Involvement of the opioid system in the central antisecretory action of alpha-2 adrenoceptor agonists in rat.
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.
Müllner
K
K
Department of Pharmacology and Pharmacotherapy, Semmelweis University, Faculty of Medicine, Budapest 1445 POB 370, Hungary. mullner@mail.matav.hu
Gyires
K
K
Furst
S
S
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000502:physiology*; D003000:Clonidine / Q000494:pharmacology; D004723:Endorphins / Q000502:physiology*; D007276:Injections, Intraventricular; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010109:Oxymetazoline / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004723:Endorphins; D009292:Narcotic Antagonists; D015016:Yohimbine; D009270:Naloxone; D010109:Oxymetazoline; D003000:Clonidine