Effect of stress and dexamethasone on immunoreactive beta-endorphin levels in rat hypothalamus and pineal.

In response to mild stress the levels of immunoreactive beta-endorphin in rat anterior pituitary, hypothalamus and pineal fell within 10 minutes from 210 to 129 pmol/lobe, 1.47 to 0.89 pmol/mg protein and 2.53 to 0.41 pmol/gland, respectively. No alterations were found to take place in beta-endorphin levels in posterior pituitary or plasma. Dexamethasone pretreatment given 18 h prior to stress resulted in significantly greater reduction of beta-endorphin levels in hypothalamus and pineal than stress alone--hypothalamic levels fell to 0.73 pmol/mg protein and pineal to 0.07 pmol/gland. Plasma beta-endorphin levels in dexamethasone pretreated stressed rats were significantly lower than in intact rats (42 fmol/ml vs. 98 fmol/ml). The almost complete disappearance of beta-endorphin from the pineal in response to stress and dexamethasone suggests that pineal does not itself synthesize the hormone but only utilizes and/or stores it. Gel filtration analysis of the beta-endorphin immunoreactivity in tissue extracts and plasma showed that anterior pituitary and plasma contain three immunoreactive components, eluting like beta-endorphin, beta-lipotropin and proopiocortin, whereas only beta-endorphin-like material was detected in posterior pituitary, hypothalamus and pineal.