Alcohol, Vol. 5, pp. 445-449. ©PergamonPress plc, 1989.Printed in the U.S.A. 0741-8329/88$3.00 + .00 Effects of Ethanol on VIP- and/or Noradrenaline-Stimulated cAMP Formation in Mouse Brain NICOLAS C. SCHAAD,* PIERRE J. MAGISTRETTI* AND MICHEL SCHORDERET*t *D(partement de Pharmacologie, Centre M~dical Universitaire rue Michel Servet 1, CH-1211 Gen~ve 4 and ~fEcole de Pharmacie, Place du Ch?tteau 3, CH-IO05 Lausanne 3 Received 17 March 1988; Accepted 18 July 1988 SCHAAD, N. C., P. J. MAGISTRET]'I AND M. SCHORDERET. Effects of ethanol on VIP- and~or noradrenaline- stimulated cAMP formation in mouse brain. ALCOHOL 5(6) 445--449, 1988.--Among several effects, ethanol (EtOH) interferes with membrane fluidity and lipid-protein interactions. As proteins are influenced by surrounding lipids, the activity of membrane-bound enzymes such as adenylate cyclase (AC) could be modulated by EtOH, as shown in potentiat- ing, at toxic concentrations, the stimulating effect of hormones or neurotransmitters. We have also found that EtOH potentiates in a dose-dependent manner (ECso= 100 mM) the cAMP production elicited by vasoactive intestinal peptide (VIP), already noticeably at 70 mM, without affecting basal cAMP levels (up to 400 raM). Propanol produces a similar potentiation, whereas methanol was inactive. Butanol (200 raM) displays toxic effects. The potentiation induced by EtOH is similar for peptide- (VIP) or monoamine- (noradrenaline) stimulated cAMP formation, suggesting a primary action at a level different from the receptor recognition sites. Finally, we have observed that EtOH potentiates the synergistic interaction between VIP and NA in stimulating cAMP formation. Ethanol Adenylate cyclase Vasoactive intestinal peptide Noradrenaline IT is now well established that ethanol (EtOH), at high con- centrations, can affect the biophysical characteristics of the proteolipid bilayer of the cell membrane (4). Evidence also exists that "physiologically relevant" concentrations of EtOH fluidize the inner core of the bilayer without affecting the membrane surface (19). EtOH can also act by disrupting fipid-protein interactions, hence directly modulate protein functions. As proteins are influenced by surrounding lipids (15), the activity of several enzymes will be affected by alco- hols. Among the enzymes present in the plasma membrane, Na+-K+-ATPase (26) and adenylate cyclase have been ex- tensively investigated in vitro. In most tissues, the activity of the former is inhibited by EtOH, whereas the latter is ac- tivated by short-chain alcohols (38). Other membrane func- tions and/or enzymes such as Ca÷+-ATPase (41), voltage- sensitive Na + and Ca ++ fluxes (2, 9, 10, 24, 25), Na ÷ pump (20), Ca ++ mobilisation (11) as well as phospholipid metabo- lism (13, 31, 36) are modulated by EtOH. Adenylate cyclase (AC) is a membrane-bound enzyme with the hormone- or neurotransmitter-receptor exposed to the extracellular space, the transduction between the recep- tor and the AC-catalytic unit being regulated by guanine- nucleotide regulatory proteins (G-proteins). The action of EtOH on AC has been investigated in vitro in several tissues. Many studies have clearly demonstrated that EtOH at high concentrations stimulates cyclic AMP (cAMP) accumulation. At lower concentrations, EtOH potentiates AC stimulation elicited by various neurotrans- mitters or hormones. At the molecular level, the site of ac- tion is still unclear. Thus, it has been shown (12) that EtOH did not influence transition temperature as assessed by Ar- rhenius plots of AC in mouse striatum, suggesting that enzyme activation by EtOH resulted from a direct effect on the enzyme or an indirect one on the regulatory proteins. These and other results (18) led to propose that EtOH could favor interactions between the G-proteins and the catalytic subunit. More recent findings obtained with cerebral cortical tissue (34) indicate that EtOH, in addition to the above ef- fect, affects the activity of the catalytic site. Such differences between mouse striatum and cerebral cortical AC have al- ready been reported (39). It should be stressed that, with few exceptions (33), the doses of EtOH routinely used to observe a statistically signif- icant effect on AC are generally higher than the concentra- tions observed in case of acute intoxication in man [150 mg/dl= 33 mM (5)]. However, the peak levels of EtOH meas- ured in brain are about 20% higher than those measured in the plasma (7). In the central nervous system, the effects of acute EtOH on AC have been assessed following activation of this enzyme by neurotransmitters or their agonists (12, 28, 29, 33, 34, 39), by autacoids such as PGEI (30), or by other agents such as 445