Effects of ethanol on basal and adenosine-induced increases in β-endorphin release and intracellular cAMP levels in hypothalamic cells

Recently we have shown that the cAMP system is involved in ethanol-regulated β-endorphin (β-EP) release from rat hypothalamic neurons in primary cultures. The cascade of events that leads to activation of cAMP following ethanol treatment in hypothalamic β-EP neurons is not apparent. In this study the role of adenosine, a cAMP regulator, in ethanol-regulated β-EP release was determined by measuring the cellular incorporation of [³H]adenosine, intracellular cAMP levels and media immunoreactive (IR) β-EP levels in cultures of rat hypothalamic cells following ethanol treatments in the presence and absence of an adenosine agonist and antagonist. Acute exposure to a 50 mM dose of ethanol for a period of 1 h increased media levels of IR-β-EP and cellular contents of cAMP, but the ethanol treatment decreased [³H]adenosine uptake. Constant exposure to a 50 mM dose of ethanol for a period of 48 h, failed to alter media levels of IR-β-EP, cell content of cAMP and [³H]adenosine uptake. The media level of IR-β-EP was elevated following treatment with adenosine receptor agonist phenyl-isopropyl adenosine (PIA) and was reduced following treatment with adenosine receptor antagonist isobutylmethylxanthine (IBMX) or with adenosine uptake inhibitor adenosine deaminase. The level of cellular cAMP was also increased by PIA but was decreased by IBMX and adenosine deaminase. The stimulatory actions of the adenosine agonist PIA on IR-β-EP release and on cAMP production were potentiated by simultaneous incubation with ethanol for 1 h. However, chronic ethanol exposure reduced PIA-induced IR-β-EP release and cAMP production. Additionally, both IBMX and adenosine deaminase reduced ethanol-induced IR-β-EP release and cAMP levels. These results suggest that ethanol inhibits adenosine uptake in IR-β-EP neurons in the hypothalamus, thereby increasing extracellular levels of adenosine and leading to activation of membrane adenosine receptors, cAMP production and IR-β-EP secretion from these neurons. Chronic ethanol desensitizes the adenosine-regulated cAMP production and IR-β-EP release from hypothalamic neurons.