Alcohol. Vol. 2, pp. 193--195,1985. ¢ Ankho InternationalInc. Printed in the U.S.A. 0741-8329/85 $3.00 + .00 Chronic Ethanol Induces Changes in Opiate Receptor Function and in Met-Enkephalin Release L. LUCCHI, R. A. RIUS, S, GOVONI 1 AND M. TRABUCCHI* Institute of Pharrnacology and Pharmacognosy, University of Milan, Milan and *Chair of Toxicology, H ad University of Rome, Rome, Italy LUCCHI. L., R. A. RIUS, S. GOVONI AND M. TRABUCCHI. Chronic ethanol induces changes in opiate receptor function and in met-enkephalin release. ALCOHOL 2(2) 193-195, 1985.--Ethanol induces supersensitivity of striatal delta-opiate receptor sites labelled by 3H-Etorphine. This effect may be ascribed to the diminished enkephalin release detected in striatal slices after chronic ethanol consumption. On the other hand, Kd values for 3H-Met-enkephalin and aH-DHM (mu-opiate receptors) specific binding are enhanced. The different sensitivity of the two classes of opiate receptors to ethanol may be due to specific effects on enkephalinergic transmission. It has been hypothesized that the decrease of aH-Met-enkephalin and 3H-DHM affinity for their receptors takes place because endogenous substances from ethanol metabolism tfor example salsolinol) behave as tt opioid agonists. This hypothesis is confirmed by "in vitro" studies demonstrating that salsolinol displaces aH-Met-enkephalin and aH-DHM but not 3H-DADLE binding. On the contrary, it seems that delta-receptors become supersensitive because of the decreased endogenous peptide release. Ethanol Opiate receptors Met-enkephalin release Salsolinol SEVERAL studies have demonstrated that ethanol and opiates show a common mechanism of action in the central nervous system. In fact, ethanol consumption antagonizes naioxone-induced hyperalgesia [!] and suppresses morphine withdrawal syndrome [6]. On the other hand, naloxone is in some cases useful to prevent [8] the effect of alcohol intoxi- cation as well as to reverse the ethanol-induced coma [9,21]. It was proposed that opiate and ethanol effects may be mediated by similar neuronal mechanisms. In this connec- tion, alcohol interaction with central neurotransmission in- cludes perturbation of the neuronal membrane structure, changes in neurotransmitter receptors and turnover, includ- ing opiate receptors and endogenous opioid peptides [7, 13, 17, 22]. It has been hypothesized that the interaction of ethanol with the opiate system is at least partially mediated by ethanol brain metabolites, such as saisolinol, derived from the condensation of acetaldehyde with catecholamines. In order to gain more information on the changes induced by ethanol in the endogenous opiate system, the present study investigates the effect of chronic ethanol and salsolinol on opiate receptor subclasses at the striatal level. In addition, the presynaptic opioid activity was evaluated by measuring basal and potassium-stimulated met-enkephalin release from striatal slices. METHOD Animals and Treatment Male Sprague-Dawley rats (Charles River, Italy) weighing 125-130 g were randomly divided into either control or ethanol treatment groups. Ethanol was administered as a 6% (v/v) aqueous solution for 25 days. Control animals received a liquid diet which contained isocaloric sucrose. The daily ethanol intake was measured; no significant difference in body weight between the ethanol-fed and sucrose-fed groups (10 animals each) was observed at the end of treatment (230+_20 g and 227__. 18 g for controls and chronic ethanol treated rats, respectively). Animals were killed by decapita- tion 3 hours after ethanol withdrawal. Chronic saisolinol treatment, in a dose of 40 mg/kg, was administered intraperi- toneally twice a day for 3 weeks. Animals were killed 1 hr after the last administration. Binding Studies ~H-Etorphine (Amersham, 45 Ci/mmoi) binding was measured according to Simon et al. [19]. Specific binding was defined as the difference between radioactivity bound in the presence or absence of the unlabelled drug at the final concentration of 10-e M. nH-DADLE (Amersham, 54 Ci/mmoi) binding was carded out following the method de- scribed by Lord et al. [10]. Specific binding was obtained from the difference in the radioactivity bound in the presence or absence of 10-6 M Leu-enkephalin. The specific binding of nH-Met-enkephalin (Amersham, 18.1 Ci/mmol) was measured according to Simantov et al. [18]. Cold Met-enkephalin at the final concentration of 10-6 M was used as displacing agent, aH-Dihydromorphine (nH-DHM) tRequests for reprints should be addressed to S. Govoni, Institute of Pharmacology and Pharmacognosy, Via A. del Sarto, 21, 20129- Milano, Italy. 193