Effects of ethanol on CRF release in vitro

Acute ethanol exposure produces activation of the brain-pituitary-adrenal (BPA) axis, resulting in the release of ACTH, beta-endorphin, and glucocorticoids. While elevated levels of plasma glucocorticoids are also found after chronic ethanol administration, plasma ACTH and beta-endorphin are normal or reduced. It is also unclear whether chronic ethanol exposure results in tolerance to the stimulatory effect of ethanol on BPA activity. To determine the site and mechanism of ethanol action on the BPA axis we studied the CRF secretory profile in a superfused rat hypothalamic preparation after chronic ethanol administration in vivo and the CRF responses after acute ethanol exposure in vitro. Superfused hypothalami from normal and pair-fed control rats released CRF-like immunoreactive material (CRF-LI) in a pulsatile manner, with a mean (+/- SE) frequency of 5.1 +/- 0.7 pulses/h. In contrast, the pulse frequency of CRF-LI release from hypothalami of rats receiving chronic ethanol treatment (fed an alcohol-containing liquid diet for 2 weeks) increased dramatically; the basal mean CRF level, pulse amplitude, and pulse duration remained unchanged. Hypothalamic CRF content was decreased. This chronic ethanol exposure also altered the dose-response characteristics of CRF release when ethanol was introduced acutely, as a pulse, into the in vitro preparation. Acute exposure to 20 mg/100 ml ethanol produced greater release of CRF-LI from control hypothalami than from chronic ethanol-exposed hypothalami. A further elevation above basal levels was produced by 200 mg/100 ml ethanol in control, but not ethanol-exposed, hypothalami. Secretion of CRF from ethanol-exposed hypothalami in response to depolarizing concentrations of potassium chloride was suppressed. Chronic ethanol treatment had no effect on CRF-LI and CRF bioactivity responses to stimulation with acetylcholine. These findings suggest the presence of a high frequency pulse-generating mechanism for CRF release in the hypothalamus. This pulsatile secretory mechanism is altered by chronic ethanol exposure of the animals in vivo. Chronic intoxication resulted in tolerance to the stimulatory effect of ethanol on CRF release in vitro.