Medicine, Budapest 1445 POB 370, Hungary. mullner@mail.matav.hu |
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Abstract: | The aim of the present study was to analyse the role of the central alpha-2 adrenoceptors in the regulation of gastric acid secretion in pylorus ligated rats. It was found that the intracerebroventricularly (icv.) injected presynaptic alpha-2 adrenoceptor agonist clonidine and the alpha-2A adrenoceptor subtype selective stimulant oxymetazoline exerted a dose dependent inhibition on gastric acid secretion. The antisecretory ED(50) values for clonidine and oxymetazoline were 20 and 7.5 nmol/rat icv., respectively. The antisecretory effect of these compounds was antagonised by the presynaptic adrenoceptor antagonist yohimbine (50 nmol/rat icv.) indicating that the action is mediated through central presynaptic alpha-2 adrenoceptors. Moreover, naloxone (50 nmol/rat icv.)--non-selective opioid antagonist--and naltrindole (0.5 nmol/rat icv.)--delta-opioid receptor selective antagonist--also decreased the antisecretory effect of clonidine and oxymetazoline suggesting that the endogenous opioid system is likely to be involved in the central antisecretory action of alpha-2 adrenoceptor stimulants. |
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Keywords: | Gastric acid secretion Clonidine Oxymetazoline Yohimbine Naloxone Naltrindole icv |
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